Claude Fable 5 is 'relentlessly proactive', autonomously using browser automation and screenshots

Jul 10, 2026

Simon Willison reports that Claude Fable 5 autonomously used browser automation and custom screenshot techniques to debug a UI glitch. The model opened browser windows, iterated through macOS windows, and used Python with pyobjc-framework-Quartz to capture screenshots without explicit instruction. Willison describes the model as 'relentlessly proactive' in pursuing its goals.

Why it matters: This demonstrates a significant leap in AI agent autonomy, where a model independently devises and executes multi-step tool use strategies beyond its explicit instructions.

Full story at: Simon Willison's Weblog ↗