diff --git a/backend/internal/handler/endpoint.go b/backend/internal/handler/endpoint.go
index 0b9930c5cc..f476a96bf2 100644
--- a/backend/internal/handler/endpoint.go
+++ b/backend/internal/handler/endpoint.go
@@ -155,8 +155,10 @@ func isBareOrSubpathOf(path, root string) bool {
 // account platform and the normalized inbound endpoint.
 //
 // Platform-specific rules:
-//   - OpenAI always forwards to /v1/responses (with optional subpath
-//     such as /v1/responses/compact preserved from the raw URL).
+//   - OpenAI and Grok default to /v1/responses (with optional subpath
+//     such as /v1/responses/compact preserved from the raw URL). Grok raw Chat
+//     requests override this through the forwarding result consumed by
+//     resolveOpenAIUpstreamEndpoint.
 //   - Anthropic  → /v1/messages
 //   - Gemini     → /v1beta/models
 //   - Antigravity → /v1/messages (Claude) or gemini (Gemini)
diff --git a/backend/internal/handler/endpoint_test.go b/backend/internal/handler/endpoint_test.go
index 96ed1292b3..ad77b652ef 100644
--- a/backend/internal/handler/endpoint_test.go
+++ b/backend/internal/handler/endpoint_test.go
@@ -121,6 +121,8 @@ func TestDeriveUpstreamEndpoint(t *testing.T) {
 		{"openai embeddings", EndpointEmbeddings, "/v1/embeddings", service.PlatformOpenAI, EndpointEmbeddings},
 		{"openai image generations", EndpointImagesGenerations, "/v1/images/generations", service.PlatformOpenAI, EndpointImagesGenerations},
 		{"openai image edits", EndpointImagesEdits, "/openai/v1/images/edits", service.PlatformOpenAI, EndpointImagesEdits},
+		{"grok chat defaults to responses without runtime result", EndpointChatCompletions, "/v1/chat/completions", service.PlatformGrok, EndpointResponses},
+		{"grok responses", EndpointResponses, "/v1/responses", service.PlatformGrok, EndpointResponses},
 		{"grok video generations", EndpointVideosGenerations, "/v1/videos/generations", service.PlatformGrok, EndpointVideosGenerations},
 		{"grok video status", EndpointVideos, "/videos/req_123", service.PlatformGrok, EndpointVideos},
 
@@ -138,6 +140,59 @@ func TestDeriveUpstreamEndpoint(t *testing.T) {
 	}
 }
 
+func TestResolveOpenAIUpstreamEndpointPrefersForwardResult(t *testing.T) {
+	tests := []struct {
+		name            string
+		account         *service.Account
+		result          *service.OpenAIForwardResult
+		runtimeEndpoint string
+		want            string
+	}{
+		{
+			name:            "grok raw chat result overrides stale context",
+			account:         &service.Account{Platform: service.PlatformGrok, Type: service.AccountTypeOAuth},
+			result:          &service.OpenAIForwardResult{UpstreamEndpoint: EndpointChatCompletions},
+			runtimeEndpoint: EndpointResponses,
+			want:            EndpointChatCompletions,
+		},
+		{
+			name:    "grok chat bridged to responses",
+			account: &service.Account{Platform: service.PlatformGrok, Type: service.AccountTypeOAuth},
+			result:  &service.OpenAIForwardResult{UpstreamEndpoint: EndpointResponses},
+			want:    EndpointResponses,
+		},
+		{
+			name:    "grok empty result keeps responses default",
+			account: &service.Account{Platform: service.PlatformGrok, Type: service.AccountTypeOAuth},
+			result:  &service.OpenAIForwardResult{},
+			want:    EndpointResponses,
+		},
+		{
+			name:            "grok raw error uses runtime endpoint",
+			account:         &service.Account{Platform: service.PlatformGrok, Type: service.AccountTypeOAuth},
+			runtimeEndpoint: EndpointChatCompletions,
+			want:            EndpointChatCompletions,
+		},
+		{
+			name:    "openai behavior remains responses",
+			account: &service.Account{Platform: service.PlatformOpenAI, Type: service.AccountTypeOAuth},
+			result:  &service.OpenAIForwardResult{},
+			want:    EndpointResponses,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			rec := httptest.NewRecorder()
+			c, _ := gin.CreateTestContext(rec)
+			c.Request = httptest.NewRequest(http.MethodPost, EndpointChatCompletions, nil)
+			c.Set(ctxKeyInboundEndpoint, EndpointChatCompletions)
+			service.SetActualOpenAIUpstreamEndpoint(c, tt.runtimeEndpoint)
+			require.Equal(t, tt.want, resolveOpenAIUpstreamEndpoint(c, tt.account, tt.result))
+		})
+	}
+}
+
 // ──────────────────────────────────────────────────────────
 // responsesSubpathSuffix
 // ──────────────────────────────────────────────────────────
diff --git a/backend/internal/handler/openai_chat_completions.go b/backend/internal/handler/openai_chat_completions.go
index f5f2522e49..9da5296c0d 100644
--- a/backend/internal/handler/openai_chat_completions.go
+++ b/backend/internal/handler/openai_chat_completions.go
@@ -5,6 +5,7 @@ import (
 	"errors"
 	"net/http"
 	"strconv"
+	"strings"
 	"time"
 
 	"github.com/Wei-Shaw/sub2api/internal/pkg/ip"
@@ -298,7 +299,7 @@ func (h *OpenAIGatewayHandler) ChatCompletions(c *gin.Context) {
 		userAgent := c.GetHeader("User-Agent")
 		clientIP := ip.GetClientIP(c)
 		inboundEndpoint := GetInboundEndpoint(c)
-		upstreamEndpoint := resolveOpenAIUpstreamEndpoint(c, account)
+		upstreamEndpoint := resolveOpenAIUpstreamEndpoint(c, account, result)
 		quotaPlatform := service.QuotaPlatform(c.Request.Context(), apiKey)
 
 		cyberBlocked := service.GetOpsCyberPolicy(c) != nil
@@ -337,14 +338,22 @@ func (h *OpenAIGatewayHandler) ChatCompletions(c *gin.Context) {
 }
 
 // resolveOpenAIUpstreamEndpoint returns the actual upstream endpoint for an
-// OpenAI account, used by every OpenAI usage-recording site. APIKey accounts
-// whose upstream is forced or probed to not support the Responses API are
-// served directly via /v1/chat/completions (the raw chat path) regardless of
-// the inbound endpoint; everything else goes through the Responses API.
-func resolveOpenAIUpstreamEndpoint(c *gin.Context, account *service.Account) string {
+// OpenAI-compatible account. A forwarding result is authoritative because a
+// single inbound route may choose raw Chat or a Responses bridge at runtime.
+// The account-based derivation remains as a fallback for existing callers and
+// forwarding paths that do not report their endpoint yet.
+func resolveOpenAIUpstreamEndpoint(c *gin.Context, account *service.Account, result *service.OpenAIForwardResult) string {
+	if result != nil {
+		if endpoint := strings.TrimSpace(result.UpstreamEndpoint); endpoint != "" {
+			return endpoint
+		}
+	}
+	if endpoint := service.GetActualOpenAIUpstreamEndpoint(c); endpoint != "" {
+		return endpoint
+	}
 	if account != nil && account.Type == service.AccountTypeAPIKey &&
 		!openai_compat.ShouldUseResponsesAPI(account.Extra) {
-		return "/v1/chat/completions"
+		return EndpointChatCompletions
 	}
 	return GetUpstreamEndpoint(c, account.Platform)
 }
diff --git a/backend/internal/handler/openai_gateway_handler.go b/backend/internal/handler/openai_gateway_handler.go
index 83e644d857..f1cb7314bb 100644
--- a/backend/internal/handler/openai_gateway_handler.go
+++ b/backend/internal/handler/openai_gateway_handler.go
@@ -522,7 +522,7 @@ func (h *OpenAIGatewayHandler) Responses(c *gin.Context) {
 		clientIP := ip.GetClientIP(c)
 		requestPayloadHash := service.HashUsageRequestPayload(body)
 		inboundEndpoint := GetInboundEndpoint(c)
-		upstreamEndpoint := resolveOpenAIUpstreamEndpoint(c, account)
+		upstreamEndpoint := resolveOpenAIUpstreamEndpoint(c, account, result)
 		quotaPlatform := service.QuotaPlatform(c.Request.Context(), apiKey)
 
 		// 使用量记录通过有界 worker 池提交，避免请求热路径创建无界 goroutine。
@@ -994,7 +994,7 @@ func (h *OpenAIGatewayHandler) Messages(c *gin.Context) {
 		clientIP := ip.GetClientIP(c)
 		requestPayloadHash := service.HashUsageRequestPayload(body)
 		inboundEndpoint := GetInboundEndpoint(c)
-		upstreamEndpoint := resolveOpenAIUpstreamEndpoint(c, account)
+		upstreamEndpoint := resolveOpenAIUpstreamEndpoint(c, account, result)
 		quotaPlatform := service.QuotaPlatform(c.Request.Context(), apiKey)
 
 		cyberBlocked := service.GetOpsCyberPolicy(c) != nil
@@ -1601,7 +1601,7 @@ func (h *OpenAIGatewayHandler) ResponsesWebSocket(c *gin.Context) {
 				}
 				h.gatewayService.ReportOpenAIAccountScheduleResult(account.ID, true, result.FirstTokenMs)
 				inboundEndpoint := GetInboundEndpoint(c)
-				upstreamEndpoint := resolveOpenAIUpstreamEndpoint(c, account)
+				upstreamEndpoint := resolveOpenAIUpstreamEndpoint(c, account, result)
 				quotaPlatform := service.QuotaPlatform(c.Request.Context(), apiKey)
 				cyberBlocked := service.GetOpsCyberPolicy(c) != nil
 				h.submitOpenAIUsageRecordTask(ctx, result, func(taskCtx context.Context) {
@@ -2441,7 +2441,7 @@ func (h *OpenAIGatewayHandler) recordCyberPolicyIfMarked(c *gin.Context, apiKey
 	var accountID int64
 	if account != nil {
 		accountID = account.ID
-		upstreamEndpoint = resolveOpenAIUpstreamEndpoint(c, account)
+		upstreamEndpoint = resolveOpenAIUpstreamEndpoint(c, account, nil)
 	}
 	stream := false
 	if v, ok := c.Get(opsStreamKey); ok {
diff --git a/backend/internal/service/openai_gateway_chat_completions.go b/backend/internal/service/openai_gateway_chat_completions.go
index 15c4e47635..533b562dc9 100644
--- a/backend/internal/service/openai_gateway_chat_completions.go
+++ b/backend/internal/service/openai_gateway_chat_completions.go
@@ -72,6 +72,16 @@ func (s *OpenAIGatewayService) ForwardAsChatCompletions(
 	}
 
 	if account.Platform == PlatformGrok {
+		if account.IsGrokOAuth() {
+			if eligible, reason := grokChatResponsesBridgeEligibility(body); eligible {
+				return s.forwardGrokChatCompletionsViaResponses(ctx, c, account, body, promptCacheKey, defaultMappedModel)
+			} else {
+				logger.L().Debug("grok chat_completions: using raw fallback",
+					zap.Int64("account_id", account.ID),
+					zap.String("reason", reason),
+				)
+			}
+		}
 		return s.forwardAsRawChatCompletions(ctx, c, account, body, defaultMappedModel)
 	}
 
diff --git a/backend/internal/service/openai_gateway_chat_completions_raw.go b/backend/internal/service/openai_gateway_chat_completions_raw.go
index 554c1b4769..7693986b0d 100644
--- a/backend/internal/service/openai_gateway_chat_completions_raw.go
+++ b/backend/internal/service/openai_gateway_chat_completions_raw.go
@@ -160,6 +160,7 @@ func (s *OpenAIGatewayService) forwardAsRawChatCompletions(
 	if err != nil {
 		return nil, err
 	}
+	SetActualOpenAIUpstreamEndpoint(c, grokChatRawEndpoint)
 	customUA := account.GetOpenAIUserAgent()
 	if customUA == "" && account.Platform == PlatformGrok {
 		customUA = "sub2api-grok/1.0"
@@ -213,6 +214,7 @@ func (s *OpenAIGatewayService) forwardAsRawChatCompletions(
 	}
 	if result != nil {
 		addOpenAIUsage(&result.Usage, bridgeUsage)
+		result.UpstreamEndpoint = grokChatRawEndpoint
 	}
 	return result, forwardErr
 }
diff --git a/backend/internal/service/openai_gateway_grok_chat_bridge.go b/backend/internal/service/openai_gateway_grok_chat_bridge.go
new file mode 100644
index 0000000000..fd6b426536
--- /dev/null
+++ b/backend/internal/service/openai_gateway_grok_chat_bridge.go
@@ -0,0 +1,320 @@
+package service
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"net/http"
+	"strings"
+	"time"
+
+	"github.com/Wei-Shaw/sub2api/internal/pkg/apicompat"
+	"github.com/Wei-Shaw/sub2api/internal/pkg/xai"
+	"github.com/gin-gonic/gin"
+)
+
+const (
+	grokChatResponsesEndpoint = "/v1/responses"
+	grokChatRawEndpoint       = "/v1/chat/completions"
+)
+
+var grokChatResponsesBridgeTopLevelFields = map[string]struct{}{
+	"model":                 {},
+	"messages":              {},
+	"stream":                {},
+	"stream_options":        {},
+	"max_tokens":            {},
+	"max_completion_tokens": {},
+	"temperature":           {},
+	"top_p":                 {},
+	"prompt_cache_key":      {},
+	"tools":                 {},
+	"tool_choice":           {},
+	"functions":             {},
+	"function_call":         {},
+}
+
+// grokChatResponsesBridgeEligibility deliberately accepts only request shapes
+// whose Chat Completions semantics are preserved by the Responses bridge.
+// Everything else stays on raw Chat Completions rather than being silently
+// dropped or rewritten.
+func grokChatResponsesBridgeEligibility(body []byte) (bool, string) {
+	var root map[string]json.RawMessage
+	if err := json.Unmarshal(body, &root); err != nil || root == nil {
+		return false, "invalid_json"
+	}
+
+	for _, field := range []string{"stop", "reasoning_effort"} {
+		if _, exists := root[field]; exists {
+			return false, "unsupported_" + field
+		}
+	}
+	for _, field := range []string{"tools", "functions"} {
+		if raw, exists := root[field]; exists && !grokChatNullOrEmptyArray(raw) {
+			return false, "unsupported_" + field
+		}
+	}
+	if raw, exists := root["tool_choice"]; exists && !grokChatNullOrNone(raw) {
+		return false, "unsupported_tool_choice"
+	}
+	if raw, exists := root["function_call"]; exists && !grokChatNullOrNone(raw) {
+		return false, "unsupported_function_call"
+	}
+	for field := range root {
+		if _, supported := grokChatResponsesBridgeTopLevelFields[field]; !supported {
+			return false, "unknown_field_" + field
+		}
+	}
+
+	var model string
+	if raw, ok := root["model"]; !ok || json.Unmarshal(raw, &model) != nil || strings.TrimSpace(model) == "" {
+		return false, "invalid_model"
+	}
+
+	if raw, ok := root["stream"]; ok {
+		var stream *bool
+		if json.Unmarshal(raw, &stream) != nil || stream == nil {
+			return false, "invalid_stream"
+		}
+	}
+	if raw, ok := root["stream_options"]; ok {
+		var options map[string]json.RawMessage
+		if json.Unmarshal(raw, &options) != nil || options == nil {
+			return false, "invalid_stream_options"
+		}
+		for field, value := range options {
+			if field != "include_usage" {
+				return false, "unknown_stream_option_" + field
+			}
+			var includeUsage *bool
+			if json.Unmarshal(value, &includeUsage) != nil || includeUsage == nil {
+				return false, "invalid_stream_include_usage"
+			}
+		}
+	}
+
+	for _, field := range []string{"max_tokens", "max_completion_tokens"} {
+		if raw, ok := root[field]; ok {
+			var value *int
+			if json.Unmarshal(raw, &value) != nil || value == nil || *value < 128 {
+				return false, "unsafe_" + field
+			}
+		}
+	}
+	if _, hasMaxTokens := root["max_tokens"]; hasMaxTokens {
+		if _, hasMaxCompletionTokens := root["max_completion_tokens"]; hasMaxCompletionTokens {
+			return false, "conflicting_max_tokens"
+		}
+	}
+	for _, field := range []string{"temperature", "top_p"} {
+		if raw, ok := root[field]; ok {
+			var value *float64
+			if json.Unmarshal(raw, &value) != nil || value == nil {
+				return false, "invalid_" + field
+			}
+		}
+	}
+	if raw, ok := root["prompt_cache_key"]; ok {
+		var key string
+		if json.Unmarshal(raw, &key) != nil {
+			return false, "invalid_prompt_cache_key"
+		}
+	}
+
+	var messages []map[string]json.RawMessage
+	rawMessages, ok := root["messages"]
+	if !ok || json.Unmarshal(rawMessages, &messages) != nil || len(messages) == 0 {
+		return false, "invalid_messages"
+	}
+	for _, message := range messages {
+		for field := range message {
+			if field != "role" && field != "content" {
+				return false, "unsafe_message_field_" + field
+			}
+		}
+		var role string
+		if raw, exists := message["role"]; !exists || json.Unmarshal(raw, &role) != nil {
+			return false, "invalid_message_role"
+		}
+		switch role {
+		case "system", "user", "assistant":
+		default:
+			return false, "unsupported_message_role_" + role
+		}
+		var content string
+		if raw, exists := message["content"]; !exists || json.Unmarshal(raw, &content) != nil {
+			// Structured content includes image_url and other parts whose exact
+			// behavior is not guaranteed by this bridge.
+			return false, "non_text_message_content"
+		}
+		if strings.TrimSpace(content) == "" {
+			return false, "empty_message_content"
+		}
+	}
+
+	return true, ""
+}
+
+func grokChatNullOrEmptyArray(raw json.RawMessage) bool {
+	if strings.TrimSpace(string(raw)) == "null" {
+		return true
+	}
+	var values []json.RawMessage
+	return json.Unmarshal(raw, &values) == nil && len(values) == 0
+}
+
+func grokChatNullOrNone(raw json.RawMessage) bool {
+	if strings.TrimSpace(string(raw)) == "null" {
+		return true
+	}
+	var value string
+	return json.Unmarshal(raw, &value) == nil && strings.EqualFold(strings.TrimSpace(value), "none")
+}
+
+func grokChatCacheIntentBody(body []byte) ([]byte, error) {
+	var root map[string]json.RawMessage
+	if err := json.Unmarshal(body, &root); err != nil {
+		return nil, err
+	}
+	for _, field := range []string{"tools", "tool_choice", "functions", "function_call"} {
+		delete(root, field)
+	}
+	return json.Marshal(root)
+}
+
+func grokChatResponsesRuntimeEligible(upstreamModel, cacheIdentity string) bool {
+	return strings.TrimSpace(upstreamModel) == "grok-4.5" && strings.TrimSpace(cacheIdentity) != ""
+}
+
+// forwardGrokChatCompletionsViaResponses converts a strictly compatible Chat
+// request into xAI Responses format and reuses the established Responses-to-
+// Chat response translators. It intentionally does not run the Codex OAuth
+// transform because Grok CLI is a separate upstream protocol.
+func (s *OpenAIGatewayService) forwardGrokChatCompletionsViaResponses(
+	ctx context.Context,
+	c *gin.Context,
+	account *Account,
+	body []byte,
+	promptCacheKey string,
+	defaultMappedModel string,
+) (*OpenAIForwardResult, error) {
+	startTime := time.Now()
+
+	var chatReq apicompat.ChatCompletionsRequest
+	if err := json.Unmarshal(body, &chatReq); err != nil {
+		return nil, fmt.Errorf("parse grok chat completions request: %w", err)
+	}
+	originalModel := chatReq.Model
+	clientStream := chatReq.Stream
+	billingModel := resolveOpenAIForwardModel(account, originalModel, defaultMappedModel)
+	upstreamModel := normalizeOpenAIModelForUpstream(account, billingModel)
+	cacheIdentity := resolveGrokCacheIdentity(c, body, promptCacheKey, upstreamModel)
+	if !grokChatResponsesRuntimeEligible(upstreamModel, cacheIdentity) {
+		return s.forwardAsRawChatCompletions(ctx, c, account, body, defaultMappedModel)
+	}
+
+	responsesReq, err := apicompat.ChatCompletionsToResponses(&chatReq)
+	if err != nil {
+		return nil, fmt.Errorf("convert grok chat completions to responses: %w", err)
+	}
+	responsesReq.Model = upstreamModel
+	responsesReq.Stream = true
+	// These fields are useful to Codex but are not needed by the Grok CLI
+	// protocol. Keep the bridge request as close as possible to native Grok.
+	responsesReq.Include = nil
+	responsesReq.Store = nil
+
+	responsesBody, err := json.Marshal(responsesReq)
+	if err != nil {
+		return nil, fmt.Errorf("marshal grok responses bridge request: %w", err)
+	}
+	responsesBody, err = patchGrokResponsesBody(responsesBody, upstreamModel)
+	if err != nil {
+		return nil, fmt.Errorf("patch grok responses bridge request: %w", err)
+	}
+	intentBody, err := grokChatCacheIntentBody(body)
+	if err != nil {
+		return nil, fmt.Errorf("normalize grok responses bridge tool intent: %w", err)
+	}
+	responsesBody, err = applyGrokResponsesCacheIdentity(responsesBody, intentBody, cacheIdentity, true)
+	if err != nil {
+		return nil, fmt.Errorf("apply grok responses bridge cache identity: %w", err)
+	}
+
+	updatedBody, policyErr := s.applyOpenAIFastPolicyToBody(ctx, account, upstreamModel, responsesBody)
+	if policyErr != nil {
+		var blocked *OpenAIFastBlockedError
+		if errors.As(policyErr, &blocked) {
+			MarkOpsClientBusinessLimited(c, OpsClientBusinessLimitedReasonLocalPolicyDenied)
+			writeChatCompletionsError(c, http.StatusForbidden, "permission_error", blocked.Message)
+		}
+		return nil, policyErr
+	}
+	responsesBody = updatedBody
+
+	token, _, err := s.GetAccessToken(ctx, account)
+	if err != nil {
+		return nil, fmt.Errorf("get grok access token: %w", err)
+	}
+	upstreamCtx, releaseUpstreamCtx := detachUpstreamContext(ctx)
+	upstreamReq, err := buildGrokResponsesRequest(upstreamCtx, c, account, responsesBody, token, cacheIdentity)
+	releaseUpstreamCtx()
+	if err != nil {
+		return nil, fmt.Errorf("build grok responses bridge request: %w", err)
+	}
+	SetActualOpenAIUpstreamEndpoint(c, grokChatResponsesEndpoint)
+
+	proxyURL := ""
+	if account.ProxyID != nil && account.Proxy != nil {
+		proxyURL = account.Proxy.URL()
+	}
+	resp, err := s.httpUpstream.Do(upstreamReq, proxyURL, account.ID, account.Concurrency)
+	if err != nil {
+		return nil, s.handleOpenAIUpstreamTransportError(ctx, c, account, err, false)
+	}
+	defer func() { _ = resp.Body.Close() }()
+
+	if resp.StatusCode >= http.StatusBadRequest {
+		respBody, upstreamMsg := s.readOpenAIUpstreamError(resp)
+		if upstreamMsg == "" {
+			upstreamMsg = fmt.Sprintf("xAI upstream returned status %d", resp.StatusCode)
+		}
+		appendOpsUpstreamError(c, OpsUpstreamErrorEvent{
+			Platform:           account.Platform,
+			AccountID:          account.ID,
+			AccountName:        account.Name,
+			UpstreamStatusCode: resp.StatusCode,
+			UpstreamRequestID:  firstNonEmpty(resp.Header.Get("x-request-id"), resp.Header.Get("xai-request-id")),
+			Kind:               "failover",
+			Message:            upstreamMsg,
+		})
+		s.handleGrokAccountUpstreamError(ctx, account, resp.StatusCode, resp.Header, respBody)
+		if s.shouldFailoverUpstreamError(resp.StatusCode) {
+			return nil, &UpstreamFailoverError{
+				StatusCode:             resp.StatusCode,
+				ResponseBody:           respBody,
+				RetryableOnSameAccount: account.IsPoolMode() && account.IsPoolModeRetryableStatus(resp.StatusCode),
+			}
+		}
+		return s.handleChatCompletionsErrorResponse(resp, c, account, billingModel)
+	}
+
+	s.updateGrokUsageSnapshot(ctx, account, xai.ParseQuotaHeaders(resp.Header, resp.StatusCode))
+
+	var result *OpenAIForwardResult
+	if clientStream {
+		result, err = s.handleChatStreamingResponse(resp, c, account, originalModel, billingModel, upstreamModel, startTime, len(body))
+	} else {
+		result, err = s.handleChatBufferedStreamingResponse(resp, c, account, originalModel, billingModel, upstreamModel, startTime)
+	}
+	if result != nil {
+		result.UpstreamEndpoint = grokChatResponsesEndpoint
+		result.ResponseHeaders = resp.Header.Clone()
+		if result.RequestID == "" {
+			result.RequestID = firstNonEmpty(resp.Header.Get("x-request-id"), resp.Header.Get("xai-request-id"))
+		}
+		result.ReasoningEffort = extractOpenAIReasoningEffortFromBody(body, upstreamModel, billingModel, originalModel)
+	}
+	return result, err
+}
diff --git a/backend/internal/service/openai_gateway_grok_chat_bridge_test.go b/backend/internal/service/openai_gateway_grok_chat_bridge_test.go
new file mode 100644
index 0000000000..0843f1ea42
--- /dev/null
+++ b/backend/internal/service/openai_gateway_grok_chat_bridge_test.go
@@ -0,0 +1,358 @@
+//go:build unit
+
+package service
+
+import (
+	"bytes"
+	"context"
+	"errors"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"strconv"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/Wei-Shaw/sub2api/internal/pkg/xai"
+	"github.com/gin-gonic/gin"
+	"github.com/stretchr/testify/require"
+	"github.com/tidwall/gjson"
+)
+
+func TestGrokChatResponsesBridgeEligibility(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name   string
+		body   string
+		want   bool
+		reason string
+	}{
+		{
+			name: "plain text chat",
+			body: `{"model":"grok","messages":[{"role":"system","content":"concise"},{"role":"user","content":"hi"}],"stream":false}`,
+			want: true,
+		},
+		{
+			name: "safe generation options",
+			body: `{"model":"grok","messages":[{"role":"user","content":"hi"}],"stream":true,"stream_options":{"include_usage":true},"max_completion_tokens":256,"temperature":0.2,"top_p":0.9,"prompt_cache_key":"session","tools":[],"functions":null,"tool_choice":"none"}`,
+			want: true,
+		},
+		{
+			name:   "stop falls back",
+			body:   `{"model":"grok","messages":[{"role":"user","content":"hi"}],"stop":"done"}`,
+			reason: "unsupported_stop",
+		},
+		{
+			name:   "developer role falls back",
+			body:   `{"model":"grok","messages":[{"role":"developer","content":"rules"},{"role":"user","content":"hi"}]}`,
+			reason: "unsupported_message_role_developer",
+		},
+		{
+			name:   "image content falls back",
+			body:   `{"model":"grok","messages":[{"role":"user","content":[{"type":"image_url","image_url":{"url":"data:image/png;base64,QQ=="}}]}]}`,
+			reason: "non_text_message_content",
+		},
+		{
+			name:   "function tools fall back",
+			body:   `{"model":"grok","messages":[{"role":"user","content":"hi"}],"tools":[{"type":"function","function":{"name":"lookup"}}]}`,
+			reason: "unsupported_tools",
+		},
+		{
+			name:   "automatic tool choice falls back",
+			body:   `{"model":"grok","messages":[{"role":"user","content":"hi"}],"tools":[],"tool_choice":"auto"}`,
+			reason: "unsupported_tool_choice",
+		},
+		{
+			name:   "reasoning effort falls back because conversion adds summary",
+			body:   `{"model":"grok","messages":[{"role":"user","content":"hi"}],"reasoning_effort":"high"}`,
+			reason: "unsupported_reasoning_effort",
+		},
+		{
+			name:   "both token limits fall back",
+			body:   `{"model":"grok","messages":[{"role":"user","content":"hi"}],"max_tokens":256,"max_completion_tokens":256}`,
+			reason: "conflicting_max_tokens",
+		},
+		{
+			name:   "empty message falls back",
+			body:   `{"model":"grok","messages":[{"role":"assistant","content":""},{"role":"user","content":"hi"}]}`,
+			reason: "empty_message_content",
+		},
+		{
+			name:   "tool history falls back",
+			body:   `{"model":"grok","messages":[{"role":"assistant","content":"","tool_calls":[]}]}`,
+			reason: "unsafe_message_field_tool_calls",
+		},
+		{
+			name:   "unknown field falls back",
+			body:   `{"model":"grok","messages":[{"role":"user","content":"hi"}],"seed":7}`,
+			reason: "unknown_field_seed",
+		},
+		{
+			name:   "small max tokens falls back because conversion clamps it",
+			body:   `{"model":"grok","messages":[{"role":"user","content":"hi"}],"max_tokens":32}`,
+			reason: "unsafe_max_tokens",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, reason := grokChatResponsesBridgeEligibility([]byte(tt.body))
+			require.Equal(t, tt.want, got)
+			require.Equal(t, tt.reason, reason)
+		})
+	}
+}
+
+func TestGrokChatResponsesRuntimeEligibility(t *testing.T) {
+	t.Parallel()
+	require.True(t, grokChatResponsesRuntimeEligible("grok-4.5", "isolated-id"))
+	require.False(t, grokChatResponsesRuntimeEligible("grok-4.3", "isolated-id"))
+	require.False(t, grokChatResponsesRuntimeEligible("grok-4.5-build-free", "isolated-id"))
+	require.False(t, grokChatResponsesRuntimeEligible("grok-4.5", ""))
+}
+
+func TestForwardGrokChatViaResponsesNonStreamingCachesAndReturnsChat(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+
+	body := []byte(`{"model":"grok","messages":[{"role":"system","content":"be concise"},{"role":"user","content":"hi"}],"stream":false,"prompt_cache_key":"stable-session","tools":[],"functions":null,"tool_choice":"none"}`)
+	recorder := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(recorder)
+	c.Request = httptest.NewRequest(http.MethodPost, grokChatRawEndpoint, bytes.NewReader(body))
+	c.Set("api_key", &APIKey{ID: 7101})
+
+	account := grokChatBridgeTestAccount(71)
+	repo := &grokQuotaAccountRepo{mockAccountRepoForPlatform: &mockAccountRepoForPlatform{
+		accountsByID: map[int64]*Account{account.ID: account},
+	}}
+	upstream := &httpUpstreamRecorder{resp: grokChatBridgeCompletedResponse("resp_grok_chat_cache", 9856)}
+	svc := &OpenAIGatewayService{
+		httpUpstream:      upstream,
+		grokTokenProvider: NewGrokTokenProvider(repo, nil),
+		accountRepo:       repo,
+	}
+
+	result, err := svc.ForwardAsChatCompletions(context.Background(), c, account, body, "", "")
+	require.NoError(t, err)
+	require.NotNil(t, result)
+	require.Equal(t, xai.DefaultCLIBaseURL+"/responses", upstream.lastReq.URL.String())
+	require.Equal(t, grokChatResponsesEndpoint, result.UpstreamEndpoint)
+	require.Equal(t, "grok-4.5", result.UpstreamModel)
+	require.Equal(t, 9908, result.Usage.InputTokens)
+	require.Equal(t, 12, result.Usage.OutputTokens)
+	require.Equal(t, 9856, result.Usage.CacheReadInputTokens)
+
+	identity := gjson.GetBytes(upstream.lastBody, "prompt_cache_key").String()
+	require.NotEmpty(t, identity)
+	require.NotEqual(t, "stable-session", identity)
+	require.Equal(t, identity, upstream.lastReq.Header.Get(grokConversationIDHeader))
+	require.Equal(t, "web_search", gjson.GetBytes(upstream.lastBody, "tools.0.type").String())
+	require.Equal(t, "x_search", gjson.GetBytes(upstream.lastBody, "tools.1.type").String())
+	require.Equal(t, grokFreeCacheDisabledToolChoice, gjson.GetBytes(upstream.lastBody, "tool_choice").String())
+	require.True(t, gjson.GetBytes(upstream.lastBody, "stream").Bool())
+	require.Equal(t, "system", gjson.GetBytes(upstream.lastBody, "input.0.role").String())
+	require.Equal(t, "user", gjson.GetBytes(upstream.lastBody, "input.1.role").String())
+	require.False(t, gjson.GetBytes(upstream.lastBody, "instructions").Exists())
+	require.False(t, gjson.GetBytes(upstream.lastBody, "include").Exists())
+	require.False(t, gjson.GetBytes(upstream.lastBody, "store").Exists())
+
+	require.Equal(t, http.StatusOK, recorder.Code)
+	require.Equal(t, "cached ok", gjson.Get(recorder.Body.String(), "choices.0.message.content").String())
+	require.Equal(t, int64(9856), gjson.Get(recorder.Body.String(), "usage.prompt_tokens_details.cached_tokens").Int())
+	require.NotNil(t, repo.updates[account.ID][grokQuotaSnapshotExtraKey])
+}
+
+func TestForwardGrokChatViaResponsesStreamingPropagatesCachedUsage(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+
+	body := []byte(`{"model":"grok","messages":[{"role":"user","content":"hi"}],"stream":true}`)
+	recorder := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(recorder)
+	c.Request = httptest.NewRequest(http.MethodPost, grokChatRawEndpoint, bytes.NewReader(body))
+	c.Set("api_key", &APIKey{ID: 7201})
+
+	account := grokChatBridgeTestAccount(72)
+	repo := &grokQuotaAccountRepo{mockAccountRepoForPlatform: &mockAccountRepoForPlatform{
+		accountsByID: map[int64]*Account{account.ID: account},
+	}}
+	upstream := &httpUpstreamRecorder{resp: grokChatBridgeCompletedResponse("resp_grok_chat_stream", 4096)}
+	svc := &OpenAIGatewayService{
+		httpUpstream:      upstream,
+		grokTokenProvider: NewGrokTokenProvider(repo, nil),
+		accountRepo:       repo,
+	}
+
+	result, err := svc.ForwardAsChatCompletions(context.Background(), c, account, body, "", "")
+	require.NoError(t, err)
+	require.NotNil(t, result)
+	require.True(t, result.Stream)
+	require.Equal(t, grokChatResponsesEndpoint, result.UpstreamEndpoint)
+	require.Equal(t, 4096, result.Usage.CacheReadInputTokens)
+	require.Contains(t, recorder.Header().Get("Content-Type"), "text/event-stream")
+	require.Contains(t, recorder.Body.String(), `"content":"cached ok"`)
+	require.Contains(t, recorder.Body.String(), `"cached_tokens":4096`)
+	require.Contains(t, recorder.Body.String(), "data: [DONE]")
+}
+
+func TestForwardGrokChatRuntimeGateFallsBackToRaw(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+
+	tests := []struct {
+		name         string
+		setAPIKey    bool
+		mappedModel  string
+		wantUpstream string
+	}{
+		{name: "missing cache identity", wantUpstream: "grok-4.5"},
+		{name: "non cache capable mapped model", setAPIKey: true, mappedModel: "grok-4.3", wantUpstream: "grok-4.3"},
+	}
+
+	for index, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			body := []byte(`{"model":"grok","messages":[{"role":"user","content":"hi"}],"stream":false}`)
+			recorder := httptest.NewRecorder()
+			c, _ := gin.CreateTestContext(recorder)
+			c.Request = httptest.NewRequest(http.MethodPost, grokChatRawEndpoint, bytes.NewReader(body))
+			if tt.setAPIKey {
+				c.Set("api_key", &APIKey{ID: int64(7301 + index)})
+			}
+
+			account := grokChatBridgeTestAccount(int64(73 + index))
+			if tt.mappedModel != "" {
+				account.Credentials["model_mapping"] = map[string]any{"grok": tt.mappedModel}
+			}
+			repo := &grokQuotaAccountRepo{mockAccountRepoForPlatform: &mockAccountRepoForPlatform{
+				accountsByID: map[int64]*Account{account.ID: account},
+			}}
+			upstream := &httpUpstreamRecorder{resp: &http.Response{
+				StatusCode: http.StatusOK,
+				Header:     http.Header{"Content-Type": []string{"application/json"}},
+				Body: io.NopCloser(strings.NewReader(
+					`{"id":"chat_raw","object":"chat.completion","model":"` + tt.wantUpstream + `","choices":[{"index":0,"message":{"role":"assistant","content":"raw ok"},"finish_reason":"stop"}],"usage":{"prompt_tokens":2,"completion_tokens":1,"total_tokens":3}}`,
+				)),
+			}}
+			svc := &OpenAIGatewayService{
+				httpUpstream:      upstream,
+				grokTokenProvider: NewGrokTokenProvider(repo, nil),
+				accountRepo:       repo,
+			}
+
+			result, err := svc.ForwardAsChatCompletions(context.Background(), c, account, body, "", "")
+			require.NoError(t, err)
+			require.NotNil(t, result)
+			require.Equal(t, xai.DefaultCLIBaseURL+"/chat/completions", upstream.lastReq.URL.String())
+			require.Equal(t, grokChatRawEndpoint, result.UpstreamEndpoint)
+			require.Equal(t, tt.wantUpstream, result.UpstreamModel)
+			require.False(t, gjson.GetBytes(upstream.lastBody, "tools").Exists())
+			require.Equal(t, "raw ok", gjson.Get(recorder.Body.String(), "choices.0.message.content").String())
+		})
+	}
+}
+
+func TestForwardGrokChatViaResponses429UsesGrokRateLimitPolicy(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+
+	body := []byte(`{"model":"grok","messages":[{"role":"user","content":"hi"}],"stream":false}`)
+	recorder := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(recorder)
+	c.Request = httptest.NewRequest(http.MethodPost, grokChatRawEndpoint, bytes.NewReader(body))
+	c.Set("api_key", &APIKey{ID: 7501})
+
+	account := grokChatBridgeTestAccount(75)
+	repo := &grokQuotaAccountRepo{mockAccountRepoForPlatform: &mockAccountRepoForPlatform{
+		accountsByID: map[int64]*Account{account.ID: account},
+	}}
+	upstream := &httpUpstreamRecorder{resp: &http.Response{
+		StatusCode: http.StatusTooManyRequests,
+		Header: http.Header{
+			"Content-Type": []string{"application/json"},
+			"Retry-After":  []string{"45"},
+		},
+		Body: io.NopCloser(strings.NewReader(`{"error":{"message":"rate limited"}}`)),
+	}}
+	svc := &OpenAIGatewayService{
+		httpUpstream:      upstream,
+		grokTokenProvider: NewGrokTokenProvider(repo, nil),
+		accountRepo:       repo,
+	}
+	before := time.Now()
+
+	result, err := svc.ForwardAsChatCompletions(context.Background(), c, account, body, "", "")
+	require.Error(t, err)
+	require.Nil(t, result)
+	var failoverErr *UpstreamFailoverError
+	require.True(t, errors.As(err, &failoverErr))
+	require.Equal(t, http.StatusTooManyRequests, failoverErr.StatusCode)
+	require.Equal(t, xai.DefaultCLIBaseURL+"/responses", upstream.lastReq.URL.String())
+	require.Equal(t, grokChatResponsesEndpoint, GetActualOpenAIUpstreamEndpoint(c))
+	require.Equal(t, 1, repo.rateLimitedCalls)
+	require.Zero(t, repo.tempUnschedCalls)
+	require.WithinDuration(t, before.Add(45*time.Second), repo.lastRateLimitResetAt, time.Second)
+	require.True(t, svc.isOpenAIAccountRuntimeBlocked(account))
+}
+
+func TestForwardGrokRawChatErrorRecordsActualEndpoint(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+
+	body := []byte(`{"model":"grok","messages":[{"role":"user","content":"hi"}],"stream":false,"stop":"done"}`)
+	recorder := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(recorder)
+	c.Request = httptest.NewRequest(http.MethodPost, grokChatRawEndpoint, bytes.NewReader(body))
+	c.Set("api_key", &APIKey{ID: 7601})
+
+	account := grokChatBridgeTestAccount(76)
+	repo := &grokQuotaAccountRepo{mockAccountRepoForPlatform: &mockAccountRepoForPlatform{
+		accountsByID: map[int64]*Account{account.ID: account},
+	}}
+	upstream := &httpUpstreamRecorder{resp: &http.Response{
+		StatusCode: http.StatusBadRequest,
+		Header:     http.Header{"Content-Type": []string{"application/json"}},
+		Body:       io.NopCloser(strings.NewReader(`{"error":{"message":"bad request"}}`)),
+	}}
+	svc := &OpenAIGatewayService{
+		httpUpstream:      upstream,
+		grokTokenProvider: NewGrokTokenProvider(repo, nil),
+		accountRepo:       repo,
+	}
+
+	result, err := svc.ForwardAsChatCompletions(context.Background(), c, account, body, "", "")
+	require.Error(t, err)
+	require.Nil(t, result)
+	require.Equal(t, xai.DefaultCLIBaseURL+"/chat/completions", upstream.lastReq.URL.String())
+	require.Equal(t, grokChatRawEndpoint, GetActualOpenAIUpstreamEndpoint(c))
+}
+
+func grokChatBridgeTestAccount(id int64) *Account {
+	return &Account{
+		ID:          id,
+		Name:        "grok-cache-bridge",
+		Platform:    PlatformGrok,
+		Type:        AccountTypeOAuth,
+		Concurrency: 1,
+		Credentials: map[string]any{
+			"access_token": "access-token",
+			"expires_at":   time.Now().Add(time.Hour).UTC().Format(time.RFC3339),
+			"base_url":     xai.DefaultCLIBaseURL,
+		},
+	}
+}
+
+func grokChatBridgeCompletedResponse(responseID string, cachedTokens int) *http.Response {
+	body := strings.Join([]string{
+		`data: {"type":"response.output_text.delta","sequence_number":0,"delta":"cached ok"}`,
+		"",
+		`data: {"type":"response.completed","sequence_number":1,"response":{"id":"` + responseID + `","object":"response","model":"grok-4.5","status":"completed","output":[{"type":"message","id":"msg_1","role":"assistant","status":"completed","content":[{"type":"output_text","text":"cached ok"}]}],"usage":{"input_tokens":9908,"output_tokens":12,"total_tokens":9920,"input_tokens_details":{"cached_tokens":` + strconv.Itoa(cachedTokens) + `}}}}`,
+		"",
+	}, "\n")
+	return &http.Response{
+		StatusCode: http.StatusOK,
+		Header: http.Header{
+			"Content-Type":                   []string{"text/event-stream"},
+			"Xai-Request-Id":                 []string{responseID + "-request"},
+			"X-Ratelimit-Limit-Requests":     []string{"10"},
+			"X-Ratelimit-Remaining-Requests": []string{"9"},
+		},
+		Body: io.NopCloser(strings.NewReader(body)),
+	}
+}
diff --git a/backend/internal/service/openai_gateway_grok_test.go b/backend/internal/service/openai_gateway_grok_test.go
index 43bdc8b33e..e87042d9b5 100644
--- a/backend/internal/service/openai_gateway_grok_test.go
+++ b/backend/internal/service/openai_gateway_grok_test.go
@@ -615,12 +615,12 @@ func TestForwardGrokMedia429ReconcilesRateLimitBeforeCustomErrorBypass(t *testin
 	require.True(t, svc.isOpenAIAccountRuntimeBlocked(account))
 }
 
-func TestForwardAsChatCompletionsForGrokUsesXAIChatCompletionsAndSnapshots(t *testing.T) {
+func TestForwardAsChatCompletionsForGrokStopFallsBackToXAIChatCompletions(t *testing.T) {
 	gin.SetMode(gin.TestMode)
 
 	recorder := httptest.NewRecorder()
 	c, _ := gin.CreateTestContext(recorder)
-	body := []byte(`{"model":"grok","messages":[{"role":"user","content":"hi"}],"stream":false,"prompt_cache_key":"raw-client-cache-key"}`)
+	body := []byte(`{"model":"grok","messages":[{"role":"user","content":"hi"}],"stream":false,"stop":"done","prompt_cache_key":"raw-client-cache-key"}`)
 	c.Request = httptest.NewRequest(http.MethodPost, "/v1/chat/completions", bytes.NewReader(body))
 	c.Set("api_key", &APIKey{ID: 5101})
 
@@ -881,12 +881,12 @@ func TestForwardGrokResponsesFailoverKeepsCacheIdentityAcrossAccounts(t *testing
 	require.Equal(t, "Bearer access-token-b", upstream.requests[1].Header.Get("Authorization"))
 }
 
-func TestForwardAsChatCompletionsForGrokStreamingUsesRawXAIChatCompletions(t *testing.T) {
+func TestForwardAsChatCompletionsForGrokStreamingStopFallsBackToRawXAIChatCompletions(t *testing.T) {
 	gin.SetMode(gin.TestMode)
 
 	recorder := httptest.NewRecorder()
 	c, _ := gin.CreateTestContext(recorder)
-	body := []byte(`{"model":"grok","messages":[{"role":"user","content":"hi"}],"stream":true}`)
+	body := []byte(`{"model":"grok","messages":[{"role":"user","content":"hi"}],"stream":true,"stop":"done"}`)
 	c.Request = httptest.NewRequest(http.MethodPost, "/v1/chat/completions", bytes.NewReader(body))
 	c.Request.Header.Set("Content-Type", "application/json")
 	c.Request.Header.Set(grokConversationIDHeader, "native-client-conversation")
diff --git a/backend/internal/service/openai_gateway_service.go b/backend/internal/service/openai_gateway_service.go
index 0d03d83dcf..208887151e 100644
--- a/backend/internal/service/openai_gateway_service.go
+++ b/backend/internal/service/openai_gateway_service.go
@@ -49,6 +49,7 @@ const (
 	openAIWSRetryBackoffMaxDefault     = 2 * time.Second
 	openAIWSRetryJitterRatioDefault    = 0.2
 	openAICompactSessionSeedKey        = "openai_compact_session_seed"
+	openAIUpstreamEndpointContextKey   = "openai_actual_upstream_endpoint"
 	codexCLIVersion                    = "0.144.1"
 	// Codex 限额快照仅用于后台展示/诊断，不需要每个成功请求都立即落库。
 	openAICodexSnapshotPersistMinInterval = 30 * time.Second
@@ -223,6 +224,9 @@ type OpenAIForwardResult struct {
 	// UpstreamModel is the actual model sent to the upstream provider after mapping.
 	// Empty when no mapping was applied (requested model was used as-is).
 	UpstreamModel string
+	// UpstreamEndpoint is the actual upstream API path used for this request.
+	// It avoids guessing when one downstream protocol can use multiple upstream endpoints.
+	UpstreamEndpoint string
 	// ServiceTier records the OpenAI Responses API service tier, e.g. "priority" / "flex".
 	// Nil means the request did not specify a recognized tier.
 	ServiceTier *string
@@ -251,6 +255,32 @@ type OpenAIForwardResult struct {
 	wsReplayInputExists bool
 }
 
+// SetActualOpenAIUpstreamEndpoint records the endpoint selected by the current
+// forwarding attempt. It covers error paths where no OpenAIForwardResult is
+// available for usage and operations logging.
+func SetActualOpenAIUpstreamEndpoint(c *gin.Context, endpoint string) {
+	if c == nil {
+		return
+	}
+	if endpoint = strings.TrimSpace(endpoint); endpoint != "" {
+		c.Set(openAIUpstreamEndpointContextKey, endpoint)
+	}
+}
+
+// GetActualOpenAIUpstreamEndpoint returns the endpoint recorded by the latest
+// forwarding attempt in this request.
+func GetActualOpenAIUpstreamEndpoint(c *gin.Context) string {
+	if c == nil {
+		return ""
+	}
+	value, exists := c.Get(openAIUpstreamEndpointContextKey)
+	if !exists {
+		return ""
+	}
+	endpoint, _ := value.(string)
+	return strings.TrimSpace(endpoint)
+}
+
 type OpenAIWSRetryMetricsSnapshot struct {
 	RetryAttemptsTotal            int64 `json:"retry_attempts_total"`
 	RetryBackoffMsTotal           int64 `json:"retry_backoff_ms_total"`