How Is Across Protocol So Fast?

tl;dr Across Protocol differs from other bridges in the way that we’re able to perform near-instantaneous transfers. When you bridge assets from L2 to L1 on optimistic rollups, you can expect a 7 day wait — not ideal, we know. When you use Across, you can expect to receive your funds in 1–2 minutes due to the speed of the relayers and our process of relayers giving funds to the user upfront, with the liquidity providers waiting through the challenge period and the relayers taking on 2 hours worth of liveness.

Across Protocol prides itself on speed. This may be apparent from our outward messaging, or perhaps you’ve done transfers on our cross-chain bridge and have experienced it yourself. With this being said, it may still be unclear exactly how we’re able to do this. This article aims to be your key to understanding exactly how we’re able to be so fast.

Let’s get into it.

To understand how we’re so fast, you’ll need to know what a relayer is. In short, a relayer “relays” information across chains. The relayer is an independent bot, separate from the core contracts.

The speed of our transactions depends on the speed of these relayers. The first one that answers the request is the one that will begin the process to fulfill the relay request.

The speed of these relayers is dependent on the relay code, which can be heavily optimized. People are economically incentivized to create exceptionally fast bots, as they want to reap the benefits that the relayers receive. The first person to receive the relay will reap the benefits, which are the “relayer fees.” These fees are set by the depositor and are a percentage of the deposited amount (to relay from origin to destination chain).

Across is able to do near-instantaneous transfers due to the fact that we operate optimistically. Typically, you can expect to receive your funds in 1–2 minutes.

In our optimistic approach, the relayer accepts the relay and provides a loan to the user. The relayer is fronting the money to the user because it trusts UMA’s Optimistic Oracle. Across differs in this sense because many other chains require multiple sign-offs, blocking the relayer from performing the relay. Nothing is blocking our relayer.

By functioning optimistically we can relay instantly, followed by a 2 hour challenge period. During this two-hour challenge period, the user is now out of the picture. They have already received their funds upfront from the relayer. This allows us to be very user-friendly. The relayer is trading places with the user in the sense that they’re willing to wait for the challenge window to complete. From the pool’s perspective, whether the user receives the funds upfront or not, there’s no difference in safety. By providing the funds upfront, we are able to provide the level of speed that you know and love from Across, with no compromise of safety.

As a side note, if something is disputed during the challenge period, the user does not endure any penalties. The user is completely out of the picture and does not accept any risk in this sense when bridging with Across, only the relayer does.

To see how this all comes together, check out the chart below showing a complete end-to-end flow of the process.

The speed of bridging with Across is dependent on the speed of the relayers, who are incentivized to be as fast as possible so they can reap the rewards from being a relayer.

Since relayers can spring into action without any on-chain triggers required, our design is the fastest that’s theoretically possible. You can’t get faster than Across Protocol.

If you’d like to learn more about Across, read our litepaper, visit our docs site, and jump into our Discord to join the conversation.