[BUG] [1M] Opus 4.6 1M context unavailable on Max 5x — works on another machine with same account

Bug Description

Claude Code v2.1.76 on WSL2 shows 200k context window for Opus 4.6 instead of 1M, despite being on the Max 5x plan. Running /model opus[1m] returns a message saying the plan does not support the feature.

The same account on a different Windows machine has 1M context working correctly.

Steps to Reproduce

1. Install Claude Code v2.1.76 via npm install -g @anthropic-ai/claude-code
2. Sign in with a Max 5x account
3. Run /context — shows 200k max, not 1M
4. Run /model opus[1m] — returns plan not supported error

Expected Behavior

Per the 1M Context GA announcement and model configuration docs, Max plan users should automatically get 1M context for Opus 4.6 with no additional configuration.

Actual Behavior

• /context shows claude-opus-4-6 · Xk / 200k tokens
• /model opus[1m] returns a "plan does not support" error
• Credentials show rateLimitTier: "default_claude_max_5x" — re-authenticating produces the same result

Troubleshooting Already Attempted

• Signed out and back in multiple times
• Deleted ~/.claude/.credentials.json and re-authenticated (fresh token, same result)
• Fully uninstalled standalone installer, reinstalled via npm
• System clock is correct

Additional Context

• The same Max 5x account works correctly with 1M context on a different Windows machine (not WSL2)
• /btw slash command is also unavailable on this machine (returns "Unknown skill")
• Both machines are Windows — the working one runs Claude Code natively, the failing one runs it inside WSL2 (Ubuntu 24.04)
• This appears to be a server-side entitlement/feature-gating issue specific to the WSL2 client

Environment

• Claude Code: 2.1.76
• OS: Ubuntu 24.04.2 LTS on WSL2 (kernel 6.6.87.2-microsoft-standard-WSL2)
• Node: v20.19.3
• npm: 10.8.2
• Install method: npm global
• Plan: Max 5x ($100/mo)

Related Issues

• #26428 — Sonnet 1M disappeared after update
• #26557 — sonnet[1m] not available on Max despite docs
• #24208 — Context display shows 200k instead of 1M
• #33159 — /btw tip shown but command returns "Unknown skill"