Claude secretly becomes stupid while doing AI research, and Anthropic is besieged by the research community
Claude Fable 5 is the main focus in the AI field today; this “mythical” model performs exceptionally well and has attracted tremendous attention.Andrej Karpathy described it as “very exciting” and an “evolutionary step that deserves a major version upgrade,” on par with the improvements brought by Claude 4.5 last November. In the SWE-bench Pro programming benchmark, Fable 5 achieved a score of 80.3%, which is 11 percentage points higher than Opus 4.8. With a Ruby codebase consisting of 50 million lines of code, Fable 5 completed the entire codebase migration in just one day; if the same task were assigned to a human team, it would take more than two months.
