diff --git a/llm/transformer/anthropic/outbound_convert.go b/llm/transformer/anthropic/outbound_convert.go
index f10b2aef9..98697d736 100644
--- a/llm/transformer/anthropic/outbound_convert.go
+++ b/llm/transformer/anthropic/outbound_convert.go
@@ -120,8 +120,15 @@ func buildBaseRequest(chatReq *llm.Request, config *Config) *MessageRequest {
 		MaxTokens:   resolveMaxTokens(chatReq),
 	}
 
+	var userID string
 	if chatReq.Metadata != nil && chatReq.Metadata["user_id"] != "" {
-		req.Metadata = &AnthropicMetadata{UserID: chatReq.Metadata["user_id"]}
+		userID = chatReq.Metadata["user_id"]
+	} else if chatReq.User != nil && *chatReq.User != "" {
+		userID = *chatReq.User
+	}
+
+	if userID != "" {
+		req.Metadata = &AnthropicMetadata{UserID: shared.SanitizeUserID(userID)}
 	}
 
 	// DeepSeek Anthropic format supports output_config.effort. When reasoning_effort
diff --git a/llm/transformer/doubao/outbound.go b/llm/transformer/doubao/outbound.go
index fbd4e7803..eb4535309 100644
--- a/llm/transformer/doubao/outbound.go
+++ b/llm/transformer/doubao/outbound.go
@@ -17,6 +17,7 @@ import (
 	"github.com/looplj/axonhub/llm/internal/pkg/xurl"
 	"github.com/looplj/axonhub/llm/transformer"
 	"github.com/looplj/axonhub/llm/transformer/openai"
+	"github.com/looplj/axonhub/llm/transformer/shared"
 )
 
 // Config holds all configuration for the Doubao outbound transformer.
@@ -142,8 +143,18 @@ func (t *OutboundTransformer) TransformRequest(
 		RequestID: "",
 	}
 
-	if llmReq.Metadata != nil {
-		doubaoReq.UserID = llmReq.Metadata["user_id"]
+	var userID string
+	if llmReq.Metadata != nil && llmReq.Metadata["user_id"] != "" {
+		userID = llmReq.Metadata["user_id"]
+	} else if llmReq.User != nil && *llmReq.User != "" {
+		userID = *llmReq.User
+	}
+
+	if userID != "" {
+		doubaoReq.UserID = shared.SanitizeUserID(userID)
+	}
+
+	if llmReq.Metadata != nil && llmReq.Metadata["request_id"] != "" {
 		doubaoReq.RequestID = llmReq.Metadata["request_id"]
 	}
 
diff --git a/llm/transformer/shared/userid.go b/llm/transformer/shared/userid.go
new file mode 100644
index 000000000..02eaf4809
--- /dev/null
+++ b/llm/transformer/shared/userid.go
@@ -0,0 +1,35 @@
+package shared
+
+import "strings"
+
+// SanitizeUserID ensures the user ID matches common platform constraints:
+// ^[a-zA-Z0-9_-]{6,128}$
+func SanitizeUserID(userID string) string {
+	if userID == "" {
+		return ""
+	}
+
+	var sb strings.Builder
+	for _, c := range userID {
+		if (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') || (c >= '0' && c <= '9') || c == '_' || c == '-' {
+			sb.WriteRune(c)
+		} else {
+			sb.WriteRune('_')
+		}
+	}
+
+	sanitized := sb.String()
+
+	if len(sanitized) < 6 {
+		sanitized = "user_" + sanitized
+		if len(sanitized) < 6 {
+			sanitized = sanitized + strings.Repeat("_", 6-len(sanitized))
+		}
+	}
+
+	if len(sanitized) > 128 {
+		sanitized = sanitized[:128]
+	}
+
+	return sanitized
+}
diff --git a/llm/transformer/zai/outbound.go b/llm/transformer/zai/outbound.go
index dfc69df8f..af5765f38 100644
--- a/llm/transformer/zai/outbound.go
+++ b/llm/transformer/zai/outbound.go
@@ -129,8 +129,18 @@ func (t *OutboundTransformer) TransformRequest(
 		RequestID: "",
 	}
 
-	if llmReq.Metadata != nil {
-		zaiReq.UserID = llmReq.Metadata["user_id"]
+	var userID string
+	if llmReq.Metadata != nil && llmReq.Metadata["user_id"] != "" {
+		userID = llmReq.Metadata["user_id"]
+	} else if llmReq.User != nil && *llmReq.User != "" {
+		userID = *llmReq.User
+	}
+
+	if userID != "" {
+		zaiReq.UserID = shared.SanitizeUserID(userID)
+	}
+
+	if llmReq.Metadata != nil && llmReq.Metadata["request_id"] != "" {
 		zaiReq.RequestID = llmReq.Metadata["request_id"]
 	}