diff --git a/backend/internal/pkg/apicompat/types.go b/backend/internal/pkg/apicompat/types.go
index f9cd5a1c..df75ce50 100644
--- a/backend/internal/pkg/apicompat/types.go
+++ b/backend/internal/pkg/apicompat/types.go
@@ -306,6 +306,37 @@ type ResponsesUsage struct {
 	OutputTokensDetails *ResponsesOutputTokensDetails `json:"output_tokens_details,omitempty"`
 }
 
+func (u *ResponsesUsage) UnmarshalJSON(data []byte) error {
+	type responsesUsageAlias ResponsesUsage
+	var aux struct {
+		responsesUsageAlias
+		PromptTokens            int                           `json:"prompt_tokens"`
+		CompletionTokens        int                           `json:"completion_tokens"`
+		PromptTokensDetails     *ResponsesInputTokensDetails  `json:"prompt_tokens_details,omitempty"`
+		CompletionTokensDetails *ResponsesOutputTokensDetails `json:"completion_tokens_details,omitempty"`
+	}
+	if err := json.Unmarshal(data, &aux); err != nil {
+		return err
+	}
+	*u = ResponsesUsage(aux.responsesUsageAlias)
+	if u.InputTokens == 0 && aux.PromptTokens != 0 {
+		u.InputTokens = aux.PromptTokens
+	}
+	if u.OutputTokens == 0 && aux.CompletionTokens != 0 {
+		u.OutputTokens = aux.CompletionTokens
+	}
+	if u.InputTokensDetails == nil && aux.PromptTokensDetails != nil {
+		u.InputTokensDetails = aux.PromptTokensDetails
+	}
+	if u.OutputTokensDetails == nil && aux.CompletionTokensDetails != nil {
+		u.OutputTokensDetails = aux.CompletionTokensDetails
+	}
+	if u.TotalTokens == 0 && (u.InputTokens != 0 || u.OutputTokens != 0) {
+		u.TotalTokens = u.InputTokens + u.OutputTokens
+	}
+	return nil
+}
+
 // ResponsesInputTokensDetails breaks down input token usage.
 type ResponsesInputTokensDetails struct {
 	CachedTokens int `json:"cached_tokens,omitempty"`
diff --git a/backend/internal/service/openai_compat_model_test.go b/backend/internal/service/openai_compat_model_test.go
index 0ba2a63f..f8b9d360 100644
--- a/backend/internal/service/openai_compat_model_test.go
+++ b/backend/internal/service/openai_compat_model_test.go
@@ -183,6 +183,63 @@ func TestForwardAsAnthropic_NormalizesRoutingAndEffortForGpt54XHigh(t *testing.T
 	t.Logf("response body: %s", rec.Body.String())
 }
 
+func TestForwardAsAnthropic_MappedClaudeModelAcceptsChatUsageShape(t *testing.T) {
+	t.Parallel()
+	gin.SetMode(gin.TestMode)
+
+	rec := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(rec)
+	body := []byte(`{"model":"claude-opus-4-7","max_tokens":16,"messages":[{"role":"user","content":"compact this"}],"stream":true}`)
+	c.Request = httptest.NewRequest(http.MethodPost, "/v1/messages", bytes.NewReader(body))
+	c.Request.Header.Set("Content-Type", "application/json")
+
+	upstreamBody := strings.Join([]string{
+		`data: {"type":"response.created","response":{"id":"resp_compact","model":"gpt-5.5","status":"in_progress","output":[]}}`,
+		"",
+		`data: {"type":"response.output_text.delta","delta":"ok"}`,
+		"",
+		`data: {"type":"response.completed","response":{"id":"resp_compact","object":"response","model":"gpt-5.5","status":"completed","output":[{"type":"message","id":"msg_1","role":"assistant","status":"completed","content":[{"type":"output_text","text":"ok"}]}],"usage":{"prompt_tokens":31,"completion_tokens":9,"total_tokens":40,"prompt_tokens_details":{"cached_tokens":11}}}}`,
+		"",
+		"data: [DONE]",
+		"",
+	}, "\n")
+	upstream := &httpUpstreamRecorder{resp: &http.Response{
+		StatusCode: http.StatusOK,
+		Header:     http.Header{"Content-Type": []string{"text/event-stream"}, "x-request-id": []string{"rid_compact_usage"}},
+		Body:       io.NopCloser(strings.NewReader(upstreamBody)),
+	}}
+
+	svc := &OpenAIGatewayService{
+		httpUpstream: upstream,
+		cfg:          &config.Config{Security: config.SecurityConfig{URLAllowlist: config.URLAllowlistConfig{Enabled: false}}},
+	}
+	account := &Account{
+		ID:          1,
+		Name:        "openai-apikey",
+		Platform:    PlatformOpenAI,
+		Type:        AccountTypeAPIKey,
+		Concurrency: 1,
+		Credentials: map[string]any{
+			"api_key":  "sk-test",
+			"base_url": "https://api.openai.com/v1",
+			"model_mapping": map[string]any{
+				"gpt-5.5": "gpt-5.5",
+			},
+		},
+	}
+
+	result, err := svc.ForwardAsAnthropic(context.Background(), c, account, body, "", "gpt-5.5")
+	require.NoError(t, err)
+	require.NotNil(t, result)
+	require.Equal(t, "claude-opus-4-7", result.Model)
+	require.Equal(t, "gpt-5.5", result.BillingModel)
+	require.Equal(t, "gpt-5.5", result.UpstreamModel)
+	require.Equal(t, 31, result.Usage.InputTokens)
+	require.Equal(t, 9, result.Usage.OutputTokens)
+	require.Equal(t, 11, result.Usage.CacheReadInputTokens)
+	require.Equal(t, "gpt-5.5", gjson.GetBytes(upstream.lastBody, "model").String())
+}
+
 func TestForwardAsAnthropic_InjectsPromptCacheKeyForAPIKeyMessagesDispatch(t *testing.T) {
 	t.Parallel()
 	gin.SetMode(gin.TestMode)
diff --git a/backend/internal/service/openai_gateway_service.go b/backend/internal/service/openai_gateway_service.go
index a2276353..97f88222 100644
--- a/backend/internal/service/openai_gateway_service.go
+++ b/backend/internal/service/openai_gateway_service.go
@@ -4709,28 +4709,47 @@ func (s *OpenAIGatewayService) parseSSEUsageBytes(data []byte, usage *OpenAIUsag
 		return
 	}
 
-	usage.InputTokens = int(gjson.GetBytes(data, "response.usage.input_tokens").Int())
-	usage.OutputTokens = int(gjson.GetBytes(data, "response.usage.output_tokens").Int())
-	usage.CacheReadInputTokens = int(gjson.GetBytes(data, "response.usage.input_tokens_details.cached_tokens").Int())
-	usage.ImageOutputTokens = int(gjson.GetBytes(data, "response.usage.output_tokens_details.image_tokens").Int())
+	if parsedUsage, ok := extractOpenAIUsageFromJSONBytes(data); ok {
+		*usage = parsedUsage
+	}
 }
 
 func extractOpenAIUsageFromJSONBytes(body []byte) (OpenAIUsage, bool) {
 	if len(body) == 0 || !gjson.ValidBytes(body) {
 		return OpenAIUsage{}, false
 	}
-	values := gjson.GetManyBytes(
-		body,
-		"usage.input_tokens",
-		"usage.output_tokens",
-		"usage.input_tokens_details.cached_tokens",
-		"usage.output_tokens_details.image_tokens",
-	)
+	if usage, ok := openAIUsageFromGJSON(gjson.GetBytes(body, "usage")); ok {
+		return usage, true
+	}
+	return openAIUsageFromGJSON(gjson.GetBytes(body, "response.usage"))
+}
+
+func openAIUsageFromGJSON(value gjson.Result) (OpenAIUsage, bool) {
+	if !value.Exists() || !value.IsObject() {
+		return OpenAIUsage{}, false
+	}
+	inputTokens := value.Get("input_tokens").Int()
+	if inputTokens == 0 {
+		inputTokens = value.Get("prompt_tokens").Int()
+	}
+	outputTokens := value.Get("output_tokens").Int()
+	if outputTokens == 0 {
+		outputTokens = value.Get("completion_tokens").Int()
+	}
+	cacheReadTokens := value.Get("input_tokens_details.cached_tokens").Int()
+	if cacheReadTokens == 0 {
+		cacheReadTokens = value.Get("prompt_tokens_details.cached_tokens").Int()
+	}
+	imageOutputTokens := value.Get("output_tokens_details.image_tokens").Int()
+	if imageOutputTokens == 0 {
+		imageOutputTokens = value.Get("completion_tokens_details.image_tokens").Int()
+	}
 	return OpenAIUsage{
-		InputTokens:          int(values[0].Int()),
-		OutputTokens:         int(values[1].Int()),
-		CacheReadInputTokens: int(values[2].Int()),
-		ImageOutputTokens:    int(values[3].Int()),
+		InputTokens:              int(inputTokens),
+		OutputTokens:             int(outputTokens),
+		CacheCreationInputTokens: int(value.Get("cache_creation_input_tokens").Int()),
+		CacheReadInputTokens:     int(cacheReadTokens),
+		ImageOutputTokens:        int(imageOutputTokens),
 	}, true
 }
 
diff --git a/backend/internal/service/openai_gateway_service_test.go b/backend/internal/service/openai_gateway_service_test.go
index d636cf27..7013a477 100644
--- a/backend/internal/service/openai_gateway_service_test.go
+++ b/backend/internal/service/openai_gateway_service_test.go
@@ -2174,6 +2174,25 @@ func TestParseSSEUsage_SelectiveParsing(t *testing.T) {
 	require.Equal(t, 13, usage.InputTokens)
 	require.Equal(t, 15, usage.OutputTokens)
 	require.Equal(t, 4, usage.CacheReadInputTokens)
+
+	svc.parseSSEUsage(`{"type":"response.completed","response":{"usage":{"prompt_tokens":21,"completion_tokens":8,"prompt_tokens_details":{"cached_tokens":6}}}}`, usage)
+	require.Equal(t, 21, usage.InputTokens)
+	require.Equal(t, 8, usage.OutputTokens)
+	require.Equal(t, 6, usage.CacheReadInputTokens)
+}
+
+func TestExtractOpenAIUsageFromJSONBytes_AcceptsResponseAndChatUsageShapes(t *testing.T) {
+	usage, ok := extractOpenAIUsageFromJSONBytes([]byte(`{"id":"resp_1","usage":{"input_tokens":3,"output_tokens":5,"input_tokens_details":{"cached_tokens":2}}}`))
+	require.True(t, ok)
+	require.Equal(t, 3, usage.InputTokens)
+	require.Equal(t, 5, usage.OutputTokens)
+	require.Equal(t, 2, usage.CacheReadInputTokens)
+
+	usage, ok = extractOpenAIUsageFromJSONBytes([]byte(`{"type":"response.completed","response":{"usage":{"prompt_tokens":13,"completion_tokens":7,"prompt_tokens_details":{"cached_tokens":4}}}}`))
+	require.True(t, ok)
+	require.Equal(t, 13, usage.InputTokens)
+	require.Equal(t, 7, usage.OutputTokens)
+	require.Equal(t, 4, usage.CacheReadInputTokens)
 }
 
 func TestExtractCodexFinalResponse_SampleReplay(t *testing.T) {
diff --git a/backend/internal/service/openai_ws_forwarder.go b/backend/internal/service/openai_ws_forwarder.go
index 77cf7d95..192ff90a 100644
--- a/backend/internal/service/openai_ws_forwarder.go
+++ b/backend/internal/service/openai_ws_forwarder.go
@@ -399,15 +399,9 @@ func parseOpenAIWSResponseUsageFromCompletedEvent(message []byte, usage *OpenAIU
 	if usage == nil || len(message) == 0 {
 		return
 	}
-	values := gjson.GetManyBytes(
-		message,
-		"response.usage.input_tokens",
-		"response.usage.output_tokens",
-		"response.usage.input_tokens_details.cached_tokens",
-	)
-	usage.InputTokens = int(values[0].Int())
-	usage.OutputTokens = int(values[1].Int())
-	usage.CacheReadInputTokens = int(values[2].Int())
+	if parsedUsage, ok := extractOpenAIUsageFromJSONBytes(message); ok {
+		*usage = parsedUsage
+	}
 }
 
 func parseOpenAIWSErrorEventFields(message []byte) (code string, errType string, errMessage string) {
diff --git a/backend/internal/service/openai_ws_forwarder_hotpath_optimization_test.go b/backend/internal/service/openai_ws_forwarder_hotpath_optimization_test.go
index 76167603..0350bde9 100644
--- a/backend/internal/service/openai_ws_forwarder_hotpath_optimization_test.go
+++ b/backend/internal/service/openai_ws_forwarder_hotpath_optimization_test.go
@@ -29,6 +29,14 @@ func TestParseOpenAIWSResponseUsageFromCompletedEvent(t *testing.T) {
 	require.Equal(t, 11, usage.InputTokens)
 	require.Equal(t, 7, usage.OutputTokens)
 	require.Equal(t, 3, usage.CacheReadInputTokens)
+
+	parseOpenAIWSResponseUsageFromCompletedEvent(
+		[]byte(`{"type":"response.completed","response":{"usage":{"prompt_tokens":19,"completion_tokens":5,"prompt_tokens_details":{"cached_tokens":4}}}}`),
+		usage,
+	)
+	require.Equal(t, 19, usage.InputTokens)
+	require.Equal(t, 5, usage.OutputTokens)
+	require.Equal(t, 4, usage.CacheReadInputTokens)
 }
 
 func TestOpenAIWSErrorEventHelpers_ConsistentWithWrapper(t *testing.T) {