Article · 2026-07-24 · 3 moments

Introducing Claude Opus 5

Introducing Claude Opus 5 I've been offline kayaking with sea otters for much of today so I haven't had a chance to put Anthropic's new model Claude Opus 5 through its paces yet. The buzz is positive, and Anthropic's description of it as a "thoughtful and proactive model that comes close to the frontier intelligence of Claude Fable 5 at half the price" sounds promising. It's currently leading the Artificial Analysis leaderboard, in front of even Fable 5. It's priced the same as Opus 4.8, and c ✦ AI generated

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GUEST Anthropic (release post)GUEST Author (narrator)HOST Simon Willison

Context

Claude Opus 5 is a thoughtful and proactive model that comes close to the frontier intelligence of Claude Fable 5 at half the price.

Anthropic positions Claude Opus 5 as nearly as capable as the frontier model Fable 5 but at significantly lower cost, and it tops the Artificial Analysis leaderboard.

transcript

Author (narrator): Anthropic's description of it as a 'thoughtful and proactive model that comes close to the frontier intelligence of Claude Fable 5 at half the price' sounds promising. It's currently leading the Artificial Analysis leaderboard, in front of even Fable 5. It's priced the same as Opus 4.8, and continues to offer a 'fast mode' at twice the cost of the base model.

Fact◆

Claude Opus 5 is better at finding vulnerabilities but has deliberately not been trained on how to exploit them, making it substantially behind Mythos 5 on exploitation.

Anthropic intentionally avoided training Opus 5 on cyber tasks, so while it has improved at finding vulnerabilities through general capability gains and comes close to Mythos 5 at detection, it remains substantially behind on exploitation — turning vulnerabilities into material threats.

transcript

Anthropic (release post): 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 finding cybersecurity vulnerabilities. However, it remains substantially behind Mythos 5 on the exploitation of those vulnerabilities—that is, in turning vulnerabilities into material cyber threats.

Example◆

Claude Opus 5 responds to impossible tasks by inventing novel solutions, such as writing its own computer vision pipeline to extract geometry from raw pixels when given no direct way to view a drawing.

In a Frontier-Bench test, Opus 5 was given a drawing of a machine part but no way to directly view it, so it wrote its own computer vision pipeline to extract the geometry from raw pixels and reconstructed the full 3D model.

transcript

Author (narrator): 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 view the 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.

gives example · 2

Highlight slides

Anthropic intentionally avoided training Opus 5 on cyber tasks✦ from: Claude Opus 5 is better at finding vulnerabilities but has deliberately not been trained on how to exploit them, making it substantially behind Mythos 5 on exploitation.Opus 5 invents novel solutions for impossible tasks✦ from: Claude Opus 5 responds to impossible tasks by inventing novel solutions, such as writing its own computer vision pipeline to extract geometry from raw pixels when given no direct way to view a drawing.Opus 5 nears Mythos 5 at detection, lags on exploitation✦ from: Claude Opus 5 is better at finding vulnerabilities but has deliberately not been trained on how to exploit them, making it substantially behind Mythos 5 on exploitation.

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