Fable 5 Raises the Bar for AI Ambition

**Nathaniel Whittemore** (0:00)
Today on the AI Daily Brief, Anthropic has officially launched Fable 5, the first of their Mythos class models.
I think fairly undisputedly, the best AI model we have ever been able to use. And yet at the same time, we are now at a level of AI models, where how to get the most out of the state of the art, isn't as simple as doing your same old prompts, but just with the new model. On today's episode, we're going to be discussing the launch, the benchmarks, the first reactions, and how to get the most out of Fable 5
The AI Daily Brief is a daily podcast and video about the most important news and discussions in AI. All right, friends, quick announcements before we dive in. Yesterday, I teased that in response to so many requests to make it easier to dissect and share specific parts of episodes, we were going to be experimenting with some new tools to do exactly that. Well, it turns out that Fable 5 liked what we had started, but thought it made some obvious errors, like not including timestamps on the little share cards with specific parts of the episode and not turning the whole thing into a pipeline that could work automatically. So it did that. And so you might be getting this sooner rather than later. Keep an eye out on the show notes and on aidailybrief.ai for more of that. But now let's talk quad Fable 5
On the one hand, this is not a particularly surprising release. First of all, it's been a couple of months now since we heard about this new mythos class of models. Some companies, of course, have had access to them through Anthropics Project Glasswing. And when we got Opus 48 just a couple of weeks ago, they made it clear that they were working hard to get to a mythos class model that they could release with sufficient guardrails that they could feel confident about it being out in the public. Now, I guess what might be a little bit surprising about it is how quick the interval was between 48 and what we got in Fable 5 But as we'll see, in a way that's much different than previous state of the art jumps, Opus 48 still has a pretty big role to play in the Fable 5 led ecosystem. Now, then over the last couple of days, rumors started getting loud that some mythos class model was coming. And a little secret for you guys out there, if the loudest AI content creators on places like X are not responding to and participating in the rumor cycle, that usually means that they have early access and that the rumors are true. In this case, they were, and on Tuesday, June 9th, we got Claude Fable 5, and some others got Claude Mythos 5
Now, first of all, let's talk about Mythos 5, as it's almost entirely irrelevant for just about everyone here. Mythos 5 is effectively the same model as Fable 5, which is the one that we got, but doesn't have all of the safeguards, many of which are controversial, that we're going to discuss in a little bit. Mythos 5 will only be available initially as part of Project Glasswing, and is being deployed to those Project Glasswing partners. Anthropic says in collaboration with the US government as an upgrade to what is available now, which is Quad Mythos Preview. They say they intend to expand access to Mythos 5 through a broader trusted access program soon, but for now it is available only for a very small set of organizations. No, the big one for us is Fable 5
So just from the name alone, you can tell that Anthropic is treating this one as a big deal. First of all, we get an entirely new naming convention. We now have Haiku, Sonnet, Opus and Fable as in a class that is above Opus. Second, think about how long it's been since we got a lab that was willing to put a full new base number on its model. Indeed, the last time that we got that was the somewhat disastrous rollout of GPT-5 last August. All of those big transformations that we got around the turn of 2026 came in model designations like Opus 4.5 and 4.6 and GPT-53 and 5.4. So clearly here, just from a naming convention alone, Anthropic is not playing. And no, they are not playing. Regular listeners will know that in general, I felt that we are at a point where benchmarks are so saturated that it's pretty hard to derive much signal from them. And that even when one new model comes out and is a point or two ahead of the closest competitor making it state of the art, vibes in real world experience can be very, very different, meaning you basically just have to test these things for yourself. Yet sometimes the leaps are big enough that the benchmarks are worth paying attention to. And that's certainly what we got here. On exploit bench, the cybersecurity benchmark, Mythos and Fable 5 score a 78% compared to, for example, GPT-55's 34%.