Simon Willison • 2/5/2026

Opus 4.6 and Codex 5.3

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The article discusses the near-simultaneous release of two major AI models: Anthropic's Opus 4.6 and OpenAI's GPT-5.3-Codex. It notes the author's difficulty in finding dramatic capability leaps over the already strong predecessors (Opus 4.5 and Codex 5.2), but highlights a compelling example from Anthropic about using Opus 4.6 for building a C compiler, similar to Cursor's FastRender project.

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#artificial intelligence #llm #Openai
Opus 4.6 and Codex 5.3

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