Relayer Nomination

What is relayer nomination?

Relayer nomination (or relayer exclusivity) provides a single relayer with a time-limited period of exclusivity to fill a given deposit. Exclusivity is assigned at deposit time via the exclusiveRelayer and exclusivityDeadline arguments to an Across deposit, and are emitted as part of the V3FundsDeposited event. The exclusiveRelayer address has until the exclusivityDeadline timestamp on the destination chain to complete the fill with no risk of collisions. If the deposit remains unfilled on the destination chain beyond exclusivityDeadline then the fill becomes available for other relayers to complete.

Why is this helpful?

Speed-based relayer competition can lead to collisions and gas price competition amongst relayers. Many relayer implementations have reached a point of maturity where additional speed gains are difficult to unlock and increasingly encroach on origin chain finality guarantees.

Relayer exclusivity provides a means of retaining the speed gains that Across has unlocked for users whilst reducing uncertainty and risk for relayers. Relayer exclusivity also provides a method of evaluating relayer performance and in terms of speed and availability, and enables a pathway to future order flow preferencing. Relayers are therefore incentivised to do the following:

• Ensure that their implementations respect the exclusiveRelayer and exclusivityDeadline fields.

• Ensure that they react promptly when their own relayer address is specified on a new deposit.

How does relayer exclusivity work?

Relayers are nominated via the Across API.

There are a few steps to becoming eligible to receive exclusive flow:

The first step is that a relayer can signal their desire to be considered for nomination by submitting a Pull Request to the Exclusive Relayer Configuration repository. This repository exists as an interim system in order to fast-track the rollout of this program.

Once a relayer has signaled interest in becoming eligible for nomination, the relayer will begin receiving a biweekly score. The score that each relayer receives depends on a few metrics:

1. Reliability on nominated fills: The first component of a relayer score is whether the relayer shows up to complete transactions that they were assigned were assigned. If a relayer fulfills a high percentage of their assigned transactions then they will have a high score, if they do not, then they will have a low score.

2. Speed on nominated fills: The second component of a relayer score is whether they fill the nominated fills in a timely fashion. Relayer fill times are benchmarked against how fast a transaction would have been filled without exclusivity because we want the user experience to be excellent independent of whether it is being fulfilled by a nominated relayer or being run via the speed-based fill system.

3. Step-in fills: The final component of a relayer score depends on the relayer's ability to step-in and fill deposits that were missed by other nominated relayers. For example, if 0x123 was nominated to make a fill but didn't make the fill by their exclusive deadline then 0x234 could "step-in" and make the fill which would earn 0x234 points on their relayer score.

A relayer that is new to the nomination ecosystem will not be able to earn points from (1) and (2) which means that they can only enter the exclusive relayer set by making step-in fills. They should also demonstrate via filling open order flow that they can fill within an appropriate amount of time, i.e. if a relayer's bot always takes 30 seconds to make a fill then we are unlikely to add that relayer to the set given that most fills expect sub-10 second transactions.

When selecting an exclusive relayer for any particular deposit, the Across API applies a selection process that considers a number of inputs, including, the relayer's own configuration preferences, their token balance on the destination chain, and their relayer score. The exact implementation and criteria for the selection process is maintained by Risk Labs and is subject to change in order to optimize user experience and minimize externalities that leak value from the system.

When is relayer exclusivity being rolled out?

Relayer exclusivity is being rolled out incrementally in the Across API on select routes in order to trial the system — At this point the majority of flow coming from the Across FE is assigned an exclusive relayer. Performance is continually monitored by the Across team and adjustments are made as required. Third-party integrators are expected to begin incorporating relayer exclusivity in Q1/Q2 2025.