Claude 5 Fable tl;dr - It is state-of-the-art on nearly all tested benchmarks of AI capability, showing exceptional performance in software engineering, knowledge work, vision, scientific research -The longer and more complex the task, the larger Fable 5’s lead over our other models -its more token-efficient than past Claude models - Fable 5 stays focused across millions of tokens in long-running tasks and improves its outputs using its own notes Fable 5 is more than just better benchmarks. It's more efficient, allows for longer work periods, offers better context management, and so much more. GPT-5.6 is just around the corner. I'm a huge Codex fan, but Fable/Mythos is in a league of its own. I'm curious to see if OpenAI will release its own Mythos. "During early testing, Stripe reported that Fable 5 compressed months of engineering into days. In a 50-million-line Ruby codebase, the model performed a codebase-wide migration in a day that would otherwise have taken a whole team over two months by hand."