We've all heard the name for weeks, so here's a quick guide on what it is and (more importantly) when to actually use it, so we don't waste money. First things first: What is Fable? (for anyone new to it). Let's imagine Anthropic's AIs like a "family of brains". The regulars are Opus, Sonnet and Haiku. Fable is the new, smartest one, the first of a new generation (the Mythos family), able to do things no other model could. Basically, it's the strongest Claude we can get. It disappeared for 3 weeks: - June 9: Fable launches, everyone's talking about it. - June 12: Amazon researchers find a trick that makes Fable point out software weaknesses (and once even write code to break in). The U.S. government blocks it, and since Anthropic can't check everyone's nationality fast enough, they switch it off for everybody. - Late June: they negotiate a deal with the government. - July 1 (today): Fable comes back on, worldwide. (By the way: other AI's like Opus 4.8, GPT-5.5 and China's Kimi K2.7 could all do the same thing that the Amazon researchers found. So it wasn't some unique "super weapon". Just a simple jailbreak that worked in other models, and those other models were powerful enough to point out those weaknesses too.) Now, the important part of this...WHEN do we use Fable instead of Opus? Is it really that powerful? Let's use an analogy. Think of a race. Opus is a great sprinter. Fable is a marathon runner that checks its own work as it goes. Fable's edge is long, hard jobs that run on their own. Anthropic's own words: "the longer and more complex the task, the larger Fable's lead." So the best option to use Fable is when the task: - takes hours or days, not minutes - has many steps and we don't want to babysit, supervise or check each one - needs to hold a LOT at once (a big codebase, a pile of documents... up to 1,000,000 tokens) - should check its own work and keep going until it's done - is genuinely hard (senior-level reasoning, a big migration, deep research)