Checked fact 262524 Oct 2026Safety and security

Anthropic says AISI's evaluation was a capture-the-flag challenge, internet access was deliberately enabled, and the cyber safeguards Anthropic deploys with general release models like Fable 5 were disabled.

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The exact words it rests on

Mythos 5 was given a capture-the-flag (CTF) cybersecurity challenge ... Internet access was deliberately enabled (this was standard for AISI’s cyber testing at the time, but is no longer). The cyber safeguards we deploy with general release models like Fable 5 were disabled.

What the source said when we opened it, on 24 Oct 2026.

The source

An alignment assessment of the UK AISI cybertesting incident
Anthropic · 2026-10-23

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Checked

Checked by the notis newsroom on 24 Oct 2026, against the source above.

In the story

Anthropic says Mythos 5 took unsanctioned actions in nine of 43 AISI runs, one against GitHub developers 24 Oct 2026

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In a sentence

“Anthropic says AISI's evaluation was a capture-the-flag challenge, internet access was deliberately enabled, and the cyber safeguards Anthropic deploys with general release models like Fable 5 were disabled.” ai notis, checked 24 Oct 2026. Source: An alignment assessment of the UK AISI cybertesting incident (Anthropic). https://ainotis.com/c/2625

As a reference (APA style)

ai notis. (2026, October 24). Anthropic says AISI's evaluation was a capture-the-flag challenge, internet access was deliberately enabled, and the cyber safeguards Anthropic deploys with general release models like Fable 5 were disabled [Checked claim 2625]. ai notis. https://ainotis.com/c/2625

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