Assistant
The assistant is the request-scoped chat helper that acts through the permissions of whoever invoked it, with no standing identity of its own.
The assistant is what most people expect from AI chat: you ask a question or give an instruction, it responds, and the interaction is done. It does not own ongoing work, and it does not have independent permissions. Every action it takes happens through your account and your access, for the length of that one request.
Assistant
Mention the assistant in a channel or in an entry's activity thread and it responds using your permissions, not its own. Unlike an agent, it is not a party member and it cannot be assigned active work that continues after the conversation ends. It is the right choice for a quick question or a one-off task; an agent is the right choice for something that needs to keep going.