Model board / Claude Mythos 5

Verified 2026-09-03 against the pages listed below. Prices are USD per 1M tokens, list rate — no committed-use, enterprise or volume discount.

limited availability; 1h cache write $20.00

the launch doc states Fable 5 and Mythos 5 share the same specs — 1M window by default, up to 128K output per request

read 0.1x input; 5m write 1.25x, 1h write 2x

Watch out

Superseded by the 5.1 revision this pass and moved to Legacy on Anthropic's own overview page. Same $10/$50 as 5.1, but cache reads cost 0.1x base here against 5.1's 0.025x — on a cache-heavy workload the newer row is strictly cheaper

What we would use it for

Approved Project Glasswing security work — Fable 5's capability with the safety classifiers removed

What this has cost, week by week

Output price at each refresh since 2026-08-06. A vendor change is the provider changing its price. Our correction means this board changed what it prints and the provider's charge did not move — the two are never merged, because publishing the second as the first would be a price rise that never happened.

Nothing has moved since we started tracking it.

Where these numbers came from

• https://platform.claude.com/docs/en/about-claude/pricing
• https://platform.claude.com/docs/en/build-with-claude/prompt-caching
• https://platform.claude.com/docs/en/about-claude/models/introducing-claude-fable-5-and-claude-mythos-5

No number on this page was written that was not read from one of those pages on 2026-09-03. If one is wrong, send us the source URL and it is corrected in the next weekly refresh, with a changelog line saying what was wrong — contact@naderu.com.

Discussed in Naderu Weekly

• The same weights, twice — 2026-08-06

The rest of the board

This row sits alongside 53 others on the model board, refreshed every week. The same data as JSON, and the terms for using it, are at /board-data.