[BUG] Claude Code is using older models in the background
Status Fixed / completed
Maintainer reply ✓ Yes — dicksontsai
Activity 5 comments · opened Sep 10, 2025 · closed Sep 11, 2025
💡 Likely answer: A maintainer (dicksontsai, collaborator)
responded on this thread — see the highlighted reply below.
Preflight Checklist
- [x] I have searched existing issues and this hasn't been reported yet
- [x] This is a single bug report (please file separate reports for different bugs)
- [x] I am using the latest version of Claude Code
What's Wrong?
I am on Anthropic's Pro plan and Claude Code is advertised to use Sonnet on this subscription. Nevertheless, it turns out that Sonnet is switched to Haiku in the background without notification. See screenshot from my recent session:
<img width="1246" height="249" alt="Image" src="https://github.com/user-attachments/assets/a1045f2c-f46f-4f72-97f9-75330271138c" />
What Should Happen?
Claude Code should use the model configured in /models or at least be more transparent about model switching.
Error Messages/Logs
> /pr-comments is fetching PR comments… 285 think deeply and evaluate whether they make sense
⎿ API Error: 400
{"type":"error","error":{"type":"invalid_request_error","message":"'claude-3-5-haiku-20241022' does
not support thinking."},"request_id":"req_011CT1E5qiHVNyfW1N4fxfcd"}
> /model
╭───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────╮
│ │
│ Select Model │
│ Switch between Claude models. Applies to this session and future Claude Code sessions. For custom model names, specify with --model. │
│ │
│ ❯ 1. Sonnet Sonnet 4 for daily use ✔ │
│ │
│ Want Opus 4.1? Run /upgrade to upgrade to MaxSteps to Reproduce
- Run Claude Code on Pro plan
- Prompt it to think deeply about a problem
- API Error surfaces saying that Haiku doesn't support thinking
Since this is happening in the background, the problem might not be constantly reproducible
Claude Model
Sonnet (default)
Is this a regression?
Yes, this worked in a previous version
Last Working Version
_No response_
Claude Code Version
v1.0.110
Platform
Anthropic API
Operating System
macOS
Terminal/Shell
VS Code integrated terminal
Additional Information
_No response_
5 Comments
Found 3 possible duplicate issues:
This issue will be automatically closed as a duplicate in 3 days.
🤖 Generated with Claude Code
I have not setup my environment to use Haiku, so this behavior is completely unexpected.
Claude Code uses Haiku for lots of minor preprocessing and validation outside the main model calls. I'm not an expert, but that might explain what you're seeing.
/pr-commentsis a built-in command (and the only built-in command) that specifically uses Haiku for processing.You're welcome to define your own version of
/pr-commentsthat uses the main conversation's model (Sonnet in your case): https://docs.anthropic.com/en/docs/claude-code/slash-commands#custom-slash-commandsThis issue has been automatically locked since it was closed and has not had any activity for 7 days. If you're experiencing a similar issue, please file a new issue and reference this one if it's relevant.