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

### Preflight Checklist

- [x] I have searched [existing issues](https://github.com/anthropics/claude-code/issues?q=is%3Aissue%20state%3Aopen%20label%3Abug) 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

```shell

```

### 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_

No repository file or test is identified in the report. Start by reproducing the two long Claude Code 2.1.260 sessions from Windows PowerShell, record /usage after each settles, and compare quota deltas with the reported weighted token costs. Done means comparable token profiles produce comparable weekly quota consumption.

Written by the indexing model from the issue text.