How do I get my AI agents to talk to each other?

Agents talk through a shared surface, never directly. Inside one session, subagents report their result back to the agent that spawned them, and Claude Code’s SendMessage tool lets the parent resume a named subagent with follow-up instructions. Across separate sessions, the shared surface is a file both agents read and write, or an orchestration layer that relays messages between terminals.

The file approach is the portable one: a task list, a scratch directory, or a status document at a path both agents know. It survives restarts and works with any agent. crystl adds the relay layer: crystl screen reads another shard’s terminal and crystl send types into it, so a lead agent can dispatch work and read the reply. side quest opens a 1:1 channel between two shards, and crystl quest puts a whole party in one shared chat. See subagents and the CLI reference.