diff --git a/sdk/cliproxy/auth/conductor.go b/sdk/cliproxy/auth/conductor.go
index b29e04db..88b12b9a 100644
--- a/sdk/cliproxy/auth/conductor.go
+++ b/sdk/cliproxy/auth/conductor.go
@@ -1627,53 +1627,60 @@ func (m *Manager) MarkResult(ctx context.Context, result Result) {
 				}
 
 				statusCode := statusCodeFromResult(result.Error)
-				switch statusCode {
-				case 401:
-					next := now.Add(30 * time.Minute)
-					state.NextRetryAfter = next
-					suspendReason = "unauthorized"
-					shouldSuspendModel = true
-				case 402, 403:
-					next := now.Add(30 * time.Minute)
-					state.NextRetryAfter = next
-					suspendReason = "payment_required"
-					shouldSuspendModel = true
-				case 404:
+				if isModelSupportResultError(result.Error) {
 					next := now.Add(12 * time.Hour)
 					state.NextRetryAfter = next
-					suspendReason = "not_found"
+					suspendReason = "model_not_supported"
 					shouldSuspendModel = true
-				case 429:
-					var next time.Time
-					backoffLevel := state.Quota.BackoffLevel
-					if result.RetryAfter != nil {
-						next = now.Add(*result.RetryAfter)
-					} else {
-						cooldown, nextLevel := nextQuotaCooldown(backoffLevel, quotaCooldownDisabledForAuth(auth))
-						if cooldown > 0 {
-							next = now.Add(cooldown)
-						}
-						backoffLevel = nextLevel
-					}
-					state.NextRetryAfter = next
-					state.Quota = QuotaState{
-						Exceeded:      true,
-						Reason:        "quota",
-						NextRecoverAt: next,
-						BackoffLevel:  backoffLevel,
-					}
-					suspendReason = "quota"
-					shouldSuspendModel = true
-					setModelQuota = true
-				case 408, 500, 502, 503, 504:
-					if quotaCooldownDisabledForAuth(auth) {
-						state.NextRetryAfter = time.Time{}
-					} else {
-						next := now.Add(1 * time.Minute)
+				} else {
+					switch statusCode {
+					case 401:
+						next := now.Add(30 * time.Minute)
 						state.NextRetryAfter = next
+						suspendReason = "unauthorized"
+						shouldSuspendModel = true
+					case 402, 403:
+						next := now.Add(30 * time.Minute)
+						state.NextRetryAfter = next
+						suspendReason = "payment_required"
+						shouldSuspendModel = true
+					case 404:
+						next := now.Add(12 * time.Hour)
+						state.NextRetryAfter = next
+						suspendReason = "not_found"
+						shouldSuspendModel = true
+					case 429:
+						var next time.Time
+						backoffLevel := state.Quota.BackoffLevel
+						if result.RetryAfter != nil {
+							next = now.Add(*result.RetryAfter)
+						} else {
+							cooldown, nextLevel := nextQuotaCooldown(backoffLevel, quotaCooldownDisabledForAuth(auth))
+							if cooldown > 0 {
+								next = now.Add(cooldown)
+							}
+							backoffLevel = nextLevel
+						}
+						state.NextRetryAfter = next
+						state.Quota = QuotaState{
+							Exceeded:      true,
+							Reason:        "quota",
+							NextRecoverAt: next,
+							BackoffLevel:  backoffLevel,
+						}
+						suspendReason = "quota"
+						shouldSuspendModel = true
+						setModelQuota = true
+					case 408, 500, 502, 503, 504:
+						if quotaCooldownDisabledForAuth(auth) {
+							state.NextRetryAfter = time.Time{}
+						} else {
+							next := now.Add(1 * time.Minute)
+							state.NextRetryAfter = next
+						}
+					default:
+						state.NextRetryAfter = time.Time{}
 					}
-				default:
-					state.NextRetryAfter = time.Time{}
 				}
 
 				auth.Status = StatusError
@@ -1883,14 +1890,65 @@ func statusCodeFromResult(err *Error) int {
 	return err.StatusCode()
 }
 
+func isModelSupportErrorMessage(message string) bool {
+	lower := strings.ToLower(strings.TrimSpace(message))
+	if lower == "" {
+		return false
+	}
+	patterns := [...]string{
+		"model_not_supported",
+		"requested model is not supported",
+		"requested model is unsupported",
+		"requested model is unavailable",
+		"model is not supported",
+		"model not supported",
+		"unsupported model",
+		"model unavailable",
+		"not available for your plan",
+		"not available for your account",
+	}
+	for _, pattern := range patterns {
+		if strings.Contains(lower, pattern) {
+			return true
+		}
+	}
+	return false
+}
+
+func isModelSupportError(err error) bool {
+	if err == nil {
+		return false
+	}
+	status := statusCodeFromError(err)
+	if status != http.StatusBadRequest && status != http.StatusUnprocessableEntity {
+		return false
+	}
+	return isModelSupportErrorMessage(err.Error())
+}
+
+func isModelSupportResultError(err *Error) bool {
+	if err == nil {
+		return false
+	}
+	status := statusCodeFromResult(err)
+	if status != http.StatusBadRequest && status != http.StatusUnprocessableEntity {
+		return false
+	}
+	return isModelSupportErrorMessage(err.Message)
+}
+
 // isRequestInvalidError returns true if the error represents a client request
 // error that should not be retried. Specifically, it treats 400 responses with
 // "invalid_request_error" and all 422 responses as request-shape failures,
-// where switching auths or pooled upstream models will not help.
+// where switching auths or pooled upstream models will not help. Model-support
+// errors are excluded so routing can fall through to another auth or upstream.
 func isRequestInvalidError(err error) bool {
 	if err == nil {
 		return false
 	}
+	if isModelSupportError(err) {
+		return false
+	}
 	status := statusCodeFromError(err)
 	switch status {
 	case http.StatusBadRequest:
diff --git a/sdk/cliproxy/auth/conductor_overrides_test.go b/sdk/cliproxy/auth/conductor_overrides_test.go
index 7aca49da..586af489 100644
--- a/sdk/cliproxy/auth/conductor_overrides_test.go
+++ b/sdk/cliproxy/auth/conductor_overrides_test.go
@@ -108,6 +108,53 @@ func (e *credentialRetryLimitExecutor) Calls() int {
 	return e.calls
 }
 
+type authFallbackExecutor struct {
+	id string
+
+	mu            sync.Mutex
+	executeCalls  []string
+	executeErrors map[string]error
+}
+
+func (e *authFallbackExecutor) Identifier() string {
+	return e.id
+}
+
+func (e *authFallbackExecutor) Execute(_ context.Context, auth *Auth, _ cliproxyexecutor.Request, _ cliproxyexecutor.Options) (cliproxyexecutor.Response, error) {
+	e.mu.Lock()
+	e.executeCalls = append(e.executeCalls, auth.ID)
+	err := e.executeErrors[auth.ID]
+	e.mu.Unlock()
+	if err != nil {
+		return cliproxyexecutor.Response{}, err
+	}
+	return cliproxyexecutor.Response{Payload: []byte(auth.ID)}, nil
+}
+
+func (e *authFallbackExecutor) ExecuteStream(context.Context, *Auth, cliproxyexecutor.Request, cliproxyexecutor.Options) (*cliproxyexecutor.StreamResult, error) {
+	return nil, &Error{HTTPStatus: 500, Message: "not implemented"}
+}
+
+func (e *authFallbackExecutor) Refresh(_ context.Context, auth *Auth) (*Auth, error) {
+	return auth, nil
+}
+
+func (e *authFallbackExecutor) CountTokens(context.Context, *Auth, cliproxyexecutor.Request, cliproxyexecutor.Options) (cliproxyexecutor.Response, error) {
+	return cliproxyexecutor.Response{}, &Error{HTTPStatus: 500, Message: "not implemented"}
+}
+
+func (e *authFallbackExecutor) HttpRequest(context.Context, *Auth, *http.Request) (*http.Response, error) {
+	return nil, nil
+}
+
+func (e *authFallbackExecutor) ExecuteCalls() []string {
+	e.mu.Lock()
+	defer e.mu.Unlock()
+	out := make([]string, len(e.executeCalls))
+	copy(out, e.executeCalls)
+	return out
+}
+
 func newCredentialRetryLimitTestManager(t *testing.T, maxRetryCredentials int) (*Manager, *credentialRetryLimitExecutor) {
 	t.Helper()
 
@@ -191,6 +238,76 @@ func TestManager_MaxRetryCredentials_LimitsCrossCredentialRetries(t *testing.T)
 	}
 }
 
+func TestManager_ModelSupportBadRequest_FallsBackAndSuspendsAuth(t *testing.T) {
+	m := NewManager(nil, nil, nil)
+	executor := &authFallbackExecutor{
+		id: "claude",
+		executeErrors: map[string]error{
+			"aa-bad-auth": &Error{
+				HTTPStatus: http.StatusBadRequest,
+				Message:    "invalid_request_error: The requested model is not supported.",
+			},
+		},
+	}
+	m.RegisterExecutor(executor)
+
+	model := "claude-opus-4-6"
+	badAuth := &Auth{ID: "aa-bad-auth", Provider: "claude"}
+	goodAuth := &Auth{ID: "bb-good-auth", Provider: "claude"}
+
+	reg := registry.GetGlobalRegistry()
+	reg.RegisterClient(badAuth.ID, "claude", []*registry.ModelInfo{{ID: model}})
+	reg.RegisterClient(goodAuth.ID, "claude", []*registry.ModelInfo{{ID: model}})
+	t.Cleanup(func() {
+		reg.UnregisterClient(badAuth.ID)
+		reg.UnregisterClient(goodAuth.ID)
+	})
+
+	if _, errRegister := m.Register(context.Background(), badAuth); errRegister != nil {
+		t.Fatalf("register bad auth: %v", errRegister)
+	}
+	if _, errRegister := m.Register(context.Background(), goodAuth); errRegister != nil {
+		t.Fatalf("register good auth: %v", errRegister)
+	}
+
+	request := cliproxyexecutor.Request{Model: model}
+	for i := 0; i < 2; i++ {
+		resp, errExecute := m.Execute(context.Background(), []string{"claude"}, request, cliproxyexecutor.Options{})
+		if errExecute != nil {
+			t.Fatalf("execute %d error = %v, want success", i, errExecute)
+		}
+		if string(resp.Payload) != goodAuth.ID {
+			t.Fatalf("execute %d payload = %q, want %q", i, string(resp.Payload), goodAuth.ID)
+		}
+	}
+
+	got := executor.ExecuteCalls()
+	want := []string{badAuth.ID, goodAuth.ID, goodAuth.ID}
+	if len(got) != len(want) {
+		t.Fatalf("execute calls = %v, want %v", got, want)
+	}
+	for i := range want {
+		if got[i] != want[i] {
+			t.Fatalf("execute call %d auth = %q, want %q", i, got[i], want[i])
+		}
+	}
+
+	updatedBad, ok := m.GetByID(badAuth.ID)
+	if !ok || updatedBad == nil {
+		t.Fatalf("expected bad auth to remain registered")
+	}
+	state := updatedBad.ModelStates[model]
+	if state == nil {
+		t.Fatalf("expected model state for %q", model)
+	}
+	if !state.Unavailable {
+		t.Fatalf("expected bad auth model state to be unavailable")
+	}
+	if state.NextRetryAfter.IsZero() {
+		t.Fatalf("expected bad auth model state cooldown to be set")
+	}
+}
+
 func TestManager_MarkResult_RespectsAuthDisableCoolingOverride(t *testing.T) {
 	prev := quotaCooldownDisabled.Load()
 	quotaCooldownDisabled.Store(false)
diff --git a/sdk/cliproxy/auth/openai_compat_pool_test.go b/sdk/cliproxy/auth/openai_compat_pool_test.go
index 5a5ecb4f..5b1bf9aa 100644
--- a/sdk/cliproxy/auth/openai_compat_pool_test.go
+++ b/sdk/cliproxy/auth/openai_compat_pool_test.go
@@ -243,6 +243,75 @@ func TestManagerExecute_OpenAICompatAliasPoolStopsOnBadRequest(t *testing.T) {
 		t.Fatalf("execute calls = %v, want only first invalid model", got)
 	}
 }
+
+func TestManagerExecute_OpenAICompatAliasPoolFallsBackOnModelSupportBadRequest(t *testing.T) {
+	alias := "claude-opus-4.66"
+	modelSupportErr := &Error{
+		HTTPStatus: http.StatusBadRequest,
+		Message:    "invalid_request_error: The requested model is not supported.",
+	}
+	executor := &openAICompatPoolExecutor{
+		id:            "pool",
+		executeErrors: map[string]error{"qwen3.5-plus": modelSupportErr},
+	}
+	m := newOpenAICompatPoolTestManager(t, alias, []internalconfig.OpenAICompatibilityModel{
+		{Name: "qwen3.5-plus", Alias: alias},
+		{Name: "glm-5", Alias: alias},
+	}, executor)
+
+	resp, err := m.Execute(context.Background(), []string{"pool"}, cliproxyexecutor.Request{Model: alias}, cliproxyexecutor.Options{})
+	if err != nil {
+		t.Fatalf("execute error = %v, want fallback success", err)
+	}
+	if string(resp.Payload) != "glm-5" {
+		t.Fatalf("payload = %q, want %q", string(resp.Payload), "glm-5")
+	}
+	got := executor.ExecuteModels()
+	want := []string{"qwen3.5-plus", "glm-5"}
+	if len(got) != len(want) {
+		t.Fatalf("execute calls = %v, want %v", got, want)
+	}
+	for i := range want {
+		if got[i] != want[i] {
+			t.Fatalf("execute call %d model = %q, want %q", i, got[i], want[i])
+		}
+	}
+}
+
+func TestManagerExecute_OpenAICompatAliasPoolFallsBackOnModelSupportUnprocessableEntity(t *testing.T) {
+	alias := "claude-opus-4.66"
+	modelSupportErr := &Error{
+		HTTPStatus: http.StatusUnprocessableEntity,
+		Message:    "The requested model is not supported.",
+	}
+	executor := &openAICompatPoolExecutor{
+		id:            "pool",
+		executeErrors: map[string]error{"qwen3.5-plus": modelSupportErr},
+	}
+	m := newOpenAICompatPoolTestManager(t, alias, []internalconfig.OpenAICompatibilityModel{
+		{Name: "qwen3.5-plus", Alias: alias},
+		{Name: "glm-5", Alias: alias},
+	}, executor)
+
+	resp, err := m.Execute(context.Background(), []string{"pool"}, cliproxyexecutor.Request{Model: alias}, cliproxyexecutor.Options{})
+	if err != nil {
+		t.Fatalf("execute error = %v, want fallback success", err)
+	}
+	if string(resp.Payload) != "glm-5" {
+		t.Fatalf("payload = %q, want %q", string(resp.Payload), "glm-5")
+	}
+	got := executor.ExecuteModels()
+	want := []string{"qwen3.5-plus", "glm-5"}
+	if len(got) != len(want) {
+		t.Fatalf("execute calls = %v, want %v", got, want)
+	}
+	for i := range want {
+		if got[i] != want[i] {
+			t.Fatalf("execute call %d model = %q, want %q", i, got[i], want[i])
+		}
+	}
+}
+
 func TestManagerExecute_OpenAICompatAliasPoolFallsBackWithinSameAuth(t *testing.T) {
 	alias := "claude-opus-4.66"
 	executor := &openAICompatPoolExecutor{