PATH Protocol

Why

A capability names a representation: fiat on a rail, or a token on a chain (PIP-0006). A treasury token and a book entry at its issuer can be the same claim. The capability does not say so. A receipt that sends the token and receives fiat then has the same shape as an exchange.

This PIP names the claim. A real-world asset (RWA) is that claim. The capability stays one representation of it, on one rail.

What an RWA is

Term	Meaning
Instrument	The claim. An issuer and an identifier. Independent of any rail.
Representation	How that claim appears on one rail. This is the capability: a token on a chain, or fiat on `book` or another rail.

Across two networks, a representation moves, or one representation is retired and another is issued. The underlying stays with the issuer. PATH carries the signed statement. It does not hold the asset.

asset_type stays fiat or token. An RWA is not a third asset type and not a rail.

The field

instrument is optional on a capability. Absent, the capability is unchanged: the asset is the fiat currency or the token.

{
  "rail": "blockchain",
  "chain": { "slug": "base", "caip2": "eip155:8453" },
  "asset_type": "token",
  "asset_code": "TBILL",
  "standard": "erc20",
  "contract": "0x1111111111111111111111111111111111111111",
  "instrument": { "issuer": "member-a", "id": "tbill-2026-03" }
}

{
  "rail": "book",
  "asset_type": "fiat",
  "asset_code": "USD",
  "instrument": { "issuer": "member-a", "id": "tbill-2026-03" }
}

The two capabilities above are two representations of one claim. An address that accepts both lists both.

Field	Rule
`issuer`	Required with `id`. When the issuer is a PATH member, the member slug. Otherwise a string the signer chooses.
`id`	Required with `issuer`. The issuer's identifier for the claim.
Together	Both present, or the whole `instrument` omitted. Never `null`.
Length	Each value is 1 to 128 characters, with no leading or trailing space.

Where it appears

A capability carries it, so the existing objects carry it in the same place:

Object	Field
Standing intent	`accepts[]`
Payment request	`accepts[]`, frozen at issue
Payment instruction	`via`
Receipt	`via`

sent and received stay amounts. They do not carry instrument. When they differ, fx stays required (PIP-0011). This PIP does not redefine exchange. A reader that sees the same instrument on two capabilities may treat them as one claim. PATH does not pair the receipts: the parties match them by instruction, rail_references, or an attestation, as in PIP-0011.

Statement

instrument is part of the signed object. It states which claim the signer means. PATH does not resolve issuer, does not keep a register of instruments, and does not check that a contract belongs to that issuer.

What stays unchanged

One capability is one rail and one asset.
On book, the asset stays fiat (PIP-0007).
route stays null. Its shape is PIP-0005. Filling it is still PIP-0004.
PATH does not set a price, take custody, or transfer title. Classification of the instrument stays with the operator.

Canonical form

These rules apply before any digest or signature, with the rules of PIP-0006.

Element	Rule
Absent `instrument`	Omitted. Never `null`.
`issuer`, `id`	Strings, as in the table above. Not normalised beyond trimming.
Order	`issuer`, then `id`.
`grammar`	An object that carries `instrument` states `grammar: 3`.

A grammar: 2 object omits instrument. A reader does not treat it as naming a claim.

Until this is implemented

Implementations omit instrument and emit grammar: 2. A grammar: 3 object is defined here and is not part of the current version.

RWA: the claim and its representations