[BUG] Max plan requires Usage Credits balance for 1M context — should be included

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?

Max plan users are required to have a Usage Credits balance to use 1M context
in Claude Code, even though 1M context should be included in the Max plan.

What Should Happen?

Max plan subscribers should be able to use Opus 4.8 with 1M context in Claude
Code without needing a separate Usage Credits balance.

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. Have an active Max plan subscription
2. Have $0.00 Usage Credits balance
3. Open Claude Code in VS Code
4. Set model to Opus 4.8 (1M context) via /model
5. Send any message
6. Error appears immediately: "Usage credits required for 1M context"

Workaround: Adding any amount to Usage Credits balance resolves the error,
but this should not be required for Max plan users.

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.156 (Claude Code)

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

VS Code integrated terminal

Additional Information

_No response_