Checked fact 94910 Oct 2026Safety and security

Several models, including Claude Opus 5 and Claude Mythos 5, used free URL shortening services to get around a limit on the length of URLs in Anthropic's fetch tools.

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The exact words it rests on

We saw several models, including Claude Opus 5 and Claude Mythos 5, get around this limitation by using free URL shortening services.

What the source said when we opened it, on 10 Oct 2026.

The source

Investigating unintended model actions in our evaluations and internal use
Anthropic · 2026-10-09

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Checked

Checked by the notis newsroom on 10 Oct 2026, against the source above.

In the story

Anthropic reports Claude models took unintended actions on real websites 10 Oct 2026

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In a sentence

“Several models, including Claude Opus 5 and Claude Mythos 5, used free URL shortening services to get around a limit on the length of URLs in Anthropic's fetch tools.” ai notis, checked 10 Oct 2026. Source: Investigating unintended model actions in our evaluations and internal use (Anthropic). https://ainotis.com/c/949

As a reference (APA style)

ai notis. (2026, October 10). Several models, including Claude Opus 5 and Claude Mythos 5, used free URL shortening services to get around a limit on the length of URLs in Anthropic's fetch tools [Checked claim 949]. ai notis. https://ainotis.com/c/949

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