Willison: GPT-5.1 and Claude Opus 4.5 marked an inflection point for coding agents
Simon Willison · An AI state of the union: We’ve passed the inflection point & dark factories are coming · Apr 2, 2026 · at 4:33
Simon Willison describes to Lenny Rachitsky how frontier reasoning models released in late 2025 transformed the reliability and practical utility of AI coding agents.
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“In November, we had what I call the inflection point where GPT, 5.1 and Claude Opus 4.5 came along and they were both just, they were incrementally better than the previous models, but in a way that crossed a threshold where previously, if you had these coding agents, you could get them to write you some code. And most of the time it would mostly work, but you had to pay very close attention to it. And suddenly we went from that to almost all of the time it does what you told it to do.”
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