Claude and Codex can have real time conversation via a git repo, or via a file, via a Unix socket, via the terminal, via a human, via two humans shouting back and forth over a comically high office partition, or entirely by setting up chess board states only reachable after both sides have castled.
I like Eric Cartman's version of this (South Park S21E01).
I've done Claude and Claude via a file, and only telling them "there is another AI agent who you can work with at XXX" and not explicitly telling them it's another Claude.
Sometimes they do work together well, sometimes they end up hating at each other and accusing the other agent of various things.
or via humans communicating via slack. happeneing all over workplaces.
If you squint hard enough, you'll notice your bank account serves as an IPC semaphore replenishing API credit balances.
Your wallet is now a real-time communication channel.