diff --git a/src/engine/anthropic.ts b/src/engine/anthropic.ts
index 7dbc5936..8c7d4c51 100644
--- a/src/engine/anthropic.ts
+++ b/src/engine/anthropic.ts
@@ -37,9 +37,14 @@ export class AnthropicEngine implements AiEngine {
       system: systemMessage,
       messages: restMessages,
       temperature: 0,
-      top_p: 0.1,
       max_tokens: this.config.maxTokensOutput
     };
+
+    // add top_p for non-4.5 models
+    if (!/claude.*-4-5/.test(params.model)) {
+      params.top_p = 0.1;
+    }
+
     try {
       const REQUEST_TOKENS = messages
         .map((msg) => tokenCount(msg.content as string) + 4)