A simple guide to how Unicity works.
There are two very different ways that sentence can be true, and nobody notices the difference until it matters.
A company keeps a book. Next to your name it says 5. You hold their promise, not the coins.
You hold the actual thing. Nobody looks you up, and nobody has to agree that it is yours.
Send a friend a photo and you still have the photo. Lovely for photos.
So something in the world has to be able to say this exact coin has already been handed over. That something is far smaller and far dumber than you would guess.
The whole design rests on one sentence.
A coin's number is worked out from the coin itself.
Change the coin by a hair and the number is completely different. Leave it alone and it is identical, every time, on every computer. Nobody has to agree about it, the same way nobody has to agree that seven eights are fifty six.
So put a wall in the world. It keeps numbers, and answers one question: have I seen this one?
Each entry is your number with a fingerprint of the deal beside it. No name, no amount, no idea what was bought. And since it only compares numbers, one wall serves every asset at once.
Real names: the aggregation layer, the Unicity Service. It stores R[sid] ← txhash, where sid = H(pred, sthash) — which is exactly what this page computes.
Send one coin down a chain of four people, then look at what actually arrived.
Every move re-masks the state, sthash' = H(sthash, x), so two states of one coin cannot be linked.
The wall holds millions of numbers. Your phone will not download it to check one payment.
So they are stacked. Two get squashed into one above them, that pair into one above them, until the whole wall is a single number at the top. To prove yours is in there you need only the handful along your own path: squash them in order and see whether you land on the top number. You do, or you don't.
Ten million entries is about 640 megabytes. The receipt is about 800 bytes, same certainty, checked offline in milliseconds.
The stack is a sparse merkle tree; the receipt is an inclusion proof.
Unicity AOS runs AI agents, the programs that do jobs for you. Claude Code, Codex and Grok plug straight into it.
On a normal computer, anything you run can do anything you can do: read any file, delete any file, reach any site, without asking. Tolerable while a human clicked every button.
Here it starts able to do nothing at all, and you hand it keys one at a time. Each key says exactly what it opens.
Some things no key reaches. Not because anyone blocked them, but because nobody handed a key.
Astrid is the engine inside AOS. One skill is a capsule, a WebAssembly component with a Capsule.toml listing everything it may touch. A key is a capability token: ed25519, scoped, expiring, revocable.
A fixed set of tools would make the keyring a cage. So it is not fixed.
Give the helper a job nothing on the ring can do, and it designs a new tool itself. But it has to write the label first, the full list of what the tool may touch, and show it to you. Nothing runs until you approve the label.
Notice what you approved. Not the code, not the helper's intentions, just the label. Everything after that is held by the same doors as every other tool.
This is Forge. The agent can “design a capsule, declare the access that capsule needs, build it, and request live installation”. You approve the boundary; it never starts before that.
One check can have one bug. So there are six in a row, from different parts of the system, and all six have to say yes.
Astrid's own list, in this order: wasm sandbox · manifest gate · ipc acl · capability token · approval gate · os sandbox.
Every decision gets written down. The clever part is the glue.
Each page carries a number made from the page before it. Change one word on page two and page three is pointing at a page that no longer exists, and so is every page after it. Type in any page below.
You cannot repair one page. You would have to redo every page after it, and the signatures still would not match.
The audit chain: signed, hash-linked JSONL, split per principal and independently verifiable.
And the two halves meet. The same company ships Sphere, a wallet that gives these agents an identity and money on the network from part one. A helper that can hold a coin, prove it spent it once, and never reach past its keys. That is the whole plan.