# PIP-0003 · Rail profiles

Named mappings from PATH’s last mile onto rails that already settle — UPI, Pix, SEPA Instant.

## Why

PATH does not replace an instant rail. It names the last mile — who, where, what is owed, who may act, whether it arrived — in a form another scheme can read. A rail profile is that mapping. Without a PIP, each integrator invents a private translation and two PATH addresses that should be able to meet, cannot.

A rail profile is not a [`gateway`](/docs/finder#holder-and-gateway). A profile is vocabulary: which PATH object is which rail object. A gateway is whose terms an answer carries. A member settling its own customers over Pix uses the profile and is not a gateway. A gateway uses the profile as well.

## What a profile is

A profile is a published table: PATH object → rail object. It is not a new pillar. It does not add a colour, a wallet, or a PATH rail. Liquidity stays reserved.

A profile includes the rows that cannot be translated. Omitting them is a non-conformity.

| PATH | Rail |
|---|---|
| PATH ID | The scheme’s customer reference, where one exists |
| PATH ADDRESS — capability | The rail identifier and the currencies the scheme carries |
| PATH ADDRESS — instruction | The scheme’s beneficiary formats, and its remittance field as `payment_reference` |
| PATH REQUEST | The claim the scheme already collects, through its request-to-pay service when it has one |
| PATH CONNECT | Who may instruct the scheme |
| PATH SETTLEMENT | The scheme’s own transaction identifiers, as `rail_references` types, quoted rather than replaced |

A profile fills the rail's entry in the rail register ([PIP-0007](/pips/0007)): `beneficiary_formats`, `rail_reference_types`, `payment_reference`, `request_overlay`. Publishing it moves the rail from `reserved` to `profiled`.

## First profiles

UPI, Pix, SEPA Instant. Each profile is a later PIP or an annex. This PIP only fixes that a profile is a document, that it is public, and that a network claiming a rail without publishing the table is non-conformant.

**A profile is written when a member first touches that rail**, not in advance of anyone using it.

What sits above or below a rail is described in that rail's profile, not as a rail of its own. SPI, the settlement system under Pix, is part of the `pix` profile. Wero is part of the `sepa-inst` profile. CoDi is the request-to-pay service of the `spei` profile.

## Rail identifiers

Rail identifiers take one spelling, fixed by the rail register ([PIP-0007](/pips/0007)): the scheme's short name, lower case, with a country suffix only on collision. A profile uses the register's identifier.

## What it is not

It is not admission to those rails. PATH cannot seat a member at UPI. A club that wants to speak UPI still admits under its own rulebook, and the rail still admits under its own.