diff --git a/backend/internal/service/upstream_response_model.go b/backend/internal/service/upstream_response_model.go
index 81869c07d9..f4e3bd4fe0 100644
--- a/backend/internal/service/upstream_response_model.go
+++ b/backend/internal/service/upstream_response_model.go
@@ -167,10 +167,33 @@ func upstreamModelMismatch(sentModel, responseModel string) *bool {
 		return nil
 	}
 	sentModel = strings.TrimSpace(sentModel)
-	mismatch := sentModel == "" || !strings.EqualFold(sentModel, responseModel)
+	mismatch := sentModel == "" || !upstreamModelsMatchForAudit(sentModel, responseModel)
 	return &mismatch
 }
 
+func upstreamModelsMatchForAudit(sentModel, responseModel string) bool {
+	if strings.EqualFold(sentModel, responseModel) {
+		return true
+	}
+
+	// xAI reports the runtime build ID for these supported public aliases.
+	// Canonicalize only for mismatch auditing; keep the raw response model for
+	// observability and for the separate response-model billing safeguards.
+	sentGrokModel := canonicalGrokBuildRuntimeModel(sentModel)
+	return sentGrokModel != "" && sentGrokModel == canonicalGrokBuildRuntimeModel(responseModel)
+}
+
+func canonicalGrokBuildRuntimeModel(model string) string {
+	switch strings.ToLower(strings.TrimSpace(model)) {
+	case "grok-4.5", "grok-4.5-latest", "grok-4.5-build":
+		return "grok-4.5-build"
+	case "grok-4.6", "grok-4.6-latest", "grok-4.6-build":
+		return "grok-4.6-build"
+	default:
+		return ""
+	}
+}
+
 func upstreamSentModel(requestedModel, upstreamModel string) string {
 	sentModel := strings.TrimSpace(upstreamModel)
 	if sentModel == "" {
diff --git a/backend/internal/service/upstream_response_model_test.go b/backend/internal/service/upstream_response_model_test.go
index a831e74e65..51374ec1f3 100644
--- a/backend/internal/service/upstream_response_model_test.go
+++ b/backend/internal/service/upstream_response_model_test.go
@@ -59,6 +59,77 @@ func TestUpstreamModelMismatchThreeStateAndCaseInsensitiveComparison(t *testing.
 	require.True(t, *mismatched)
 }
 
+func TestUpstreamModelMismatchTreatsGrokBuildRuntimeIDsAsAliases(t *testing.T) {
+	tests := []struct {
+		name          string
+		sentModel     string
+		responseModel string
+	}{
+		{
+			name:          "issue 5634 grok 4.6",
+			sentModel:     "grok-4.6",
+			responseModel: "grok-4.6-build",
+		},
+		{
+			name:          "grok 4.6 latest",
+			sentModel:     "grok-4.6-latest",
+			responseModel: "grok-4.6-build",
+		},
+		{
+			name:          "issue 5647 grok 4.5 latest",
+			sentModel:     "grok-4.5-latest",
+			responseModel: "grok-4.5-build",
+		},
+		{
+			name:          "grok 4.5 canonical",
+			sentModel:     "grok-4.5",
+			responseModel: "GROK-4.5-BUILD",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			mismatch := upstreamModelMismatch(tt.sentModel, tt.responseModel)
+
+			require.NotNil(t, mismatch)
+			require.False(t, *mismatch)
+		})
+	}
+}
+
+func TestUpstreamModelMismatchDoesNotCollapseDifferentModels(t *testing.T) {
+	tests := []struct {
+		name          string
+		sentModel     string
+		responseModel string
+	}{
+		{
+			name:          "different grok versions",
+			sentModel:     "grok-4.5",
+			responseModel: "grok-4.6-build",
+		},
+		{
+			name:          "unrelated build suffix",
+			sentModel:     "gpt-5.5",
+			responseModel: "gpt-5.5-build",
+		},
+		{
+			name:          "different grok runtime",
+			sentModel:     "grok-build-0.1",
+			responseModel: "grok-4.5-build",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			mismatch := upstreamModelMismatch(tt.sentModel, tt.responseModel)
+
+			require.NotNil(t, mismatch)
+			require.True(t, *mismatch)
+		})
+	}
+}
+
 func TestObserveOpenAISSEBodyIgnoresMalformedPayload(t *testing.T) {
 	observer := &upstreamResponseModelObserver{}
 	observeOpenAISSEBody(observer, "data: not-json\n\ndata: {\"type\":\"response.completed\",\"response\":{\"model\":\"gpt-5.4\"}}\n\n")