Claude Opus 4.5 requests return error 400
Nobody has claimed this yet.
Assessment
- Difficulty
- 3/5
- Estimated time
- 1-2 days
- Newbie friendliness
- 35/100
Research direction
Start with the attached Copilot for Xcode log and the Agent request path used when Claude Opus 4.5 is selected. Inspect the outgoing request body, especially the thinking blocks identified in the 400 response, and compare it with the model's expected format. Done means an Agent request with Claude Opus 4.5 is accepted instead of returning this error.
Written by the indexing model from the issue text.
Description
Describe the bug
When making an Agent request using Claude Opus 4.5 I have been getting the same error message all day:
Sorry, an error occurred while generating a response. Details: unhandled status from server: 400 {"error": {"message": "messages.1.content.0.thinking: each thinking block must contain thinking","code":"invalid_request_body"}} Request ID: xxx
Versions
- Copilot for Xcode: 0.46.0
- Xcode: 26.2.0
- macOS: 26.2
Steps to reproduce
- Select Claude Opus 4.5 as model
- Select Agent mode
- Enter prompt
- Error is returned
Screenshots
Logs
github-copilot-for-xcode.log
Additional context
Attempted the following to try and resolve:
- Signing out then back in
- Cleaning DerivedData/Copilot cache
- Restarting device
- Uninstalling / Reinstalling Copilot
- Dominant language
- Swift
- Stars
- 6.3k
- Forks
- 2k
- Avg merge
- 3d 21h
- Merged PRs (30d)
- 2
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
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