diff --git a/transformers/request-anthropic.js b/transformers/request-anthropic.js
index 0c88377..50b9844 100644
--- a/transformers/request-anthropic.js
+++ b/transformers/request-anthropic.js
@@ -163,6 +163,7 @@ export function getAnthropicHeaders(authHeader, clientHeaders = {}, isStreaming
     'accept': 'application/json',
     'content-type': 'application/json',
     'anthropic-version': clientHeaders['anthropic-version'] || '2023-06-01',
+    'authorization': authHeader || '',
     'x-api-provider': 'anthropic',
     'x-factory-client': 'cli',
     'x-session-id': sessionId,
@@ -170,14 +171,6 @@ export function getAnthropicHeaders(authHeader, clientHeaders = {}, isStreaming
     'user-agent': getUserAgent(),
     'x-stainless-timeout': '600',
     'connection': 'keep-alive'
-  };
-
-  // Prefer client-provided x-api-key for anthropic endpoint format
-  if (clientHeaders['x-api-key']) {
-    headers['x-api-key'] = clientHeaders['x-api-key'];
-  } else if (authHeader) {
-    // If no client x-api-key, use authorization header (from FACTORY_API_KEY or refresh token)
-    headers['authorization'] = authHeader;
   }
 
   // Handle anthropic-beta header based on reasoning configuration