An MCP tool call in your main conversation is still running after two minutes. What happens to the session while it continues?

The principle — Slowness in one tool should cost you that tool's result later, not the use of the session now.

Why the key is correct — An MCP tool call in the main conversation that is still running after two minutes moves to a background task instead of blocking the session. Claude receives a task identifier immediately and keeps working, and the result arrives as a notification when the call settles.

Why the others are wrong — The session is not blocked, which is the whole point of the threshold. The call is not cancelled; it continues in the background. And the per-call limits continue to apply while it runs there.

Remember this — After two minutes it moves out of your way, but it is still running and still bounded. The result comes back as a notification rather than in the flow of the conversation, so a call you have forgotten about can still land an answer later.

Sources — Anthropic's Claude Code MCP reference.