# PIP-0004 · Composable liquidity, still reserved

Keep the settlement `route` field empty until a later PIP specifies who may fill it.

## Why this exists

`route` is on every settlement receipt and is never populated. That is not an omission. It is a hole declared on purpose so that routing arrives later as an extension rather than as a migration for everyone who has already shipped.

This PIP records the refusal to fill `route` in v0.1, and the conditions under which a later PIP may.

## Rule, for now

Implementations MUST accept `route` and MUST leave it empty. A non-empty `route` in v0.1 is a non-conformity. PATH does not run a rail, and a network that puts its own corridor into `route` is inventing a PATH Liquidity that was not specified.

## When a later PIP may fill it

Only when all of these are true:

1. The field has a single canonical meaning across networks.
2. A receipt with a route and a receipt without one remain verifiable as the same kind of object.
3. Filling it does not require PATH to admit members or to hold balances.

Until then the status of this PIP is Backlog, and PATH LIQUIDITY stays reserved.