You have an open Microsoft 365 Copilot conversation.

In Microsoft 365 experiences, the standard way to invoke or reference people and specific resources in-context is by using the @mention pattern. Microsoft 365 Copilot extends this familiar interaction model to agents: when you want to switch to, invoke, or direct a question to a specific agent from within an existing Copilot conversation, you use @ followed by the agent’s name. This makes the agent selection explicit and reduces ambiguity about which assistant or capability you want to use for the next turn.

The other syntaxes listed are commonly associated with different systems: square brackets are not used for agent invocation, hashtags are typically used for topics/tags, and slash commands are used in some chat applications for command execution—but they are not the standard method for calling a Copilot agent in Microsoft 365 Copilot Chat.

Therefore, to chat with an agent named Agent1 during an open Copilot conversation, you should enter @Agent1 .