[BUG] Claude Code desktop app sends invalid model IDs for subscription-authenticated users (400 error on all models)

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?

Claude Code desktop app sends bare API model IDs (e.g. claude-opus-4-8)
to the subscription backend, which requires us.anthropic.*-prefixed IDs.
Every model fails with 400 error. Happens on fresh install. All models tried.

What Should Happen?

Subscription-authenticated users should be able to use Claude Code desktop
app normally. Model IDs should be translated correctly for the subscription
backend, or the subscription backend should accept standard API model IDs.

Error Messages/Logs

API Error (claude-opus-4-8): 400 The provided model identifier is invalid..
  Try switching to us.anthropic.claude-opus-4-7.
API Error (claude-sonnet-4-6): 400 The provided model identifier is invalid.. Try switching to us.anthropic.claude-sonnet-4-5-20250929-v1:0.
An API error occurred
API Error (claude-opus-4-6): 400 The provided model identifier is invalid.. Try switching to us.anthropic.claude-opus-4-5-20251101-v1:0.
API Error (claude-sonnet-5): 400 The provided model identifier is invalid.. Try switching to us.anthropic.claude-sonnet-4-6.

Steps to Reproduce

1. Log into Claude Code desktop app using Claude.ai subscription (not API key)
2. Open any project or start new conversation
3. Send any message (e.g. "Hello")
4. 400 error returned immediately on every model
5. Reproduced across all available models in /model list
6. Reproduced after full uninstall and reinstall

Claude Model

Not sure / Multiple models

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

1.17377.2

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Other

Additional Information

_No response_