Expose detailed completion token usage

docs/public/api-reference/fabro-api.yaml

@@ -8507,15 +8507,38 @@ components:
           description: Provider-specific options.
 
     CompletionUsage:
+      description: >
+        Five disjoint token buckets for one completion. `input_tokens` excludes
+        cache reads and writes, while `output_tokens` excludes reasoning tokens
+        when the provider reports them separately.
       type: object
-      required: [input_tokens, output_tokens]
+      required:
+        - input_tokens
+        - output_tokens
+        - reasoning_tokens
+        - cache_read_tokens
+        - cache_write_tokens
       properties:
         input_tokens:
           type: integer
           format: int64
+          description: Number of uncached input tokens consumed.
         output_tokens:
           type: integer
           format: int64
+          description: Number of non-reasoning output tokens generated.
+        reasoning_tokens:
+          type: integer
+          format: int64
+          description: Number of separately reported reasoning tokens.
+        cache_read_tokens:
+          type: integer
+          format: int64
+          description: Number of input tokens served from a provider cache.
+        cache_write_tokens:
+          type: integer
+          format: int64
+          description: Number of input tokens written to a provider cache.
 
     CompletionResponse:
       type: object

lib/apps/fabro-server/src/server/handler/completions.rs

@@ -4,10 +4,10 @@ use std::sync::Arc;
 use fabro_model::{Catalog, ModelSelectionError};
 
 use super::super::{
-    ApiError, AppState, CompletionResponse, CompletionToolChoiceMode, CompletionUsage,
-    CreateCompletionRequest, FinishReason, GenerateParams, IntoResponse, Json, LlmMessage,
-    LlmRequest, ProviderId, RequiredUser, Response, Router, State, StatusCode, ToolChoice,
-    ToolDefinition, Ulid, error, generate_object, info, post, warn,
+    ApiError, AppState, CompletionResponse, CompletionToolChoiceMode, CreateCompletionRequest,
+    FinishReason, GenerateParams, IntoResponse, Json, LlmMessage, LlmRequest, ProviderId,
+    RequiredUser, Response, Router, State, StatusCode, ToolChoice, ToolDefinition, Ulid, error,
+    generate_object, info, post, warn,
 };
 use super::llm_sse;
 
@@ -169,10 +169,7 @@ async fn create_completion(
                         provider: selected_provider,
                         message: response.message,
                         stop_reason,
-                        usage: CompletionUsage {
-                            input_tokens:  response.usage.input_tokens,
-                            output_tokens: response.usage.output_tokens,
-                        },
+                        usage: response.usage,
                         output,
                         cost_usd: response.cost_usd,
                         cost_source: response.cost_source,
@@ -192,10 +189,7 @@ async fn create_completion(
                         provider: ProviderId::new(response.provider),
                         message: response.message,
                         stop_reason,
-                        usage: CompletionUsage {
-                            input_tokens:  response.usage.input_tokens,
-                            output_tokens: response.usage.output_tokens,
-                        },
+                        usage: response.usage,
                         output: None,
                         cost_usd: response.cost_usd,
                         cost_source: response.cost_source,

lib/apps/fabro-server/src/server/tests.rs

@@ -15272,6 +15272,73 @@ async fn create_completion_unknown_provider_returns_clear_error() {
     );
 }
 
+#[tokio::test]
+async fn create_completion_returns_disjoint_usage_buckets() {
+    let upstream = MockServer::start();
+    let completion = upstream.mock(|when, then| {
+        when.method(POST).path("/chat/completions");
+        then.status(200)
+            .header("content-type", "application/json")
+            .json_body(json!({
+                "id": "chatcmpl-usage",
+                "model": "kimi-k3",
+                "choices": [{
+                    "message": {"role": "assistant", "content": "OK"},
+                    "finish_reason": "stop"
+                }],
+                "usage": {
+                    "prompt_tokens": 200,
+                    "completion_tokens": 30,
+                    "total_tokens": 230,
+                    "prompt_tokens_details": {
+                        "cached_tokens": 50,
+                        "cache_write_tokens": 100
+                    },
+                    "completion_tokens_details": {
+                        "reasoning_tokens": 20
+                    }
+                }
+            }));
+    });
+    let state = TestAppStateBuilder::new()
+        .provider_base_url("kimi", upstream.base_url())
+        .vault_entries([(EnvVars::KIMI_API_KEY, "test-kimi-api-key")])
+        .build();
+    let app = crate::test_support::build_test_router(state);
+
+    let req = Request::builder()
+        .method("POST")
+        .uri(api("/completions"))
+        .header("content-type", "application/json")
+        .body(Body::from(
+            json!({
+                "provider": "kimi",
+                "model": "kimi-k3",
+                "stream": false,
+                "messages": [{
+                    "role": "user",
+                    "content": [{"kind": "text", "data": "hi"}]
+                }]
+            })
+            .to_string(),
+        ))
+        .unwrap();
+
+    let response = app.oneshot(req).await.unwrap();
+    let body = response_json!(response, StatusCode::OK).await;
+    assert_eq!(
+        body["usage"],
+        json!({
+            "input_tokens": 50,
+            "output_tokens": 10,
+            "reasoning_tokens": 20,
+            "cache_read_tokens": 50,
+            "cache_write_tokens": 100
+        })
+    );
+    completion.assert();
+}
+
 #[tokio::test]
 async fn create_completion_default_model_uses_app_state_catalog() {
     let upstream = MockServer::start();

lib/foundation/fabro-api/build.rs

@@ -461,6 +461,7 @@ fn main() {
             "fabro_types::PendingInterviewRecord",
             &[],
         ),
+        ("CompletionUsage", "fabro_model::TokenCounts", &[]),
         ("BilledTokenCounts", "fabro_types::BilledTokenCounts", &[]),
         ("BillingModelRef", "fabro_model::ModelRef", &[]),
         ("BillingSpeed", "fabro_model::Speed", &[]),

lib/foundation/fabro-api/src/lib.rs

@@ -22,6 +22,7 @@ pub mod types {
     pub use fabro_model::{
         CostSource, Model, ModelCosts, ModelFeatures, ModelLimits, ModelRef as BillingModelRef,
         ModelTestMode, Provider, ReasoningEffort, ReasoningEffortFeature, Speed as BillingSpeed,
+        TokenCounts as CompletionUsage,
     };
     pub use fabro_types::run_event::AgentSessionActivatedProps;
     pub use fabro_types::settings::run::McpHttpProtocol;

lib/foundation/fabro-api/tests/completion_usage_round_trip.rs

@@ -0,0 +1,59 @@
+use std::any::{TypeId, type_name};
+
+use fabro_api::types::CompletionUsage as ApiCompletionUsage;
+use fabro_model::TokenCounts;
+use serde_json::json;
+
+#[test]
+fn completion_usage_reuses_canonical_type() {
+    assert_same_type::<ApiCompletionUsage, TokenCounts>();
+}
+
+#[test]
+fn completion_usage_json_matches_openapi_shape() {
+    let usage = TokenCounts {
+        input_tokens:       10,
+        output_tokens:      20,
+        reasoning_tokens:   3,
+        cache_read_tokens:  4,
+        cache_write_tokens: 5,
+    };
+
+    let json = serde_json::to_value(&usage).unwrap();
+    assert_eq!(json["input_tokens"], 10);
+    assert_eq!(json["output_tokens"], 20);
+    assert_eq!(json["reasoning_tokens"], 3);
+    assert_eq!(json["cache_read_tokens"], 4);
+    assert_eq!(json["cache_write_tokens"], 5);
+
+    let round_trip: ApiCompletionUsage = serde_json::from_value(json).unwrap();
+    assert_eq!(round_trip, usage);
+}
+
+#[test]
+fn completion_usage_keeps_zero_counts_present() {
+    let json = serde_json::to_value(TokenCounts::default()).unwrap();
+    assert_eq!(
+        json,
+        json!({
+            "input_tokens": 0,
+            "output_tokens": 0,
+            "reasoning_tokens": 0,
+            "cache_read_tokens": 0,
+            "cache_write_tokens": 0
+        })
+    );
+
+    let round_trip: ApiCompletionUsage = serde_json::from_value(json).unwrap();
+    assert_eq!(round_trip, TokenCounts::default());
+}
+
+fn assert_same_type<T: 'static, U: 'static>() {
+    assert_eq!(
+        TypeId::of::<T>(),
+        TypeId::of::<U>(),
+        "{} should be the same type as {}",
+        type_name::<T>(),
+        type_name::<U>()
+    );
+}

lib/packages/fabro-api-client/src/models/completion-usage.ts

@@ -14,7 +14,28 @@
 
 
 
+/**
+ * Five disjoint token buckets for one completion. `input_tokens` excludes cache reads and writes, while `output_tokens` excludes reasoning tokens when the provider reports them separately.
+ */
 export interface CompletionUsage {
+    /**
+     * Number of uncached input tokens consumed.
+     */
     'input_tokens': number;
+    /**
+     * Number of non-reasoning output tokens generated.
+     */
     'output_tokens': number;
+    /**
+     * Number of separately reported reasoning tokens.
+     */
+    'reasoning_tokens': number;
+    /**
+     * Number of input tokens served from a provider cache.
+     */
+    'cache_read_tokens': number;
+    /**
+     * Number of input tokens written to a provider cache.
+     */
+    'cache_write_tokens': number;
 }