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[ARTICLE · art-72806] src=simonwillison.net ↗ pub= topic=artificial-intelligence verified=true sentiment=· neutral

Introducing Claude Opus 5

Anthropic released Claude Opus 5, priced the same as Opus 4.8 with a fast mode at twice the cost, featuring improved general capabilities that led to substantial gains in finding cybersecurity vulnerabilities despite not being trained on cyber tasks. In one Frontier-Bench task, Opus 5 wrote its own computer vision pipeline to reconstruct a 3D FreeCAD model from a drawing it could not directly view. Anthropic published a prompting guide for the model.

read1 min views1 publishedJul 24, 2026

It's priced the same as Opus 4.8, and continues to offer a "fast mode" at twice the cost of the base model.

Based on this anecdote in the release post it sounds like it might be relentlessly proactive:k On one Frontier-Bench task, Opus 5 was given a drawing of a machine part and asked to write code to rebuild it as a 3D FreeCAD model. However, in this task, the model was intentionally given no way to directly viewthe drawing. Opus 5 responded by writing its own computer vision pipeline to pull the geometry from the raw pixels, then reconstructed the full machine part.

It's better at finding vulnerabilities but has deliberately not been trained on how to exploit them. Hopefully this means the US government won't shut it down!

As with its predecessor, Opus 4.8, we’ve intentionally avoided training Opus 5 on cyber tasks. The model has nevertheless improved substantially on these tasks as a result of becoming more generally capable, and it comes close to Mythos 5 at

findingcybersecurity vulnerabilities. However, it remains substantially behind Mythos 5 on theexploitationof those vulnerabilities—that is, in turning vulnerabilities into material cyber threats.

Anthropic have published a prompting guide for Claude Opus 5. The first pelican I got was missing the bicycle wheels; the second attempt was better.

Tags: ai, generative-ai, llms, anthropic, claude, llm-release

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