This is a super exciting release - Claude Fable 5 is the same underlying model as Mythos but with added safeguards. The benchmarks are great and it's SOTA on everything by a margin but I'll add that *qualitatively* also, this is a major-version-bump-deserving step change forward (imo of the same order as Claude 4.5 was in November), peaking especially for long problem-solving sessions on very difficult problems. You can give it a lot more ambitious tasks than what you're used to, the model "gets it" and it will just go, and it's never felt this tempting to stop looking at the code at all (but don't do this in prod!). The model still has quirks that people will run into and the safeguards are configured to be a little too trigger happy for launch, which can hopefully be tuned over time.
I feel a lot of things changing as working software increasingly comes out on a tap. The Jevon's paradox kicks in and I feel my own demand for software growing substantially. You can ask for anything - explainers, visualizers, dashboards, bespoke single-use apps (e.g. a full wandb that is hyper-specific just for your project), you can 10X your test suite, auto-optimize code, run giant research projects with custom HTML for the results, anything! "Free your mind" (Matrix ref). Really looking forward to all the things people build!
The first prompt I always run on a new model to test legal capabilities is “Draft an S-1”
Immediately gives a good sense of the model's general capabilities. Can tell from the length of the S-1, formatting, structure and writing how big a jump in general and legal performance the new model is likely to be. We’ve found that just length correlates extremely well to how well the model will work in our legal agents.
Screenshots show SpaceX S-1 drafted by Fable 5, Opus 4.8 and the actual one filed. Very clear that Fable 5 is a big step up from Opus 4.8 which is already significantly stronger than most other models at this task. The formatting and structure is significantly better and is also reflected in our LAB benchmark (13% vs. 10%).
Super impressed in early testing of this model both on benchmark and in product. Huge congrats to the @anthropic team because this is very clearly a big step forward in model capabilities.
Introducing Claude Fable 5: a Mythos-class model that we’ve made safe for general use.
Its capabilities exceed those of any model we’ve ever made generally available.
Our internal data shows Claude is accelerating AI development—a possible path to recursive self-improvement, or AI autonomously building a more capable successor.
It’s happening faster than we thought, and the implications deserve greater attention. https://t.co/OVVPJO7VQx
Anthropic now has a team dedicated to AI and the rule of law — and we've just opened our first role.
@AnthropicAI has studied what AI means for the economy. This team asks a different question: what will it mean for executive power, for courts and elections — and for the public deliberation that constitutional democracy ultimately rests on?
We're looking for someone with real depth in both AI and the law — a legal scholar, political scientist, or experienced government hand who can reason about frontier systems and the institutions they will affect.
If that's you, or someone you know: https://t.co/668HDz1lhf
Introducing Claude Opus 4.8: it builds on Opus 4.7 with sharper judgment, more honesty about its own progress, and the ability to work independently for longer than its predecessors.
Available today at the same price.