Graceful model version transitions

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 Claude Code updates, older model versions (e.g. claude-opus-4-5-20250514) can disappear from the available model list without warning. Users who preferred the previous model have no migration path — the model simply stops being selectable.

What Should Happen?

1. Reasonable overlap period — Maintain both the previous and new model versions for up to a year. Users need time to evaluate the new model in their actual workflows before losing access to the previous one.
2. Changelog visibility — Surface model availability changes in release notes

Error Messages/Logs

Steps to Reproduce

• Upgrade Claude Code → previous model silently removed from /model list
• /model claude-opus-4-5-20250514 → "Model not found"
• No deprecation warning, no migration period

Claude Model

Not sure / Multiple models

Is this a regression?

Yes, this worked in a previous version

Last Working Version

2.1.30

Claude Code Version

2.1.50

Platform

Anthropic API

Operating System

Other Linux

Terminal/Shell

Xterm

Additional Information

This is disruptive when:

• The replacement model has different strengths/weaknesses (not a strict upgrade)
• There's no changelog or notice explaining the change