Accounts on the same billing method share a single rate limit quota pool

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report
• [x] I am using the latest version of Claude Code

What's Wrong?

Accounts sharing the same billing method have their usage quotas linked server-side, causing all accounts under the same payment method to hit rate limits simultaneously — even if only one account is actively being used.

Evidence from the OAuth usage API (/api/oauth/usage):

| Accounts | Session | Weekly | Reset Times | Extra Usage |
|----------|---------|--------|-------------|-------------|
| claude1, claude5, claude6, claude7 | 100% (identical) | 83% (identical) | Same reset times | Same |
| claude4, claude8 | 0% session | 100% weekly | Same reset times | used_credits: 63299, utilization: 31.65% (identical) |
| claude2, claude3 | Independent | Independent | Different reset times | Independent |

• Accounts 1/5/6/7 are on the same billing method → identical utilization and reset times
• Accounts 4/8 are on another shared billing method → identical extra_usage data and reset times
• Accounts 2/3 are on separate billing → fully independent quotas

What Should Happen?

Each account's rate limit should be tracked independently, regardless of the billing method. A Max subscription is per-account, so the quota should be per-account as well. Sharing a quota pool across accounts that happen to use the same credit card is unexpected and undocumented behavior.

Related Issues

• #41788 — Max 20 plan: rate limit 100% exhausted within ~70 minutes
• #41590 — New account immediately hits rate limit with zero usage
• #38335, #38239, #41663, #41084 — Various rate limit reports

How to Reproduce

1. Create multiple Claude Max accounts using the same billing method
2. Use only one account actively
3. Check /api/oauth/usage on the other accounts — they will show the same utilization percentages and reset times

Claude Code Version

2.1.89