Duet runs on Claude Opus 5.5 and you can't pick another model. It carries over the memory, skills and connectors from your Claude account, and it has a virtual machine with its own browser, so tasks keep going after you close your laptop.
It reads and drafts on its own. Before it sends a message, makes a payment, signs a document or deletes anything, it shows you the action and waits for approval. Some things stay blocked even if you approve them, like trading securities or moving money between accounts.
The limits are worth reading before you join. It checks your accounts at set intervals rather than all the time (Anthropic says constant checking would burn through plan limits), so something urgent can land between checks. You can't watch or take over its browser. Microsoft 365 isn't supported yet, Slack works with limits, and it isn't on Team or Enterprise plans. It shares your plan's usage limits with the rest of Claude.