[BUG] Sends effort parameter when using custom model

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?

When I use Claude code with a custom client (AWS Bedrock backend), all prompts fail with the following error message:

API Error: 400 >{"errorCode":"CUSTOM_CLIENT","errorName":"LanguageModelService:LlmHttpClientError","errorInstanceId":"XXXX","parameters":{"modelCreator":"Optional[ANTHROPIC]","responseBody":" Optional[{\"message\":\"This model does not support the effort parameter.\"}]","modelBackendId":"Optional[BEDROCK]","errorType":"Optional[VALIDATION_EXCEPTION]","errorMessage":"Optional[This model does not support the effort parameter.]","errorCode":"Optional.empty","statusCode":"400"}}

What Should Happen?

Claude should send its response.

Error Messages/Logs

API Error: 400 >{"errorCode":"CUSTOM_CLIENT","errorName":"LanguageModelService:LlmHttpClientError","errorInstanceId":"XXXX","parameters":{"modelCreator":"Optional[ANTHROPIC]","responseBody":" Optional[{\"message\":\"This model does not support the effort parameter.\"}]","modelBackendId":"Optional[BEDROCK]","errorType":"Optional[VALIDATION_EXCEPTION]","errorMessage":"Optional[This model does not support the effort parameter.]","errorCode":"Optional.empty","statusCode":"400"}}

Steps to Reproduce

1. Install latest Claude code.
2. Point it to a custom model.
3. Send a prompt.

Claude Model

Sonnet (default)

Is this a regression?

Yes, this worked in a previous version

Last Working Version

2.1.112

Claude Code Version

2.1.141 (Claude Code)

Platform

AWS Bedrock

Operating System

Ubuntu/Debian Linux

Terminal/Shell

Other

Additional Information

Previously fixed in https://github.com/anthropics/claude-code/issues/30795, but now fails. I only have access to the specified custom model so this failure entirely blocks me from upgrading Claude code.