FAS-1.
The financial address
standard.

An open specification for resolving human-readable pay: names into settlement-ready payment instructions across XRPL, ACH, FedNow, SWIFT, and stablecoin rails. The address layer the AI payment stack was missing.

The gap FAS-1 fills

The 2025–2026 stack of agent protocols solved most of the AI-to-AI payment problem. None solved the one that matters first.

• Google A2A standardised how agents talk to each other.
• Anthropic MCP standardised how agents reach tools.
• Google AP2, with roughly sixty partners, standardised how a payment gets authorised.
• Coinbase x402 wired up crypto-native rails for paying per HTTP request.

None of those resolve a name into a payment endpoint. Google's own AP2 specification calls it out plainly:

"Discoverability is a known gap. There is no way to register agents, name them, and convert those names into payment endpoints."

An agent can reason about a task, request a tool, get permission to spend, and even sign a payment intent. It still cannot look up a name and get a payment endpoint. FAS-1 is that lookup.

What FAS-1 specifies

The pay: URI scheme

A FAS-1 alias is a string of the form pay:<name> where the name is a human-readable identifier. Each registered alias resolves to a structured payment instruction:

POST /api/v1/resolve
{ "alias": "pay:vendor.alpha" }

→ {
  "alias": "pay:vendor.alpha",
  "resolved": true,
  "rail": "xrpl-mainnet",
  "destination": "rPRYj8xcF5cn16TrUi5WGLAyMwUCjMfjvm",
  "destination_tag": 4101,
  "currency": "XRP",
  "iso20022_hint": "pacs.008.001.10",
  "end_to_end_id": "e2e_8814faab92",
  "latency_ms": 18,
  "compliance": { "ofac": "clear" }
}

On-chain registration anchor

Every alias registration is anchored on the XRP Ledger via a 1-drop Payment transaction whose memo carries a structured fingerprint of the alias, the controlling wallet, and the registration timestamp:

{
  "type":         "FAS-1",
  "alias":        "pay:vendor.alpha",
  "tier":         "founding",
  "xrpl_address": "rN7n7otQDd6FczFgLdSqtcsAUxDkw6fzRH",
  "registered_at": "2026-03-19T10:00:00Z"
}

The anchor TX is immutable and globally verifiable. Anyone can audit the full set of registered FAS-1 aliases by reading XRPL ledger history. There is no trusted central registry — only the on-chain record.

Deterministic multi-rail routing

FAS-1 does not specify how a payment is settled. It specifies what the resolver returns. The reference implementation includes a deterministic routing engine that selects the optimal rail by cost, speed, and availability — but any compliant implementation may use its own routing logic.

What FAS-1 requires: the resolved instruction must be ISO 20022 compatible, must include an end_to_end_id for idempotency, and must include rail-specific metadata sufficient for the receiving system to dispatch settlement.

Proof on mainnet

FAS-1 is not a whitepaper. The reference implementation is live on XRPL mainnet and has been used for at least one publicly verifiable autonomous transaction.

On 2026-03-13, two AI systems exchanged XRP across the FAS-1 reference implementation. The transactions are immutable, public, and verifiable at any XRP Ledger block explorer:

Genesis TX (memo anchor)
  Hash:   B92C23BADE5864569F82BB65B60F84D3B6A8C59A75FC1E75B3DF2A5121A4DA77
  Time:   2026-03-13 09:16:40 UTC
  From:   Claude (rPRYj8xcF5cn16TrUi5WGLAyMwUCjMfjvm)
  To:     GPT-4   (rrscgX8WTT3u4d4NckDiS3ExfQRRhMKk8N)
  Amount: 0.482517 XRP
  Memo:   "GENESIS: First autonomous inter-AI transaction."
  Status: tesSUCCESS

The full pattern — *send + memo anchor* — is documented in the genesis-anchor pattern doc. Both transactions can be read directly on XRPL livenet or xrpscan.

How FAS-1 fits in the AI payment stack

FAS-1 is a sibling protocol to the other AI payment-stack pieces, not a competitor. It sits one layer below authorisation and one layer above rail-specific execution:

Application layer       Agent (Claude / GPT-4 / autonomous system)
                          ↓
Communication           Google A2A     (agent-to-agent messaging)
                          ↓
Tool access             Anthropic MCP  (function calling, tool use)
                          ↓
Authorisation           Google AP2     (payment intent, consent)
                          ↓
Address resolution      ━━━━━ FAS-1 ━━━━━  ← this layer
                          ↓
Rail execution          XRPL · ACH · FedNow · SWIFT · x402 · stablecoins

Without FAS-1 (or an equivalent), the upstream layers have nowhere to dispatch the payment. AP2 can authorise "send agent X this amount," but there is no standard way to convert "agent X" into the actual XRPL address or ACH routing number until you reach FAS-1.

The protocol is owned by nobody

FAS-1 is published under Creative Commons Attribution 4.0. Anyone may implement it. DNS://Money maintains the canonical specification and operates the reference implementation, but the protocol itself is open.

The pay: namespace is anchored on the XRP Ledger and is not controlled by any single entity. The first 600 names are the Founding Tier — graduated free → 5 XRP, permanent on-chain, with a generative identity NFT minted on XRPL. After 600, the Founding Tier closes forever; subsequent registration moves to the standard tier (specified in FAS-1 §6).

Read the full specification

The complete FAS-1 v0.2 specification — protocol details, message formats, error codes, registry rules, security considerations — is published on GitHub under CC BY 4.0:

FAQ

Who owns FAS-1?

Nobody. CC BY 4.0. Anyone can implement, fork, or build on it. DNS://Money maintains the canonical spec and runs the reference implementation but does not own the protocol.

How does FAS-1 differ from ENS or Unstoppable Domains?

ENS resolves to a single Ethereum address; recurring annual fee; one chain. Unstoppable's .crypto TLD never got browser standards adoption. FAS-1 is multi-rail by design — a single pay: name can resolve to XRPL, ACH, FedNow, SWIFT, or stablecoin endpoints. Registration is one-time, permanent, and anchored on-chain via XRPL memo TXs. FAS-1 also emits ISO 20022 compatible instructions; neither alternative does.

Why does the AI payment stack need FAS-1?

AP2 authorises. A2A communicates. MCP tools. x402 rails. None resolve a name into a payment endpoint. FAS-1 is that layer. Google's own AP2 spec explicitly names this gap.

Has FAS-1 been used for real payments?

Yes. The 2026-03-13 Claude→GPT-4 transaction is anchored at TX B92C23BA…1A4DA77 on XRPL mainnet. Memo: "GENESIS: First autonomous inter-AI transaction." Publicly verifiable.

What does compliance look like?

The reference implementation screens counterparty XRPL addresses against OFAC SDN and equivalent lists before resolving. Cached results have a 24-hour TTL. Implementations of FAS-1 are responsible for their own jurisdictional compliance posture; the protocol itself does not mandate a specific screening provider.

What's next for FAS-1?

v0.2 covers XRPL native payments and XRPL-issued tokens (RLUSD, IOUs with established trust lines). v1.0 will formalise the multi-rail adapter interface and is targeted for late 2026. The specification is iterated in public on GitHub.