[BUG] opusplan fails with 400 error when ANTHROPIC_DEFAULT_OPUS_MODEL points to 4.7 using the new thinking API format

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?

Using /model opusplan crashes with a 400 API error when ANTHROPIC_DEFAULT_OPUS_MODEL is set to a model that requires the new adaptive thinking API format (e.g. claude-opus-4-7).

Claude Code sends thinking.type.enabled but newer models require thinking.type.adaptive + output_config.effort. Models that have adopted the new thinking API require thinking: { type: "adaptive" } + output_config: { effort: "..." } instead.

What Should Happen?

opusplan works with claude-opus-4-7, using the new thinking API format. Models that have adopted the new thinking API require thinking: { type: "adaptive" } + output_config: { effort: "..." } instead.

Error Messages/Logs

API Error: 400
{"type":"error","error":{"type":"invalid_request_error","message":"\"thinking.type.enabled\" is not supported for this model. Use \"thinking.type.adaptive\" and \"output_config.effort\" to control thinking behavior."},"request_id":"req_011Ca8FdBuWpqDJZZbMQnhiS"}

Steps to Reproduce

1. Set ANTHROPIC_DEFAULT_OPUS_MODEL=claude-opus-4-7 via export ANTHROPIC_DEFAULT_OPUS_MODEL=claude-opus-4-7 or in ~/.zshrc
2. run claude > /model opusplan
3. ask Claude to enter planning mode i.e. "go into planning mode" > 400 error

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.109

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_