[BUG] Desktop app automatically switches model from Opus to Sonnet via /model command (Max subscription)

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?

On Claude Desktop app (macOS) with Max subscription, the model is frequently and automatically switched from Opus 4.6 (1M context) back to Sonnet.

Critically, this is not just a UI display issue — a /model command is automatically sent in the conversation, producing the message "Set model to claude-sonnet-4-6". The user did not initiate this command. This started after a recent update around March 25-27, 2026.

Steps to Reproduce

Scenario 1: Switching between Code and Chat tabs

1. Select Opus from the model dropdown in Code tab
2. Switch to the Chat tab
3. Switch back to the Code tab
4. A /model command is automatically sent, switching the model to Sonnet

Scenario 2: Navigating to Settings/Usage

1. Select Opus from the model dropdown
2. Click the avatar (bottom-left) → view Usage / Settings
3. Navigate back to the conversation
4. Model has reverted to Sonnet

Scenario 3: During normal usage

1. Select Opus from the model dropdown
2. Use Claude Code for a while
3. The model silently switches back to Sonnet without any user action on the model selector

The issue is intermittent — it does not happen every single time, but frequently enough to be disruptive.

What Should Happen?

Model selection should persist as Opus until the user explicitly changes it. No /model command should be sent without user action.

Error Messages/Logs

No error messages. A /model command is automatically triggered, returning "Set model to claude-sonnet-4-6".

Claude Model

Opus 4.6 (1M context) — model ID: claude-opus-4-6[1m]

Is this a regression?

Yes, this started around March 25-27, 2026.

Claude Code Version

Desktop app version: 1.1.9310

Platform

Anthropic API

Operating System

macOS 26.4 (Build 25E246)

Terminal/Shell

N/A (using Claude Code within Desktop app)

Additional Information

• ~/.claude/settings.json has "model": "claude-opus-4-6[1m]" configured, but does not prevent the reset
• Users may not notice the silent switch, ending up using Sonnet unintentionally