add model param

Author: devalog

fern/snippets/ask-fern-config.mdx

@@ -50,3 +50,12 @@ ai-search:
   See Anthropic's [prompting guide](https://docs.anthropic.com/en/docs/build-with-claude/prompt-engineering/overview) for ideas and examples.
 </ParamField>
 
+<ParamField path="ai-search.model" type="string" required={false} toc={true}>
+  The AI model to use for Ask Fern responses. Options:
+  - `claude-3.5` - Claude 3.5 Sonnet
+  - `claude-3.7` - Claude 3.7 Sonnet (default)
+  - `claude-4` - Claude 4 Opus
+  - `command-a` - Cohere Command A
+  
+  If not specified, Ask Fern uses `claude-3.7`.
+</ParamField>