[BUG] Same token cost, 6-12x difference in weekly quota consumed (Fable 5.1, Max 20x)

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [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?

Quota consumption disproportionate to token usage (Fable 5.1, Max 20x)

Two Claude Code sessions, same model, same plan, 2026-09-04:

| | Session A | Session B |
|---|---|---|
| Tokens | 221.2k in / 235.4k out / 513M cache read / 6.2M cache write | 129.3k in / 116.4k out / 550M cache read / 4.3M cache write |
| Weighted cost | ~60.5M | ~61.1M |
| Weekly quota consumed | ~60% | 5-10% |

Weighted cost = input-equivalents (cache read 0.1x, cache write 1.25x, output 5x input).

Problem: Identical token cost within 1%. Quota consumption differs ~6-12x.
Session B is marginally more expensive by token weight yet consumed far less quota.

Ruled out: counter lag (post-session readings), bucket mismatch (both weekly_scoped), model mismatch (both Fable 5.1).

What Should Happen?

Expected: Quota consumption scales with weighted token cost. Two sessions within 1% on tokens should consume comparable quota.

Actual: ~6-12x difference.

Error Messages/Logs

Steps to Reproduce

Steps to reproduce:

1. Run a long agentic Claude Code session on Fable 5.1 (Max 20x), high cache-read volume.
2. Record /usage after the session settles.
3. Run a second session with comparable token profile.
4. Record /usage again.
5. Compare quota deltas against weighted token cost — they diverge ~6-12x.

Claude Model

Other

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.260 (Claude Code)

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

PowerShell

Additional Information

_No response_