The reported effects vary by target, including escaping a browser sandbox, accessing data or causing denial of service. These were laboratory tests rather than observed real attacks. Fixes are available according to the sources reviewed; Chrome 156 specifically credits an Anthropic researcher assisted by Claude.
The Hacker News notes that public documents do not establish human involvement at every step. Producing the full chains with little assistance therefore remains Anthropic's claim; the model's name has not been disclosed.