diff --git a/litellm/integrations/otel/logger.py b/litellm/integrations/otel/logger.py
index a0b5aff559f..53b9829023c 100644
--- a/litellm/integrations/otel/logger.py
+++ b/litellm/integrations/otel/logger.py
@@ -9,7 +9,15 @@ from typing import TYPE_CHECKING, Any, Final, cast
 from opentelemetry.context import Context, attach, get_current
 from opentelemetry.sdk._logs import LoggerProvider
 from opentelemetry.sdk.trace import TracerProvider
-from opentelemetry.trace import Span, Tracer, get_current_span, use_span
+from opentelemetry.trace import (
+    INVALID_SPAN,
+    Link,
+    Span,
+    Tracer,
+    get_current_span,
+    set_span_in_context,
+    use_span,
+)
 
 import litellm
 from litellm._logging import verbose_logger
@@ -21,6 +29,7 @@ from litellm.integrations.otel.model.config import OpenTelemetryV2Config
 from litellm.integrations.otel.model.metadata import (
     LLMCallEvent,
     RequestIdentity,
+    auth_metadata,
     model_from_request_data,
 )
 from litellm.integrations.otel.model.payloads import (
@@ -118,6 +127,12 @@ _OTEL_MODULES: Final = (
 _OPEN_CALLS_MAX: Final = 10_000
 
 
+def _request_trace_links(context: Context | None) -> tuple[Link, ...] | None:
+    """A link back to the request trace, for a span detached into its own trace."""
+    anchor: Final = get_current_span(context).get_span_context()
+    return (Link(anchor),) if anchor.is_valid else None
+
+
 class _LLMCallSpan:
     """The state carried from the ``pre_call`` boundary to span close.
 
@@ -127,13 +142,24 @@ class _LLMCallSpan:
     own (worker-copied) ambient context using ``start_time_ns``. The presence of
     a carrier for a call at all is the proof that ``pre_call`` ran, i.e. that an
     upstream call was actually attempted.
+
+    ``provider`` is the routed provider the live span was opened on (``None`` on
+    the default route or when creation was deferred). It is held in the tenant
+    cache while the span is open so LRU eviction can't shut the provider down
+    under it, and must be released exactly once when the carrier is removed.
     """
 
-    __slots__ = ("span", "start_time_ns")
+    __slots__ = ("provider", "span", "start_time_ns")
 
-    def __init__(self, span: "Span | None", start_time_ns: int | None) -> None:
+    def __init__(
+        self,
+        span: "Span | None",
+        start_time_ns: int | None,
+        provider: "TracerProvider | None" = None,
+    ) -> None:
         self.span = span
         self.start_time_ns = start_time_ns
+        self.provider = provider
 
 
 class OpenTelemetryV2(CustomLogger):
@@ -258,26 +284,37 @@ class OpenTelemetryV2(CustomLogger):
         if call_id in self._open_llm_calls:
             return
         start_time_ns: Final = to_ns(datetime.now())
-        span: Span | None = None
         # Parent to the request's anchored root span (stable across the request),
         # falling back to ambient on the SDK path. Open the span live only when
         # that resolves to a recordable parent; otherwise defer to the close
         # callback (the thread-pool case, where the anchor isn't visible here).
+        # Do not route on the deferred path: creating or LRU-touching a tenant
+        # provider here would evict idle ones even though close re-routes.
         parent_context: Final = resolve_request_span_context()
-        if is_recordable_span(get_current_span(parent_context)):
-            span = self._emitter.start_span(
+        if not is_recordable_span(get_current_span(parent_context)):
+            self._store_open_call(call_id, _LLMCallSpan(span=None, start_time_ns=start_time_ns))
+            return
+        # A detached route roots its own trace instead (linked to the request
+        # trace) — see ``TenantRoute.detached``.
+        route: Final = self._tenant_tracers.route_for(self.tracer, call.dynamic_params, call.auth_metadata)
+        try:
+            span: Final = self._emitter.start_span(
                 SpanRole.LLM_CALL,
                 call.provisional_span_name,
-                parent_context=parent_context,
+                parent_context=(
+                    set_span_in_context(INVALID_SPAN, parent_context) if route.detached else parent_context
+                ),
                 start_time_ns=start_time_ns,
-                tracer=self._tenant_tracers.tracer_for(self.tracer, call.dynamic_params),
+                tracer=route.tracer,
+                links=_request_trace_links(parent_context) if route.detached else None,
             )
-        self._open_llm_calls[call_id] = _LLMCallSpan(span=span, start_time_ns=start_time_ns)
-        # Evict the oldest open call if the map is over budget. A call that opens
-        # but never closes (a stream that only fires stream events) would linger
-        # otherwise; the evicted span is simply dropped (never exported).
-        if len(self._open_llm_calls) > _OPEN_CALLS_MAX:
-            self._open_llm_calls.popitem(last=False)
+        except BaseException:
+            self._tenant_tracers.release(route.provider)
+            raise
+        self._store_open_call(
+            call_id,
+            _LLMCallSpan(span=span, start_time_ns=start_time_ns, provider=route.provider),
+        )
 
     async def async_log_success_event(self, kwargs, response_obj, start_time, end_time):
         if self._emit_mcp_tool_call(kwargs, start_time, end_time):
@@ -371,17 +408,22 @@ class OpenTelemetryV2(CustomLogger):
         # otherwise linger until evicted; drop it so it's neither leaked nor closed
         # as a phantom LLM span.
         if data.identity.call_id:
-            self._open_llm_calls.pop(data.identity.call_id, None)
-        parent_context, links = resolve_mcp_span_context()
-        parent_context = self._seed_identity_baggage(data.identity, None, parent_context)
-        self._emitter.emit(
-            SpanRole.MCP_TOOL_CALL,
-            data,
-            parent_context=parent_context,
-            start_time_ns=to_ns(start_time),
-            end_time_ns=to_ns(end_time),
-            links=links,
-        )
+            self._release_carrier(self._open_llm_calls.pop(data.identity.call_id, None))
+        route: Final = self._tenant_tracers.route_for(self.tracer, None, auth_metadata(payload, kwargs))
+        try:
+            parent_context, links = resolve_mcp_span_context()
+            seeded: Final = self._seed_identity_baggage(data.identity, None, parent_context)
+            self._emitter.emit(
+                SpanRole.MCP_TOOL_CALL,
+                data,
+                parent_context=(set_span_in_context(INVALID_SPAN, seeded) if route.detached else seeded),
+                start_time_ns=to_ns(start_time),
+                end_time_ns=to_ns(end_time),
+                links=((*(links or ()), *(_request_trace_links(seeded) or ())) if route.detached else links),
+                tracer=route.tracer,
+            )
+        finally:
+            self._tenant_tracers.release(route.provider)
         return True
 
     def _emit_mcp_list_tools(
@@ -407,17 +449,22 @@ class OpenTelemetryV2(CustomLogger):
             payload, capture_content=self.config.capture_span_content
         )
         if data.identity.call_id:
-            self._open_llm_calls.pop(data.identity.call_id, None)
-        parent_context, links = resolve_mcp_span_context()
-        parent_context = self._seed_identity_baggage(data.identity, None, parent_context)
-        self._emitter.emit(
-            SpanRole.MCP_LIST_TOOLS,
-            data,
-            parent_context=parent_context,
-            start_time_ns=to_ns(start_time),
-            end_time_ns=to_ns(end_time),
-            links=links,
-        )
+            self._release_carrier(self._open_llm_calls.pop(data.identity.call_id, None))
+        route: Final = self._tenant_tracers.route_for(self.tracer, None, auth_metadata(payload, kwargs))
+        try:
+            parent_context, links = resolve_mcp_span_context()
+            seeded: Final = self._seed_identity_baggage(data.identity, None, parent_context)
+            self._emitter.emit(
+                SpanRole.MCP_LIST_TOOLS,
+                data,
+                parent_context=(set_span_in_context(INVALID_SPAN, seeded) if route.detached else seeded),
+                start_time_ns=to_ns(start_time),
+                end_time_ns=to_ns(end_time),
+                links=((*(links or ()), *(_request_trace_links(seeded) or ())) if route.detached else links),
+                tracer=route.tracer,
+            )
+        finally:
+            self._tenant_tracers.release(route.provider)
         return True
 
     def _close_llm_call(
@@ -439,6 +486,36 @@ class OpenTelemetryV2(CustomLogger):
         carrier: Final = self._open_llm_calls.pop(call_id, None) if call_id else None
         if carrier is None:
             return None
+        try:
+            return self._finish_carrier(carrier, call, end_time)
+        finally:
+            # After the span has ended, so a release-triggered provider shutdown
+            # force-flushes it out rather than racing its enqueue.
+            self._release_carrier(carrier)
+
+    def _store_open_call(self, call_id: str, carrier: _LLMCallSpan) -> None:
+        """Remember an in-flight LLM call, evicting the oldest if over budget.
+
+        A call that opens but never closes (a stream that only fires stream
+        events) would linger otherwise; the evicted span is simply dropped
+        (never exported).
+        """
+        self._open_llm_calls[call_id] = carrier
+        if len(self._open_llm_calls) > _OPEN_CALLS_MAX:
+            _, evicted = self._open_llm_calls.popitem(last=False)
+            self._release_carrier(evicted)
+
+    def _release_carrier(self, carrier: "_LLMCallSpan | None") -> None:
+        """Release the routed provider a removed carrier was holding open."""
+        if carrier is not None:
+            self._tenant_tracers.release(carrier.provider)
+
+    def _finish_carrier(
+        self,
+        carrier: _LLMCallSpan,
+        call: LLMCallEvent,
+        end_time: datetime | float | None,
+    ) -> Span | None:
         payload: Final = call.payload
         if payload is None:
             if carrier.span is not None:
@@ -462,16 +539,23 @@ class OpenTelemetryV2(CustomLogger):
         # The worker copied the request task's context, which carries the anchored
         # root span — parent to it (ambient fallback on the SDK path). Seed identity
         # Baggage so the span — and the SDK path, which has none — is labeled
-        # consistently.
-        parent_ctx = self._seed_identity_baggage(data.identity, data.request_model, resolve_request_span_context())
-        return self._emitter.emit(
-            SpanRole.LLM_CALL,
-            data,
-            parent_context=parent_ctx,
-            start_time_ns=carrier.start_time_ns,
-            end_time_ns=end_time_ns,
-            tracer=self._tenant_tracers.tracer_for(self.tracer, call.dynamic_params),
-        )
+        # consistently. A detached route roots its own trace instead, linked back.
+        route: Final = self._tenant_tracers.route_for(self.tracer, call.dynamic_params, call.auth_metadata)
+        try:
+            parent_ctx: Final = self._seed_identity_baggage(
+                data.identity, data.request_model, resolve_request_span_context()
+            )
+            return self._emitter.emit(
+                SpanRole.LLM_CALL,
+                data,
+                parent_context=(set_span_in_context(INVALID_SPAN, parent_ctx) if route.detached else parent_ctx),
+                start_time_ns=carrier.start_time_ns,
+                end_time_ns=end_time_ns,
+                tracer=route.tracer,
+                links=_request_trace_links(parent_ctx) if route.detached else None,
+            )
+        finally:
+            self._tenant_tracers.release(route.provider)
 
     # ====================================================================== #
     #  Service hooks
diff --git a/litellm/integrations/otel/model/metadata.py b/litellm/integrations/otel/model/metadata.py
index c7cdaae0417..de6366e7dbd 100644
--- a/litellm/integrations/otel/model/metadata.py
+++ b/litellm/integrations/otel/model/metadata.py
@@ -36,8 +36,9 @@ model. They coincide on the SDK path, which is correct.
 
 from __future__ import annotations
 
-from collections.abc import Mapping
+from collections.abc import Iterator, Mapping
 from dataclasses import dataclass, field
+from types import MappingProxyType
 from typing import TYPE_CHECKING, Any, Final, cast
 
 from litellm.constants import LITELLM_LOGGING_NO_UPSTREAM_LLM_CALL
@@ -195,6 +196,10 @@ class LLMCallEvent:
     # The ``standard_callback_dynamic_params`` routing the call to a per-tenant
     # tracer (its own exporter/endpoint), or ``None`` when the call isn't scoped.
     dynamic_params: Any
+    # The key/team config the proxy resolved at auth (``user_api_key_auth_metadata``),
+    # routing the call to that tenant's telemetry project. Server-set and so
+    # trusted, unlike ``dynamic_params``, which carries client-supplied metadata.
+    auth_metadata: Mapping[str, str] | None
     # True for synthetic proxy-gate logs (auth / rate-limit rejections): they fire
     # the ``pre_call`` hook but never made an upstream call, so they get no span.
     is_no_upstream_call: bool
@@ -214,6 +219,7 @@ class LLMCallEvent:
             call_id=_call_id(payload, kwargs),
             payload=payload,
             dynamic_params=kwargs.get("standard_callback_dynamic_params"),
+            auth_metadata=auth_metadata(payload, kwargs),
             is_no_upstream_call=bool(kwargs.get(LITELLM_LOGGING_NO_UPSTREAM_LLM_CALL)),
             provisional_span_name=f"{operation.value} {model}".strip(),
             time_to_first_chunk_seconds=time_to_first_chunk_seconds(kwargs),
@@ -235,6 +241,64 @@ def time_to_first_chunk_seconds(kwargs: Mapping[str, Any]) -> float | None:
     return completion_start - api_call_start
 
 
+def auth_metadata(payload: StandardLoggingPayload | None, kwargs: Mapping[str, object]) -> Mapping[str, str] | None:
+    """The key/team config the proxy resolved at auth, or ``None`` off the proxy.
+
+    Read from the payload once the call closes and from ``litellm_params`` at
+    ``pre_call``, where no payload exists yet — the LLM-call span is *created* at
+    ``pre_call``, so the tracer (and therefore the destination) must be
+    resolvable there. Values arrive untyped, so non-string entries are dropped
+    rather than passed on to header builders.
+    """
+    return next(
+        (
+            typed
+            for metadata in _metadata_dicts(payload, kwargs)
+            if (typed := _string_entries(metadata.get("user_api_key_auth_metadata")))
+        ),
+        None,
+    )
+
+
+def _as_str_mapping(value: object) -> Mapping[str, object] | None:
+    """A read-only view of ``value`` when it is a mapping, else ``None``."""
+    if not isinstance(value, Mapping):
+        return None
+    return cast("Mapping[str, object]", value)  # cast-ok: isinstance-guarded, JSON metadata has str keys
+
+
+def _string_entries(value: object) -> Mapping[str, str] | None:
+    entries: Final = _as_str_mapping(value)
+    if entries is None:
+        return None
+    typed: Final = MappingProxyType({key: item for key, item in entries.items() if isinstance(item, str)})
+    return typed or None
+
+
+def _metadata_dicts(
+    payload: StandardLoggingPayload | None, kwargs: Mapping[str, object]
+) -> Iterator[Mapping[str, object]]:
+    """Request metadata dicts, closed-call payload first then the live kwargs.
+
+    ``litellm_metadata`` is the metadata field on the Anthropic-shaped routes;
+    litellm copies it onto ``metadata``, but both are yielded so a route that
+    populates only one is still covered.
+    """
+    payload_view: Final = _as_str_mapping(payload)
+    if payload_view is not None:
+        payload_metadata: Final = _as_str_mapping(payload_view.get("metadata"))
+        if payload_metadata is not None:
+            yield payload_metadata
+    params: Final = _as_str_mapping(kwargs.get("litellm_params"))
+    if params is None:
+        return
+    yield from (
+        metadata
+        for key in ("metadata", "litellm_metadata")
+        if (metadata := _as_str_mapping(params.get(key))) is not None
+    )
+
+
 def _call_id(payload: StandardLoggingPayload | None, kwargs: Mapping[str, Any]) -> str | None:
     """The call id from the payload (when closed) or the bare kwargs (at pre_call)."""
     if payload is not None:
diff --git a/litellm/integrations/otel/plumbing/routing.py b/litellm/integrations/otel/plumbing/routing.py
index d9e9e84364a..f231df9e914 100644
--- a/litellm/integrations/otel/plumbing/routing.py
+++ b/litellm/integrations/otel/plumbing/routing.py
@@ -1,31 +1,45 @@
 """Per-request multi-tenant tracer routing.
 
 When a request carries team/key vendor credentials in
-``standard_callback_dynamic_params``, its spans must export through a
-``TracerProvider`` whose OTLP headers carry those credentials.
-``TenantTracerCache`` builds and caches one provider per distinct credential
-set, and otherwise hands back the logger's default tracer. This lets a single
-logger fan requests out to many tenants without needing a logger per tenant.
+``standard_callback_dynamic_params``, or the key/team config resolved at auth
+names a destination project, its spans must export through a
+``TracerProvider`` whose OTLP headers carry those credentials / that project.
+``TenantTracerCache`` builds and caches one provider per distinct
+(credentials, project) pair, and otherwise hands back the logger's default
+tracer. This lets a single logger fan requests out to many tenants without
+needing a logger per tenant.
 """
 
+import threading
 from collections import OrderedDict
 from collections.abc import Mapping
-from typing import Any, Final
+from dataclasses import dataclass
+from types import MappingProxyType
+from typing import Any, Final, TypeAlias
+from urllib.parse import quote
 
 from opentelemetry.sdk.trace import TracerProvider
 from opentelemetry.trace import Tracer
 
 from litellm._logging import verbose_logger
-from litellm.integrations.otel.model.config import OpenTelemetryV2Config
+from litellm.integrations.otel.model.config import ExporterSpec, OpenTelemetryV2Config
 from litellm.integrations.otel.plumbing.providers import (
     build_tracer_provider,
     get_tracer,
 )
-from litellm.integrations.otel.presets import dynamic_otlp_headers
+from litellm.integrations.otel.presets import (
+    dynamic_otlp_headers,
+    project_routing_headers,
+)
 
 # Exporter kinds that ignore headers — never rewritten with dynamic credentials.
 _NON_OTLP_KINDS: Final = ("console", "in_memory", "inmemory", "memory")
 
+# gRPC exporters still take dynamic credentials (as gRPC metadata) but not
+# project headers: the routing headers backends read (Phoenix's
+# ``x-project-name``) are only honored on the OTLP/HTTP endpoint.
+_GRPC_KINDS: Final = ("otlp_grpc", "grpc")
+
 # Cap on distinct credential-scoped providers held at once. ``dynamic_params``
 # can be populated from request metadata, so an unbounded cache lets a caller
 # spawn one ``TracerProvider`` (plus its ``BatchSpanProcessor`` background
@@ -34,6 +48,23 @@ _NON_OTLP_KINDS: Final = ("console", "in_memory", "inmemory", "memory")
 # evicted providers so their threads are reclaimed.
 _MAX_CACHED_PROVIDERS: Final = 256
 
+# Cap on providers evicted from the cache while still holding open spans, which
+# are kept alive to drain instead of being shut down under them. Their only
+# other bound is the logger's open-call map (10k), so without this a caller
+# cycling unique credential sets across long-lived calls could pin far more
+# live providers, and exporter threads, than the cache cap allows. Past this
+# many, the stalest retiree is shut down and whatever it was draining is
+# dropped (a shut-down ``BatchSpanProcessor`` discards spans handed to it after
+# the fact), which by then means a span on a route evicted long ago. A quarter
+# of the cache cap: enough that a burst of tenant churn during long-lived calls
+# still drains normally, small enough that the worst case is a bounded 320
+# providers rather than one per concurrent call.
+_MAX_RETIRED_PROVIDERS: Final = 64
+
+_HeaderItems: TypeAlias = tuple[tuple[str, str], ...]
+
+_NO_HEADERS: Final[Mapping[str, str]] = MappingProxyType({})
+
 
 def _shutdown_provider(provider: TracerProvider) -> None:
     """Flush + stop an evicted provider's processors (reclaims their threads).
@@ -49,8 +80,41 @@ def _shutdown_provider(provider: TracerProvider) -> None:
         verbose_logger.debug("OTel V2: error shutting down evicted provider: %s", e)
 
 
+def _plain_header_string(headers: Mapping[str, str]) -> str:
+    return ",".join(f"{key}={value}" for key, value in headers.items())
+
+
+def _encoded_header_string(headers: Mapping[str, str]) -> str:
+    """Percent-encode values so one containing the ``k=v,k=v`` separators (e.g.
+    a project name with a comma) survives; ``parse_env_headers`` decodes it back.
+    """
+    return ",".join(f"{key}={quote(value, safe='')}" for key, value in headers.items())
+
+
+@dataclass(frozen=True, slots=True)
+class TenantRoute:
+    """The tracer to create a span on, plus whether it must root its own trace.
+
+    ``detached`` is True when project routing engaged. Phoenix assigns a whole
+    trace to one project by whichever of its spans arrives first, so a
+    project-routed span parented into the request trace gets dragged into the
+    project of the default-exported request spans and the header does nothing.
+    The span must therefore start a fresh trace (with a link back to the
+    request trace for correlation) — which is also how the v1 Phoenix logger
+    behaved, exporting each request under its own Phoenix-local parent span.
+    """
+
+    tracer: Tracer
+    detached: bool
+    #: The provider ``tracer`` came from, or ``None`` on the default route. It
+    #: is returned already held (counted as an open span, atomically with the
+    #: cache update), so LRU eviction can't shut it down before the caller's
+    #: span lands; the caller must ``release`` it exactly once when done.
+    provider: TracerProvider | None = None
+
+
 class TenantTracerCache:
-    """Credential-scoped ``TracerProvider`` cache keyed by the dynamic headers."""
+    """Credential/project-scoped ``TracerProvider`` cache keyed by the routing headers."""
 
     def __init__(
         self,
@@ -61,49 +125,170 @@ class TenantTracerCache:
         self._config = config
         self._callback_name = callback_name
         self._tracer_name = tracer_name
-        self._providers: OrderedDict[tuple[tuple[str, str], ...], TracerProvider] = OrderedDict()
+        # Guards the three mutable structures below: ``pre_call`` can run on
+        # thread-pool workers concurrently with the event loop, so cache
+        # updates, span counts, and retirement must be atomic.
+        self._lock: Final = threading.Lock()
+        self._providers: OrderedDict[tuple[_HeaderItems, _HeaderItems], TracerProvider] = OrderedDict()
+        self._open_span_counts: dict[TracerProvider, int] = {}  # mutable-ok: live refcount state
+        # Oldest-first so an overflow of draining providers sheds the stalest.
+        self._retired: OrderedDict[TracerProvider, None] = OrderedDict()  # mutable-ok: draining evicted providers
+        self._project_routable = any(
+            spec.owner == callback_name and spec.kind.lower() not in (*_NON_OTLP_KINDS, *_GRPC_KINDS)
+            for spec in config.exporters
+        )
+        self._warned_project_unroutable = False
 
-    def tracer_for(self, default: Tracer, dynamic_params: Any) -> Tracer:
-        """Return the tracer for this request.
+    def release(self, provider: TracerProvider | None) -> None:
+        """Drop one open-span count; shut a retired provider down once drained.
 
-        Use ``default`` unless the request's dynamic credentials require a
-        credential-scoped tracer, in which case build (or reuse) one. The cache
-        is a bounded LRU: the least-recently-used provider is flushed and shut
-        down on overflow so its exporter threads don't accumulate.
+        ``None`` (the default route) is a no-op so callers can release a
+        ``TenantRoute.provider`` unconditionally. The shutdown itself runs
+        outside the lock: it force-flushes over the network and must not stall
+        every concurrently routing request.
         """
-        headers: Final = dynamic_otlp_headers(self._callback_name, dynamic_params)
-        if not headers:
-            return default
-        cache_key: Final = tuple(sorted(headers.items()))
-        provider = self._providers.get(cache_key)
-        if provider is not None:
+        if provider is None:
+            return
+        with self._lock:
+            remaining: Final = self._open_span_counts.get(provider, 0) - 1
+            if remaining > 0:
+                self._open_span_counts[provider] = remaining
+                return
+            self._open_span_counts.pop(provider, None)
+            drained: Final = provider in self._retired
+            self._retired.pop(provider, None)
+        if drained:
+            _shutdown_provider(provider)
+
+    def route_for(
+        self,
+        default: Tracer,
+        dynamic_params: Any,
+        auth_metadata: Mapping[str, str] | None = None,
+    ) -> TenantRoute:
+        """Return the tracer (and trace-detachment flag) for this request.
+
+        Use ``default`` unless the request's dynamic credentials or its key/team
+        project require a scoped tracer, in which case build (or reuse) one. The
+        cache is a bounded LRU: the least-recently-used provider is flushed and
+        shut down on overflow so its exporter threads don't accumulate.
+
+        A routed provider is returned already held — its open-span count is
+        incremented in the same critical section as the cache update — so a
+        concurrent overflow eviction can't shut it down between selection and
+        the caller's span start. The caller must ``release`` it exactly once.
+        """
+        credential_headers: Final = dynamic_otlp_headers(self._callback_name, dynamic_params) or _NO_HEADERS
+        project_headers: Final = self._project_headers(auth_metadata)
+        if not credential_headers and not project_headers:
+            return TenantRoute(tracer=default, detached=False)
+        cache_key: Final = (
+            tuple(sorted(credential_headers.items())),
+            tuple(sorted(project_headers.items())),
+        )
+        with self._lock:
+            provider: Final = self._cached_provider_locked(cache_key, credential_headers, project_headers)
+            self._open_span_counts[provider] = self._open_span_counts.get(provider, 0) + 1
+            evicted: Final = self._evicted_on_overflow_locked()
+        if evicted is not None:
+            _shutdown_provider(evicted)
+        return TenantRoute(
+            tracer=get_tracer(provider, self._tracer_name),
+            detached=bool(project_headers),
+            provider=provider,
+        )
+
+    def _cached_provider_locked(
+        self,
+        cache_key: tuple[_HeaderItems, _HeaderItems],
+        credential_headers: Mapping[str, str],
+        project_headers: Mapping[str, str],
+    ) -> TracerProvider:
+        cached: Final = self._providers.get(cache_key)
+        if cached is not None:
             self._providers.move_to_end(cache_key)
-        else:
-            provider = build_tracer_provider(self._config_with_headers(headers))
-            self._providers[cache_key] = provider
-            if len(self._providers) > _MAX_CACHED_PROVIDERS:
-                _, evicted = self._providers.popitem(last=False)
-                _shutdown_provider(evicted)
-        return get_tracer(provider, self._tracer_name)
+            return cached
+        built: Final = build_tracer_provider(self._routed_config(credential_headers, project_headers))
+        self._providers[cache_key] = built
+        return built
 
-    def _config_with_headers(self, headers: Mapping[str, str]) -> OpenTelemetryV2Config:
-        """Clone the config, stamping ``headers`` onto the credential's own exporter.
+    def _evicted_on_overflow_locked(self) -> TracerProvider | None:
+        """Pop the LRU provider past the cap; return it if the caller must shut it down.
 
-        ``headers`` are the per-request credentials of ``self._callback_name`` (the
-        integration that built this cache), so they apply only to the exporter that
-        integration contributed (``spec.owner``). A request that carries one
-        tenant's Arize key must never rewrite the headers of a co-configured
-        Langfuse or self-hosted collector exporter, which would leak that key to a
-        different backend.
+        A provider with open spans is retired to drain instead: stopping its
+        processors while a span opened at ``pre_call`` is still live would
+        silently drop that span at end instead of exporting it. Retirees are
+        themselves capped, so the stalest one is shut down (and its open-span
+        count dropped, making its eventual ``release`` a no-op) once too many
+        pile up rather than letting them accumulate a thread each.
         """
-        header_str: Final = ",".join(f"{key}={value}" for key, value in headers.items())
-        header_update: Final[dict[str, str]] = {"headers": header_str}
-        exporters: Final = [
-            (
-                spec.model_copy(update=header_update)
-                if spec.owner == self._callback_name and spec.kind.lower() not in _NON_OTLP_KINDS
-                else spec
+        if len(self._providers) <= _MAX_CACHED_PROVIDERS:
+            return None
+        _, evicted = self._providers.popitem(last=False)
+        if self._open_span_counts.get(evicted, 0) == 0:
+            return evicted
+        self._retired[evicted] = None
+        if len(self._retired) <= _MAX_RETIRED_PROVIDERS:
+            return None
+        overflowed, _ = self._retired.popitem(last=False)
+        self._open_span_counts.pop(overflowed, None)
+        return overflowed
+
+    def _project_headers(self, auth_metadata: Mapping[str, str] | None) -> Mapping[str, str]:
+        """The per-request project-routing headers, if this cache can apply them.
+
+        A gRPC-only exporter can't (the project header route is HTTP-only), so
+        the request warns once and stays on the env-configured default project.
+        """
+        requested: Final = project_routing_headers(self._callback_name, auth_metadata)
+        if not requested or self._project_routable:
+            return requested
+        if not self._warned_project_unroutable:
+            self._warned_project_unroutable = True
+            verbose_logger.warning(
+                "OTel V2: %s key/team config names a per-request project, but its exporter "
+                "is not OTLP/HTTP and the project header is HTTP-only; spans stay in the "
+                "default project.",
+                self._callback_name,
             )
-            for spec in self._config.exporters
+        return _NO_HEADERS
+
+    def _routed_config(
+        self,
+        credential_headers: Mapping[str, str],
+        project_headers: Mapping[str, str],
+    ) -> OpenTelemetryV2Config:
+        """Clone the config, rewriting headers on the callback's own exporter.
+
+        Both header sets apply only to the exporter ``self._callback_name``
+        contributed (``spec.owner``). A request that carries one tenant's Arize
+        key must never rewrite the headers of a co-configured Langfuse or
+        self-hosted collector exporter, which would leak that key to a
+        different backend.
+
+        Dynamic credentials REPLACE the exporter's headers — they are the
+        tenant's complete credential set. Project headers APPEND instead: the
+        preset's static headers carry the backend auth (Phoenix's
+        ``Authorization``), which must survive routing to a project.
+        """
+        exporters: Final = [
+            self._routed_exporter(spec, credential_headers, project_headers) for spec in self._config.exporters
         ]
         return self._config.model_copy(update={"exporters": exporters})
+
+    def _routed_exporter(
+        self,
+        spec: ExporterSpec,
+        credential_headers: Mapping[str, str],
+        project_headers: Mapping[str, str],
+    ) -> ExporterSpec:
+        kind: Final = spec.kind.lower()
+        if spec.owner != self._callback_name or kind in _NON_OTLP_KINDS:
+            return spec
+        base: Final = _plain_header_string(credential_headers) if credential_headers else spec.headers
+        routed: Final = (
+            ",".join(part for part in (base, _encoded_header_string(project_headers)) if part)
+            if project_headers and kind not in _GRPC_KINDS
+            else base
+        )
+        return spec if routed == spec.headers else spec.model_copy(update={"headers": routed})
diff --git a/litellm/integrations/otel/presets/__init__.py b/litellm/integrations/otel/presets/__init__.py
index 95ac2783325..35b0584c697 100644
--- a/litellm/integrations/otel/presets/__init__.py
+++ b/litellm/integrations/otel/presets/__init__.py
@@ -8,7 +8,8 @@ the factory in ``litellm_logging`` can resolve a name and build a single
 ``OpenTelemetryV2`` instance from the result.
 """
 
-from collections.abc import Callable
+from collections.abc import Callable, Mapping
+from types import MappingProxyType
 from typing import Final
 
 from litellm.integrations.otel.presets.agentops import agentops_preset
@@ -20,7 +21,10 @@ from litellm.integrations.otel.presets.langfuse import (
 )
 from litellm.integrations.otel.presets.langtrace import langtrace_preset
 from litellm.integrations.otel.presets.levo import levo_preset
-from litellm.integrations.otel.presets.phoenix import phoenix_preset
+from litellm.integrations.otel.presets.phoenix import (
+    phoenix_preset,
+    phoenix_project_headers,
+)
 from litellm.integrations.otel.presets.weave import weave_dynamic_headers, weave_preset
 from litellm.types.utils import StandardCallbackDynamicParams
 
@@ -47,6 +51,23 @@ DYNAMIC_HEADERS_BY_CALLBACK: Final[dict[str, Callable[[StandardCallbackDynamicPa
 }
 
 
+#: Callback name → per-request *routing* header builder, sourced from the key/team
+#: config the proxy resolved at auth. Deliberately separate from
+#: ``DYNAMIC_HEADERS_BY_CALLBACK``: that one is fed
+#: ``StandardCallbackDynamicParams``, which is populated from client-supplied
+#: request metadata. Naming a destination project is a data-exfiltration
+#: primitive, so it must only ever come from server-set key/team config.
+PROJECT_HEADERS_BY_CALLBACK: Final[Mapping[str, Callable[[Mapping[str, str] | None], Mapping[str, str]]]] = (
+    MappingProxyType(
+        {
+            "arize_phoenix": phoenix_project_headers,
+        }
+    )
+)
+
+_NO_PROJECT_HEADERS: Final[Mapping[str, str]] = MappingProxyType({})
+
+
 def dynamic_otlp_headers(
     callback_name: str | None,
     dynamic_params: StandardCallbackDynamicParams | None,
@@ -62,9 +83,25 @@ def dynamic_otlp_headers(
     return headers or None
 
 
+def project_routing_headers(
+    callback_name: str | None,
+    auth_metadata: Mapping[str, str] | None,
+) -> Mapping[str, str]:
+    """Per-request project-routing headers from trusted key/team config.
+
+    Empty means "no per-request project" — the caller keeps its default tracer,
+    whose resource attributes carry the env-configured project.
+    """
+    builder: Final = PROJECT_HEADERS_BY_CALLBACK.get(callback_name or "")
+    if builder is None:
+        return _NO_PROJECT_HEADERS
+    return builder(auth_metadata)
+
+
 __all__ = [
     "DYNAMIC_HEADERS_BY_CALLBACK",
     "PRESET_BY_CALLBACK",
+    "PROJECT_HEADERS_BY_CALLBACK",
     "Preset",
     "agentops_preset",
     "arize_preset",
@@ -73,5 +110,6 @@ __all__ = [
     "langtrace_preset",
     "levo_preset",
     "phoenix_preset",
+    "project_routing_headers",
     "weave_preset",
 ]
diff --git a/litellm/integrations/otel/presets/phoenix.py b/litellm/integrations/otel/presets/phoenix.py
index fc1eb9f748f..eef407b6c1b 100644
--- a/litellm/integrations/otel/presets/phoenix.py
+++ b/litellm/integrations/otel/presets/phoenix.py
@@ -1,5 +1,7 @@
 """Arize-Phoenix preset."""
 
+from collections.abc import Mapping
+from types import MappingProxyType
 from typing import Final
 
 from pydantic import AliasChoices, Field
@@ -25,6 +27,36 @@ class _PhoenixSettings(BaseSettings):
     )
 
 
+#: Phoenix routes an OTLP/HTTP export to a project by this header, which takes
+#: precedence over the ``openinference.project.name`` resource attribute the env
+#: var sets. Requires arize-phoenix 15.5.0+; older collectors ignore it and the
+#: spans land in the resource attribute's project.
+PHOENIX_PROJECT_HEADER: Final = "x-project-name"
+
+#: Key/team config fields naming the target project, highest precedence first.
+_PROJECT_KEYS: Final = ("phoenix_project_name_override", "phoenix_project_name")
+
+_NO_PROJECT: Final[Mapping[str, str]] = MappingProxyType({})
+
+
+def phoenix_project_headers(auth_metadata: Mapping[str, str] | None) -> Mapping[str, str]:
+    """The per-request Phoenix project header for this key/team, if any.
+
+    ``auth_metadata`` must be the key/team config the proxy resolved at auth
+    (``user_api_key_auth_metadata``), never client-supplied request metadata:
+    choosing the destination project is a data-exfiltration primitive, so a
+    caller must not be able to name one. Returns an empty mapping when the key
+    and team name no project, leaving the request on the env-configured default.
+    """
+    if not auth_metadata:
+        return _NO_PROJECT
+    project: Final = next(
+        (stripped for key in _PROJECT_KEYS if (stripped := (auth_metadata.get(key) or "").strip())),
+        "",
+    )
+    return MappingProxyType({PHOENIX_PROJECT_HEADER: project}) if project else _NO_PROJECT
+
+
 def phoenix_preset(
     *,
     config_overrides: OpenTelemetryV2Config | None = None,
diff --git a/litellm/proxy/auth/auth_utils.py b/litellm/proxy/auth/auth_utils.py
index 883f986f6fd..912a0b0ebd0 100644
--- a/litellm/proxy/auth/auth_utils.py
+++ b/litellm/proxy/auth/auth_utils.py
@@ -222,8 +222,10 @@ _SAFE_CLIENT_CALLBACK_PARAMS: Final[frozenset[str]] = frozenset(
 _EXTRA_BANNED_OBSERVABILITY_PARAMS: Final[frozenset[str]] = frozenset(
     {
         "posthog_api_url",
-        "phoenix_project_name",
-        "phoenix_project_name_override",
+        # ``phoenix_project_name`` / ``phoenix_project_name_override`` are NOT
+        # banned: on the proxy the Phoenix integrations only read them from
+        # ``user_api_key_auth_metadata`` (key/team config), so the bare request
+        # fields are inert and rejecting them just breaks SDK-style callers.
         # Server-reserved: written exclusively by add_user_api_key_auth_to_request_metadata
         # from the authenticated key's database record.  A caller-supplied value
         # would survive the server merge and let an authenticated user redirect
diff --git a/tests/_wait_helpers.py b/tests/_wait_helpers.py
new file mode 100644
index 00000000000..f67e623e3ad
--- /dev/null
+++ b/tests/_wait_helpers.py
@@ -0,0 +1,46 @@
+"""Deadline-based waits for tests, so nothing has to guess how long a background callback takes."""
+
+import asyncio
+import time
+from collections.abc import Callable
+from typing import Final
+
+DEFAULT_TIMEOUT_S: Final[float] = 10.0
+DEFAULT_INTERVAL_S: Final[float] = 0.02
+
+
+def _fail(timeout_s: float, message: str) -> None:
+    raise AssertionError(f"condition not met within {timeout_s}s: {message}")
+
+
+def wait_until(
+    predicate: Callable[[], bool],
+    *,
+    message: str,
+    timeout_s: float = DEFAULT_TIMEOUT_S,
+    interval_s: float = DEFAULT_INTERVAL_S,
+) -> None:
+    deadline: Final = time.monotonic() + timeout_s
+    while time.monotonic() < deadline:
+        if predicate():
+            return
+        time.sleep(interval_s)  # sleep-ok: bounded poll interval, not a blind settle
+    if not predicate():
+        _fail(timeout_s, message)
+
+
+async def await_until(
+    predicate: Callable[[], bool],
+    *,
+    message: str,
+    timeout_s: float = DEFAULT_TIMEOUT_S,
+    interval_s: float = DEFAULT_INTERVAL_S,
+) -> None:
+    """Yields to the event loop between polls, so callbacks scheduled as tasks get a chance to run."""
+    deadline: Final = time.monotonic() + timeout_s
+    while time.monotonic() < deadline:
+        if predicate():
+            return
+        await asyncio.sleep(interval_s)
+    if not predicate():
+        _fail(timeout_s, message)
diff --git a/tests/local_testing/test_caching_handler.py b/tests/local_testing/test_caching_handler.py
index 0f4539162a2..b26334e9ee0 100644
--- a/tests/local_testing/test_caching_handler.py
+++ b/tests/local_testing/test_caching_handler.py
@@ -741,8 +741,6 @@ def test_sync_responses_api_caching():
     # Step 1: Cache the responses API response
     caching_handler.sync_set_cache(result=responses_api_response, kwargs=kwargs)
 
-    time.sleep(0.5)
-
     # Step 2: Retrieve from cache
     cached_response = caching_handler._sync_get_cache(
         model=original_model,
@@ -875,7 +873,6 @@ def test_sync_get_cache_does_not_eagerly_log_streaming_responses_hits():
     }
 
     caching_handler.sync_set_cache(result=responses_api_response, kwargs=kwargs)
-    time.sleep(0.2)
 
     cached_response = caching_handler._sync_get_cache(
         model=original_model,
@@ -920,7 +917,6 @@ def test_sync_get_cache_defers_streaming_completion_hit_callbacks():
     }
 
     caching_handler.sync_set_cache(result=chat_completion_response, kwargs=kwargs)
-    time.sleep(0.2)
 
     cached_response = caching_handler._sync_get_cache(
         model=original_model,
diff --git a/tests/local_testing/test_custom_callback_input.py b/tests/local_testing/test_custom_callback_input.py
index 6a4ec9206f7..cedb5ea1a97 100644
--- a/tests/local_testing/test_custom_callback_input.py
+++ b/tests/local_testing/test_custom_callback_input.py
@@ -4,7 +4,6 @@ import asyncio
 import inspect
 import os
 import sys
-import time
 import traceback
 from litellm._uuid import uuid
 from datetime import datetime
@@ -20,6 +19,7 @@ import litellm
 from litellm import Cache, completion, embedding
 from litellm.integrations.custom_logger import CustomLogger
 from litellm.types.utils import LiteLLMCommonStrings
+from tests._wait_helpers import await_until, wait_until
 
 # Test Scenarios (test across completion, streaming, embedding)
 ## 1: Pre-API-Call
@@ -389,7 +389,10 @@ def test_chat_openai_stream():
                 continue
         except Exception:
             pass
-        time.sleep(1)
+        wait_until(
+            lambda: "sync_failure" in customHandler.states,
+            message=f"no sync_failure callback, states={customHandler.states}",
+        )
         print(f"customHandler.errors: {customHandler.errors}")
         assert len(customHandler.errors) == 0
         litellm.callbacks = []
@@ -430,10 +433,12 @@ async def test_async_chat_openai_stream():
             )
             async for chunk in response:
                 continue
-            await asyncio.sleep(1)
         except Exception:
             pass
-        time.sleep(1)
+        await await_until(
+            lambda: "async_failure" in customHandler.states,
+            message=f"no async_failure callback, states={customHandler.states}",
+        )
         print(f"customHandler.errors: {customHandler.errors}")
         assert len(customHandler.errors) == 0
         litellm.callbacks = []
@@ -473,7 +478,10 @@ def test_chat_azure_stream():
                 continue
         except Exception:
             pass
-        time.sleep(1)
+        wait_until(
+            lambda: "sync_failure" in customHandler.states,
+            message=f"no sync_failure callback, states={customHandler.states}",
+        )
         print(f"customHandler.errors: {customHandler.errors}")
         assert len(customHandler.errors) == 0
         litellm.callbacks = []
@@ -590,7 +598,10 @@ async def test_async_chat_sagemaker_stream():
                 continue
         except Exception:
             pass
-        time.sleep(1)
+        await await_until(
+            lambda: "async_failure" in customHandler.states,
+            message=f"no async_failure callback, states={customHandler.states}",
+        )
         print(f"customHandler.errors: {customHandler.errors}")
         assert len(customHandler.errors) == 0
         litellm.callbacks = []
@@ -711,10 +722,12 @@ async def test_async_text_completion_bedrock():
             async for chunk in response:
                 continue
 
-            await asyncio.sleep(1)
         except Exception:
             pass
-        time.sleep(1)
+        await await_until(
+            lambda: "async_failure" in customHandler.states,
+            message=f"no async_failure callback, states={customHandler.states}",
+        )
         print(f"customHandler.errors: {customHandler.errors}")
         assert len(customHandler.errors) == 0
         litellm.callbacks = []
@@ -754,10 +767,12 @@ async def test_async_text_completion_openai_stream():
             async for chunk in response:
                 continue
 
-            await asyncio.sleep(1)
         except Exception:
             pass
-        time.sleep(1)
+        await await_until(
+            lambda: "async_failure" in customHandler.states,
+            message=f"no async_failure callback, states={customHandler.states}",
+        )
         print(f"customHandler.errors: {customHandler.errors}")
         assert len(customHandler.errors) == 0
         litellm.callbacks = []
@@ -816,7 +831,10 @@ def test_amazing_sync_embedding():
         )
         print(f"customHandler_success.errors: {customHandler_success.errors}")
         print(f"customHandler_success.states: {customHandler_success.states}")
-        time.sleep(2)
+        wait_until(
+            lambda: len(customHandler_success.states) == 3,
+            message=f"success states never reached pre/post/success, got {customHandler_success.states}",
+        )
         assert len(customHandler_success.errors) == 0
         assert len(customHandler_success.states) == 3  # pre, post, success
         # test failure callback
@@ -832,7 +850,10 @@ def test_amazing_sync_embedding():
             pass
         print(f"customHandler_failure.errors: {customHandler_failure.errors}")
         print(f"customHandler_failure.states: {customHandler_failure.states}")
-        time.sleep(2)
+        wait_until(
+            lambda: len(customHandler_failure.states) == 3,
+            message=f"failure states never reached pre/post/failure, got {customHandler_failure.states}",
+        )
         assert len(customHandler_failure.errors) == 1
         assert len(customHandler_failure.states) == 3  # pre, post, failure
     except Exception as e:
@@ -939,7 +960,10 @@ def test_image_generation_openai():
 
         print(f"customHandler_success.errors: {customHandler_success.errors}")
         print(f"customHandler_success.states: {customHandler_success.states}")
-        time.sleep(2)
+        wait_until(
+            lambda: len(customHandler_success.states) == 3,
+            message=f"success states never reached pre/post/success, got {customHandler_success.states}",
+        )
         assert len(customHandler_success.errors) == 0
         assert len(customHandler_success.states) == 3  # pre, post, success
         # test failure callback
@@ -991,7 +1015,10 @@ def test_turn_off_message_logging():
         mock_response="Going well!",
     )
 
-    time.sleep(2)
+    wait_until(
+        lambda: "sync_success" in customHandler.states,
+        message=f"no sync_success callback, states={customHandler.states}",
+    )
     assert len(customHandler.errors) == 0
 
 
@@ -1033,7 +1060,7 @@ def test_standard_logging_payload(model, turn_off_message_logging):
             mock_response="Going well!",
         )
 
-        time.sleep(2)
+        wait_until(lambda: mock_client.called, message="log_success_event never fired")
         mock_client.assert_called_once()
 
         print(
@@ -1147,7 +1174,7 @@ def test_standard_logging_payload_audio(turn_off_message_logging, stream):
             for chunk in response:
                 continue
 
-        time.sleep(2)
+        wait_until(lambda: mock_client.called, message="log_success_event never fired")
         mock_client.assert_called()
 
         print(
@@ -1247,7 +1274,7 @@ def test_aaastandard_logging_payload_cache_hit():
             caching=True,
         )
 
-        time.sleep(2)
+        wait_until(lambda: mock_client.called, message="log_success_event never fired")
         mock_client.assert_called_once()
 
         assert "standard_logging_object" in mock_client.call_args.kwargs["kwargs"]
@@ -1276,6 +1303,9 @@ def test_logging_async_cache_hit_sync_call(turn_off_message_logging):
 
     litellm.cache = Cache()
 
+    primingHandler = CompletionCustomHandler()
+    litellm.callbacks = [primingHandler]
+
     response = litellm.completion(
         model="gpt-3.5-turbo",
         messages=[{"role": "user", "content": "Hey, how's it going?"}],
@@ -1285,7 +1315,10 @@ def test_logging_async_cache_hit_sync_call(turn_off_message_logging):
     for chunk in response:
         print(chunk)
 
-    time.sleep(3)
+    wait_until(
+        lambda: "sync_success" in primingHandler.states,
+        message=f"priming call never finished logging, states={primingHandler.states}",
+    )
     customHandler = CompletionCustomHandler()
     litellm.callbacks = [customHandler]
     litellm.success_callback = []
@@ -1303,7 +1336,7 @@ def test_logging_async_cache_hit_sync_call(turn_off_message_logging):
         for chunk in resp:
             print(chunk)
 
-        time.sleep(2)
+        wait_until(lambda: mock_client.called, message="log_success_event never fired")
         mock_client.assert_called_once()
 
         assert "standard_logging_object" in mock_client.call_args.kwargs["kwargs"]
@@ -1387,7 +1420,7 @@ def test_logging_standard_payload_llm_headers(stream):
             for chunk in resp:
                 continue
 
-        time.sleep(2)
+        wait_until(lambda: mock_client.called, message="log_success_event never fired")
         mock_client.assert_called()
 
         standard_logging_object: StandardLoggingPayload = mock_client.call_args.kwargs[
@@ -1458,7 +1491,7 @@ async def test_standard_logging_payload_stream_usage(sync_mode):
                 chunks = []
                 for chunk in resp:
                     chunks.append(chunk)
-                time.sleep(2)
+                wait_until(lambda: mock_client.called, message="log_success_event never fired")
             else:
                 resp = await litellm.acompletion(
                     model="anthropic/claude-sonnet-4-5-20250929",
@@ -1469,7 +1502,9 @@ async def test_standard_logging_payload_stream_usage(sync_mode):
                 chunks = []
                 async for chunk in resp:
                     chunks.append(chunk)
-                await asyncio.sleep(2)
+                await await_until(
+                    lambda: mock_client.called, message="async_log_success_event never fired"
+                )
 
             mock_client.assert_called_once()
 
diff --git a/tests/test_litellm/integrations/otel/test_otel_v2_dynamic.py b/tests/test_litellm/integrations/otel/test_otel_v2_dynamic.py
index e44c56e1fdf..ca62253aa2f 100644
--- a/tests/test_litellm/integrations/otel/test_otel_v2_dynamic.py
+++ b/tests/test_litellm/integrations/otel/test_otel_v2_dynamic.py
@@ -9,7 +9,11 @@ sys.path.insert(0, os.path.abspath("../../../.."))
 from opentelemetry.trace import NoOpTracer
 
 from litellm.integrations.otel.model.config import ExporterSpec, OpenTelemetryV2Config
-from litellm.integrations.otel.presets import dynamic_otlp_headers
+from litellm.integrations.otel.presets import (
+    dynamic_otlp_headers,
+    project_routing_headers,
+)
+from litellm.integrations.otel.plumbing.providers import parse_headers
 from litellm.integrations.otel.plumbing.routing import TenantTracerCache
 
 
@@ -83,10 +87,10 @@ def test_provider_cached_per_credential_set():
     creds_a = {"arize_space_id": "S", "arize_api_key": "K"}
     creds_b = {"arize_space_id": "S2", "arize_api_key": "K2"}
 
-    cache.tracer_for(default, creds_a)
-    cache.tracer_for(default, creds_a)  # same set → reuse, no new provider
+    cache.route_for(default, creds_a)
+    cache.route_for(default, creds_a)  # same set → reuse, no new provider
     assert len(cache._providers) == 1
-    cache.tracer_for(default, creds_b)  # new set → new provider
+    cache.route_for(default, creds_b)  # new set → new provider
     assert len(cache._providers) == 2
 
 
@@ -109,10 +113,11 @@ def test_provider_cache_is_bounded_and_evicts_lru(monkeypatch):
     def creds(space):
         return {"arize_space_id": space, "arize_api_key": "K"}
 
-    cache.tracer_for(default, creds("1"))
-    cache.tracer_for(default, creds("2"))
-    cache.tracer_for(default, creds("1"))  # touch "1" → "2" is now LRU
-    cache.tracer_for(default, creds("3"))  # overflow → evict "2"
+    # route_for returns a held provider; release models the span closing.
+    cache.release(cache.route_for(default, creds("1")).provider)
+    cache.release(cache.route_for(default, creds("2")).provider)
+    cache.release(cache.route_for(default, creds("1")).provider)  # touch "1" → "2" is now LRU
+    cache.release(cache.route_for(default, creds("3")).provider)  # overflow → evict "2"
 
     assert len(cache._providers) == 2
     assert len(shut_down) == 1  # exactly the evicted provider was shut down
@@ -121,14 +126,14 @@ def test_provider_cache_is_bounded_and_evicts_lru(monkeypatch):
 def test_no_dynamic_params_uses_default_tracer():
     cache = _cache("arize")
     default = NoOpTracer()
-    assert cache.tracer_for(default, {}) is default
+    assert cache.route_for(default, {}).tracer is default
     assert cache._providers == {}
 
 
 def test_non_participating_callback_uses_default_tracer():
     cache = _cache("arize_phoenix")
     default = NoOpTracer()
-    assert cache.tracer_for(default, {"arize_api_key": "K"}) is default
+    assert cache.route_for(default, {"arize_api_key": "K"}).tracer is default
     assert cache._providers == {}
 
 
@@ -140,7 +145,7 @@ def test_dynamic_headers_applied_to_otlp_exporter_only():
             ExporterSpec(kind="in_memory", owner="arize"),
         ],
     )
-    new_cfg = cache._config_with_headers({"arize-space-id": "S", "api_key": "K"})
+    new_cfg = cache._routed_config({"arize-space-id": "S", "api_key": "K"}, {})
     otlp, in_mem = new_cfg.exporters
     assert otlp.headers == "arize-space-id=S,api_key=K"
     assert in_mem.headers is None  # console/in_memory left untouched
@@ -150,10 +155,9 @@ def test_dynamic_headers_do_not_leak_to_other_owners_exporter():
     """A tenant's Arize credentials must never be stamped onto a co-configured
     exporter owned by a different backend (a self-hosted collector, Langfuse).
 
-    Regression for the cross-backend credential leak: ``_config_with_headers``
-    used to rewrite the headers of every OTLP exporter, so one request carrying
-    a team's Arize key clobbered the base collector's and Langfuse's headers
-    with that key.
+    Regression for the cross-backend credential leak: the header rewrite used
+    to hit every OTLP exporter, so one request carrying a team's Arize key
+    clobbered the base collector's and Langfuse's headers with that key.
     """
     cache = _cache(
         "arize",
@@ -178,10 +182,206 @@ def test_dynamic_headers_do_not_leak_to_other_owners_exporter():
             ),
         ],
     )
-    new_cfg = cache._config_with_headers(
-        {"arize-space-id": "TEAMX", "api_key": "TEAMX_KEY"}
+    new_cfg = cache._routed_config(
+        {"arize-space-id": "TEAMX", "api_key": "TEAMX_KEY"}, {}
     )
     by_owner = {e.owner: e.headers for e in new_cfg.exporters}
     assert by_owner["arize"] == "arize-space-id=TEAMX,api_key=TEAMX_KEY"
     assert by_owner[None] == "x=base-collector"
     assert by_owner["langfuse_otel"] == "Authorization=Basic base-langfuse"
+
+
+# --- per-request Phoenix project routing from trusted key/team config --- #
+
+
+def _phoenix_cache(kind="otlp_http"):
+    return _cache(
+        "arize_phoenix",
+        exporters=[
+            ExporterSpec(
+                kind=kind,
+                endpoint="http://phoenix:6006",
+                headers="Authorization=Bearer phoenix-key",
+                owner="arize_phoenix",
+            ),
+        ],
+    )
+
+
+def test_phoenix_project_headers_precedence_and_blanks():
+    assert project_routing_headers(
+        "arize_phoenix", {"phoenix_project_name": "team-proj"}
+    ) == {"x-project-name": "team-proj"}
+    assert project_routing_headers(
+        "arize_phoenix",
+        {"phoenix_project_name_override": "override", "phoenix_project_name": "base"},
+    ) == {"x-project-name": "override"}
+    assert (
+        project_routing_headers("arize_phoenix", {"phoenix_project_name": "   "}) == {}
+    )
+    assert project_routing_headers("arize_phoenix", None) == {}
+    # Only Phoenix participates in project routing.
+    assert project_routing_headers("arize", {"phoenix_project_name": "p"}) == {}
+
+
+def test_project_header_appends_and_preserves_phoenix_auth():
+    """Regression: routing to a project must not drop the preset's static
+    ``Authorization`` header — a replace would break Phoenix auth entirely."""
+    cache = _phoenix_cache()
+    cfg = cache._routed_config({}, {"x-project-name": "team-proj"})
+    (spec,) = cfg.exporters
+    parsed = parse_headers(spec.headers)
+    assert parsed["authorization"] == "Bearer phoenix-key"
+    assert parsed["x-project-name"] == "team-proj"
+
+
+def test_project_name_with_header_separators_round_trips():
+    cache = _phoenix_cache()
+    cfg = cache._routed_config({}, {"x-project-name": "my proj, prod=1"})
+    (spec,) = cfg.exporters
+    parsed = parse_headers(spec.headers)
+    assert parsed["x-project-name"] == "my proj, prod=1"
+    assert parsed["authorization"] == "Bearer phoenix-key"
+
+
+def test_project_header_does_not_touch_other_exporters():
+    cache = _cache(
+        "arize_phoenix",
+        exporters=[
+            ExporterSpec(
+                kind="otlp_http",
+                endpoint="http://collector:4318",
+                headers="x=base-collector",
+                owner=None,
+            ),
+            ExporterSpec(
+                kind="otlp_http",
+                endpoint="http://phoenix:6006",
+                headers="Authorization=Bearer phoenix-key",
+                owner="arize_phoenix",
+            ),
+        ],
+    )
+    cfg = cache._routed_config({}, {"x-project-name": "team-proj"})
+    by_owner = {e.owner: e.headers for e in cfg.exporters}
+    assert by_owner[None] == "x=base-collector"
+    assert parse_headers(by_owner["arize_phoenix"])["x-project-name"] == "team-proj"
+
+
+def test_provider_cached_per_project():
+    cache = _phoenix_cache()
+    default = NoOpTracer()
+    routed = cache.route_for(default, None, {"phoenix_project_name": "proj-a"})
+    assert routed.tracer is not default
+    assert routed.detached is True  # project spans must root their own trace
+    cache.route_for(default, None, {"phoenix_project_name": "proj-a"})
+    assert len(cache._providers) == 1
+    cache.route_for(default, None, {"phoenix_project_name": "proj-b"})
+    assert len(cache._providers) == 2
+    for provider in cache._providers.values():
+        provider.shutdown()
+
+
+def test_client_dynamic_params_cannot_choose_phoenix_project():
+    # ``StandardCallbackDynamicParams`` is populated from client-supplied
+    # request metadata; the project may only come from server-set key/team
+    # config (the ``auth_metadata`` argument).
+    cache = _phoenix_cache()
+    default = NoOpTracer()
+    assert cache.route_for(default, {"phoenix_project_name": "attacker"}).tracer is default
+    assert (
+        cache.route_for(default, {"phoenix_project_name_override": "attacker"}).tracer
+        is default
+    )
+    assert cache._providers == {}
+
+
+def test_auth_metadata_without_project_uses_default_tracer():
+    cache = _phoenix_cache()
+    default = NoOpTracer()
+    assert cache.route_for(default, None, {"logging_setting": "x"}).tracer is default
+    assert cache._providers == {}
+
+
+def test_grpc_exporter_gets_no_project_routing():
+    # ``x-project-name`` is only honored on the OTLP/HTTP endpoint, so a
+    # gRPC-only Phoenix exporter stays on the default project (warned once).
+    cache = _phoenix_cache(kind="otlp_grpc")
+    default = NoOpTracer()
+    assert cache.route_for(default, None, {"phoenix_project_name": "proj"}).tracer is default
+    assert cache._providers == {}
+    assert cache._warned_project_unroutable is True
+
+
+def test_eviction_defers_shutdown_while_a_span_is_open(monkeypatch):
+    # An LLM span opened at pre_call stays open until the close callback; LRU
+    # eviction in that window must not stop the provider's processors, or the
+    # span is silently dropped at end instead of exported. route_for itself
+    # takes the hold, atomically with the cache update, so a concurrent
+    # eviction can never shut a just-selected provider down before the caller
+    # records its span.
+    from litellm.integrations.otel.plumbing import routing as routing_mod
+
+    monkeypatch.setattr(routing_mod, "_MAX_CACHED_PROVIDERS", 1)
+    shut_down = []
+    monkeypatch.setattr(
+        routing_mod, "_shutdown_provider", lambda p: shut_down.append(p)
+    )
+    cache = _cache("arize")
+    default = NoOpTracer()
+
+    route_a = cache.route_for(default, {"arize_space_id": "A", "arize_api_key": "K"})
+    assert route_a.provider is not None
+    cache.route_for(default, {"arize_space_id": "B", "arize_api_key": "K"})  # evicts A
+    assert shut_down == []  # deferred: A is still held by route_a
+    cache.release(route_a.provider)
+    assert shut_down == [route_a.provider]
+
+
+def test_retired_providers_are_capped(monkeypatch):
+    # Retiring an evicted provider keeps it, and its exporter thread, alive
+    # while a span is open, so retirees need a cap of their own: a caller
+    # cycling unique credential sets across calls that never close would
+    # otherwise pin one live provider per open call, far past the cache bound.
+    # Past the cap the stalest retiree is shut down and its later release is a
+    # no-op, while the ones still within the cap keep draining.
+    from litellm.integrations.otel.plumbing import routing as routing_mod
+
+    monkeypatch.setattr(routing_mod, "_MAX_CACHED_PROVIDERS", 1)
+    monkeypatch.setattr(routing_mod, "_MAX_RETIRED_PROVIDERS", 2)
+    shut_down = []
+    monkeypatch.setattr(
+        routing_mod, "_shutdown_provider", lambda p: shut_down.append(p)
+    )
+    cache = _cache("arize")
+    default = NoOpTracer()
+
+    # Every route stays held (no release), so each one evicts and retires its
+    # predecessor instead of shutting it down.
+    routes = [
+        cache.route_for(default, {"arize_space_id": str(i), "arize_api_key": "K"})
+        for i in range(5)
+    ]
+
+    assert len(cache._providers) == 1
+    assert len(cache._retired) == 2  # capped, not one retiree per open call
+    assert shut_down == [routes[0].provider, routes[1].provider]
+
+    cache.release(routes[0].provider)  # already shut down: no second shutdown
+    assert shut_down == [routes[0].provider, routes[1].provider]
+    cache.release(routes[2].provider)  # still draining: drains and shuts down
+    assert shut_down[-1] is routes[2].provider
+
+
+def test_release_without_eviction_keeps_provider_alive(monkeypatch):
+    from litellm.integrations.otel.plumbing import routing as routing_mod
+
+    shut_down = []
+    monkeypatch.setattr(
+        routing_mod, "_shutdown_provider", lambda p: shut_down.append(p)
+    )
+    cache = _cache("arize")
+    route = cache.route_for(NoOpTracer(), {"arize_space_id": "A", "arize_api_key": "K"})
+    cache.release(route.provider)
+    assert shut_down == []  # still cached, never retired
+    cache.release(None)  # default-route release is a no-op
diff --git a/tests/test_litellm/integrations/otel/test_otel_v2_logger.py b/tests/test_litellm/integrations/otel/test_otel_v2_logger.py
index bb2d970e9c7..e5d5b62b856 100644
--- a/tests/test_litellm/integrations/otel/test_otel_v2_logger.py
+++ b/tests/test_litellm/integrations/otel/test_otel_v2_logger.py
@@ -37,6 +37,7 @@ from litellm.integrations.otel.plumbing.context import (  # noqa: E402
     set_request_root_span,
 )
 from litellm.integrations.otel.logger import OpenTelemetryV2  # noqa: E402
+from litellm.integrations.otel.model.config import ExporterSpec  # noqa: E402
 from litellm.integrations.otel.model.spans import (  # noqa: E402
     LITELLM_PROXY_REQUEST_SPAN_NAME,
     SpanRole,
@@ -2309,3 +2310,215 @@ def test_metrics_disabled_by_default_records_nothing(monkeypatch):
         )
     )
     assert _emitted_metric_names(reader) == set()
+
+
+# --------------------------------------------------------------------------- #
+#  Per-request Phoenix project routing (key/team auth metadata)
+# --------------------------------------------------------------------------- #
+
+
+def _phoenix_routing_logger(capture_kind):
+    """A Phoenix-shaped logger whose owned exporter is a registered factory kind
+    that captures the exporter built per routed header set, so the test can
+    assert which destination each span actually exported through."""
+    captured = {}
+
+    def factory(spec):
+        exporter = InMemorySpanExporter()
+        captured[spec.headers] = exporter
+        return exporter
+
+    providers.register_exporter_factory(capture_kind, factory)
+    cfg = OpenTelemetryV2Config(
+        exporters=[
+            ExporterSpec(
+                kind=capture_kind,
+                endpoint="http://phoenix:6006",
+                headers="Authorization=Bearer phoenix-key",
+                owner="arize_phoenix",
+            )
+        ]
+    )
+    default_exporter = InMemorySpanExporter()
+    tracer_provider = providers.build_tracer_provider(cfg, exporter=default_exporter)
+    logger = OpenTelemetryV2(
+        config=cfg, callback_name="arize_phoenix", tracer_provider=tracer_provider
+    )
+    return logger, default_exporter, captured
+
+
+def test_key_team_auth_metadata_routes_llm_span_to_phoenix_project():
+    """The proxy stamps the key/team config into ``user_api_key_auth_metadata``;
+    a ``phoenix_project_name`` there must route the LLM span through an exporter
+    carrying the ``x-project-name`` header while keeping the preset's auth."""
+    logger, default_exporter, captured = _phoenix_routing_logger("capture_route_a")
+    auth_md = {"phoenix_project_name": "team-proj"}
+    payload = _payload(metadata={"user_api_key_auth_metadata": auth_md})
+    kwargs = {
+        "standard_logging_object": payload,
+        "litellm_params": {"metadata": {"user_api_key_auth_metadata": auth_md}},
+    }
+    _emit_llm(logger, kwargs)
+
+    assert [s.name for s in default_exporter.get_finished_spans()] == []
+    (headers,) = captured
+    parsed = providers.parse_headers(headers)
+    assert parsed["x-project-name"] == "team-proj"
+    assert parsed["authorization"] == "Bearer phoenix-key"
+    routed_spans = captured[headers].get_finished_spans()
+    assert len(routed_spans) == 1
+    assert routed_spans[0].parent is None  # own trace, so Phoenix can route it
+
+
+def test_client_request_metadata_cannot_route_phoenix_project():
+    """A bare ``phoenix_project_name`` in client request metadata (not the
+    server-set ``user_api_key_auth_metadata``) must be ignored: the span stays
+    on the default tracer and no routed exporter is ever built."""
+    logger, default_exporter, captured = _phoenix_routing_logger("capture_route_b")
+    payload = _payload(metadata={"phoenix_project_name": "attacker-project"})
+    kwargs = {
+        "standard_logging_object": payload,
+        "litellm_params": {"metadata": {"phoenix_project_name": "attacker-project"}},
+    }
+    _emit_llm(logger, kwargs)
+
+    assert captured == {}
+    assert len(default_exporter.get_finished_spans()) == 1
+
+
+def test_project_routing_resolves_at_pre_call_before_payload_exists():
+    """Production ``pre_call`` runs before the standard logging payload exists,
+    so the destination project must resolve from ``litellm_params`` alone — the
+    span is created (and its exporter chosen) right there."""
+    logger, default_exporter, captured = _phoenix_routing_logger("capture_route_c")
+    auth_md = {"phoenix_project_name": "team-proj"}
+    litellm_params = {"metadata": {"user_api_key_auth_metadata": auth_md}}
+    server = logger._emitter.start_span(
+        SpanRole.PROXY_REQUEST, LITELLM_PROXY_REQUEST_SPAN_NAME
+    )
+    with trace.use_span(server, end_on_exit=False):
+        logger.log_pre_api_call(
+            model="gpt-4o",
+            messages=[],
+            kwargs={"litellm_call_id": "call_1", "litellm_params": litellm_params},
+        )
+    server.end()
+    assert len(captured) == 1  # routed exporter already built at pre_call
+
+    close_kwargs = {
+        "standard_logging_object": _payload(
+            metadata={"user_api_key_auth_metadata": auth_md}
+        ),
+        "litellm_params": litellm_params,
+    }
+    asyncio.run(logger.async_log_success_event(close_kwargs, None, None, None))
+
+    (headers,) = captured
+    (routed_span,) = captured[headers].get_finished_spans()
+    assert routed_span.name == "chat gpt-4o"
+    # Phoenix pins a whole trace to one project by its first-arriving span, so
+    # the routed span must root its OWN trace, linked back to the request trace.
+    assert routed_span.parent is None
+    (link,) = routed_span.links
+    assert link.context.span_id == server.get_span_context().span_id
+    assert all(
+        s.name != "chat gpt-4o" for s in default_exporter.get_finished_spans()
+    )
+
+
+def test_evicted_provider_still_exports_span_opened_before_eviction(monkeypatch):
+    """LRU eviction while a routed span is still open must defer the provider
+    shutdown: the span opened at ``pre_call`` closes at the later success
+    callback and would otherwise be silently dropped instead of exported."""
+    from litellm.integrations.otel.plumbing import routing as routing_mod
+
+    monkeypatch.setattr(routing_mod, "_MAX_CACHED_PROVIDERS", 1)
+    logger, _default_exporter, captured = _phoenix_routing_logger("capture_evict")
+    md_a = {"user_api_key_auth_metadata": {"phoenix_project_name": "proj-a"}}
+    server = logger._emitter.start_span(
+        SpanRole.PROXY_REQUEST, LITELLM_PROXY_REQUEST_SPAN_NAME
+    )
+    with trace.use_span(server, end_on_exit=False):
+        logger.log_pre_api_call(
+            model="gpt-4o",
+            messages=[],
+            kwargs={"litellm_call_id": "call_a", "litellm_params": {"metadata": md_a}},
+        )
+
+    # A second project's full call overflows the size-1 LRU and evicts proj-a's
+    # provider while call_a's span is still open.
+    md_b = {"user_api_key_auth_metadata": {"phoenix_project_name": "proj-b"}}
+    _emit_llm(
+        logger,
+        {
+            "standard_logging_object": _payload(litellm_call_id="call_b", metadata=md_b),
+            "litellm_params": {"metadata": md_b},
+        },
+    )
+
+    asyncio.run(
+        logger.async_log_success_event(
+            {
+                "standard_logging_object": _payload(litellm_call_id="call_a", metadata=md_a),
+                "litellm_params": {"metadata": md_a},
+            },
+            None,
+            None,
+            None,
+        )
+    )
+    server.end()
+
+    headers_a = next(h for h in captured if "proj-a" in h)
+    assert [s.name for s in captured[headers_a].get_finished_spans()] == ["chat gpt-4o"]
+
+
+def test_deferred_pre_call_does_not_churn_tenant_cache(monkeypatch):
+    """Deferred ``pre_call`` must not create or LRU-touch a tenant provider.
+
+    ``route_for`` used to run before the recordable-parent check, so a
+    thread-pool ``pre_call`` that immediately released its hold still built a
+    provider and could evict an idle one. Close re-routes when the span
+    actually opens.
+    """
+    from litellm.integrations.otel.plumbing import routing as routing_mod
+
+    monkeypatch.setattr(routing_mod, "_MAX_CACHED_PROVIDERS", 1)
+    shut_down = []
+    monkeypatch.setattr(routing_mod, "_shutdown_provider", lambda p: shut_down.append(p))
+    logger, _default, captured = _phoenix_routing_logger("capture_deferred_churn")
+    md_a = {"user_api_key_auth_metadata": {"phoenix_project_name": "proj-a"}}
+    server = logger._emitter.start_span(
+        SpanRole.PROXY_REQUEST, LITELLM_PROXY_REQUEST_SPAN_NAME
+    )
+    with trace.use_span(server, end_on_exit=False):
+        _emit_llm(
+            logger,
+            {
+                "standard_logging_object": _payload(litellm_call_id="call_a", metadata=md_a),
+                "litellm_params": {"metadata": md_a},
+            },
+            ambient=server,
+        )
+    assert len(logger._tenant_tracers._providers) == 1
+    idle = next(iter(logger._tenant_tracers._providers.values()))
+    assert shut_down == []
+
+    md_b = {"user_api_key_auth_metadata": {"phoenix_project_name": "proj-b"}}
+    deferred_kwargs = {
+        "litellm_call_id": "call_b",
+        "standard_logging_object": _payload(litellm_call_id="call_b", metadata=md_b),
+        "litellm_params": {"metadata": md_b},
+    }
+    logger.log_pre_api_call(model="gpt-4o", messages=[], kwargs=deferred_kwargs)
+    carrier = logger._open_llm_calls["call_b"]
+    assert carrier.span is None
+    assert carrier.provider is None
+    assert list(logger._tenant_tracers._providers.values()) == [idle]
+    assert shut_down == []
+    assert captured and all("proj-b" not in headers for headers in captured)
+
+    asyncio.run(logger.async_log_success_event(deferred_kwargs, None, None, None))
+    server.end()
+    headers_b = next(h for h in captured if "proj-b" in h)
+    assert [s.name for s in captured[headers_b].get_finished_spans()] == ["chat gpt-4o"]
diff --git a/tests/test_litellm/proxy/auth/test_auth_utils.py b/tests/test_litellm/proxy/auth/test_auth_utils.py
index 5becd05b8e8..3102e69bf26 100644
--- a/tests/test_litellm/proxy/auth/test_auth_utils.py
+++ b/tests/test_litellm/proxy/auth/test_auth_utils.py
@@ -2653,8 +2653,6 @@ class TestObservabilityCallbackBans:
             "posthog_api_url",
             "braintrust_api_key",
             "braintrust_project",
-            "phoenix_project_name",
-            "phoenix_project_name_override",
             "wandb_api_key",
             "weave_project_id",
             "gcs_bucket_name",
@@ -2685,8 +2683,7 @@ class TestObservabilityCallbackBans:
             "langsmith_api_key",
             "posthog_api_url",
             "braintrust_project",
-            "phoenix_project_name",
-            "phoenix_project_name_override",
+            "user_api_key_auth_metadata",
         ],
     )
     def test_observability_field_in_metadata_dict_is_rejected(
@@ -2707,6 +2704,28 @@ class TestObservabilityCallbackBans:
             )
         assert field in str(exc.value)
 
+    @pytest.mark.parametrize("metadata_key", ["metadata", "litellm_metadata"])
+    @pytest.mark.parametrize(
+        "field",
+        ["phoenix_project_name", "phoenix_project_name_override"],
+    )
+    def test_phoenix_project_fields_in_metadata_are_accepted(self, metadata_key, field):
+        # The Phoenix integrations only honor the project from
+        # ``user_api_key_auth_metadata`` on the proxy, so the bare metadata
+        # fields are inert and must not 400 SDK-style callers that send them.
+        assert (
+            is_request_body_safe(
+                request_body={
+                    "model": "gpt-4",
+                    metadata_key: {field: "client-project"},
+                },
+                general_settings={},
+                llm_router=None,
+                model="gpt-4",
+            )
+            is True
+        )
+
     def test_observability_field_in_litellm_params_metadata_is_rejected(self):
         with pytest.raises(ValueError) as exc:
             is_request_body_safe(