tl;dr: Claude Duet is a new proactive agent from Anthropic, powered by Opus 5.5, that runs continuously in a cloud computer and messages users when tasks are done or decisions are needed—handling things like morning briefs, inbox triage, invoice reminders, and building docs/decks. It uses the existing Claude account's memory, skills, and connectors, and asks for approval before sensitive actions like sending messages or payments. Currently a research preview via waitlist for US Pro and Max subscribers, available on iOS, Android, and web.