diff --git a/apps/api/internal/clients/clients_test.go b/apps/api/internal/clients/clients_test.go
index a4cce96..da8563c 100644
--- a/apps/api/internal/clients/clients_test.go
+++ b/apps/api/internal/clients/clients_test.go
@@ -149,15 +149,19 @@ func TestOpenAIClientChatContract(t *testing.T) {
 
 func TestOpenAIClientChatStreamContract(t *testing.T) {
 	var gotStream bool
+	var gotIncludeUsage bool
 	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		var body map[string]any
 		if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
 			t.Fatalf("decode request: %v", err)
 		}
 		gotStream, _ = body["stream"].(bool)
+		streamOptions, _ := body["stream_options"].(map[string]any)
+		gotIncludeUsage, _ = streamOptions["include_usage"].(bool)
 		w.Header().Set("Content-Type", "text/event-stream")
-		_, _ = w.Write([]byte("data: {\"id\":\"chatcmpl-stream\",\"object\":\"chat.completion.chunk\",\"model\":\"deepseek-v4-flash\",\"choices\":[{\"delta\":{\"content\":\"hello\"}}]}\n\n"))
-		_, _ = w.Write([]byte("data: {\"id\":\"chatcmpl-stream\",\"object\":\"chat.completion.chunk\",\"model\":\"deepseek-v4-flash\",\"choices\":[{\"delta\":{\"content\":\" world\"},\"finish_reason\":\"stop\"}],\"usage\":{\"prompt_tokens\":1,\"completion_tokens\":2,\"total_tokens\":3}}\n\n"))
+		_, _ = w.Write([]byte("data: {\"id\":\"chatcmpl-stream\",\"object\":\"chat.completion.chunk\",\"model\":\"deepseek-v4-flash\",\"choices\":[{\"delta\":{\"content\":\"hello\"}}],\"usage\":null}\n\n"))
+		_, _ = w.Write([]byte("data: {\"id\":\"chatcmpl-stream\",\"object\":\"chat.completion.chunk\",\"model\":\"deepseek-v4-flash\",\"choices\":[{\"delta\":{\"content\":\" world\"},\"finish_reason\":\"stop\"}],\"usage\":null}\n\n"))
+		_, _ = w.Write([]byte("data: {\"id\":\"chatcmpl-stream\",\"object\":\"chat.completion.chunk\",\"model\":\"deepseek-v4-flash\",\"choices\":[],\"usage\":{\"prompt_tokens\":1,\"completion_tokens\":2,\"total_tokens\":3}}\n\n"))
 		_, _ = w.Write([]byte("data: [DONE]\n\n"))
 	}))
 	defer server.Close()
@@ -182,6 +186,9 @@ func TestOpenAIClientChatStreamContract(t *testing.T) {
 	if !gotStream {
 		t.Fatalf("expected upstream stream request")
 	}
+	if !gotIncludeUsage {
+		t.Fatalf("expected upstream stream_options.include_usage=true")
+	}
 	if response.Usage.TotalTokens != 3 {
 		t.Fatalf("unexpected usage: %+v", response.Usage)
 	}
diff --git a/apps/api/internal/clients/openai.go b/apps/api/internal/clients/openai.go
index 8dcd1a8..534f148 100644
--- a/apps/api/internal/clients/openai.go
+++ b/apps/api/internal/clients/openai.go
@@ -25,6 +25,7 @@ func (c OpenAIClient) Run(ctx context.Context, request Request) (Response, error
 	body := cloneBody(request.Body)
 	body["model"] = upstreamModelName(request.Candidate)
 	stream := request.Stream || boolValue(body, "stream")
+	ensureOpenAIStreamUsage(body, request.Kind, stream)
 	raw, _ := json.Marshal(body)
 	req, err := http.NewRequestWithContext(ctx, http.MethodPost, joinURL(request.Candidate.BaseURL, endpoint), bytes.NewReader(raw))
 	if err != nil {
@@ -91,6 +92,20 @@ func cloneBody(body map[string]any) map[string]any {
 	return out
 }
 
+func ensureOpenAIStreamUsage(body map[string]any, kind string, stream bool) {
+	if !stream || kind != "chat.completions" {
+		return
+	}
+	streamOptions := map[string]any{}
+	if existing, ok := body["stream_options"].(map[string]any); ok {
+		for key, value := range existing {
+			streamOptions[key] = value
+		}
+	}
+	streamOptions["include_usage"] = true
+	body["stream_options"] = streamOptions
+}
+
 func joinURL(base string, path string) string {
 	base = strings.TrimRight(strings.TrimSpace(base), "/")
 	if base == "" {