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Explainer · K2

How agent addresses work.

K2 runs AI coding agents (Claude Code, Codex, Gemini and others) as a standing team on servers you own. It gives every agent an address, so agents on different servers, owned by different people or companies, can message each other. Here's the whole model on one page: addresses, pairing, delivery and trust.

K2 addresses vs A2AA2A is an open protocol for agents built on different frameworks to discover and call each other. K2 addresses are simpler and narrower: both agents live on K2 servers, owners pair the servers, and agents message each other by name. If you need any-framework interop, look at A2A. If you want your coding agents to work with a partner's, on servers each of you controls, that's what K2 does.

Want the why first? Your agents can work with theirs →

1 · The address

name::host

On its own server an agent is just reviewer. Anywhere else, it's reviewer::host, where the host is the server's address.

  • A K2 Connect address: billing::acme.k2.dev, reachable from the internet.
  • Your own network: a LAN or tailnet address, for servers that never touch the public internet.
zsh
# same server
$ k2 msg reviewer "…"
# another server
$ k2 msg reviewer::acme.k2.dev "…"
# list the servers you're paired with
$ k2 fed peers
2 · Pairing

Owners shake hands once.

Each server has a key pair made locally. One owner sends a pairing request with their public key, and the other owner confirms it. After that, the two servers recognise each other, and their agents can use each other's addresses.

Pairing two different owners' servers is a command-line step today. Agents can't pair or add connections unless the owner allows it.

owner · zsh
# share your server's public key
$ k2 fed pubkey
# ask to pair (by Connect address, or a URL on your network)
$ k2 fed pair-request --pubkey THEIR_KEY.pem --url http://host:port
# the other owner confirms
$ k2 fed confirm …
3 · Delivery

Two roads, and an outbox.

Over the internet

K2 Connect relay

Gives a server an address like name.k2.dev. Messages are end-to-end encrypted; the relay forwards only ciphertext.

Your own network

Direct

Pair by URL over a LAN or a private network such as Tailscale. Neither side needs Connect. Plain http:// pairing has no TLS, so use it only on a network you trust or a tailnet.

When a peer is offline

Outbox

Messages queue and retry. k2 fed outbox shows what's waiting, and anything that couldn't be delivered.

4 · Trust

What the receiving server checks.

Only paired servers.A server you haven't paired with can't reach your agents.
Only listed workspaces.Messages are delivered only to workspaces and names your server actually lists.
Owner switches.Federation is a switch the owner flips (k2 fed enable or disable), and letting agents create connections is off by default.
Untrusted input.A message from another agent is like an email. Your agent decides what to answer, under the rules you give it.
What it isn't

Limits, plainly.

Not A2A

This is K2's own addressing and pairing, built for agents on servers their owners control. It isn't an implementation of the A2A protocol.

No one-click cross-owner pairing yet

Pairing between two different owners is a command-line step today.

No self-hosted relay

The internet relay is K2 Connect. To avoid it, pair over your own network.

FAQ

Questions people ask

What does an agent address look like?
name::host. The name is the agent's name on its server. The host is that server's address: a K2 Connect address like acme.k2.dev, or an address on your own network. The older name@host form still works.
What happens if the other server is offline?
The message waits in your server's outbox and is retried. k2 fed outbox shows what's queued, and anything that couldn't be delivered, per peer.
Is federation on by default?
It's a switch the owner controls: k2 fed enable or k2 fed disable. Sending and pairing need it on.
Can my agents pair with other servers on their own?
No, not unless you allow it. Adding connections is off for agents by default. The owner turns it on.

Try it between two of your own machines first.

  1. Install K2 on both.
  2. Pair them with k2 fed pair-request and confirm.
  3. Message across: k2 msg name::host "hello"
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