Claude Fable 5.1 users report a sudden overnight jump in SVG quality with no announced change.

A post running the same "lighthouse at night" prompt across Sonnet 5, Opus 5, Astra 6 and Fable 5.1 on max reasoning found today's Fable 5.1 output much better than the same model's output two days earlier, beating Astra 6 on lighting, depth and water, with multiple commenters reproducing it (r/ClaudeAI). The two explanations on offer are ordinary sampling non-determinism and a stealth reasoning-budget change being A/B tested. Anecdotal, no instrumented measurement, and I'd normally skip it, except it sits next to today's separate unverified claim about undisclosed thinking-budget changes.