[BUG] Sonnet 1M context window unavailable on Max 20x subscription - regression from ~2 weeks ago

What's wrong

The sonnet[1m] model option appears in the model selector but returns an error when selected: "The long context beta is not yet available for this subscription."

This feature was working approximately 2 weeks ago and stopped without any notification. I'm on the Max 20x plan (highest paid tier).

Environment:

• Claude Code version: 2.0.75
• VS Code extension version: 2.0.75
• OS: macOS Sequoia 15.x
• Subscription: Max 20x plan

What should happen

Max 20x subscribers should have access to the 1M token context window for Sonnet, as we did previously. At minimum, the option should not appear in the model selector if it's not available.

Steps to reproduce

1. Open Claude Code (VS Code extension or CLI) as a Max 20x subscriber
2. Run /model sonnet[1m] or select from model picker
3. Send any message
4. Error appears: "The long context beta is not yet available for this subscription."

Additional context

• Similar to closed issue #10219 but this is a regression - it was working before
• Heavy MCP server usage (45K+ tokens at startup) makes 200K context insufficient
• This is workflow-breaking for legitimate Max subscribers
• No communication was sent about this change