diff --git a/v2/src/core/agent-loop.mjs b/v2/src/core/agent-loop.mjs
index 36e7a3f..49e9a56 100644
--- a/v2/src/core/agent-loop.mjs
+++ b/v2/src/core/agent-loop.mjs
@@ -240,7 +240,8 @@ async function callAnthropic(model, state, toolDefs, settings, stream) {
         body.thinking = { type: 'enabled', budget_tokens: settings.thinkingBudget || 10000 };
     }
 
-    const res = await fetch('https://api.anthropic.com/v1/messages', {
+    const baseUrl = process.env.ANTHROPIC_BASE_URL || 'https://api.anthropic.com';
+    const res = await fetch(`${baseUrl}/v1/messages`, {
         method: 'POST',
         headers: {
             'Content-Type': 'application/json',