diff --git a/backend/internal/pkg/antigravity/oauth.go b/backend/internal/pkg/antigravity/oauth.go
index 8a8bed92d9..7c963d9e51 100644
--- a/backend/internal/pkg/antigravity/oauth.go
+++ b/backend/internal/pkg/antigravity/oauth.go
@@ -50,7 +50,7 @@ const (
 )
 
 // defaultUserAgentVersion 可通过环境变量 ANTIGRAVITY_USER_AGENT_VERSION 配置，默认 1.20.5
-var defaultUserAgentVersion = "1.20.5"
+var defaultUserAgentVersion = "1.21.9"
 
 // defaultClientSecret 可通过环境变量 ANTIGRAVITY_OAUTH_CLIENT_SECRET 配置
 var defaultClientSecret = "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"
diff --git a/backend/internal/pkg/antigravity/oauth_test.go b/backend/internal/pkg/antigravity/oauth_test.go
index 3a093fe657..9850af17e1 100644
--- a/backend/internal/pkg/antigravity/oauth_test.go
+++ b/backend/internal/pkg/antigravity/oauth_test.go
@@ -690,7 +690,7 @@ func TestConstants_值正确(t *testing.T) {
 	if RedirectURI != "http://localhost:8085/callback" {
 		t.Errorf("RedirectURI 不匹配: got %s", RedirectURI)
 	}
-	if GetUserAgent() != "antigravity/1.20.5 windows/amd64" {
+	if GetUserAgent() != "antigravity/1.21.9 windows/amd64" {
 		t.Errorf("UserAgent 不匹配: got %s", GetUserAgent())
 	}
 	if SessionTTL != 30*time.Minute {