Anthropic on Tuesday launched Claude Fable 5.1 as its generally available flagship and Claude Mythos 5.1 for vetted U.S. partners, the company said. The two share the same weights. Mythos 5.1 runs with looser cybersecurity and biology safeguards through trusted-access programs. The 5.1 pair returns a Fable-class model after last week’s export-letter takedown of Fable 5 and Mythos 5.
Fable 5.1 is live today on Anthropic’s API and through Amazon Web Services, Google Cloud, and Microsoft Azure, Anthropic said. The model id is claude-fable-5-1. List prices are unchanged from Fable 5: $10 per million input tokens and $50 per million output tokens. Cache reads, where the model reuses context it has already processed, now cost $0.25 per million tokens, 75 percent less than before. Anthropic said that cut should lower typical token bills by about 25 percent, and up to about 45 percent on highly agentic work.
Mythos 5.1 is not a public API SKU. Anthropic said it is identical to Fable 5.1 except for more permissive safeguards for vetted cyberdefenders and life-science users. For now it is limited to a set of U.S. organizations. Broader domestic and international access, the company said, depends on coordination with the U.S. government. Cyber Verification and Life Sciences Verification are the two programs named on the post.
Anthropic called Fable 5.1 its most capable generally available model for coding and knowledge work, and posted in-house scores showing gains over Fable 5 on agentic coding and related tests. Those figures are the company’s. Independent third-party results are not in the announcement.
This is a product drop, not a recap of last week’s removal. The news for most developers is the public Fable 5.1 endpoint and the cheaper cache reads. The news for a smaller set of U.S. labs is a Mythos variant with the same model and fewer locks.
Same weights. Different keys. The price cut that most API users will see first is on the reread, not the sticker.
Sources
https://www.anthropic.com/claude-fable-and-mythos-5-1
https://www.anthropic.com/claude/fable