[BUG] Opusplan mode falls back to Sonnet 4.5 instead of 4.6 on AWS Bedrock

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 using /model opusplan with AWS Bedrock, Claude Code falls back to Sonnet 4.5
(us.anthropic.claude-sonnet-4-5-20250929-v1:0) instead of using Sonnet 4.6 as expected.
Individual model selections (/model opus and /model sonnet) correctly use the 4.6 versions.

What Should Happen?

Opusplan mode should display:
Set model to Opus 4.6 in plan mode, else Sonnet 4.6

And the statusline should show claude-sonnet-4-6 (or the Bedrock equivalent) when not in plan mode.

Error Messages/Logs

Steps to Reproduce

1. Configure Claude Code for AWS Bedrock with a profile that has access to both Opus 4.6 and Sonnet 4.6
2. Run /model opusplan
3. Observe the model shown in the statusline

Claude Model

None

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.76

Platform

AWS Bedrock

Operating System

macOS

Terminal/Shell

Other

Additional Information

<img width="1190" height="419" alt="Image" src="https://github.com/user-attachments/assets/f88b4d52-269f-4bde-86d9-4c32c4ec1022" />

<img width="643" height="268" alt="Image" src="https://github.com/user-attachments/assets/26c6b318-4bf9-4de9-b26a-f4f1c920653d" />

<img width="466" height="168" alt="Image" src="https://github.com/user-attachments/assets/5a850973-ede0-48e1-a507-e91c188fc0b5" />