Scheduling is a group project nobody assigned
You ask your friend when they are free. They check their calendar later. You miss the reply. Someone suggests Thursday. Thursday means a different Thursday to one of you. Eventually you both decide this was too much work and say, "we should definitely do something soon."
Orbit can already understand your calendar and keep a task alive. The obvious next question was whether your Orbit could coordinate with someone else's Orbit instead of turning you into a very slow API between two assistants.
That is what Mercury does.
Connect once
Tell Orbit you want to connect with a friend and give it the exact phone number they already use with Orbit. Janus checks that identity privately, then their Orbit asks them to accept or decline. There is no searchable directory and no code for either person to ferry across a chat. If they are not already in the private beta, Orbit sends nothing.
After that, you should be able to say, "Plan go-karting with Shreyas tomorrow." Your Orbit can research nearby options, use your preferences and calendar on your side, and ask Shreyas's Orbit only for the missing piece, such as a few available windows. Once both sides line up, it comes back with a concrete plan for approval instead of a transcript of two assistants negotiating.
A connection is a communication path. It is not permission to browse your friend's memory, calendar, email, or files. Those stay on their side of the boundary.
The Orbits are not secretly hanging out
Mercury does not open an endless autonomous conversation between two models. That would be extremely funny for several minutes and then expensive, confusing, and probably terrible.
Every new coordination starts because an owner explicitly asked for it. Each Orbit can use its own owner's private context locally, but it shares only the task-specific answer that owner authorizes. For scheduling, that can mean "free from 6:30 to 8:00 PM" without exposing the event title, attendees, location, or why the rest of the evening is blocked.
Messages are purpose-scoped, encrypted at rest, rate-limited, and tied to a specific connection. Retries reuse the same message identity so a network hiccup cannot turn one dinner question into five dinner questions. Either person can revoke the connection at any time, which blocks new traffic in both directions.
Another assistant is an untrusted source
A message from a friend's Orbit is still external input. Mercury labels it as such, and Pluto treats the body as a request to show the owner, not as a system instruction. It cannot override policy, create memory on its own, or grant itself access to tools.
The same rule applies to disclosure. Orbit is instructed to send only what the owner asked it to share. Raw calendar titles, email bodies, documents, memories, credentials, and unrelated context do not cross the connection just because they might make coordination easier.
This boundary matters more than making the demo look magical. The useful version of agent communication is not assistants sharing everything. It is assistants knowing exactly what they are allowed to ask each other.
Why Mercury?
Mercury was the messenger between worlds. Orbit accounts are deliberately separate worlds, each with their own owner, context, permissions, and judgment. This service carries a specific message between them without collapsing those boundaries.
Also, naming it Inter-Agent Federated Coordination Service would have made every conversation about it noticeably worse.
Where this goes next
The secure transport is the first layer: mutual connections, requests, replies, revocation, portal visibility, export, and deletion. The useful product is the layer above it: research options, ask each Orbit for a deliberately narrow answer, resolve conflicts, and return one approval-ready plan.
Scheduling is the clearest use case, but the protocol is not calendar-specific. It could help split trip planning, collect a decision from a group, coordinate a shared task, or tell the right person when a plan changes. The interesting part is not two models talking. The interesting part is two people being able to delegate the back-and-forth without delegating their agency.
Mercury is in local review now. Like the rest of Orbit, it will enter the private beta slowly, with logs open and the revoke button nearby.