[BUG]

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?

Model switcher in desktop app drops [1m] suffix, causing context window to silently shrink from 1M to 200K and losing conversation history

What Should Happen?

When switching models via the UI model picker (e.g. from Opus to Sonnet), the [1m] context window suffix should be preserved. If I had opus[1m] (1M context) and switch to Sonnet via UI, it should become sonnet[1m], not just sonnet.

Error Messages/Logs

No error message — the context silently shrinks from 1M to 200K tokens.

Before switch: model = "opus[1m]", context used ~700K tokens
After UI switch to Sonnet: model = "sonnet" (suffix dropped)
Result: 500K tokens of conversation history lost, cannot be recovered.

Global settings.json had: "model": "opus[1m]"
UI model switcher overwrote it to: "sonnet" (without [1m])

The /model chat command works correctly:
  /model sonnet[1m]  → keeps 1M context ✓
  UI picker → Sonnet  → drops to 200K   ✗

Steps to Reproduce

1. Set global settings: "model": "opus[1m]" in ~/.claude/settings.json
2. Start a new session — context window is 1M tokens ✓
3. Build up conversation to ~500-700K tokens
4. Use the UI model picker (top of the window) to switch to Sonnet
5. Observe: model is now "sonnet" without [1m] suffix
6. Context window shrinks to 200K — all content above 200K is lost
7. Compare: typing /model sonnet[1m] in chat preserves the 1M context correctly

Expected: UI picker should carry over the [1m] suffix when switching models
Actual: UI picker writes bare model name, losing extended context configuration

Platform: Windows 11 desktop app

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

Claude 1.9659.2 (390d6c) 2026-05-28T21:50:01.000Z

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_