Error 400 “Invalid signature in thinking block”
Some users encounter the following error:
API Error: 400 {"type":"error","error":{"type":"invalid_request_error","message":"messages.1.content.0: Invalid `signature` in
`thinking` block"},"request_id":"req_011CYc2cTJr6BJ6Tti3qfPhf"}Cause
This error occurs because the thinking block signature in the current session context is inconsistent with the server side. This typically happens when the session state changes.
Solution
Depending on whether you need to preserve the current session context, there are two approaches:
Method 1: Restart Claude Directly (without preserving context)
When the session context is not important, simply use the /clear command or restart Claude Code to resolve the issue.
Method 2: Preserve the Session Context
If you need to keep your current session content, choose the appropriate action based on how you use Claude Code:
Command Line (CLI) Users
Export the session
Use the /export command to copy the current session content to your clipboard.
Clear the session
Use the /clear command to clear the current session.
Restore the session
Paste the clipboard content back into the input box to restore the context.
