diff --git a/src/mcpd/src/services/llm/adapters/anthropic.ts b/src/mcpd/src/services/llm/adapters/anthropic.ts
index 4f2f185..a8ddd5f 100644
--- a/src/mcpd/src/services/llm/adapters/anthropic.ts
+++ b/src/mcpd/src/services/llm/adapters/anthropic.ts
@@ -182,9 +182,15 @@ export class AnthropicAdapter implements LlmAdapter {
   }
 
   private headers(ctx: InferContext): Record<string, string> {
+    // Claude subscription / Claude Code keys are OAuth tokens (`sk-ant-oat…`)
+    // and authenticate via Bearer, not x-api-key — mirror the mcplocal client
+    // adapter so an OAuth key works as a server-side fallback Llm.
+    const isOAuth = ctx.apiKey.startsWith('sk-ant-oat');
     return {
       'Content-Type': 'application/json',
-      'x-api-key': ctx.apiKey,
+      ...(isOAuth
+        ? { Authorization: `Bearer ${ctx.apiKey}` }
+        : { 'x-api-key': ctx.apiKey }),
       'anthropic-version': ANTHROPIC_VERSION,
     };
   }