Confusing billing for Sonnet 4.6 1M context: 'extra usage' despite available plan tokens

Summary

The model picker in Claude Code lets users select "Sonnet 4.6 (1M context)" without making it clear that this variant draws from a separate "extra usage" pool rather than the normal plan budget. Users with significant plan tokens remaining are silently blocked or billed extra, which feels like a foot-gun.

What happened

• Active plan with meaningful token budget remaining.
• Selected Sonnet 4.6 with 1M context window via /model.
• Ran into "extra usage required" / degraded behavior despite having plan tokens left.
• Switched to Opus 4.6 (1M context) and it worked normally on the same plan.

The confusion: why does Sonnet 4.6 1M require "extra usage" when Opus 4.6 1M does not, on the same plan and same remaining budget? And why isn't this surfaced in the /model picker before the selection commits?

Why it feels like a foot-gun

1. The /model menu shows "Sonnet 4.6 (1M context)" as a normal option with no indication it's metered differently than other variants in the same list.
2. There's no pre-flight warning ("this model draws from extra-usage pool, continue?") before switching.
3. The failure mode is not a clear "you need to enable extra usage" dialog — it's ambiguous degraded behavior that users interpret as the 1M context feature being broken.
4. Opus 4.6 1M behaving differently from Sonnet 4.6 1M on the same plan is counterintuitive — users reasonably expect "1M context" to be one feature with one billing rule across model tiers.

Requested fixes

• Label the picker. Show which model variants draw from plan budget vs. extra-usage in /model, inline, before selection.
• Pre-flight warning. If a user selects a variant that will consume extra-usage, surface a one-time confirmation with the actual rate.
• Consistent rules across tiers. Either both Sonnet and Opus 1M context cost extra, or neither does. The asymmetry is the root of the confusion.
• Clearer failure messages. When the model is unavailable on the current plan, say exactly that ("Sonnet 4.6 1M requires extra-usage billing; enable in settings"), not a silent degradation.

Environment

• Claude Code (latest as of 2026-04-10)
• macOS (Darwin 25.4.0)
• Plan: Max plan with 1M context access

Feedback tone

I want to pay for the service. I don't want to be surprised by which specific variant of the same context window triggers overage billing. Make the billing rules legible in the picker and this goes away.