feat(proxy): offload spend tracking to a pod-local spend worker sidecar

Inference workers publish one compact typed SpendEvent per success over a
unix socket or loopback TCP; an opt-in sidecar (python -m gateway.spend_worker)
runs the unchanged _ProxyDBLogger cost pipeline against the pod's pgbouncer.
Default off (LITELLM_SPEND_WORKER_ENABLED). Also reuses the preset cache key
in get_logging_payload instead of hashing the request body

Co-Authored-By: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

gateway/spend_worker.py

@@ -0,0 +1,43 @@
+"""Spend sidecar entrypoint for the gateway image.
+
+Assembles ``DATABASE_URL`` the way ``gateway.launch`` does, but instead of starting a PgBouncer it
+points the URL at the one the gateway container already runs on the pod's loopback (the sidecar
+must see the same ``DATABASE_URL`` inputs and ``LITELLM_PGBOUNCER_*`` values as the gateway
+container), then hands off to ``litellm.proxy.spend_worker``.
+
+Run with:
+    python -m gateway.spend_worker [--address unix:///var/run/litellm/spend-worker.sock]
+"""
+
+import os
+import sys
+from collections.abc import Mapping, Sequence
+from typing import Final
+
+from litellm.proxy.db.db_url_settings import DatabaseURLSettings
+from litellm.proxy.db.pgbouncer import PgBouncerError, PgBouncerSettings, pooled_database_url
+from litellm.proxy.spend_worker import main as spend_worker_main
+
+
+def pod_pgbouncer_database_url(pgbouncer: PgBouncerSettings, environ: Mapping[str, str]) -> str | PgBouncerError | None:
+    """The gateway container's PgBouncer URL for ``environ["DATABASE_URL"]``, or None when PgBouncer is off."""
+    if not pgbouncer.enabled:
+        return None
+    upstream_url: Final = environ.get("DATABASE_URL")
+    if upstream_url is None:
+        return PgBouncerError("LITELLM_PGBOUNCER_ENABLED is set but no DATABASE_URL could be assembled")
+    return pooled_database_url(upstream_url, pgbouncer)
+
+
+def main(argv: Sequence[str]) -> None:
+    DatabaseURLSettings.from_env().apply_to_env()
+    pooled: Final = pod_pgbouncer_database_url(PgBouncerSettings(), os.environ)
+    if isinstance(pooled, PgBouncerError):
+        sys.exit(f"LiteLLM spend worker: cannot use the pod's pgbouncer: {pooled.reason}")
+    if pooled is not None:
+        os.environ["DATABASE_URL"] = pooled
+    spend_worker_main(argv)
+
+
+if __name__ == "__main__":
+    main(sys.argv[1:])

helm/litellm-helm/templates/_helpers.tpl

@@ -161,3 +161,156 @@ taken before the change, which by that point no longer exists.
 {{- fail (printf "postgresql.image.tag must be pinned to an explicit version when db.deployStandalone is true (got %q). An unpinned tag can start a different PostgreSQL major against the existing data directory, which makes the database unreadable and is not recoverable in place. Crossing a major version requires a dump and restore." $tag) -}}
 {{- end -}}
 {{- end -}}
+
+{{/*
+Environment shared by the proxy container and the opt-in spend worker sidecar:
+database, pgbouncer, master key, redis, user envVars. Both containers must see
+the same DATABASE_URL and REDIS_* so the sidecar reaches the pod's pgbouncer
+and the same spend transaction buffer.
+*/}}
+{{- define "litellm.proxyEnv" -}}
+- name: HOST
+  value: "{{ .Values.listen | default "0.0.0.0" }}"
+- name: PORT
+  value: {{ .Values.service.port | quote}}
+{{- if .Values.db.deployStandalone }}
+- name: DATABASE_USERNAME
+  valueFrom:
+    secretKeyRef:
+      name: {{ include "litellm.fullname" . }}-dbcredentials
+      key: username
+- name: DATABASE_PASSWORD
+  valueFrom:
+    secretKeyRef:
+      name: {{ include "litellm.fullname" . }}-dbcredentials
+      key: password
+- name: DATABASE_HOST
+  value: {{ .Release.Name }}-postgresql
+- name: DATABASE_NAME
+  value: litellm
+{{- else if .Values.db.useExisting }}
+- name: DATABASE_USERNAME
+  valueFrom:
+    secretKeyRef:
+      name: {{ .Values.db.secret.name }}
+      key: {{ .Values.db.secret.usernameKey }}
+- name: DATABASE_PASSWORD
+  valueFrom:
+    secretKeyRef:
+      name: {{ .Values.db.secret.name }}
+      key: {{ .Values.db.secret.passwordKey }}
+- name: DATABASE_HOST
+  {{- if .Values.db.secret.endpointKey }}
+  valueFrom:
+    secretKeyRef:
+      name: {{ .Values.db.secret.name }}
+      key: {{ .Values.db.secret.endpointKey }}
+  {{- else }}
+  value: {{ .Values.db.endpoint }}
+  {{- end }}
+- name: DATABASE_NAME
+  value: {{ .Values.db.database }}
+- name: DATABASE_URL
+  value: {{ .Values.db.url | quote }}
+{{- end }}
+{{- if and .Values.db.useExisting .Values.db.readReplicaUrl .Values.db.secret.readReplicaEndpointKey (not .Values.db.secret.readReplicaUrlKey) }}
+- name: DATABASE_READER_HOST
+  valueFrom:
+    secretKeyRef:
+      name: {{ .Values.db.secret.name }}
+      key: {{ .Values.db.secret.readReplicaEndpointKey }}
+{{- end }}
+{{- if and .Values.db.useExisting .Values.db.secret.readReplicaUrlKey }}
+- name: DATABASE_URL_READ_REPLICA
+  valueFrom:
+    secretKeyRef:
+      name: {{ .Values.db.secret.name }}
+      key: {{ .Values.db.secret.readReplicaUrlKey }}
+{{- else if .Values.db.readReplicaUrl }}
+- name: DATABASE_URL_READ_REPLICA
+  value: {{ .Values.db.readReplicaUrl | quote }}
+{{- end }}
+{{- if .Values.db.connectionPool.enabled }}
+- name: LITELLM_PGBOUNCER_ENABLED
+  value: "true"
+- name: LITELLM_PGBOUNCER_MAX_DB_CONNECTIONS
+  value: {{ .Values.db.connectionPool.maxDbConnections | quote }}
+- name: LITELLM_PGBOUNCER_MAX_CLIENT_CONN
+  value: {{ .Values.db.connectionPool.maxClientConn | quote }}
+{{- end }}
+- name: PROXY_MASTER_KEY
+  valueFrom:
+    secretKeyRef:
+      name: {{ .Values.masterkeySecretName | default (printf "%s-masterkey" (include "litellm.fullname" .)) }}
+      key: {{ .Values.masterkeySecretKey | default "masterkey" }}
+{{- if .Values.redis.enabled }}
+- name: REDIS_HOST
+  value: {{ include "litellm.redis.serviceName" . }}
+- name: REDIS_PORT
+  value: {{ include "litellm.redis.port" . | quote }}
+- name: REDIS_PASSWORD
+  valueFrom:
+    secretKeyRef:
+      name: {{ include "redis.secretName" .Subcharts.redis }}
+      key: {{include "redis.secretPasswordKey" .Subcharts.redis }}
+{{- end }}
+{{- /*
+  Inject LITELLM_LOG only when envVars does not already define it.
+*/}}
+{{- if and .Values.logLevel (not (hasKey (default dict .Values.envVars) "LITELLM_LOG")) }}
+- name: LITELLM_LOG
+  value: {{ .Values.logLevel | quote }}
+{{- end }}
+{{- if .Values.envVars }}
+{{- range $key, $val := .Values.envVars }}
+- name: {{ $key }}
+  value: {{ $val | quote }}
+{{- end }}
+{{- end }}
+{{- with .Values.extraEnvVars }}
+{{ toYaml . }}
+{{- end }}
+{{- if .Values.billingMetrics.enabled }}
+{{ include "litellm.billingMetricsEnv" . }}
+{{- end }}
+{{- if .Values.metricsServer.enabled }}
+{{- if eq (int .Values.metricsServer.port) (int .Values.service.port) }}
+{{- fail "metricsServer.port must differ from service.port" }}
+{{- end }}
+- name: PROMETHEUS_METRICS_PORT
+  value: {{ .Values.metricsServer.port | quote }}
+{{- end }}
+{{- if .Values.migrationJob.enabled }}
+# Schema updates are owned by the dedicated migrations Job; skip
+# the proxy's startup `prisma db push` so N replicas don't race
+# one DB on every rollout. Placed last (after envVars and
+# extraEnvVars) so this override can't be silently shadowed by a
+# user-supplied DISABLE_SCHEMA_UPDATE under last-wins duplicate-env
+# semantics — same pattern the migrations Job uses.
+- name: DISABLE_SCHEMA_UPDATE
+  value: "true"
+{{- end }}
+{{- end -}}
+
+{{/*
+Directory of the spend worker's unix socket, shared between the two containers
+through an emptyDir. Empty when the sidecar is off or uses 127.0.0.1 TCP.
+*/}}
+{{- define "litellm.spendWorker.socketDir" -}}
+{{- if and .Values.spendWorker.enabled (hasPrefix "unix://" .Values.spendWorker.address) -}}
+{{- dir (trimPrefix "unix://" .Values.spendWorker.address) -}}
+{{- end -}}
+{{- end -}}
+
+{{- define "litellm.spendWorkerEnv" -}}
+- name: LITELLM_SPEND_WORKER_ENABLED
+  value: "true"
+- name: LITELLM_SPEND_WORKER_ADDRESS
+  value: {{ .Values.spendWorker.address | quote }}
+- name: LITELLM_SPEND_WORKER_BUFFER_SIZE
+  value: {{ .Values.spendWorker.bufferSize | quote }}
+- name: LITELLM_SPEND_WORKER_ON_UNAVAILABLE
+  value: {{ .Values.spendWorker.onUnavailable | quote }}
+- name: LITELLM_SPEND_WORKER_DRAIN_TIMEOUT_SECONDS
+  value: {{ .Values.spendWorker.drainTimeoutSeconds | quote }}
+{{- end -}}

helm/litellm-helm/templates/deployment.yaml

@@ -56,126 +56,9 @@ spec:
           image: "{{ .Values.image.repository }}:{{ .Values.image.tag | default .Chart.AppVersion }}"
           imagePullPolicy: {{ .Values.image.pullPolicy }}
           env:
-            - name: HOST
-              value: "{{ .Values.listen | default "0.0.0.0" }}"
-            - name: PORT
-              value: {{ .Values.service.port | quote}}
-            {{- if .Values.db.deployStandalone }}
-            - name: DATABASE_USERNAME
-              valueFrom:
-                secretKeyRef:
-                  name: {{ include "litellm.fullname" . }}-dbcredentials
-                  key: username
-            - name: DATABASE_PASSWORD
-              valueFrom:
-                secretKeyRef:
-                  name: {{ include "litellm.fullname" . }}-dbcredentials
-                  key: password
-            - name: DATABASE_HOST
-              value: {{ .Release.Name }}-postgresql
-            - name: DATABASE_NAME
-              value: litellm
-            {{- else if .Values.db.useExisting }}
-            - name: DATABASE_USERNAME
-              valueFrom:
-                secretKeyRef:
-                  name: {{ .Values.db.secret.name }}
-                  key: {{ .Values.db.secret.usernameKey }}
-            - name: DATABASE_PASSWORD
-              valueFrom:
-                secretKeyRef:
-                  name: {{ .Values.db.secret.name }}
-                  key: {{ .Values.db.secret.passwordKey }}
-            - name: DATABASE_HOST
-              {{- if .Values.db.secret.endpointKey }}
-              valueFrom:
-                secretKeyRef:
-                  name: {{ .Values.db.secret.name }}
-                  key: {{ .Values.db.secret.endpointKey }}
-              {{- else }}
-              value: {{ .Values.db.endpoint }}
-              {{- end }}
-            - name: DATABASE_NAME
-              value: {{ .Values.db.database }}
-            - name: DATABASE_URL
-              value: {{ .Values.db.url | quote }}
-            {{- end }}
-            {{- if and .Values.db.useExisting .Values.db.readReplicaUrl .Values.db.secret.readReplicaEndpointKey (not .Values.db.secret.readReplicaUrlKey) }}
-            - name: DATABASE_READER_HOST
-              valueFrom:
-                secretKeyRef:
-                  name: {{ .Values.db.secret.name }}
-                  key: {{ .Values.db.secret.readReplicaEndpointKey }}
-            {{- end }}
-            {{- if and .Values.db.useExisting .Values.db.secret.readReplicaUrlKey }}
-            - name: DATABASE_URL_READ_REPLICA
-              valueFrom:
-                secretKeyRef:
-                  name: {{ .Values.db.secret.name }}
-                  key: {{ .Values.db.secret.readReplicaUrlKey }}
-            {{- else if .Values.db.readReplicaUrl }}
-            - name: DATABASE_URL_READ_REPLICA
-              value: {{ .Values.db.readReplicaUrl | quote }}
-            {{- end }}
-            {{- if .Values.db.connectionPool.enabled }}
-            - name: LITELLM_PGBOUNCER_ENABLED
-              value: "true"
-            - name: LITELLM_PGBOUNCER_MAX_DB_CONNECTIONS
-              value: {{ .Values.db.connectionPool.maxDbConnections | quote }}
-            - name: LITELLM_PGBOUNCER_MAX_CLIENT_CONN
-              value: {{ .Values.db.connectionPool.maxClientConn | quote }}
-            {{- end }}
-            - name: PROXY_MASTER_KEY
-              valueFrom:
-                secretKeyRef:
-                  name: {{ .Values.masterkeySecretName | default (printf "%s-masterkey" (include "litellm.fullname" .)) }}
-                  key: {{ .Values.masterkeySecretKey | default "masterkey" }}
-            {{- if .Values.redis.enabled }}
-            - name: REDIS_HOST
-              value: {{ include "litellm.redis.serviceName" . }}
-            - name: REDIS_PORT
-              value: {{ include "litellm.redis.port" . | quote }}
-            - name: REDIS_PASSWORD
-              valueFrom:
-                secretKeyRef:
-                  name: {{ include "redis.secretName" .Subcharts.redis }}
-                  key: {{include "redis.secretPasswordKey" .Subcharts.redis }}
-            {{- end }}
-            {{- /*
-              Inject LITELLM_LOG only when envVars does not already define it.
-            */}}
-            {{- if and .Values.logLevel (not (hasKey (default dict .Values.envVars) "LITELLM_LOG")) }}
-            - name: LITELLM_LOG
-              value: {{ .Values.logLevel | quote }}
-            {{- end }}
-            {{- if .Values.envVars }}
-            {{- range $key, $val := .Values.envVars }}
-            - name: {{ $key }}
-              value: {{ $val | quote }}
-            {{- end }}
-            {{- end }}
-            {{- with .Values.extraEnvVars }}
-              {{- toYaml . | nindent 12 }}
-            {{- end }}
-            {{- if .Values.billingMetrics.enabled }}
-            {{- include "litellm.billingMetricsEnv" . | nindent 12 }}
-            {{- end }}
-            {{- if .Values.metricsServer.enabled }}
-            {{- if eq (int .Values.metricsServer.port) (int .Values.service.port) }}
-            {{- fail "metricsServer.port must differ from service.port" }}
-            {{- end }}
-            - name: PROMETHEUS_METRICS_PORT
-              value: {{ .Values.metricsServer.port | quote }}
-            {{- end }}
-            {{- if .Values.migrationJob.enabled }}
-            # Schema updates are owned by the dedicated migrations Job; skip
-            # the proxy's startup `prisma db push` so N replicas don't race
-            # one DB on every rollout. Placed last (after envVars and
-            # extraEnvVars) so this override can't be silently shadowed by a
-            # user-supplied DISABLE_SCHEMA_UPDATE under last-wins duplicate-env
-            # semantics — same pattern the migrations Job uses.
-            - name: DISABLE_SCHEMA_UPDATE
-              value: "true"
+            {{- include "litellm.proxyEnv" . | nindent 12 }}
+            {{- if .Values.spendWorker.enabled }}
+            {{- include "litellm.spendWorkerEnv" . | nindent 12 }}
             {{- end }}
           envFrom:
           {{- range .Values.environmentSecrets }}
@@ -253,6 +136,10 @@ spec:
           {{- if .Values.billingMetrics.enabled }}
             {{- include "litellm.billingMetricsVolumeMounts" . | nindent 12 }}
           {{- end }}
+          {{- if include "litellm.spendWorker.socketDir" . }}
+            - name: spend-worker-socket
+              mountPath: {{ include "litellm.spendWorker.socketDir" . }}
+          {{- end }}
           {{- with .Values.volumeMounts }}
             {{- toYaml . | nindent 12 }}
           {{- end }}
@@ -260,6 +147,51 @@ spec:
           lifecycle:
             {{- toYaml . | nindent 12 }}
           {{- end }}
+      {{- if .Values.spendWorker.enabled }}
+        - name: {{ include "litellm.name" . }}-spend-worker
+          securityContext:
+            {{- toYaml .Values.securityContext | nindent 12 }}
+          image: "{{ .Values.image.repository }}:{{ .Values.image.tag | default .Chart.AppVersion }}"
+          imagePullPolicy: {{ .Values.image.pullPolicy }}
+          command: {{ toYaml .Values.spendWorker.command | nindent 12 }}
+          env:
+            {{- include "litellm.proxyEnv" . | nindent 12 }}
+            {{- include "litellm.spendWorkerEnv" . | nindent 12 }}
+            - name: LITELLM_JOB_ROLE
+              value: spend_worker
+            {{- if not (hasKey (default dict .Values.envVars) "CONFIG_FILE_PATH") }}
+            - name: CONFIG_FILE_PATH
+              value: /etc/litellm/config.yaml
+            {{- end }}
+          envFrom:
+          {{- range .Values.environmentSecrets }}
+            - secretRef:
+                name: {{ . }}
+          {{- end }}
+          {{- range .Values.environmentConfigMaps }}
+            - configMapRef:
+                name: {{ . }}
+          {{- end }}
+          resources:
+            {{- toYaml .Values.spendWorker.resources | nindent 12 }}
+          volumeMounts:
+            - name: litellm-config
+              mountPath: /etc/litellm/config.yaml
+              subPath: config.yaml
+          {{- if include "litellm.spendWorker.socketDir" . }}
+            - name: spend-worker-socket
+              mountPath: {{ include "litellm.spendWorker.socketDir" . }}
+          {{- end }}
+          {{ if .Values.securityContext.readOnlyRootFilesystem }}
+            - name: tmp
+              mountPath: /tmp
+            - name: cache
+              mountPath: /.cache
+          {{- end }}
+          {{- with .Values.volumeMounts }}
+            {{- toYaml . | nindent 12 }}
+          {{- end }}
+      {{- end }}
       {{- with .Values.extraContainers }}
         {{- tpl (toYaml .) $ | nindent 8 }}
       {{- end }}
@@ -288,6 +220,11 @@ spec:
         {{- if .Values.billingMetrics.enabled }}
         {{- include "litellm.billingMetricsVolumes" . | nindent 8 }}
         {{- end }}
+        {{- if include "litellm.spendWorker.socketDir" . }}
+        - name: spend-worker-socket
+          emptyDir:
+            sizeLimit: 1Mi
+        {{- end }}
       {{- with .Values.volumes }}
         {{- toYaml . | nindent 8 }}
       {{- end }}

helm/litellm-helm/templates/hpa.yaml

@@ -18,6 +18,15 @@ spec:
   {{- end }}
   metrics:
     {{- if .Values.autoscaling.targetCPUUtilizationPercentage }}
+    {{- if and .Values.spendWorker.enabled .Values.spendWorker.scaleOnProxyContainerCpu }}
+    - type: ContainerResource
+      containerResource:
+        name: cpu
+        container: {{ include "litellm.name" . }}
+        target:
+          type: Utilization
+          averageUtilization: {{ .Values.autoscaling.targetCPUUtilizationPercentage }}
+    {{- else }}
     - type: Resource
       resource:
         name: cpu
@@ -25,6 +34,7 @@ spec:
           type: Utilization
           averageUtilization: {{ .Values.autoscaling.targetCPUUtilizationPercentage }}
     {{- end }}
+    {{- end }}
     {{- if .Values.autoscaling.targetMemoryUtilizationPercentage }}
     - type: Resource
       resource:

helm/litellm-helm/tests/spend_worker_tests.yaml

@@ -0,0 +1,214 @@
+suite: test spend worker sidecar
+templates:
+  - deployment.yaml
+  - hpa.yaml
+  - configmap-litellm.yaml
+tests:
+  - it: should run the proxy alone with no spend worker env by default
+    template: deployment.yaml
+    asserts:
+      - lengthEqual:
+          path: spec.template.spec.containers
+          count: 1
+      - notContains:
+          path: spec.template.spec.containers[0].env
+          content:
+            name: LITELLM_SPEND_WORKER_ENABLED
+            value: "true"
+      - notContains:
+          path: spec.template.spec.volumes
+          content:
+            name: spend-worker-socket
+          any: true
+
+  - it: should add the sidecar on the same image and point both containers at the unix socket
+    template: deployment.yaml
+    set:
+      image.tag: test
+      db.connectionPool.enabled: true
+      spendWorker.enabled: true
+      spendWorker.resources:
+        requests:
+          cpu: 500m
+          memory: 1Gi
+        limits:
+          cpu: "1"
+          memory: 2Gi
+    asserts:
+      - lengthEqual:
+          path: spec.template.spec.containers
+          count: 2
+      - equal:
+          path: spec.template.spec.containers[1].name
+          value: litellm-spend-worker
+      - equal:
+          path: spec.template.spec.containers[1].image
+          value: ghcr.io/berriai/litellm:test
+      - equal:
+          path: spec.template.spec.containers[1].command
+          value: [python, -m, gateway.spend_worker]
+      - equal:
+          path: spec.template.spec.containers[1].resources.requests.cpu
+          value: 500m
+      - equal:
+          path: spec.template.spec.containers[1].resources.limits.memory
+          value: 2Gi
+      - contains:
+          path: spec.template.spec.containers[0].env
+          content:
+            name: LITELLM_SPEND_WORKER_ENABLED
+            value: "true"
+      - contains:
+          path: spec.template.spec.containers[0].env
+          content:
+            name: LITELLM_SPEND_WORKER_ADDRESS
+            value: unix:///var/run/litellm/spend-worker.sock
+      - contains:
+          path: spec.template.spec.containers[0].env
+          content:
+            name: LITELLM_SPEND_WORKER_BUFFER_SIZE
+            value: "1000"
+      - contains:
+          path: spec.template.spec.containers[0].env
+          content:
+            name: LITELLM_SPEND_WORKER_ON_UNAVAILABLE
+            value: fallback
+      - notContains:
+          path: spec.template.spec.containers[0].env
+          content:
+            name: LITELLM_JOB_ROLE
+            value: spend_worker
+      - contains:
+          path: spec.template.spec.containers[1].env
+          content:
+            name: LITELLM_JOB_ROLE
+            value: spend_worker
+      - contains:
+          path: spec.template.spec.containers[1].env
+          content:
+            name: LITELLM_SPEND_WORKER_ADDRESS
+            value: unix:///var/run/litellm/spend-worker.sock
+      - contains:
+          path: spec.template.spec.containers[1].env
+          content:
+            name: CONFIG_FILE_PATH
+            value: /etc/litellm/config.yaml
+      - contains:
+          path: spec.template.spec.containers[1].env
+          content:
+            name: DATABASE_HOST
+            value: RELEASE-NAME-postgresql
+      - contains:
+          path: spec.template.spec.containers[1].env
+          content:
+            name: DATABASE_PASSWORD
+            valueFrom:
+              secretKeyRef:
+                name: RELEASE-NAME-litellm-dbcredentials
+                key: password
+      - contains:
+          path: spec.template.spec.containers[1].env
+          content:
+            name: LITELLM_PGBOUNCER_ENABLED
+            value: "true"
+      - contains:
+          path: spec.template.spec.containers[1].env
+          content:
+            name: LITELLM_PGBOUNCER_MAX_DB_CONNECTIONS
+            value: "20"
+      - contains:
+          path: spec.template.spec.containers[0].volumeMounts
+          content:
+            name: spend-worker-socket
+            mountPath: /var/run/litellm
+      - contains:
+          path: spec.template.spec.containers[1].volumeMounts
+          content:
+            name: spend-worker-socket
+            mountPath: /var/run/litellm
+      - contains:
+          path: spec.template.spec.containers[1].volumeMounts
+          content:
+            name: litellm-config
+            mountPath: /etc/litellm/config.yaml
+            subPath: config.yaml
+      - contains:
+          path: spec.template.spec.volumes
+          content:
+            name: spend-worker-socket
+            emptyDir:
+              sizeLimit: 1Mi
+
+  - it: should skip the socket volume and pass the policy through on tcp transport
+    template: deployment.yaml
+    set:
+      spendWorker.enabled: true
+      spendWorker.address: tcp://127.0.0.1:4100
+      spendWorker.onUnavailable: drop
+      spendWorker.bufferSize: 50
+      envVars:
+        CONFIG_FILE_PATH: /custom/config.yaml
+    asserts:
+      - lengthEqual:
+          path: spec.template.spec.containers
+          count: 2
+      - notContains:
+          path: spec.template.spec.containers[1].env
+          content:
+            name: CONFIG_FILE_PATH
+            value: /etc/litellm/config.yaml
+      - contains:
+          path: spec.template.spec.containers[1].env
+          content:
+            name: CONFIG_FILE_PATH
+            value: /custom/config.yaml
+      - contains:
+          path: spec.template.spec.containers[0].env
+          content:
+            name: LITELLM_SPEND_WORKER_ADDRESS
+            value: tcp://127.0.0.1:4100
+      - contains:
+          path: spec.template.spec.containers[0].env
+          content:
+            name: LITELLM_SPEND_WORKER_ON_UNAVAILABLE
+            value: drop
+      - contains:
+          path: spec.template.spec.containers[0].env
+          content:
+            name: LITELLM_SPEND_WORKER_BUFFER_SIZE
+            value: "50"
+      - notContains:
+          path: spec.template.spec.volumes
+          content:
+            name: spend-worker-socket
+          any: true
+
+  - it: should keep the pod-wide cpu metric unless asked to scale on the proxy container
+    template: hpa.yaml
+    set:
+      autoscaling.enabled: true
+      spendWorker.enabled: true
+    asserts:
+      - equal: { path: "spec.metrics[0].type", value: Resource }
+      - equal: { path: "spec.metrics[0].resource.name", value: cpu }
+
+  - it: should scale on the proxy container's cpu only when opted in
+    template: hpa.yaml
+    set:
+      autoscaling.enabled: true
+      spendWorker.enabled: true
+      spendWorker.scaleOnProxyContainerCpu: true
+    asserts:
+      - equal: { path: "spec.metrics[0].type", value: ContainerResource }
+      - equal: { path: "spec.metrics[0].containerResource.name", value: cpu }
+      - equal: { path: "spec.metrics[0].containerResource.container", value: litellm }
+      - equal: { path: "spec.metrics[0].containerResource.target.averageUtilization", value: 60 }
+      - isNull: { path: "spec.metrics[0].resource" }
+
+  - it: should not switch to the container metric while the sidecar is off
+    template: hpa.yaml
+    set:
+      autoscaling.enabled: true
+      spendWorker.scaleOnProxyContainerCpu: true
+    asserts:
+      - equal: { path: "spec.metrics[0].type", value: Resource }

helm/litellm-helm/values.yaml

@@ -190,6 +190,48 @@ metricsServer:
   enabled: false
   port: 4001
 
+# Opt-in sidecar that runs the post-response spend pipeline (cost calculation,
+# spend logs, spend counters, budget reservation reconciliation) so the proxy's
+# uvicorn workers only serialise a compact typed event and go back to serving
+# inference. Same image and tag as the proxy, second container in the same pod,
+# fed over loopback (a unix socket on a shared emptyDir, or 127.0.0.1 TCP). It
+# reuses the pod's in-container pgbouncer (db.connectionPool) and the same Redis
+# spend transaction buffer, so the per-pod DB connection budget is unchanged.
+# Delivery is at-most-once inside the pod: events already handed to the sidecar
+# are lost if it crashes before writing them; events the workers could not hand
+# over follow onUnavailable. Both containers drain on SIGTERM within
+# terminationGracePeriodSeconds
+spendWorker:
+  enabled: false
+  # unix:///<dir>/<file>.sock (the <dir> becomes a shared emptyDir) or tcp://127.0.0.1:<port>
+  address: unix:///var/run/litellm/spend-worker.sock
+  # Events each uvicorn worker holds in memory while the sidecar is slow or restarting
+  bufferSize: 1000
+  # fallback: run the pipeline in the worker when the sidecar is unreachable or the
+  # buffer is full (spend stays exact, that request costs proxy CPU again)
+  # drop: count and discard the event instead (spend under-reports)
+  onUnavailable: fallback
+  # How long the workers keep pushing buffered events on shutdown, and how long the
+  # sidecar keeps serving its open connections after SIGTERM
+  drainTimeoutSeconds: 10
+  command:
+    - python
+    - -m
+    - gateway.spend_worker
+  # Sized independently of the proxy container; the pipeline is CPU bound
+  resources: {}
+  # requests:
+  #   cpu: 500m
+  #   memory: 1Gi
+  # limits:
+  #   cpu: "1"
+  #   memory: 2Gi
+  # When autoscaling.enabled, swap the pod-wide cpu Resource metric for an
+  # autoscaling/v2 ContainerResource metric on the proxy container only, so the
+  # sidecar's CPU never scales inference replicas. Needs Kubernetes 1.30+ (or the
+  # HPAContainerMetrics feature gate on 1.27 to 1.29)
+  scaleOnProxyContainerCpu: false
+
 resources:
   {}
   # Unset by default so the chart installs on small clusters such as Minikube, and so an

litellm/proxy/db/pgbouncer.py

@@ -235,6 +235,12 @@ def plan_pgbouncer(
     return PgBouncerPlan(ini=ini, userlist=userlist, pooled_url=pooled_url)
 
 
+def pooled_database_url(upstream_url: str, settings: PgBouncerSettings) -> str | PgBouncerError:
+    """The loopback URL of a PgBouncer another container in the pod already runs for ``upstream_url``."""
+    plan: Final = plan_pgbouncer(upstream_url, settings, runtime_dir=Path("/nonexistent"), run_as_user=None)
+    return plan if isinstance(plan, PgBouncerError) else plan.pooled_url
+
+
 def write_pgbouncer_files(plan: PgBouncerPlan, runtime_dir: Path, run_as_user: str | None) -> Path:
     """Write the ini and userlist (both hold the password, so mode 0600) and return the ini path.
 

litellm/proxy/hooks/proxy_track_cost_callback.py

@@ -27,12 +27,22 @@ from litellm.proxy.db.db_spend_update_writer import (
     get_llm_router,
 )
 from litellm.proxy.litellm_pre_call_utils import LiteLLMProxyRequestSetup
+from litellm.proxy.spend_tracking.spend_event import (
+    SpendEventBuildError,
+    SpendEventDecodeError,
+    build_spend_event,
+    decode_spend_event,
+    is_offloadable_success,
+    spend_event_callback_args,
+)
+from litellm.proxy.spend_tracking.spend_event_producer import SpendEventProducer
 from litellm.proxy.spend_tracking.spend_log_error_logger import (
     should_suppress_spend_log_tracebacks,
     spend_log_error,
 )
 from litellm.proxy.spend_tracking.spend_tracking_utils import (
     _sanitize_error_information_for_spend_logs,
+    _should_store_prompts_and_responses_in_spend_logs,
     get_request_model_access_groups,
 )
 from litellm.proxy.utils import ProxyUpdateSpend
@@ -71,8 +81,28 @@ _CAPTURED_IDENTITY_CALL_TYPES: Final[frozenset[str]] = frozenset(
 
 
 class _ProxyDBLogger(CustomLogger):
+    def __init__(self, spend_event_producer: SpendEventProducer | None = None) -> None:
+        super().__init__()
+        self.spend_event_producer = spend_event_producer
+
     async def async_log_success_event(self, kwargs, response_obj, start_time, end_time):
-        await self._PROXY_track_cost_callback(kwargs, response_obj, start_time, end_time)
+        if self.spend_event_producer is None or not is_offloadable_success(response_obj):
+            await self._PROXY_track_cost_callback(kwargs, response_obj, start_time, end_time)
+            return
+        event: Final = build_spend_event(
+            kwargs,
+            response_obj,
+            start_time,
+            end_time,
+            store_bodies=_should_store_prompts_and_responses_in_spend_logs(),
+        )
+        if isinstance(event, SpendEventBuildError):
+            verbose_proxy_logger.warning(
+                "spend worker: tracking cost in-process, event not buildable: %s", event.reason
+            )
+            await self._PROXY_track_cost_callback(kwargs, response_obj, start_time, end_time)
+            return
+        await self.spend_event_producer.publish(event)
 
     async def async_post_call_failure_hook(
         self,
@@ -503,6 +533,16 @@ def _write_spend_metadata_to_kwargs(kwargs: dict, metadata: dict) -> None:
                     bucket[key] = value
 
 
+async def run_spend_event(line: bytes) -> None:
+    """Run the unchanged cost pipeline on a serialized spend event (sidecar consumer and in-process fallback)."""
+    event: Final = decode_spend_event(line)
+    if isinstance(event, SpendEventDecodeError):
+        verbose_proxy_logger.error("spend worker: discarding undecodable spend event: %s", event.reason)
+        return
+    args: Final = spend_event_callback_args(event)
+    await _ProxyDBLogger()._PROXY_track_cost_callback(args.kwargs, args.response_obj, args.start_time, args.end_time)
+
+
 def _is_unbilled_interaction_response(completion_response: object) -> bool:
     from litellm.interactions.background_cost_polling import missing_usage_is_expected
     from litellm.types.interactions import InteractionsAPIResponse

litellm/proxy/proxy_server.py

@@ -453,7 +453,7 @@ from litellm.proxy.hooks.model_max_budget_limiter import (
 from litellm.proxy.hooks.prompt_injection_detection import (
     _OPTIONAL_PromptInjectionDetection,
 )
-from litellm.proxy.hooks.proxy_track_cost_callback import _ProxyDBLogger
+from litellm.proxy.hooks.proxy_track_cost_callback import _ProxyDBLogger, run_spend_event
 from litellm.proxy.image_endpoints.endpoints import router as image_router
 from litellm.proxy.list_api.common import (
     PROBLEM_TYPE_BASE,
@@ -576,6 +576,11 @@ from litellm.proxy.plugin_routes import (
 from litellm.proxy.plugin_routes import (
     router as plugin_router,
 )
+from litellm.proxy.spend_tracking.spend_event_producer import (
+    SpendEventProducer,
+    SpendWorkerSettings,
+    build_spend_event_producer,
+)
 from litellm.types.proxy.management_endpoints.management_v1 import ProblemDetail
 
 try:
@@ -1362,6 +1367,8 @@ async def proxy_startup_event(app: FastAPI) -> AsyncGenerator[None, None]:
         except Exception as e:
             verbose_proxy_logger.error("Error stopping DB health watchdog task: %s", e)
 
+    await _drain_spend_event_producer_on_shutdown()
+
     await _flush_spend_logs_queue_on_shutdown()
 
     await proxy_config.stop_config_sync_subscriber()
@@ -2441,16 +2448,27 @@ def load_from_azure_key_vault(use_azure_key_vault: bool = False):
         )
 
 
+spend_event_producer: SpendEventProducer | None = None
+
+
 def cost_tracking():
-    global prisma_client
+    global prisma_client, spend_event_producer
     if prisma_client is not None:
         from litellm.integrations.shadow_eval_logger import ShadowEvalLogger
 
-        litellm.logging_callback_manager.add_litellm_callback(_ProxyDBLogger())
-        litellm.logging_callback_manager.add_litellm_async_success_callback(_ProxyDBLogger())
+        spend_event_producer = build_spend_event_producer(SpendWorkerSettings(), fallback=run_spend_event)
+        litellm.logging_callback_manager.add_litellm_callback(_ProxyDBLogger(spend_event_producer))
+        litellm.logging_callback_manager.add_litellm_async_success_callback(_ProxyDBLogger(spend_event_producer))
         litellm.logging_callback_manager.add_litellm_callback(ShadowEvalLogger())
 
 
+async def _drain_spend_event_producer_on_shutdown() -> None:
+    if spend_event_producer is None:
+        return
+    await spend_event_producer.close(drain_timeout=SpendWorkerSettings().drain_timeout_seconds)
+    verbose_proxy_logger.info("spend worker: producer drained on shutdown. stats=%s", spend_event_producer.stats())
+
+
 # Bounds authoritative DB re-reads when enforcing a budget against a
 # stale-low spend counter: at most one DB read per counter per window.
 SPEND_DB_FLOOR_CACHE_TTL_SECONDS: Final = 5

litellm/proxy/spend_tracking/spend_event.py

@@ -0,0 +1,418 @@
+"""Compact, typed success event handed from an inference worker to the spend sidecar.
+
+``build_spend_event`` runs on the inference worker right after ``Logging.async_success_handler``
+has built the ``standard_logging_object`` (so the cost is already known). It validates the success
+callback's ``kwargs`` into the projection ``_PROXY_track_cost_callback`` and
+``DBSpendUpdateWriter.update_database`` actually read: identities and metadata, timings, usage, the
+standard logging payload without its prompt/response bodies, and the tool names. The request
+messages, the raw ``proxy_server_request`` body and the full response travel only when spend logs
+are configured to store prompts and responses. The cache key is the preset key the caching layer
+already computed, never a fresh hash over the request body.
+
+``spend_event_callback_args`` rebuilds the ``(kwargs, response_obj, start_time, end_time)`` tuple
+the existing cost pipeline consumes, so the sidecar runs the unchanged pipeline against the event.
+"""
+
+from collections.abc import Mapping, Sequence
+from dataclasses import dataclass
+from datetime import datetime
+from types import MappingProxyType
+from typing import Final, Literal, TypeAlias
+
+from pydantic import BaseModel, ConfigDict, TypeAdapter, ValidationError
+from typing_extensions import NotRequired, ReadOnly, TypedDict
+
+import litellm
+from litellm.proxy._types import UserAPIKeyAuth
+from litellm.proxy.db.spend_log_tool_index import response_tool_call_names
+from litellm.types.interactions import InteractionsAPIResponse
+from litellm.types.utils import LiteLLMBatch, Usage
+
+SPEND_EVENT_VERSION: Final = 1
+CACHE_OFF_KEY: Final = "Cache OFF"
+
+ObjectMapping: TypeAlias = Mapping[str, object]
+
+_UNSERIALIZABLE_METADATA_KEYS: Final = frozenset({"user_api_key_auth", "litellm_parent_otel_span"})
+_STANDARD_LOGGING_BODY_KEYS: Final = frozenset({"messages", "response"})
+_STANDARD_LOGGING_DROPPED_KEYS: Final = frozenset({"model_parameters"})
+_NOT_OFFLOADED_RESPONSE_TYPES: Final = (LiteLLMBatch, InteractionsAPIResponse)
+
+
+class _LitellmParams(TypedDict, total=False):
+    api_base: ReadOnly[str | None]
+    custom_llm_provider: ReadOnly[str | None]
+    litellm_call_id: ReadOnly[str | None]
+    user_api_key_end_user_id: ReadOnly[str | None]
+    metadata: ReadOnly[ObjectMapping | None]
+    litellm_metadata: ReadOnly[ObjectMapping | None]
+    proxy_server_request: ReadOnly[ObjectMapping | None]
+    preset_cache_key: ReadOnly[str | None]
+
+
+class _DynamicParams(TypedDict, total=False):
+    turn_off_message_logging: ReadOnly[bool | None]
+
+
+class _RequestBody(TypedDict, total=False):
+    tools: ReadOnly[Sequence[ObjectMapping] | None]
+
+
+class _PassthroughPayload(TypedDict, total=False):
+    request_body: ReadOnly[_RequestBody | None]
+
+
+class _ToolCallFunction(TypedDict):
+    name: ReadOnly[str]
+    arguments: ReadOnly[str]
+
+
+class _ToolCall(TypedDict):
+    id: ReadOnly[str | None]
+    type: ReadOnly[Literal["function"]]
+    function: ReadOnly[_ToolCallFunction]
+
+
+class _ToolCallMessage(TypedDict):
+    role: ReadOnly[Literal["assistant"]]
+    content: ReadOnly[None]
+    tool_calls: ReadOnly[Sequence[_ToolCall]]
+
+
+class _ToolCallChoice(TypedDict):
+    index: ReadOnly[int]
+    finish_reason: ReadOnly[Literal["tool_calls"]]
+    message: ReadOnly[_ToolCallMessage]
+
+
+class CompactResponse(TypedDict, total=False):
+    """What the spend pipeline reads off a response: its id, usage and which tools it called."""
+
+    id: ReadOnly[object]
+    model: ReadOnly[object]
+    usage: ReadOnly[object]
+    usage_info: ReadOnly[object]
+    status: ReadOnly[object]
+    background: ReadOnly[object]
+    choices: ReadOnly[Sequence[_ToolCallChoice]]
+
+
+class _SuccessKwargs(TypedDict, total=False):
+    """The success callback's ``kwargs`` (``Logging.model_call_details``), validated and projected."""
+
+    litellm_call_id: ReadOnly[str | None]
+    call_type: ReadOnly[str | None]
+    model: ReadOnly[str | None]
+    custom_llm_provider: ReadOnly[str | None]
+    stream: ReadOnly[bool | None]
+    complete_streaming_response: ReadOnly[object]
+    cache_hit: ReadOnly[bool | None]
+    response_cost: ReadOnly[float | None]
+    completion_start_time: ReadOnly[datetime | None]
+    agent_id: ReadOnly[str | None]
+    litellm_trace_id: ReadOnly[str | None]
+    litellm_params: ReadOnly[_LitellmParams]
+    standard_logging_object: ReadOnly[ObjectMapping | None]
+    standard_callback_dynamic_params: ReadOnly[_DynamicParams | None]
+    combined_usage_object: ReadOnly[Usage | None]
+    realtime_tools: ReadOnly[Sequence[object] | None]
+    realtime_tool_calls: ReadOnly[Sequence[object] | None]
+    tools: ReadOnly[Sequence[ObjectMapping] | None]
+    passthrough_logging_payload: ReadOnly[_PassthroughPayload | None]
+
+
+class _FunctionToolFunction(TypedDict):
+    name: ReadOnly[str]
+
+
+class _FunctionTool(TypedDict):
+    type: ReadOnly[Literal["function"]]
+    function: ReadOnly[_FunctionToolFunction]
+
+
+class SpendCallbackKwargs(TypedDict):
+    """The ``kwargs`` handed to ``_PROXY_track_cost_callback`` on the sidecar."""
+
+    litellm_call_id: ReadOnly[str | None]
+    call_type: ReadOnly[str | None]
+    model: ReadOnly[str | None]
+    custom_llm_provider: ReadOnly[str | None]
+    stream: ReadOnly[bool | None]
+    cache_hit: ReadOnly[bool | None]
+    response_cost: ReadOnly[float | None]
+    completion_start_time: ReadOnly[datetime | None]
+    agent_id: ReadOnly[str | None]
+    litellm_trace_id: ReadOnly[str | None]
+    litellm_params: ReadOnly[_LitellmParams]
+    standard_logging_object: ReadOnly[ObjectMapping | None]
+    standard_callback_dynamic_params: ReadOnly[_DynamicParams | None]
+    combined_usage_object: ReadOnly[Usage | None]
+    realtime_tools: ReadOnly[Sequence[object] | None]
+    realtime_tool_calls: ReadOnly[Sequence[object] | None]
+    tools: ReadOnly[Sequence[_FunctionTool] | None]
+    complete_streaming_response: NotRequired[ReadOnly[CompactResponse | None]]
+
+
+_NO_LITELLM_PARAMS: Final[_LitellmParams] = {}
+_SUCCESS_KWARGS: Final = TypeAdapter(_SuccessKwargs)
+_OBJECT_MAPPING: Final = TypeAdapter(ObjectMapping)
+_COMPACT_RESPONSE: Final = TypeAdapter(CompactResponse)
+
+
+class SpendEvent(BaseModel):
+    model_config = ConfigDict(frozen=True, extra="forbid")
+
+    version: Literal[1]
+    litellm_call_id: str | None
+    call_type: str | None
+    model: str | None
+    custom_llm_provider: str | None
+    stream: bool | None
+    complete_streaming_response: bool
+    cache_hit: bool | None
+    response_cost: float | None
+    start_time: datetime
+    end_time: datetime
+    completion_start_time: datetime | None
+    agent_id: str | None
+    litellm_trace_id: str | None
+    litellm_params: _LitellmParams
+    standard_logging_object: ObjectMapping | None
+    standard_callback_dynamic_params: _DynamicParams | None
+    response: CompactResponse | None
+    combined_usage: ObjectMapping | None
+    realtime_tools: Sequence[object] | None
+    realtime_tool_calls: Sequence[object] | None
+    request_tool_names: tuple[str, ...]
+
+
+@dataclass(frozen=True, slots=True)
+class SpendEventCallbackArgs:
+    kwargs: SpendCallbackKwargs
+    response_obj: CompactResponse | None
+    start_time: datetime
+    end_time: datetime
+
+
+@dataclass(frozen=True, slots=True)
+class SpendEventBuildError:
+    reason: str
+
+
+@dataclass(frozen=True, slots=True)
+class SpendEventDecodeError:
+    reason: str
+
+
+def is_offloadable_success(response_obj: object) -> bool:
+    """Batch retrieves and interaction polls branch on the concrete response class, so they stay in-process."""
+    return not isinstance(response_obj, _NOT_OFFLOADED_RESPONSE_TYPES)
+
+
+def _json_fallback(value: object) -> str:
+    return str(value)
+
+
+def _mapping_or_none(value: object) -> ObjectMapping | None:
+    try:
+        return _OBJECT_MAPPING.validate_python(value)
+    except ValidationError:
+        return None
+
+
+def _drop_keys(mapping: ObjectMapping, keys: frozenset[str]) -> ObjectMapping:
+    return MappingProxyType({key: value for key, value in mapping.items() if key not in keys})
+
+
+def _budget_reservation(metadata: ObjectMapping) -> ObjectMapping | None:
+    """The admission-time reservation, wherever the request setup left it, so the sidecar can reconcile it."""
+    direct: Final = _mapping_or_none(metadata.get("user_api_key_budget_reservation"))
+    if direct is not None:
+        return direct
+    auth: Final = metadata.get("user_api_key_auth")
+    if isinstance(auth, UserAPIKeyAuth):
+        return auth.budget_reservation
+    auth_mapping: Final = _mapping_or_none(auth)
+    return _mapping_or_none(auth_mapping.get("budget_reservation")) if auth_mapping is not None else None
+
+
+def _metadata_for_event(
+    metadata: ObjectMapping | None, budget_reservation: ObjectMapping | None
+) -> ObjectMapping | None:
+    if metadata is None:
+        return None
+    kept: Final = _drop_keys(metadata, _UNSERIALIZABLE_METADATA_KEYS)
+    if budget_reservation is None:
+        return kept
+    return MappingProxyType({**kept, "user_api_key_budget_reservation": budget_reservation})
+
+
+def _litellm_params_for_event(
+    litellm_params: _LitellmParams, cache_key: str | None, store_bodies: bool
+) -> _LitellmParams:
+    metadata: Final = litellm_params.get("metadata")
+    litellm_metadata: Final = litellm_params.get("litellm_metadata")
+    budget_reservation: Final = next(
+        (
+            reservation
+            for source in (litellm_metadata, metadata)
+            if source is not None and (reservation := _budget_reservation(source)) is not None
+        ),
+        None,
+    )
+    projected: Final[_LitellmParams] = {
+        "api_base": litellm_params.get("api_base"),
+        "custom_llm_provider": litellm_params.get("custom_llm_provider"),
+        "litellm_call_id": litellm_params.get("litellm_call_id"),
+        "user_api_key_end_user_id": litellm_params.get("user_api_key_end_user_id"),
+        "metadata": _metadata_for_event(metadata, budget_reservation),
+        "litellm_metadata": _metadata_for_event(litellm_metadata, budget_reservation),
+        "proxy_server_request": litellm_params.get("proxy_server_request") if store_bodies else None,
+        "preset_cache_key": cache_key,
+    }
+    return projected
+
+
+def _standard_logging_for_event(sl_object: ObjectMapping | None, store_bodies: bool) -> ObjectMapping | None:
+    if sl_object is None:
+        return None
+    dropped: Final = (
+        _STANDARD_LOGGING_DROPPED_KEYS if store_bodies else _STANDARD_LOGGING_DROPPED_KEYS | _STANDARD_LOGGING_BODY_KEYS
+    )
+    return _drop_keys(sl_object, dropped)
+
+
+def _tool_call(name: str) -> _ToolCall:
+    tool_call: Final[_ToolCall] = {"id": None, "type": "function", "function": {"name": name, "arguments": "{}"}}
+    return tool_call
+
+
+def _tool_call_choice(names: Sequence[str]) -> _ToolCallChoice:
+    choice: Final[_ToolCallChoice] = {
+        "index": 0,
+        "finish_reason": "tool_calls",
+        "message": {"role": "assistant", "content": None, "tool_calls": tuple(_tool_call(name) for name in names)},
+    }
+    return choice
+
+
+def _compact_response(response_obj: object) -> CompactResponse | None:
+    """Usage, identity and tool calls of the response, in chat-completions shape, without the content."""
+    dumped: Final = response_obj.model_dump() if isinstance(response_obj, BaseModel) else _mapping_or_none(response_obj)
+    if dumped is None:
+        return None
+    scalars: Final = _COMPACT_RESPONSE.validate_python(_drop_keys(dumped, frozenset({"choices"})))
+    tool_call_names: Final = response_tool_call_names(response_obj)
+    if not tool_call_names:
+        return scalars
+    with_tool_calls: Final[CompactResponse] = {**scalars, "choices": (_tool_call_choice(tool_call_names),)}
+    return with_tool_calls
+
+
+def _tool_name(tool: ObjectMapping) -> str | None:
+    """Chat tools nest the name under ``function``; Anthropic and Responses API tools keep it at the top."""
+    function: Final = _mapping_or_none(tool.get("function"))
+    name: Final = function.get("name") if function is not None else tool.get("name")
+    return name.strip() if isinstance(name, str) and name.strip() else None
+
+
+def _request_tool_names(kwargs: _SuccessKwargs) -> tuple[str, ...]:
+    passthrough: Final = kwargs.get("passthrough_logging_payload")
+    request_body: Final = passthrough.get("request_body") if passthrough is not None else None
+    passthrough_tools: Final = request_body.get("tools") if request_body is not None else None
+    return tuple(
+        name
+        for source in (kwargs.get("tools"), passthrough_tools)
+        if source is not None
+        for tool in source
+        if (name := _tool_name(tool)) is not None
+    )
+
+
+def preset_spend_log_cache_key(litellm_params: _LitellmParams) -> str | None:
+    """The key the caching layer already stored in ``litellm_params``, or ``Cache OFF``; never hashes the body."""
+    if litellm.cache is None:
+        return CACHE_OFF_KEY
+    return litellm_params.get("preset_cache_key")
+
+
+def _function_tool(name: str) -> _FunctionTool:
+    tool: Final[_FunctionTool] = {"type": "function", "function": {"name": name}}
+    return tool
+
+
+def build_spend_event(
+    raw_kwargs: ObjectMapping, response_obj: object, start_time: datetime, end_time: datetime, store_bodies: bool
+) -> bytes | SpendEventBuildError:
+    """Validate the success callback's kwargs and serialize the event once, as a single JSON line."""
+    try:
+        kwargs: Final = _SUCCESS_KWARGS.validate_python(raw_kwargs)
+    except ValidationError as error:
+        return SpendEventBuildError(reason=str(error))
+    litellm_params: Final = kwargs.get("litellm_params", _NO_LITELLM_PARAMS)
+    sl_object: Final = kwargs.get("standard_logging_object")
+    cache_key: Final = preset_spend_log_cache_key(litellm_params)
+    response_cost: Final = sl_object.get("response_cost") if sl_object is not None else kwargs.get("response_cost")
+    combined_usage: Final = kwargs.get("combined_usage_object")
+    event: Final = SpendEvent(
+        version=SPEND_EVENT_VERSION,
+        litellm_call_id=kwargs.get("litellm_call_id"),
+        call_type=kwargs.get("call_type"),
+        model=kwargs.get("model"),
+        custom_llm_provider=kwargs.get("custom_llm_provider"),
+        stream=kwargs.get("stream"),
+        complete_streaming_response="complete_streaming_response" in kwargs,
+        cache_hit=kwargs.get("cache_hit"),
+        response_cost=response_cost if isinstance(response_cost, (int, float)) else None,
+        start_time=start_time,
+        end_time=end_time,
+        completion_start_time=kwargs.get("completion_start_time"),
+        agent_id=kwargs.get("agent_id"),
+        litellm_trace_id=kwargs.get("litellm_trace_id"),
+        litellm_params=_litellm_params_for_event(litellm_params, cache_key, store_bodies),
+        standard_logging_object=_standard_logging_for_event(sl_object, store_bodies),
+        standard_callback_dynamic_params=kwargs.get("standard_callback_dynamic_params"),
+        response=_compact_response(response_obj),
+        combined_usage=combined_usage.model_dump() if combined_usage is not None else None,
+        realtime_tools=kwargs.get("realtime_tools"),
+        realtime_tool_calls=kwargs.get("realtime_tool_calls"),
+        request_tool_names=_request_tool_names(kwargs),
+    )
+    return event.model_dump_json(fallback=_json_fallback).encode() + b"\n"
+
+
+def decode_spend_event(line: bytes) -> SpendEvent | SpendEventDecodeError:
+    try:
+        return SpendEvent.model_validate_json(line)
+    except ValidationError as error:
+        return SpendEventDecodeError(reason=str(error))
+
+
+def spend_event_callback_args(event: SpendEvent) -> SpendEventCallbackArgs:
+    """The ``(kwargs, response_obj, start_time, end_time)`` the in-process cost callback receives."""
+    tools: Final = tuple(_function_tool(name) for name in event.request_tool_names)
+    kwargs: Final[SpendCallbackKwargs] = {
+        "litellm_call_id": event.litellm_call_id,
+        "call_type": event.call_type,
+        "model": event.model,
+        "custom_llm_provider": event.custom_llm_provider,
+        "stream": event.stream,
+        "cache_hit": event.cache_hit,
+        "response_cost": event.response_cost,
+        "completion_start_time": event.completion_start_time,
+        "agent_id": event.agent_id,
+        "litellm_trace_id": event.litellm_trace_id,
+        "litellm_params": event.litellm_params,
+        "standard_logging_object": event.standard_logging_object,
+        "standard_callback_dynamic_params": event.standard_callback_dynamic_params,
+        "combined_usage_object": Usage.model_validate(event.combined_usage)
+        if event.combined_usage is not None
+        else None,
+        "realtime_tools": event.realtime_tools,
+        "realtime_tool_calls": event.realtime_tool_calls,
+        "tools": tools or None,
+    }
+    if not event.complete_streaming_response:
+        return SpendEventCallbackArgs(kwargs, event.response, event.start_time, event.end_time)
+    streaming_kwargs: Final[SpendCallbackKwargs] = {**kwargs, "complete_streaming_response": event.response}
+    return SpendEventCallbackArgs(streaming_kwargs, event.response, event.start_time, event.end_time)

litellm/proxy/spend_tracking/spend_event_producer.py

@@ -0,0 +1,276 @@
+"""Fire-and-forget push of serialized spend events from an inference worker to the pod-local sidecar.
+
+``LITELLM_SPEND_WORKER_ENABLED=true`` turns the push on in the gateway; the sidecar process sets
+``LITELLM_JOB_ROLE=spend_worker`` and always runs the pipeline in-process. Events queue in a bounded
+in-memory buffer that a single writer task flushes over a unix socket or loopback TCP connection.
+When the sidecar is unreachable, the buffer is full, or the connection breaks mid-write, each affected
+event follows ``LITELLM_SPEND_WORKER_ON_UNAVAILABLE``: ``fallback`` runs the existing cost pipeline in
+the worker, ``drop`` counts it and moves on. Transitions are logged with the counters, so a sidecar
+outage is visible without scraping anything.
+
+Delivery is at-most-once: a sidecar crash loses the events already handed to its socket. Events from
+one uvicorn worker are handled in the order it produced them; events from different workers interleave,
+exactly like the in-process callbacks do today.
+"""
+
+import asyncio
+import time
+from collections.abc import Awaitable, Callable
+from dataclasses import dataclass
+from typing import Final, Literal, TypeAlias
+from urllib.parse import urlsplit
+
+from pydantic import AliasChoices, Field
+from pydantic_settings import BaseSettings, SettingsConfigDict
+
+from litellm._logging import verbose_proxy_logger
+
+SPEND_WORKER_ENV_PREFIX: Final = "LITELLM_SPEND_WORKER_"
+SPEND_WORKER_JOB_ROLE: Final = "spend_worker"
+DEFAULT_SPEND_WORKER_ADDRESS: Final = "unix:///var/run/litellm/spend-worker.sock"
+RECONNECT_BACKOFF_SECONDS: Final = 1.0
+DROP_LOG_EVERY: Final = 1000
+
+UnavailablePolicy: TypeAlias = Literal["fallback", "drop"]
+PublishOutcome: TypeAlias = Literal["queued", "fallback", "dropped"]
+
+
+class SpendWorkerSettings(BaseSettings):
+    """``LITELLM_SPEND_WORKER_*`` env vars, shared by the gateway producer and the sidecar consumer."""
+
+    model_config = SettingsConfigDict(
+        env_prefix=SPEND_WORKER_ENV_PREFIX, case_sensitive=False, extra="ignore", frozen=True, populate_by_name=True
+    )
+
+    enabled: bool = False
+    address: str = DEFAULT_SPEND_WORKER_ADDRESS
+    buffer_size: int = Field(default=1000, ge=1)
+    on_unavailable: UnavailablePolicy = "fallback"
+    drain_timeout_seconds: float = Field(default=10.0, gt=0)
+    connect_timeout_seconds: float = Field(default=1.0, gt=0)
+    job_role: str | None = Field(default=None, validation_alias=AliasChoices("LITELLM_JOB_ROLE"))
+
+    @property
+    def produces(self) -> bool:
+        return self.enabled and self.job_role != SPEND_WORKER_JOB_ROLE
+
+
+@dataclass(frozen=True, slots=True)
+class UnixAddress:
+    path: str
+
+
+@dataclass(frozen=True, slots=True)
+class TcpAddress:
+    host: str
+    port: int
+
+
+@dataclass(frozen=True, slots=True)
+class AddressError:
+    reason: str
+
+
+SpendWorkerAddress: TypeAlias = UnixAddress | TcpAddress
+
+
+def parse_spend_worker_address(address: str) -> SpendWorkerAddress | AddressError:
+    """``unix:///path/to.sock`` or ``tcp://127.0.0.1:port``."""
+    parsed: Final = urlsplit(address)
+    if parsed.scheme == "unix" and parsed.path:
+        return UnixAddress(path=parsed.path)
+    if parsed.scheme == "tcp" and parsed.hostname and parsed.port is not None:
+        return TcpAddress(host=parsed.hostname, port=parsed.port)
+    return AddressError(reason=f"expected unix:///path or tcp://host:port, got {address!r}")
+
+
+async def open_spend_worker_connection(
+    address: SpendWorkerAddress, timeout: float
+) -> tuple[asyncio.StreamReader, asyncio.StreamWriter]:
+    match address:
+        case UnixAddress(path=path):
+            return await asyncio.wait_for(asyncio.open_unix_connection(path), timeout)
+        case TcpAddress(host=host, port=port):
+            return await asyncio.wait_for(asyncio.open_connection(host, port), timeout)
+
+
+def build_spend_event_producer(
+    settings: SpendWorkerSettings, fallback: Callable[[bytes], Awaitable[None]]
+) -> "SpendEventProducer | None":
+    """The gateway producer for these settings, or ``None`` when the pipeline stays in-process."""
+    if not settings.produces:
+        return None
+    address: Final = parse_spend_worker_address(settings.address)
+    if isinstance(address, AddressError):
+        verbose_proxy_logger.error("spend worker: %s; running the spend pipeline in-process", address.reason)
+        return None
+    verbose_proxy_logger.info(
+        "spend worker: offloading spend tracking to %s (buffer=%d, on_unavailable=%s)",
+        settings.address,
+        settings.buffer_size,
+        settings.on_unavailable,
+    )
+    return SpendEventProducer(
+        address=address,
+        on_unavailable=settings.on_unavailable,
+        buffer_size=settings.buffer_size,
+        connect_timeout=settings.connect_timeout_seconds,
+        fallback=fallback,
+    )
+
+
+@dataclass(frozen=True, slots=True)
+class SpendEventProducerStats:
+    queued: int
+    sent: int
+    fallback: int
+    dropped: int
+    connected: bool
+
+
+class SpendEventProducer:
+    """Bounded buffer plus one writer task per process; see the module docstring for the contract."""
+
+    def __init__(
+        self,
+        address: SpendWorkerAddress,
+        on_unavailable: UnavailablePolicy,
+        buffer_size: int,
+        connect_timeout: float,
+        fallback: Callable[[bytes], Awaitable[None]],
+        clock: Callable[[], float] = time.monotonic,
+    ) -> None:
+        self._address = address
+        self._on_unavailable = on_unavailable
+        self._buffer_size = buffer_size
+        self._connect_timeout = connect_timeout
+        self._fallback = fallback
+        self._clock = clock
+        self._queue: asyncio.Queue[bytes] | None = None
+        self._writer_task: asyncio.Task[None] | None = None
+        self._writer: asyncio.StreamWriter | None = None
+        self._closing = False
+        self._next_connect_at = 0.0
+        self._queued = 0
+        self._sent = 0
+        self._fallback_count = 0
+        self._dropped = 0
+
+    def stats(self) -> SpendEventProducerStats:
+        return SpendEventProducerStats(
+            queued=self._queued,
+            sent=self._sent,
+            fallback=self._fallback_count,
+            dropped=self._dropped,
+            connected=self._writer is not None,
+        )
+
+    async def publish(self, line: bytes) -> PublishOutcome:
+        """Hand one serialized event to the writer task, or apply the unavailable policy right away."""
+        if self._closing or self._clock() < self._next_connect_at:
+            return await self._unavailable(line, "sidecar unreachable")
+        queue: Final = self._ensure_writer()
+        try:
+            queue.put_nowait(line)
+        except asyncio.QueueFull:
+            return await self._unavailable(line, "buffer full")
+        self._queued += 1
+        return "queued"
+
+    async def close(self, drain_timeout: float) -> None:
+        """Flush the buffer for up to ``drain_timeout`` seconds, then apply the unavailable policy to the rest."""
+        self._closing = True
+        queue: Final = self._queue
+        task: Final = self._writer_task
+        if queue is None or task is None:
+            return
+        try:
+            await asyncio.wait_for(queue.join(), drain_timeout)
+        except asyncio.TimeoutError:
+            verbose_proxy_logger.warning(
+                "spend worker: %s events still buffered after %.1fs drain timeout", queue.qsize(), drain_timeout
+            )
+        task.cancel()
+        try:
+            await task
+        except asyncio.CancelledError:
+            pass
+        while not queue.empty():
+            await self._unavailable(queue.get_nowait(), "shutdown")
+        await self._disconnect()
+
+    def _ensure_writer(self) -> asyncio.Queue[bytes]:
+        if self._queue is None:
+            self._queue = asyncio.Queue(maxsize=self._buffer_size)
+        if self._writer_task is None or self._writer_task.done():
+            self._writer_task = asyncio.get_running_loop().create_task(self._run_writer(self._queue))
+        return self._queue
+
+    async def _run_writer(self, queue: asyncio.Queue[bytes]) -> None:
+        while True:
+            line = await queue.get()
+            try:
+                await self._send(line)
+            finally:
+                queue.task_done()
+
+    async def _send(self, line: bytes) -> None:
+        writer: Final = await self._connect()
+        if writer is None:
+            await self._unavailable(line, "sidecar unreachable")
+            return
+        try:
+            writer.write(line)
+            await writer.drain()
+        except (ConnectionError, OSError) as error:
+            await self._disconnect()
+            self._next_connect_at = self._clock() + RECONNECT_BACKOFF_SECONDS
+            await self._unavailable(line, f"write failed: {error}")
+            return
+        self._sent += 1
+
+    async def _connect(self) -> asyncio.StreamWriter | None:
+        if self._writer is not None:
+            return self._writer
+        if self._clock() < self._next_connect_at:
+            return None
+        try:
+            _, writer = await open_spend_worker_connection(self._address, self._connect_timeout)
+        except (ConnectionError, OSError, asyncio.TimeoutError) as error:
+            self._next_connect_at = self._clock() + RECONNECT_BACKOFF_SECONDS
+            verbose_proxy_logger.warning(
+                "spend worker: cannot reach %s (%s); applying %s policy for %.0fs. stats=%s",
+                self._address,
+                error,
+                self._on_unavailable,
+                RECONNECT_BACKOFF_SECONDS,
+                self.stats(),
+            )
+            return None
+        self._writer = writer
+        verbose_proxy_logger.info("spend worker: connected to %s. stats=%s", self._address, self.stats())
+        return writer
+
+    async def _disconnect(self) -> None:
+        writer: Final = self._writer
+        self._writer = None
+        if writer is None:
+            return
+        writer.close()
+        try:
+            await writer.wait_closed()
+        except (ConnectionError, OSError):
+            pass
+
+    async def _unavailable(self, line: bytes, reason: str) -> PublishOutcome:
+        if self._on_unavailable == "fallback":
+            self._fallback_count += 1
+            try:
+                await self._fallback(line)
+            except Exception:
+                verbose_proxy_logger.exception("spend worker: in-process fallback failed (%s)", reason)
+            return "fallback"
+        self._dropped += 1
+        if self._dropped % DROP_LOG_EVERY == 1:
+            verbose_proxy_logger.warning("spend worker: dropping spend event (%s). stats=%s", reason, self.stats())
+        return "dropped"

litellm/proxy/spend_tracking/spend_tracking_utils.py

@@ -533,10 +533,12 @@ def get_logging_payload(kwargs, response_obj, start_time, end_time) -> SpendLogs
                 additional_usage_values["cache_creation_input_tokens"] = cache_write_tokens
     clean_metadata["additional_usage_values"] = additional_usage_values
 
-    if litellm.cache is not None:
-        cache_key = litellm.cache.get_cache_key(**kwargs)
-    else:
+    if litellm.cache is None:
         cache_key = "Cache OFF"
+    elif litellm_params.get("preset_cache_key") is not None:
+        cache_key = litellm_params["preset_cache_key"]
+    else:
+        cache_key = litellm.cache.get_cache_key(**kwargs)
     if cache_hit is True:
         import time
 

litellm/proxy/spend_worker.py

@@ -0,0 +1,160 @@
+"""Spend sidecar: consume spend events from the pod's inference workers and run the cost pipeline.
+
+Runs the proxy startup lifespan (config, Prisma, Redis transaction buffer, scheduled spend flushes)
+without serving HTTP, then listens on ``LITELLM_SPEND_WORKER_ADDRESS`` for newline-delimited spend
+events. Each event goes through the unchanged ``_ProxyDBLogger._PROXY_track_cost_callback``, so
+spend logs, spend counters, budget reservation reconciliation and cache updates happen exactly as
+they would in-process, just in this container. Events are handled in order per producer connection
+(one per uvicorn worker); a slow pipeline fills the socket buffer and the producer's bounded queue,
+which is the backpressure that triggers its fallback or drop policy. ``SIGTERM`` stops accepting
+connections, finishes the events already sent, then runs the proxy shutdown (which flushes the
+buffered spend transactions).
+
+    LITELLM_JOB_ROLE=spend_worker python -m litellm.proxy.spend_worker [--address unix:///path.sock]
+"""
+
+import asyncio
+import os
+import signal
+import sys
+from collections.abc import Awaitable, Callable, Sequence
+from pathlib import Path
+from typing import Final
+
+from litellm._logging import verbose_proxy_logger
+from litellm.proxy.spend_tracking.spend_event_producer import (
+    SPEND_WORKER_JOB_ROLE,
+    AddressError,
+    SpendWorkerAddress,
+    SpendWorkerSettings,
+    TcpAddress,
+    UnixAddress,
+    parse_spend_worker_address,
+)
+
+MAX_EVENT_BYTES: Final = 64 * 1024 * 1024
+
+
+class SpendEventConsumer:
+    """Accepts producer connections and runs ``handler`` on every line each one sends, in order."""
+
+    def __init__(self, handler: Callable[[bytes], Awaitable[None]]) -> None:
+        self._handler = handler
+        self._open_connections = 0
+        self._idle = asyncio.Event()
+        self._idle.set()
+        self._received = 0
+        self._handled = 0
+        self._failed = 0
+
+    @property
+    def received(self) -> int:
+        return self._received
+
+    @property
+    def handled(self) -> int:
+        return self._handled
+
+    @property
+    def failed(self) -> int:
+        return self._failed
+
+    async def serve(self, address: SpendWorkerAddress) -> asyncio.Server:
+        match address:
+            case UnixAddress(path=path):
+                socket_path: Final = Path(path)
+                socket_path.parent.mkdir(parents=True, exist_ok=True)
+                socket_path.unlink(missing_ok=True)
+                return await asyncio.start_unix_server(self._on_connection, path=path, limit=MAX_EVENT_BYTES)
+            case TcpAddress(host=host, port=port):
+                return await asyncio.start_server(self._on_connection, host=host, port=port, limit=MAX_EVENT_BYTES)
+
+    async def _on_connection(self, reader: asyncio.StreamReader, writer: asyncio.StreamWriter) -> None:
+        self._open_connections += 1
+        self._idle.clear()
+        try:
+            while line := await reader.readline():
+                if not line.endswith(b"\n"):
+                    verbose_proxy_logger.error("spend worker: discarding truncated spend event (%d bytes)", len(line))
+                    break
+                self._received += 1
+                await self._handle(line)
+        except (ConnectionError, asyncio.IncompleteReadError, asyncio.LimitOverrunError) as error:
+            verbose_proxy_logger.warning("spend worker: producer connection ended abnormally: %s", error)
+        finally:
+            writer.close()
+            self._open_connections -= 1
+            if self._open_connections == 0:
+                self._idle.set()
+
+    async def _handle(self, line: bytes) -> None:
+        try:
+            await self._handler(line)
+            self._handled += 1
+        except Exception:
+            self._failed += 1
+            verbose_proxy_logger.exception("spend worker: spend event failed")
+
+    async def drain(self, timeout: float) -> int:
+        """Keep serving the open connections until every producer hangs up, or ``timeout`` seconds pass.
+
+        Returns how many producer connections were still open when the timeout hit.
+        """
+        try:
+            await asyncio.wait_for(self._idle.wait(), timeout)
+        except TimeoutError:
+            pass
+        return self._open_connections
+
+
+def _install_stop_signals(loop: asyncio.AbstractEventLoop, stop: asyncio.Event) -> None:
+    for signum in (signal.SIGTERM, signal.SIGINT):
+        loop.add_signal_handler(signum, stop.set)
+
+
+async def run_spend_worker(address: SpendWorkerAddress, drain_timeout: float) -> None:
+    from fastapi import FastAPI
+
+    from litellm.proxy.hooks.proxy_track_cost_callback import run_spend_event
+    from litellm.proxy.proxy_server import proxy_startup_event
+
+    stop: Final = asyncio.Event()
+    _install_stop_signals(asyncio.get_running_loop(), stop)
+    consumer: Final = SpendEventConsumer(handler=run_spend_event)
+    async with proxy_startup_event(FastAPI()):
+        server: Final = await consumer.serve(address)
+        verbose_proxy_logger.info("spend worker: listening on %s", address)
+        await stop.wait()
+        server.close()
+        still_open: Final = await consumer.drain(drain_timeout)
+        verbose_proxy_logger.info(
+            "spend worker: stopping. received=%d handled=%d failed=%d connections_cut=%d",
+            consumer.received,
+            consumer.handled,
+            consumer.failed,
+            still_open,
+        )
+
+
+def _address_argument(argv: Sequence[str], default: str) -> str | AddressError:
+    match tuple(argv):
+        case ():
+            return default
+        case ("--address", value):
+            return value
+        case _:
+            return AddressError(f"usage: python -m litellm.proxy.spend_worker [--address ADDRESS], got {tuple(argv)}")
+
+
+def main(argv: Sequence[str]) -> None:
+    os.environ.setdefault("LITELLM_JOB_ROLE", SPEND_WORKER_JOB_ROLE)
+    settings: Final = SpendWorkerSettings()
+    raw_address: Final = _address_argument(argv, default=settings.address)
+    address: Final = raw_address if isinstance(raw_address, AddressError) else parse_spend_worker_address(raw_address)
+    if isinstance(address, AddressError):
+        sys.exit(f"LiteLLM spend worker: {address.reason}")
+    asyncio.run(run_spend_worker(address, drain_timeout=settings.drain_timeout_seconds))
+
+
+if __name__ == "__main__":
+    main(sys.argv[1:])

litellm/utils.py

@@ -1843,6 +1843,9 @@ def client(original_function):
                 elif _caching_handler_response.embedding_all_elements_cache_hit is True:
                     return _caching_handler_response.final_embedding_cached_response
 
+            if _llm_caching_handler.preset_cache_key is not None:
+                logging_obj.litellm_params["preset_cache_key"] = _llm_caching_handler.preset_cache_key
+
             # CHECK MAX TOKENS
             if (
                 kwargs.get("max_tokens", None) is not None

tests/test_litellm/proxy/hooks/test_proxy_track_cost_callback.py

@@ -5,14 +5,20 @@ from unittest.mock import AsyncMock, MagicMock, patch
 import pytest
 
 from litellm.litellm_core_utils.internal_call_metadata import MODEL_ACCESS_GROUP_METADATA_KEY
-from litellm.proxy._types import UserAPIKeyAuth
+from litellm.proxy._types import SpendLogsPayload, UserAPIKeyAuth
+from litellm.proxy.db.spend_log_tool_index import response_tool_call_names
 from litellm.proxy.hooks.proxy_track_cost_callback import (
     _get_budget_reservation_from_metadata,
     _ProxyDBLogger,
     _should_track_cost_callback,
     _update_database_and_spend_counters,
+    run_spend_event,
 )
-from litellm.types.utils import CallTypes, Usage
+from litellm.proxy.spend_tracking.spend_event import SpendEventDecodeError, build_spend_event, decode_spend_event
+from litellm.proxy.spend_tracking.spend_event_producer import SpendEventProducer, UnixAddress
+from litellm.proxy.spend_tracking.spend_tracking_utils import get_logging_payload
+from litellm.proxy.spend_worker import SpendEventConsumer
+from litellm.types.utils import CallTypes, ModelResponse, Usage
 
 
 @pytest.mark.asyncio
@@ -2096,3 +2102,216 @@ async def test_spend_counters_keep_every_granted_group_when_the_deployment_is_un
     )
 
     assert charged == ("premium", "tier0")
+
+
+def _offload_kwargs() -> dict:
+    big_prompt = "x" * 10_000
+    reservation = {"reserved_cost": 0.5, "entries": [{"counter_key": "key:hash-1", "reserved_cost": 0.5}]}
+    return {
+        "litellm_call_id": "call-1",
+        "call_type": "acompletion",
+        "model": "gpt-4o",
+        "custom_llm_provider": "openai",
+        "stream": False,
+        "cache_hit": None,
+        "response_cost": 0.0125,
+        "completion_start_time": datetime(2026, 1, 1, 0, 0, 1),
+        "messages": [{"role": "user", "content": big_prompt}],
+        "tools": [{"type": "function", "function": {"name": "get_weather", "parameters": {"type": "object"}}}],
+        "litellm_params": {
+            "api_base": "https://api.openai.com",
+            "preset_cache_key": None,
+            "proxy_server_request": {"body": {"messages": [{"role": "user", "content": big_prompt}]}},
+            "metadata": {
+                "user_api_key": "hash-1",
+                "user_api_key_hash": "hash-1",
+                "user_api_key_alias": "alias-1",
+                "user_api_key_user_id": "user-1",
+                "user_api_key_team_id": "team-1",
+                "user_api_key_org_id": "org-1",
+                "user_api_key_end_user_id": "end-user-1",
+                "user_api_key_auth": UserAPIKeyAuth(api_key="hash-1", budget_reservation=reservation),
+                "model_group": "gpt-4o",
+                "model_info": {"id": "deployment-1"},
+                "tags": ["tag-a"],
+            },
+        },
+        "standard_logging_object": {
+            "id": "chatcmpl-1",
+            "trace_id": "trace-1",
+            "response_cost": 0.0125,
+            "model": "gpt-4o-2024-08-06",
+            "model_id": "deployment-1",
+            "model_group": "gpt-4o",
+            "api_base": "https://api.openai.com",
+            "custom_llm_provider": "openai",
+            "prompt_tokens": 5000,
+            "completion_tokens": 4000,
+            "total_tokens": 9000,
+            "request_tags": ["tag-a"],
+            "request_model_access_groups": ["premium"],
+            "messages": [{"role": "user", "content": big_prompt}],
+            "response": {"choices": [{"message": {"content": "y" * 10_000}}]},
+            "model_parameters": {"temperature": 0.1},
+            "metadata": {
+                "user_api_key_hash": "hash-1",
+                "user_api_key_end_user_id": "end-user-1",
+                "usage_object": {"prompt_tokens": 5000, "completion_tokens": 4000, "total_tokens": 9000},
+            },
+            "hidden_params": {"litellm_overhead_time_ms": 3},
+            "model_map_information": {},
+            "cost_breakdown": {"input_cost": 0.0125, "output_cost": 0.0},
+        },
+    }
+
+
+def _offload_response() -> ModelResponse:
+    return ModelResponse(
+        id="chatcmpl-1",
+        model="gpt-4o-2024-08-06",
+        choices=[
+            {
+                "index": 0,
+                "message": {
+                    "role": "assistant",
+                    "content": None,
+                    "tool_calls": [
+                        {"id": "call-1", "type": "function", "function": {"name": "get_weather", "arguments": "{}"}}
+                    ],
+                },
+                "finish_reason": "tool_calls",
+            }
+        ],
+        usage=Usage(prompt_tokens=5000, completion_tokens=4000, total_tokens=9000),
+    )
+
+
+class _RecordingHandler:
+    def __init__(self) -> None:
+        self.lines: list[bytes] = []  # mutable-ok: test double records the events the sidecar received
+
+    async def __call__(self, line: bytes) -> None:
+        self.lines.append(line)
+
+
+async def _no_fallback(line: bytes) -> None:
+    raise AssertionError("the sidecar was reachable, nothing should fall back")
+
+
+@pytest.mark.asyncio
+async def test_async_log_success_event_hands_the_sidecar_a_compact_event_and_skips_the_pipeline(tmp_path):
+    handler = _RecordingHandler()
+    consumer = SpendEventConsumer(handler)
+    address = UnixAddress(path=str(tmp_path / "spend.sock"))
+    server = await consumer.serve(address)
+    producer = SpendEventProducer(
+        address=address, on_unavailable="fallback", buffer_size=10, connect_timeout=1.0, fallback=_no_fallback
+    )
+    logger = _ProxyDBLogger(producer)
+
+    with (
+        patch("litellm.proxy.proxy_server.proxy_logging_obj") as mock_proxy_logging,
+        patch("litellm.proxy.proxy_server.increment_spend_counters", new_callable=AsyncMock) as counters,
+    ):
+        mock_proxy_logging.db_spend_update_writer.update_database = AsyncMock()
+        await logger.async_log_success_event(_offload_kwargs(), _offload_response(), datetime.now(), datetime.now())
+        await producer.close(drain_timeout=5.0)
+        server.close()
+        assert await consumer.drain(timeout=5.0) == 0
+
+    mock_proxy_logging.db_spend_update_writer.update_database.assert_not_awaited()
+    counters.assert_not_awaited()
+    assert producer.stats().sent == 1
+    assert len(handler.lines) == 1
+    assert len(handler.lines[0]) < 4_000
+    event = decode_spend_event(handler.lines[0])
+    assert not isinstance(event, SpendEventDecodeError)
+    assert event.litellm_params["metadata"]["user_api_key_team_id"] == "team-1"
+    assert event.response_cost == 0.0125
+
+
+@pytest.mark.asyncio
+async def test_async_log_success_event_keeps_batch_retrieves_in_process():
+    producer = SpendEventProducer(
+        address=UnixAddress(path="/nonexistent/spend.sock"),
+        on_unavailable="drop",
+        buffer_size=10,
+        connect_timeout=1.0,
+        fallback=_no_fallback,
+    )
+    logger = _ProxyDBLogger(producer)
+    kwargs = _batch_retrieve_kwargs(CallTypes.aretrieve_batch.value)
+
+    with patch("litellm.proxy.proxy_server.proxy_logging_obj") as mock_proxy_logging:
+        mock_proxy_logging.db_spend_update_writer.update_database = AsyncMock()
+        await logger.async_log_success_event(
+            kwargs, _retrieved_batch("in_progress", output_file_id=None), datetime.now(), datetime.now()
+        )
+
+    assert producer.stats().queued == 0
+
+
+async def _spend_row_written_by(run) -> tuple[SpendLogsPayload, dict, tuple[str, ...]]:
+    with (
+        patch("litellm.proxy.proxy_server.proxy_logging_obj") as mock_proxy_logging,
+        patch("litellm.proxy.proxy_server.increment_spend_counters", new_callable=AsyncMock) as counters,
+        patch("litellm.proxy.proxy_server.update_cache", new_callable=AsyncMock),
+    ):
+        mock_proxy_logging.db_spend_update_writer.update_database = AsyncMock(return_value=True)
+        mock_proxy_logging.slack_alerting_instance.customer_spend_alert = AsyncMock()
+        await run()
+        mock_proxy_logging.db_spend_update_writer.update_database.assert_awaited_once()
+        written = mock_proxy_logging.db_spend_update_writer.update_database.await_args.kwargs
+        counters.assert_awaited_once()
+        counted = dict(counters.await_args.kwargs)
+
+    row = get_logging_payload(
+        kwargs=written["kwargs"],
+        response_obj=written["completion_response"],
+        start_time=written["start_time"],
+        end_time=written["end_time"],
+    )
+    return row, counted, response_tool_call_names(written["completion_response"])
+
+
+@pytest.mark.asyncio
+async def test_sidecar_writes_the_same_spend_row_and_counters_as_the_in_process_path():
+    start_time = datetime(2026, 1, 1, 0, 0, 0)
+    end_time = datetime(2026, 1, 1, 0, 0, 2)
+
+    async def in_process() -> None:
+        await _ProxyDBLogger()._PROXY_track_cost_callback(
+            _offload_kwargs(), _offload_response(), start_time=start_time, end_time=end_time
+        )
+
+    async def via_sidecar() -> None:
+        line = build_spend_event(_offload_kwargs(), _offload_response(), start_time, end_time, store_bodies=False)
+        assert isinstance(line, bytes)
+        await run_spend_event(line)
+
+    in_process_row, in_process_counters, in_process_tools = await _spend_row_written_by(in_process)
+    sidecar_row, sidecar_counters, sidecar_tools = await _spend_row_written_by(via_sidecar)
+
+    assert sidecar_row == in_process_row
+    assert in_process_row["spend"] == 0.0125
+    assert in_process_row["team_id"] == "team-1"
+    assert in_process_row["end_user"] == "end-user-1"
+    assert in_process_row["total_tokens"] == 9000
+    assert in_process_row["model_id"] == "deployment-1"
+    assert in_process_row["request_tags"] == '["tag-a"]'
+    assert in_process_row["messages"] == "{}"
+    assert in_process_row["response"] == "{}"
+    assert sidecar_counters == in_process_counters
+    assert in_process_counters["token"] == "hash-1"
+    assert in_process_counters["response_cost"] == 0.0125
+    assert in_process_counters["budget_reservation"]["reserved_cost"] == 0.5
+    assert in_process_counters["model_access_groups"] == ("premium",)
+    assert sidecar_tools == in_process_tools == ("get_weather",)
+
+
+@pytest.mark.asyncio
+async def test_sidecar_ignores_an_undecodable_event():
+    with patch("litellm.proxy.proxy_server.proxy_logging_obj") as mock_proxy_logging:
+        mock_proxy_logging.db_spend_update_writer.update_database = AsyncMock()
+        await run_spend_event(b"garbage\n")
+    mock_proxy_logging.db_spend_update_writer.update_database.assert_not_awaited()

tests/test_litellm/proxy/spend_tracking/test_spend_event.py

@@ -0,0 +1,213 @@
+import json
+from datetime import datetime
+from typing import Final
+
+import pytest
+
+import litellm
+from litellm.caching.caching import Cache
+from litellm.proxy._types import UserAPIKeyAuth
+from litellm.proxy.spend_tracking.spend_event import (
+    CACHE_OFF_KEY,
+    SpendEventBuildError,
+    SpendEventDecodeError,
+    build_spend_event,
+    decode_spend_event,
+    is_offloadable_success,
+    spend_event_callback_args,
+)
+from litellm.types.utils import LiteLLMBatch, ModelResponse, Usage
+
+_BIG_PROMPT: Final = "x" * 20_000
+_RESERVATION: Final = {
+    "reserved_cost": 0.5,
+    "entries": [{"counter_key": "key:hash", "reserved_cost": 0.5}],
+    "finalized": False,
+    "input_cost": 0.1,
+    "input_tokens": 5000,
+}
+
+
+def _response(tool_name: str | None = None) -> ModelResponse:
+    tool_calls: Final = (
+        [{"id": "call-1", "type": "function", "function": {"name": tool_name, "arguments": "{}"}}]
+        if tool_name is not None
+        else None
+    )
+    return ModelResponse(
+        id="chatcmpl-1",
+        model="gpt-4o-2024-08-06",
+        choices=[
+            {
+                "index": 0,
+                "message": {"role": "assistant", "content": "y" * 20_000, "tool_calls": tool_calls},
+                "finish_reason": "tool_calls" if tool_name else "stop",
+            }
+        ],
+        usage=Usage(prompt_tokens=5000, completion_tokens=4000, total_tokens=9000),
+    )
+
+
+def _success_kwargs(preset_cache_key: str | None = "preset-key") -> dict:
+    return {
+        "litellm_call_id": "call-1",
+        "call_type": "acompletion",
+        "model": "gpt-4o",
+        "custom_llm_provider": "openai",
+        "stream": False,
+        "cache_hit": None,
+        "response_cost": 0.0125,
+        "completion_start_time": datetime(2026, 1, 1, 0, 0, 1),
+        "messages": [{"role": "user", "content": _BIG_PROMPT}],
+        "tools": [{"type": "function", "function": {"name": "get_weather", "parameters": {"type": "object"}}}],
+        "litellm_params": {
+            "api_base": "https://api.openai.com",
+            "preset_cache_key": preset_cache_key,
+            "proxy_server_request": {"body": {"messages": [{"role": "user", "content": _BIG_PROMPT}]}},
+            "metadata": {
+                "user_api_key": "hash-1",
+                "user_api_key_user_id": "user-1",
+                "user_api_key_team_id": "team-1",
+                "user_api_key_org_id": "org-1",
+                "user_api_key_end_user_id": "end-user-1",
+                "user_api_key_auth": UserAPIKeyAuth(api_key="hash-1", budget_reservation=dict(_RESERVATION)),
+                "model_group": "gpt-4o",
+                "model_info": {"id": "deployment-1"},
+                "tags": ["tag-a"],
+                "litellm_parent_otel_span": object(),
+            },
+        },
+        "standard_logging_object": {
+            "response_cost": 0.0125,
+            "model": "gpt-4o-2024-08-06",
+            "model_id": "deployment-1",
+            "request_tags": ["tag-a"],
+            "request_model_access_groups": ["premium"],
+            "messages": [{"role": "user", "content": _BIG_PROMPT}],
+            "response": {"choices": [{"message": {"content": "y" * 20_000}}]},
+            "model_parameters": {"temperature": 0.1},
+            "metadata": {"user_api_key_hash": "hash-1", "usage_object": {"prompt_tokens": 5000}},
+            "hidden_params": {"litellm_overhead_time_ms": 3},
+            "model_map_information": {},
+        },
+    }
+
+
+def _build(kwargs: dict, response: object, store_bodies: bool = False) -> bytes:
+    line: Final = build_spend_event(
+        kwargs, response, datetime(2026, 1, 1), datetime(2026, 1, 1, 0, 0, 2), store_bodies=store_bodies
+    )
+    assert isinstance(line, bytes)
+    return line
+
+
+def test_event_is_compact_and_omits_bodies_by_default():
+    line: Final = _build(_success_kwargs(), _response(tool_name="get_weather"))
+    assert line.endswith(b"\n")
+    assert len(line) < 4_000
+    assert _BIG_PROMPT.encode() not in line
+    assert b"yyyy" not in line
+    decoded: Final = json.loads(line)
+    assert "messages" not in decoded["standard_logging_object"]
+    assert "response" not in decoded["standard_logging_object"]
+    assert decoded["litellm_params"]["proxy_server_request"] is None
+
+
+def test_event_carries_bodies_when_spend_logs_store_them():
+    line: Final = _build(_success_kwargs(), _response(), store_bodies=True)
+    decoded: Final = json.loads(line)
+    assert decoded["standard_logging_object"]["messages"][0]["content"] == _BIG_PROMPT
+    assert decoded["standard_logging_object"]["response"]["choices"][0]["message"]["content"] == "y" * 20_000
+    assert decoded["litellm_params"]["proxy_server_request"]["body"]["messages"][0]["content"] == _BIG_PROMPT
+
+
+def test_round_trip_preserves_identity_usage_reservation_and_tools():
+    line: Final = _build(_success_kwargs(), _response(tool_name="get_weather"))
+    event: Final = decode_spend_event(line)
+    assert not isinstance(event, SpendEventDecodeError)
+    args: Final = spend_event_callback_args(event)
+
+    metadata: Final = args.kwargs["litellm_params"]["metadata"]
+    assert metadata is not None
+    assert (metadata["user_api_key"], metadata["user_api_key_team_id"], metadata["user_api_key_org_id"]) == (
+        "hash-1",
+        "team-1",
+        "org-1",
+    )
+    assert metadata["user_api_key_budget_reservation"] == _RESERVATION
+    assert "user_api_key_auth" not in metadata
+    assert "litellm_parent_otel_span" not in metadata
+    assert args.kwargs["standard_logging_object"]["request_model_access_groups"] == ["premium"]
+    assert args.kwargs["standard_logging_object"]["response_cost"] == 0.0125
+    assert args.kwargs["tools"] == ({"type": "function", "function": {"name": "get_weather"}},)
+    assert args.kwargs["completion_start_time"] == datetime(2026, 1, 1, 0, 0, 1)
+    assert (args.start_time, args.end_time) == (datetime(2026, 1, 1), datetime(2026, 1, 1, 0, 0, 2))
+    assert args.response_obj is not None
+    assert args.response_obj["id"] == "chatcmpl-1"
+    assert args.response_obj["usage"]["prompt_tokens"] == 5000
+    assert args.response_obj["usage"]["completion_tokens"] == 4000
+    tool_calls: Final = args.response_obj["choices"][0]["message"]["tool_calls"]
+    assert [call["function"]["name"] for call in tool_calls] == ["get_weather"]
+    assert "complete_streaming_response" not in args.kwargs
+
+
+def test_streaming_event_reconstructs_complete_streaming_response():
+    kwargs: Final = {**_success_kwargs(), "stream": True, "complete_streaming_response": _response()}
+    event: Final = decode_spend_event(_build(kwargs, _response()))
+    assert not isinstance(event, SpendEventDecodeError)
+    args: Final = spend_event_callback_args(event)
+    assert args.kwargs["stream"] is True
+    assert args.kwargs["complete_streaming_response"] == args.response_obj
+
+
+class _HashingCache(Cache):
+    def __init__(self) -> None:
+        pass
+
+    def get_cache_key(self, **kwargs) -> str:
+        raise AssertionError("the fast path must not hash the request body")
+
+
+@pytest.mark.parametrize(
+    ("cache", "preset", "expected"),
+    [
+        (None, "preset-key", CACHE_OFF_KEY),
+        (_HashingCache(), "preset-key", "preset-key"),
+        (_HashingCache(), None, None),
+    ],
+)
+def test_event_reuses_preset_cache_key_and_never_hashes(monkeypatch, cache, preset, expected):
+    monkeypatch.setattr(litellm, "cache", cache)
+    decoded: Final = json.loads(_build(_success_kwargs(preset_cache_key=preset), _response()))
+    assert decoded["litellm_params"]["preset_cache_key"] == expected
+
+
+def test_unbuildable_kwargs_fall_back_to_in_process_tracking():
+    kwargs: Final = {**_success_kwargs(), "response_cost": "not-a-number"}
+    assert isinstance(
+        build_spend_event(kwargs, _response(), datetime.now(), datetime.now(), False), SpendEventBuildError
+    )
+
+
+def test_undecodable_line_is_an_error_value():
+    assert isinstance(decode_spend_event(b'{"version": 2}\n'), SpendEventDecodeError)
+    assert isinstance(decode_spend_event(b"not json\n"), SpendEventDecodeError)
+
+
+def test_batch_retrieves_stay_in_process():
+    assert is_offloadable_success(_response()) is True
+    assert is_offloadable_success(None) is True
+    assert (
+        is_offloadable_success(
+            LiteLLMBatch(
+                id="batch-1",
+                completion_window="24h",
+                created_at=1,
+                endpoint="/v1/chat/completions",
+                input_file_id="f",
+                object="batch",
+                status="completed",
+            )
+        )
+        is False
+    )

tests/test_litellm/proxy/spend_tracking/test_spend_event_producer.py

@@ -0,0 +1,165 @@
+import asyncio
+from pathlib import Path
+from typing import Final
+
+import pytest
+
+from litellm.proxy.spend_tracking.spend_event_producer import (
+    AddressError,
+    SpendEventProducer,
+    SpendWorkerSettings,
+    TcpAddress,
+    UnixAddress,
+    build_spend_event_producer,
+    parse_spend_worker_address,
+)
+
+
+class _Sidecar:
+    """A unix-socket server that records every line it receives, standing in for the spend worker."""
+
+    def __init__(self, path: Path) -> None:
+        self.path = path
+        self.lines: list[bytes] = []  # mutable-ok: test double records what the producer sent
+        self._server: asyncio.Server | None = None
+
+    async def __aenter__(self) -> "_Sidecar":
+        self._server = await asyncio.start_unix_server(self._on_connection, path=str(self.path))
+        return self
+
+    async def __aexit__(self, *exc: object) -> None:
+        assert self._server is not None
+        self._server.close()
+        await self._server.wait_closed()
+
+    async def _on_connection(self, reader: asyncio.StreamReader, writer: asyncio.StreamWriter) -> None:
+        while line := await reader.readline():
+            self.lines.append(line)
+        writer.close()
+
+
+class _Fallback:
+    def __init__(self) -> None:
+        self.lines: list[bytes] = []  # mutable-ok: test double records what fell back to in-process
+
+    async def __call__(self, line: bytes) -> None:
+        self.lines.append(line)
+
+
+def _producer(path: Path, fallback: _Fallback, on_unavailable="fallback", buffer_size: int = 100) -> SpendEventProducer:
+    return SpendEventProducer(
+        address=UnixAddress(path=str(path)),
+        on_unavailable=on_unavailable,
+        buffer_size=buffer_size,
+        connect_timeout=1.0,
+        fallback=fallback,
+    )
+
+
+def test_parse_spend_worker_address():
+    assert parse_spend_worker_address("unix:///var/run/litellm/spend-worker.sock") == UnixAddress(
+        path="/var/run/litellm/spend-worker.sock"
+    )
+    assert parse_spend_worker_address("tcp://127.0.0.1:4100") == TcpAddress(host="127.0.0.1", port=4100)
+    assert isinstance(parse_spend_worker_address("redis://localhost:6379"), AddressError)
+    assert isinstance(parse_spend_worker_address("tcp://127.0.0.1"), AddressError)
+
+
+def test_gateway_produces_only_when_enabled_and_not_the_sidecar_itself():
+    fallback: Final = _Fallback()
+    assert build_spend_event_producer(SpendWorkerSettings(enabled=False), fallback) is None
+    assert build_spend_event_producer(SpendWorkerSettings(enabled=True, job_role="spend_worker"), fallback) is None
+    assert build_spend_event_producer(SpendWorkerSettings(enabled=True, address="redis://x"), fallback) is None
+    assert isinstance(build_spend_event_producer(SpendWorkerSettings(enabled=True), fallback), SpendEventProducer)
+
+
+def test_settings_read_the_documented_env(monkeypatch):
+    monkeypatch.setenv("LITELLM_SPEND_WORKER_ENABLED", "true")
+    monkeypatch.setenv("LITELLM_SPEND_WORKER_ADDRESS", "tcp://127.0.0.1:4100")
+    monkeypatch.setenv("LITELLM_SPEND_WORKER_BUFFER_SIZE", "50")
+    monkeypatch.setenv("LITELLM_SPEND_WORKER_ON_UNAVAILABLE", "drop")
+    monkeypatch.setenv("LITELLM_JOB_ROLE", "spend_worker")
+    settings: Final = SpendWorkerSettings()
+    assert (settings.enabled, settings.address, settings.buffer_size, settings.on_unavailable) == (
+        True,
+        "tcp://127.0.0.1:4100",
+        50,
+        "drop",
+    )
+    assert settings.produces is False
+
+
+@pytest.mark.asyncio
+async def test_events_reach_the_sidecar_once_and_in_order(tmp_path: Path):
+    fallback: Final = _Fallback()
+    async with _Sidecar(tmp_path / "spend.sock") as sidecar:
+        producer: Final = _producer(sidecar.path, fallback)
+        outcomes: Final = [await producer.publish(f"event-{i}\n".encode()) for i in range(20)]
+        await producer.close(drain_timeout=5.0)
+        await asyncio.sleep(0.05)
+
+    assert outcomes == ["queued"] * 20
+    assert sidecar.lines == [f"event-{i}\n".encode() for i in range(20)]
+    assert fallback.lines == []
+    stats: Final = producer.stats()
+    assert (stats.queued, stats.sent, stats.fallback, stats.dropped) == (20, 20, 0, 0)
+
+
+@pytest.mark.asyncio
+async def test_unreachable_sidecar_falls_back_in_process_and_backs_off(tmp_path: Path):
+    fallback: Final = _Fallback()
+    producer: Final = _producer(tmp_path / "missing.sock", fallback)
+    first: Final = await producer.publish(b"event-1\n")
+    await asyncio.sleep(0.05)
+    second: Final = await producer.publish(b"event-2\n")
+    await producer.close(drain_timeout=5.0)
+
+    assert first == "queued"
+    assert second == "fallback"
+    assert fallback.lines == [b"event-1\n", b"event-2\n"]
+    stats: Final = producer.stats()
+    assert (stats.sent, stats.fallback, stats.dropped, stats.connected) == (0, 2, 0, False)
+
+
+@pytest.mark.asyncio
+async def test_drop_policy_counts_instead_of_running_in_process(tmp_path: Path):
+    fallback: Final = _Fallback()
+    producer: Final = _producer(tmp_path / "missing.sock", fallback, on_unavailable="drop")
+    await producer.publish(b"event-1\n")
+    await producer.close(drain_timeout=5.0)
+    assert await producer.publish(b"event-2\n") == "dropped"
+
+    assert fallback.lines == []
+    assert producer.stats().dropped == 2
+
+
+@pytest.mark.asyncio
+async def test_full_buffer_applies_the_unavailable_policy_immediately(tmp_path: Path):
+    fallback: Final = _Fallback()
+    async with _Sidecar(tmp_path / "spend.sock") as sidecar:
+        producer: Final = _producer(sidecar.path, fallback, buffer_size=2)
+        outcomes: Final = [await producer.publish(f"event-{i}\n".encode()) for i in range(3)]
+        await producer.close(drain_timeout=5.0)
+        await asyncio.sleep(0.05)
+
+    assert outcomes == ["queued", "queued", "fallback"]
+    assert fallback.lines == [b"event-2\n"]
+    assert sidecar.lines == [b"event-0\n", b"event-1\n"]
+
+
+@pytest.mark.asyncio
+async def test_close_flushes_buffered_events_then_refuses_new_ones(tmp_path: Path):
+    fallback: Final = _Fallback()
+    async with _Sidecar(tmp_path / "spend.sock") as sidecar:
+        producer: Final = _producer(sidecar.path, fallback)
+        for i in range(50):
+            await producer.publish(f"event-{i}\n".encode())
+        assert sidecar.lines == []
+        await producer.close(drain_timeout=5.0)
+        await asyncio.sleep(0.05)
+        after_close: Final = await producer.publish(b"late\n")
+
+    assert len(sidecar.lines) == 50
+    assert after_close == "fallback"
+    assert fallback.lines == [b"late\n"]
+    assert producer.stats().connected is False

tests/test_litellm/proxy/spend_tracking/test_spend_tracking_utils.py

@@ -1,8 +1,8 @@
 import asyncio
 import datetime
 import json
-from datetime import timezone
 from collections.abc import Mapping
+from datetime import timezone
 from typing import Any, Final, cast
 from unittest.mock import AsyncMock, MagicMock, patch
 
@@ -19,7 +19,7 @@ from litellm.constants import (
     SESSION_ID_OMITTED_METADATA_KEY,
 )
 from litellm.litellm_core_utils.safe_json_dumps import safe_dumps
-from litellm.proxy._types import UserAPIKeyAuth
+from litellm.proxy._types import SpendLogsPayload, UserAPIKeyAuth
 from litellm.proxy.litellm_pre_call_utils import LiteLLMProxyRequestSetup
 from litellm.proxy.spend_tracking.spend_tracking_utils import (
     _get_messages_for_spend_logs_payload,
@@ -39,7 +39,6 @@ from litellm.proxy.spend_tracking.spend_tracking_utils import (
     get_logging_payload,
     get_spend_logs_id,
 )
-from litellm.proxy._types import SpendLogsPayload
 from litellm.proxy.utils import hash_token
 from litellm.types.utils import (
     StandardLoggingHiddenParams,
@@ -81,6 +80,48 @@ def test_get_logging_payload_maps_openai_cached_tokens_to_cache_read_input_token
     assert additional_usage_values["prompt_tokens_details"]["cached_tokens"] == 123
 
 
+class _HashingCache(litellm.Cache):
+    def __init__(self) -> None:
+        pass
+
+    def get_cache_key(self, **kwargs) -> str:
+        raise AssertionError("a preset cache key must be reused instead of hashing the request")
+
+
+def _cache_key_in_spend_log(monkeypatch: pytest.MonkeyPatch, cache: litellm.Cache | None, preset: str | None) -> str:
+    monkeypatch.setattr(litellm, "cache", cache)
+    payload: Final = get_logging_payload(
+        kwargs={
+            "model": "gpt-4o-mini",
+            "messages": [{"role": "user", "content": "x" * 10_000}],
+            "litellm_params": {"metadata": {"user_api_key": "test-key"}, "preset_cache_key": preset},
+        },
+        response_obj=litellm.ModelResponse(id="chatcmpl-test", choices=[], usage=litellm.Usage()),
+        start_time=datetime.datetime.now(timezone.utc),
+        end_time=datetime.datetime.now(timezone.utc),
+    )
+    return payload["cache_key"]
+
+
+def test_get_logging_payload_reuses_the_preset_cache_key_instead_of_hashing_the_body(monkeypatch):
+    assert _cache_key_in_spend_log(monkeypatch, _HashingCache(), "preset-key") == "preset-key"
+
+
+def test_get_logging_payload_records_cache_off_without_hashing(monkeypatch):
+    assert _cache_key_in_spend_log(monkeypatch, None, None) == "Cache OFF"
+
+
+def test_get_logging_payload_still_hashes_when_caching_is_on_and_no_preset_key_exists(monkeypatch):
+    class _RecordingCache(litellm.Cache):
+        def __init__(self) -> None:
+            pass
+
+        def get_cache_key(self, **kwargs) -> str:
+            return "hashed-from-" + kwargs["model"]
+
+    assert _cache_key_in_spend_log(monkeypatch, _RecordingCache(), None) == "hashed-from-gpt-4o-mini"
+
+
 _TRACE_ONLY_STANDARD_LOGGING: Final = cast(
     StandardLoggingPayload,
     {

tests/test_litellm/proxy/test_spend_worker.py

@@ -0,0 +1,97 @@
+import asyncio
+from pathlib import Path
+from typing import Final
+
+import pytest
+
+from litellm.proxy.spend_tracking.spend_event_producer import (
+    AddressError,
+    SpendEventProducer,
+    TcpAddress,
+    UnixAddress,
+    open_spend_worker_connection,
+)
+from litellm.proxy.spend_worker import SpendEventConsumer, _address_argument
+
+
+class _Handler:
+    def __init__(self, fail_on: bytes | None = None) -> None:
+        self.lines: list[bytes] = []  # mutable-ok: test double records the events the consumer handed over
+        self._fail_on = fail_on
+
+    async def __call__(self, line: bytes) -> None:
+        if line == self._fail_on:
+            raise RuntimeError("pipeline failed")
+        self.lines.append(line)
+
+
+async def _no_fallback(line: bytes) -> None:
+    raise AssertionError(f"unexpected fallback for {line!r}")
+
+
+@pytest.mark.asyncio
+@pytest.mark.parametrize("transport", ["unix", "tcp"])
+async def test_consumer_handles_each_producer_line_once_in_order(tmp_path: Path, transport: str):
+    handler: Final = _Handler(fail_on=b"event-3\n")
+    consumer: Final = SpendEventConsumer(handler)
+    server: Final = await consumer.serve(
+        UnixAddress(path=str(tmp_path / "spend.sock")) if transport == "unix" else TcpAddress("127.0.0.1", 0)
+    )
+    address: Final = (
+        UnixAddress(path=str(tmp_path / "spend.sock"))
+        if transport == "unix"
+        else TcpAddress("127.0.0.1", server.sockets[0].getsockname()[1])
+    )
+    producer: Final = SpendEventProducer(
+        address=address, on_unavailable="fallback", buffer_size=100, connect_timeout=1.0, fallback=_no_fallback
+    )
+    for i in range(6):
+        await producer.publish(f"event-{i}\n".encode())
+    await producer.close(drain_timeout=5.0)
+
+    server.close()
+    assert await consumer.drain(timeout=5.0) == 0
+    assert handler.lines == [f"event-{i}\n".encode() for i in range(6) if i != 3]
+    assert (consumer.received, consumer.handled, consumer.failed) == (6, 5, 1)
+
+
+@pytest.mark.asyncio
+async def test_consumer_discards_a_truncated_trailing_event(tmp_path: Path):
+    handler: Final = _Handler()
+    consumer: Final = SpendEventConsumer(handler)
+    address: Final = UnixAddress(path=str(tmp_path / "spend.sock"))
+    server: Final = await consumer.serve(address)
+    _, writer = await open_spend_worker_connection(address, timeout=1.0)
+    writer.write(b"whole\npartial-without-newline")
+    await writer.drain()
+    writer.close()
+    await writer.wait_closed()
+    await asyncio.sleep(0.05)
+
+    server.close()
+    assert await consumer.drain(timeout=5.0) == 0
+    assert handler.lines == [b"whole\n"]
+    assert consumer.received == 1
+
+
+@pytest.mark.asyncio
+async def test_drain_reports_producers_still_connected_after_the_timeout(tmp_path: Path):
+    consumer: Final = SpendEventConsumer(_Handler())
+    address: Final = UnixAddress(path=str(tmp_path / "spend.sock"))
+    server: Final = await consumer.serve(address)
+    _, writer = await open_spend_worker_connection(address, timeout=1.0)
+    await asyncio.sleep(0.05)
+
+    server.close()
+    assert await consumer.drain(timeout=0.1) == 1
+    writer.close()
+    await writer.wait_closed()
+    assert await consumer.drain(timeout=5.0) == 0
+
+
+def test_address_argument():
+    assert _address_argument((), default="unix:///tmp/x.sock") == "unix:///tmp/x.sock"
+    assert _address_argument(("--address", "tcp://127.0.0.1:4100"), default="unix:///tmp/x.sock") == (
+        "tcp://127.0.0.1:4100"
+    )
+    assert isinstance(_address_argument(("--listen", "x"), default="unix:///tmp/x.sock"), AddressError)