[BUG] Extra Usage silently charged at 0% plan usage after mid-window Max 5x → 20x upgrade

Preflight Checklist

• [x] I have searched existing issues — related but distinct from #40340, #31655, #32544 (see below)
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Related issues #40340 and #31655 report that upgrading from Pro/5x to Max 20x causes persistent rate limit errors until re-login. My case has the same trigger but a worse outcome: instead of being blocked, requests went through and were silently billed to Extra Usage while the plan usage meter stayed at 0%.

Upgraded Max 5x → Max 20x mid-session. The 5-hour window reset to 0%. Continued using Opus 4.6 in Claude Code. The meter never moved off 0%, but Extra Usage was being drained the entire time. No transition notification was shown.

Additional symptom: the 5-hour session window was not behaving normally. Instead of being anchored to a fixed endpoint (e.g., start at 6:30 PM, end at 10:59PM), it kept rolling forward relative to the current time — always showing "resets in 5 hours from the last time the most recent message was sent, The window never counted down.

Workaround: Disabling Extra Usage in Settings fixed the problem. After disabling, requests started billing against the plan allocation normally and the usage meter began reflecting actual consumption.

Claude Model

Opus 4.6

Platform

Claude Code CLI

Operating System

macOS

What Should Happen?

Requests should bill against the new plan's included capacity (which was at 0%), not Extra Usage. If Extra Usage activates, the meter should reflect 100% and the user should be notified.

Steps to Reproduce

1. Have Max 5x with Extra Usage enabled
2. Upgrade to Max 20x mid-session
3. 5-hour window resets to 0% and starts rolling forward continuously
4. Continue using Claude Code (Opus 4.6)
5. Usage meter stays at 0%, Extra Usage balance drains silently
6. Disable Extra Usage → plan usage resumes normal behavior

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

Unknown

Claude Code Version

2.1.87

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

iTerm2