fix: add Claude Fable 5.1 pricing row, keep Fable 5 as history - #5635
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Fable 5.1 shipped 2026-09-01 with the same $10/$50 per-1M input/output rate as Fable 5, but a 75% cheaper cache-read rate ($1.00 -> $0.25/1M, i.e. 0.1x -> 0.025x its input rate) while cache-write stays at the standard 1.25x. Adds a dedicated modelPricing.js row plus a scoped cache-multiplier override rather than touching the existing claude-fable-5 row, so /devtools/usage keeps accurate historical rates for both generations. The bare "fable" family-match fallback now resolves to the newest generation, matching the existing opus-bump convention.
PRICING_AS_OF advanced to 2026-09-01, past the documented 2026-08-31 intro-pricing cutoff, but claude-sonnet-5 still priced at the $2/$10 intro rate instead of the $3/$15 standard rate its own comment names — understating post-cutoff usage estimates.
The prior commit (address review (codex)) bumped claude-sonnet-5 to the $3/$15 rate the stale comment described as taking effect 2026-09-01. Anthropic cancelled that increase on 2026-08-10 and confirmed the $2/$10 intro rate is now the permanent standard price (verified against platform.claude.com/docs/en/about-claude/pricing). Restores the correct rate and updates the comment instead of the number.
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Summary
claude-fable-5-1row tomodelPricing.js's billing-rate table: same $10/$50 per-1M input/output as Fable 5, but a 75% cheaper cache-read rate ($1.00 → $0.25/1M) confirmed from Anthropic's own Fable 5.1 announcement and VentureBeat's pricing breakdown. Cache-write stays at the standard 1.25x.claude-fable-5is kept as its own row (not renamed/removed) so/devtools/usagekeeps accurate historical rates for prior Fable 5 usage."fable"family-match fallback (for ids the table doesn't otherwise recognize) now resolves to the newest generation, mirroring the existingOPUS_MODEL_IDSnewest-first convention already used for opus version bumps.Test plan
cd server && npx vitest run lib/modelPricing.test.js— 41/41 passing, including two new/updated cases covering the new rate row and the cache-multiplier override.