An internal instruction that guides Claude's behavior was completely rewritten. It used to be narrow advice about setting an HTML <title> tag. It now gives much broader guidance on when Claude should publish a finished piece of work as an Artifact (a standalone piece of content like a document or app shown alongside the chat) or through a first-party document connector (an integration the host explicitly designates as such) — including giving the person a link to it, offering rather than immediately publishing a page when it's unclear whether that's wanted, and never treating a connector as first-party unless the host has said so.
This changes how Claude decides whether to hand you a finished artifact directly, publish it to a connected document service, or just offer it, so results should better match what you actually intended to do with the output.