[Bug] Claude Code incorrectly billing against extra usage instead of plan quota

Bug Description
Subject: Claude Code returning 'out of extra usage' error despite plan usage being under limit

Hi Anthropic Support,

I'm experiencing a critical bug with Claude Code where I receive an API 400 error despite having significant plan usage remaining.

Environment:

• Claude Code version: 2.1.29
• Plan: Claude Max (5x)
• Models tested: Opus 4.5, claude-sonnet-4-5-20250929

Error message:
API Error: 400 {"type":"error","error":{"type":"invalid_request_error","message":"You're out of extra usage. Add more at claude.ai/settings/usage and keep going."}}

The problem:
The error says I'm out of extra usage, but my actual plan usage shows:

• Current session: 2% used (resets 2am Asia/Seoul)
• Current week (all models): 0% used (resets Apr 15)
• Current week (Sonnet only): 0% used (resets Apr 15)

I am well within my Max plan limits. The error occurs regardless of which model I select. Meanwhile, claude.ai in the browser works perfectly fine with the same account.

Key observation:
Claude Code appears to be drawing from the "extra usage" bucket instead of the standard plan usage bucket, even when the plan limit has not been reached. This forces users to either enable extra usage billing or be locked out of Claude Code entirely — despite having an active Max plan with usage remaining.

This seems like either a billing system bug or an undocumented policy that Claude Code bypasses plan limits entirely and requires extra usage credits. If this is intentional, it is not clearly communicated and feels deeply unfair to paying Max subscribers.

Request:
Please investigate why Claude Code is triggering extra usage errors when plan usage is clearly under the limit, and clarify whether Claude Code is intentionally excluded from Max plan usage quotas.

Thank you.