Claude Fable 5 系统卡解读：319页中的20个关键点

Anthropic is definitely riding the exponential. At least when it comes to the length of their release notes. They're trying to kill me, man. 319 pages. But more seriously, of course, Claude Fable 5 is both quantitatively and qualitatively a significant step forward in AI capabilities. Yes, their system card is long, but 9 hours of reading later, let me bring you the 20 highlights or so that you may have missed while everyone was having a meltdown on social media. I've probably tested the model in about a hundred different ways and scoured the results across both famous benchmarks, like the ones that Anthropic want you to look at, as well as quiet independent ones. And of course, my own private benchmark. Before we begin then, what is the TLDR?

Well, um yeah, it's a good model. Not if you get blocked, of course, but damn, yeah, it's good. I haven't felt somewhat unnerved by release in quite a while, so that's definitely worth saying. Anyway, let's begin with those blocks, because it might be one of the first things you notice when using Fable 5. At least up until June 22nd, when it's apparently being taken off subscriptions. Doesn't matter if you're pro or max, you won't be able to use it. They're tired of subsidizing poorer users. They want us all to spend usage credits. Pay for the actual cost of this massive model. It was a minute after the release of Fable 5. And I'd just been having a conversation with Opus 4.8 about getting more fermented food for my gut bacteria. I didn't realize how useful it would be to have sauerkraut or kimchi, for example. And I asked Fable 5, after switching to the model, "Review this chat for additional recommendations." Yes, I know I misspelled review. This got flagged as a biology request, so the chat got paused. And by the way, if you think that's heavy-handed, just wait until you dive into the system card. Things get really quite wild, and I don't use superlatives like that often. Before we leave the practicals, we might one day get Fable 5 back on subscriptions like Pro or Max or Team when sufficient compute capacity allows Anthropic to do so. Second, even if you're not done philosophically digesting the import of Claude Fable 5, rest assured that more capable models are arriving in the coming months. Reading between the lines of the system card and various interviews, it looks like Fable or Mythos finished training around February, and of course 4 months is a long time in AI. So, it could well be that Anthropic researchers are right now using the next-gen model. In case, by the way, you're a little bit confused by the names, Mythos 5 and Fable 5 are the same underlying model weights. It's just that Fable 5 has more safeguards. Note though, as I predicted in my previous video, Mythos 5 or Fable 5 is an improvement over Mythos preview. Safeguards aside, the Fable 5 model we're getting now is an improvement over the Mythos preview model that sent many into panic back in April. Albeit generally speaking, as mentioned on page 50, the improvement is moderate. But don't be confused. Just because Mythos 5 or Fable 5 with the safeguards is only a moderate improvement over Mythos preview, that doesn't mean it isn't a significant improvement over Opus 4.8. And yes, over GPT 5.5 and Gemini 3.1 Pro as well. If you can look past the safeguards, it's clearly the best model out there. Though there are some nuances in some areas as I'll get to. Trust me, if I try to TLDR this video, the TLDR would also last about 5 minutes. Just before we dive deeper into the detail though, I just want you to have a visceral sense of the power of this model. I asked in a single prompt, "Write a Pokémon clone, but set in the Redwall universe." And look at what it came up with. It's got a soundtrack that I'm muting, but dozens of playable levels and interactions you can have with the characters. Of course, it's also got menus and playable characters and companions that you can bring into the adventure. The prompt took 2 minutes to write, but the game has up to an hour of play time, I would say. I've published it online if you want to play along, too. The model seems to enjoy hard work, and more on that later. Look at this impressive idea from Ethan Mollick of an isochronic passage chart. Essentially, you can click anywhere on a world map and see how long it would take to get there realistically based on real data from New York City. Hours and hours and hours of agentic research that the model would do, albeit you can never trust it perfectly, but we could just spend the whole video going through such visceral and impressive examples. But that would be too much fun, because this 319-page system card contains dozens of bombshells like this one. So, you know how they block Claude for requests relating to biology?

What about if you're using it for machine learning research?Maybe you're a competitor like OpenAI or DeepSeek, and want to use Fable 5 for frontier LLM development, maybe building pre-training pipelines, for example. Well, Anthropic have instituted invisible safeguards, things like steering vectors, prompt modification, that will silently steer the model away from effective answers. You could say sabotage those attempts. Again, these safeguards will not be visible to the user. Of course, most of you will not be using Fable 5 to accelerate machine learning, but still, one top OpenAI researcher under an alias said this is effectively a stun lock on Anthropic's adversaries. It's some real end game stuff. The reference is to preserve their lead, Anthropic is preventing OpenAI from gaining such capability. Which Which us nicely to perhaps the cheekiest part of the system card. And if I was being overly solipsistic, I would say one of these lines is directed straight at me because I have often quoted how Anthropic used to say that they do not wish to advance the rate of AI capabilities. If you've been watching the channel, I've quoted that many times. It was a 2023 quote. Well, here they say that yes, we are concerned about the risks of accelerating the overall pace of AI development. But what we meant by that, our particular concern, is accelerating other AI developers. Those that pose similar risks but without having commensurate safeguards. Read cynically, that is a direct swap from not wanting to advance the rate of AI capabilities 2023 to not wanting to advance the rate of other people's AI capabilities 2026. They kind of defend themselves and say, "Well, we laid out that shift in this February 2026 risk report." But if you dive into that risk report on page 87, they admit that they are causing much of this acceleration dynamic via demonstrating commercial viability, which leads to more investment, more compute, and therefore greater acceleration in AI capabilities. I just wish that they were a bit more blunt and honest. We started as a safety lab who only made models because that's how you could study them. But then when we saw ChatGPT blow up, we thought we could get in that game, too. It'll be worth any safety concerns though because maybe we can use the models to double human lifespan. Now, before many parts of the audience become too concerned though, we are not close to any kind of recursive self-improvement according to Anthropic. For example, Mythos 5 or Fable 5 does not seem close to being able to substitute for their own research scientists. One of the ways they judge that is that they do not observe a sustained AI attributable two times acceleration in the pace of our AI progress. Think of it again as a step change, not an elevator to the top of the steps. Now, I was quite surprised that the report began with such an intense focus on the biological capabilities of Fable 5. The more you read of the beginning section, the more it makes sense though, and I think there are three interesting reasons why. First, here is that opening paragraph but annotated by a former OpenAI safety researcher. Anthropic say, "On chemical and biological r