diff --git a/backend/internal/pkg/xai/models.go b/backend/internal/pkg/xai/models.go
index 25584f0843..c60c400ac3 100644
--- a/backend/internal/pkg/xai/models.go
+++ b/backend/internal/pkg/xai/models.go
@@ -8,15 +8,24 @@ import (
 // runtimeMappingOpts holds operator-configured defaults applied when Grok
 // accounts leave credentials.model_mapping empty. Updated from settings.
 var runtimeMappingOpts atomic.Value // ModelMappingOptions
+var runtimeMappingVersion atomic.Uint64
 
 func init() {
 	runtimeMappingOpts.Store(ModelMappingOptions{})
+	runtimeMappingVersion.Store(1)
 }
 
 // SetRuntimeModelMappingOptions updates process-wide defaults used by
 // DefaultModelMapping (e.g. after settings load). Safe for concurrent use.
 func SetRuntimeModelMappingOptions(opts ModelMappingOptions) {
 	runtimeMappingOpts.Store(opts)
+	runtimeMappingVersion.Add(1)
+}
+
+// RuntimeModelMappingVersion changes whenever runtime mapping options change.
+// Account-level caches include it so settings updates take effect without a restart.
+func RuntimeModelMappingVersion() uint64 {
+	return runtimeMappingVersion.Load()
 }
 
 // RuntimeModelMappingOptions returns the last options set via SetRuntimeModelMappingOptions.
diff --git a/backend/internal/service/account.go b/backend/internal/service/account.go
index ab54d3c805..eceaed0613 100644
--- a/backend/internal/service/account.go
+++ b/backend/internal/service/account.go
@@ -71,6 +71,7 @@ type Account struct {
 	modelMappingCacheRawPtr         uintptr
 	modelMappingCacheRawLen         int
 	modelMappingCacheRawSig         uint64
+	modelMappingCacheRuntimeVersion uint64
 
 	// header_overrides 热路径缓存（非持久化字段，同 model_mapping 缓存先例）
 	headerOverrideCache               map[string]string
@@ -553,6 +554,7 @@ func stringMappingFromRaw(raw any) map[string]string {
 }
 
 func (a *Account) GetModelMapping() map[string]string {
+	runtimeVersion := xai.RuntimeModelMappingVersion()
 	credentialsPtr := mapPtr(a.Credentials)
 	rawMapping, _ := a.Credentials["model_mapping"].(map[string]any)
 	rawPtr := mapPtr(rawMapping)
@@ -563,7 +565,8 @@ func (a *Account) GetModelMapping() map[string]string {
 	if a.modelMappingCacheReady &&
 		a.modelMappingCacheCredentialsPtr == credentialsPtr &&
 		a.modelMappingCacheRawPtr == rawPtr &&
-		a.modelMappingCacheRawLen == rawLen {
+		a.modelMappingCacheRawLen == rawLen &&
+		a.modelMappingCacheRuntimeVersion == runtimeVersion {
 		rawSig = modelMappingSignature(rawMapping)
 		rawSigReady = true
 		if a.modelMappingCacheRawSig == rawSig {
@@ -582,6 +585,7 @@ func (a *Account) GetModelMapping() map[string]string {
 	a.modelMappingCacheRawPtr = rawPtr
 	a.modelMappingCacheRawLen = rawLen
 	a.modelMappingCacheRawSig = rawSig
+	a.modelMappingCacheRuntimeVersion = runtimeVersion
 	return mapping
 }
 
diff --git a/backend/internal/service/account_wildcard_test.go b/backend/internal/service/account_wildcard_test.go
index 6ce804bb16..15c5a66fa1 100644
--- a/backend/internal/service/account_wildcard_test.go
+++ b/backend/internal/service/account_wildcard_test.go
@@ -6,8 +6,31 @@ import (
 	"testing"
 
 	"github.com/Wei-Shaw/sub2api/internal/domain"
+	"github.com/Wei-Shaw/sub2api/internal/pkg/xai"
 )
 
+func TestGrokAccountModelMappingCacheInvalidatesWithRuntimeSettings(t *testing.T) {
+	original := xai.RuntimeModelMappingOptions()
+	t.Cleanup(func() { xai.SetRuntimeModelMappingOptions(original) })
+	account := &Account{Platform: PlatformGrok, Credentials: map[string]any{}}
+
+	xai.SetRuntimeModelMappingOptions(xai.ModelMappingOptions{})
+	requireMappedModel(t, account, "claude-sonnet-4-5", "claude-sonnet-4-5")
+
+	xai.SetRuntimeModelMappingOptions(xai.ModelMappingOptions{
+		DefaultText:          "grok-build-0.1",
+		EnableCrossClientMap: true,
+	})
+	requireMappedModel(t, account, "claude-sonnet-4-5", "grok-build-0.1")
+}
+
+func requireMappedModel(t *testing.T, account *Account, requested, expected string) {
+	t.Helper()
+	if actual := account.GetMappedModel(requested); actual != expected {
+		t.Fatalf("GetMappedModel(%q) = %q, want %q", requested, actual, expected)
+	}
+}
+
 func TestMatchWildcard(t *testing.T) {
 	tests := []struct {
 		name     string