Max plan subscriber rejected from opus[1m] — "not available for your account"

Description

On a Max plan ($200/month), attempting to use opus[1m] is rejected with:

Opus 4.6 with 1M context is not available for your account.
Learn more: https://code.claude.com/docs/en/model-config#extended-context-with-1m

The linked documentation explicitly states:

On Max, Team, and Enterprise plans, Opus is automatically upgraded to 1M context with no additional configuration.

This is different from #23432

Issue #23432 reports /context displaying 200k instead of 1M (a display/statusline bug). This issue is about the system actively denying 1M access at the account entitlement level. The error message confirms the account is not recognized as having 1M access — it's not just a display problem.

Steps to reproduce

1. Be on a Max plan ($200/month)
2. Open Claude Code
3. Run /model opus[1m]
4. Observe: "Opus 4.6 with 1M context is not available for your account"

Expected behavior

1M context should be available — per the documentation, Max plan includes it with no additional configuration.

Environment

• Claude Code v2.1.97
• macOS Darwin 25.3.0
• Model: claude-opus-4-6
• Plan: Max ($200/month)

Additional context

• /model opus works fine (but gives 200k context per #23432)
• /context shows 46.5k/200k tokens — confirming the 200k cap from #23432
• No CLAUDE_CODE_BLOCKING_LIMIT_OVERRIDE env var set
• CLAUDE_CODE_DISABLE_1M_CONTEXT is NOT set
• The documentation says "If you don't see it, try restarting your session" — restarting does not help

Related: #23432