Unclear how 1M context billing works on Max subscription

Question

When selecting a 1M context model (e.g. claude-opus-4-6[1m]), Claude Code shows "Billed as extra usage." However, the actual billing behavior on a Max subscription is unclear.

Observed behavior (Max 5x plan)

• Activated claude-opus-4-6[1m] in a session
• Extra Usage ($24.35/$42.50) did not change over ~50 minutes of active use
• Session quota went from 8% → 67% in that time (much faster than normal)
• Weekly quota went from 26% → 31%
• Context was ~32% filled (~320K tokens)

Questions

1. Does 1M context on Max consume Extra Usage or regular quota? The "Billed as extra usage" message suggests the former, but our Extra Usage balance didn't change. Regular quota consumed faster instead.

1. Why is quota consumed faster? Two possible mechanisms — unclear which (or both) apply:

• Larger context = more tokens per message. With ~320K context, every roundtrip naturally sends more tokens. This alone would explain faster quota drain without any special multiplier.
• 2x rate multiplier. API pricing doubles when a request exceeds 200K input tokens. Does Max subscription apply a similar penalty multiplier on top of the naturally higher token count?

1. What does "Billed as extra usage" actually mean for Max subscribers? If it just means faster quota consumption (not actual Extra Usage charges), the message is misleading.

1. Is there documentation on this? We couldn't find clear answers for how the >200K API pricing threshold translates to subscription-based usage.

Environment

• Claude Code (latest)
• Max 5x subscription
• Model: claude-opus-4-6[1m]

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