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smart_toyAI/PROMPT ENGINEERING

Opus 4.6 and Codex 5.3

sourceSimon Willison
calendar_todayFebruary 5, 2026
schedule1 min read
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EXECUTIVE SUMMARY

New AI Models Released: Opus 4.6 and Codex 5.3 Set to Transform Development

Summary

Two significant AI model releases occurred recently, with Anthropic launching Opus 4.6 and OpenAI introducing GPT-5.3-Codex. Both models promise enhanced capabilities, although their predecessors were already highly effective.

Key Points

  • Anthropic released Opus 4.6.
  • OpenAI launched GPT-5.3-Codex, available only via the Codex app, not yet in their API.
  • Both models were released within 15 minutes of each other.
  • Previous models, Codex 5.2 and Opus 4.5, were already performing well, making it challenging to identify new tasks for the latest versions.
  • Nicholas Carlini from Anthropic highlighted Opus 4.6's capabilities in building a C compiler using parallel Claudes.
  • The models are part of the ongoing evolution in generative AI and large language models (LLMs).

Analysis

The release of Opus 4.6 and Codex 5.3 signifies a continued advancement in AI capabilities, particularly in the realm of prompt engineering and software development. As these models become integrated into workflows, they may enhance productivity and innovation in coding and other technical tasks.

Conclusion

IT professionals should explore the potential applications of these new models in their development processes. Staying updated on their capabilities can lead to improved efficiency and effectiveness in software engineering tasks.