[BUG] Sonnet 4.6 incorrectly requires 1M context credits on Pro plan (Desktop)

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?

Selecting Sonnet 4.6 in Claude Code (Desktop entrypoint) on a Pro plan returns:

API Error: Usage credits required for 1M context · turn on usage credits at claude.ai/settings/usage, or use --model to switch to standard context

I am on the Pro plan and have not opted into pay-as-you-go usage credits. Sonnet 4.6 should use the standard 200K context window that Pro covers, not the 1M variant.

Repro:

1. Open Claude Code (Desktop, version 2.1.150)
2. /model claude-sonnet-4-6
3. Send any prompt (e.g. "hello")
4. Error appears immediately.

Confirmed:

• Opus 4.7 works fine on the same machine, same session.
• Sonnet 4.6 works fine on a second computer signed into the same account.
• Plan usage: 15% of 5-hour limit, 14% of weekly — nowhere near any cap.
• autoCompactWindow in settings.json is 150000 (below 200K).
• No CLAUDE_CONTEXT_* / 1M-related env variables are set.
• Already tried: updating from 2.1.34 → 2.1.150, /logout + /login.
• Workaround: Sonnet 4.5 works.

Environment:

• Claude Code: 2.1.150
• Entrypoint: claude-desktop
• OS: Windows 11
• Plan: Pro

What Should Happen?

Sonnet 4.6 should respond normally using the standard 200K context window covered by the Pro plan, the same way it does on my other computer signed into the same account, and the same way Opus 4.7 works on this machine.

Error Messages/Logs

API Error: Usage credits required for 1M context · turn on usage credits at claude.ai/settings/usage, or use --model to switch to standard context

Steps to Reproduce

1. Open Claude Code in Claude Desktop (version 2.1.150 on Windows 11, Pro plan).
2. Run /model claude-sonnet-4-6 to select Sonnet 4.6.
3. Send any prompt, e.g. hello.
4. Observe the error: "Usage limit reached — API Error: Usage credits required for 1M context..."

Expected: Sonnet 4.6 responds using standard 200K context covered by Pro.
Actual: Error demanding usage credits for 1M context.

Note: switching to /model claude-opus-4-7 in the same session works fine, and Sonnet 4.6 works on a different computer signed into the same account.

Claude Model

Sonnet (default)

Is this a regression?

No, this never worked

Last Working Version

_No response_

Claude Code Version

2.1.150 (Claude Code)

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

PowerShell

Additional Information

Configuration (~/.claude/settings.json):

{
  "autoCompactWindow": 150000,
  "autoUpdatesChannel": "latest",
  "theme": "dark",
  "autoCompactEnabled": true,
  "enabledPlugins": {
    "frontend-design@claude-plugins-official": true
  }
}

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