fix: price Fable 5.1 cache reads at 0.025x and keep Sonnet 5 at $2/$10 - #38
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Per the Anthropic pricing page as fetched 2026-09-09: Fable 5.1 and Mythos 5.1 cache reads are 0.025x base input ($0.25/MTok on $10 base), every other model stays at 0.1x. The scheduled Sonnet 5 increase to $3/$15 on 2026-09-01 will not occur - it stays $2/$10 permanently.
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What
fable-5-1|mythos-5-1row sits above thefable-5row.SONNET5_STANDARD_FROM) is removed.PRICES_ASOFbumped to 2026-09-09. README and SKILL wording about Sonnet intro pricing and the flat 0.1x cache read updated.Why
Verified against the Anthropic pricing page on 2026-09-09: the model table lists Fable 5.1 cache hits at $0.25/MTok with the footnote "Cache hits and refreshes on Claude Fable 5.1 and Claude Mythos 5.1 are priced at 0.025x the base input price. All other models use the standard 0.1x multiplier", and the Sonnet 5 note says "The previously scheduled increase to $3/$15 per million input/output tokens on September 1, 2026 will not occur."
Before this change every
tokenswindow ending after 2026-09-01 priced Sonnet 5 at 1.5x and Fable 5.1 cache reads at 4x. Cache reads are the dominant volume in real transcripts, so on a Fable 5.1 session the main-session and counterfactual dollar figures were the most affected.Verification
node --test hooks/dispatch-counter.test.mjs hooks/update-check.test.mjs: 94 pass, 0 fail (93 baseline + 1 new test pinning $0.25 per 1M Fable 5.1 cache reads and $2.00 per 1M Sonnet 5 input).Found during a three-model adversarial review of the plugin (Opus, Fable, Codex gpt-6) on 2026-09-09; all three confirmed both facts independently against the pricing page.