diff --git a/config.example.yaml b/config.example.yaml
index fb29477d9b..3718a07a1e 100644
--- a/config.example.yaml
+++ b/config.example.yaml
@@ -212,11 +212,11 @@ nonstream-keepalive-interval: 0
 #       - name: "kimi-k2.5"
 #         alias: "claude-opus-4.66"
 
-# Vertex API keys (Vertex-compatible endpoints, use API key + base URL)
+# Vertex API keys (Vertex-compatible endpoints, base-url is optional)
 # vertex-api-key:
 #   - api-key: "vk-123..."                        # x-goog-api-key header
 #     prefix: "test"                              # optional: require calls like "test/vertex-pro" to target this credential
-#     base-url: "https://example.com/api"         # e.g. https://zenmux.ai/api
+#     base-url: "https://example.com/api"         # optional, e.g. https://zenmux.ai/api; falls back to Google Vertex when omitted
 #     proxy-url: "socks5://proxy.example.com:1080" # optional per-key proxy override
 #     # proxy-url: "direct" # optional: explicit direct connect for this credential
 #     headers:
diff --git a/internal/api/handlers/management/config_lists.go b/internal/api/handlers/management/config_lists.go
index 503179c11c..083d4e31ef 100644
--- a/internal/api/handlers/management/config_lists.go
+++ b/internal/api/handlers/management/config_lists.go
@@ -509,8 +509,12 @@ func (h *Handler) PutVertexCompatKeys(c *gin.Context) {
 	}
 	for i := range arr {
 		normalizeVertexCompatKey(&arr[i])
+		if arr[i].APIKey == "" {
+			c.JSON(400, gin.H{"error": fmt.Sprintf("vertex-api-key[%d].api-key is required", i)})
+			return
+		}
 	}
-	h.cfg.VertexCompatAPIKey = arr
+	h.cfg.VertexCompatAPIKey = append([]config.VertexCompatKey(nil), arr...)
 	h.cfg.SanitizeVertexCompatKeys()
 	h.persist(c)
 }
diff --git a/internal/config/config.go b/internal/config/config.go
index 7bd137e0db..a11c741efc 100644
--- a/internal/config/config.go
+++ b/internal/config/config.go
@@ -621,7 +621,7 @@ func LoadConfigOptional(configFile string, optional bool) (*Config, error) {
 	// Sanitize Gemini API key configuration and migrate legacy entries.
 	cfg.SanitizeGeminiKeys()
 
-	// Sanitize Vertex-compatible API keys: drop entries without base-url
+	// Sanitize Vertex-compatible API keys.
 	cfg.SanitizeVertexCompatKeys()
 
 	// Sanitize Codex keys: drop entries without base-url
diff --git a/internal/config/vertex_compat.go b/internal/config/vertex_compat.go
index 5f6c7c88cd..c13e438df7 100644
--- a/internal/config/vertex_compat.go
+++ b/internal/config/vertex_compat.go
@@ -20,9 +20,9 @@ type VertexCompatKey struct {
 	// Prefix optionally namespaces model aliases for this credential (e.g., "teamA/vertex-pro").
 	Prefix string `yaml:"prefix,omitempty" json:"prefix,omitempty"`
 
-	// BaseURL is the base URL for the Vertex-compatible API endpoint.
+	// BaseURL optionally overrides the Vertex-compatible API endpoint.
 	// The executor will append "/v1/publishers/google/models/{model}:action" to this.
-	// Example: "https://zenmux.ai/api" becomes "https://zenmux.ai/api/v1/publishers/google/models/..."
+	// When empty, requests fall back to the default Vertex API base URL.
 	BaseURL string `yaml:"base-url,omitempty" json:"base-url,omitempty"`
 
 	// ProxyURL optionally overrides the global proxy for this API key.
@@ -71,10 +71,6 @@ func (cfg *Config) SanitizeVertexCompatKeys() {
 		}
 		entry.Prefix = normalizeModelPrefix(entry.Prefix)
 		entry.BaseURL = strings.TrimSpace(entry.BaseURL)
-		if entry.BaseURL == "" {
-			// BaseURL is required for Vertex API key entries
-			continue
-		}
 		entry.ProxyURL = strings.TrimSpace(entry.ProxyURL)
 		entry.Headers = NormalizeHeaders(entry.Headers)
 		entry.ExcludedModels = NormalizeExcludedModels(entry.ExcludedModels)