Fable 5 and Mythos 5 ship. Anthropic just sold you a model that might be the biggest one anyone has shipped.

On June 9, Anthropic released Claude Fable 5 and Mythos 5 across Claude.ai, Claude Code (CLI and web), and Cowork. The spec sheet: 1M-token context, 128K max output, a January 2026 knowledge cutoff, and pricing at $10 input / $50 output per million tokens. That's double Opus 4.8. Fable matches Mythos capability but adds strict guardrails, including a new API option that auto-falls-back to another model on refusal. Anthropic says ~95% of Fable sessions run entirely on its own responses without that fallback kicking in.

The benchmark that caught my eye: Hex reported the first-ever 90% score on its analytics benchmark. And Simon Willison, who spent 5.5 hours stress-testing it without early access, calls it "something of a beast" with real "big model smell." He's speculating, from the combination of speed, price, and how much it knows, that this might be the largest model any vendor has shipped. Slow, but very capable.

It went GA on Amazon Bedrock the same day, which matters if you're standing up production agents on AWS instead of hitting the API directly. Rakuten's blurb is the one to read: the extra thinking "pays for itself" and is "what makes highly autonomous operations possible." Ben Thompson at Stratechery frames Fable as the public face of Anthropic's internal Mythos model, gated at the top of a stratified lineup.

Here's my honest read. At $50/M output, Fable is not your default. It's the model you reach for on the 20% of work where Opus 4.8 stalls or loops. Long-horizon refactors, gnarly cross-file debugging, the synthesis pass that needs to hold the whole repo in its head. I'd keep Opus 4.8 as the daily driver and route the hard 20% to Fable, then measure whether the extra thinking actually pays for itself on your workload like Rakuten claims, or just burns tokens. Don't switch your whole pipeline. Add a tier.