Across Protocol, one of the most widely used token bridges connecting Ethereum L1 <> L2s, recently released a new roadmap. In its announcement article, Across emphasizes doing “more with less”. Along the same lines, here’s a simplified breakdown of their comprehensive roadmap aiming to understand Across’s vision and future plans from first principles.
What is Across? A look back.
Across is one of the most widely used token bridges connecting Ethereum <> L2s. It offers low-cost, fast, and optimistically validated bridging on top of UMA’s Optimistic Oracle.
Stats — Over $1.5B in volume across 5 supported chains in 1.5 years.
Focus — Maximizing capital-efficient token bridging by unifying liquidity and absorbing finality risk.
Across’ Vision – A look ahead.
Across’s roadmap shows the bridge is making an effort to continue offering cross-chain tech focused on moving tokens across chains efficiently. Here’s how Across plans to do so:
1. Expanding support to multiple EVM chains through the Universal Bridging Adapter (UBA).
Similar to Connext and Hop, Across believes in canonical bridge maximalism – where canonical bridges (aka native bridges) are used to pass messages or send tokens across chains for rebalancing a liquidity network’s liquidity pools. Canonical Bridge Maximalism has become quite popular recently as canonical bridges have the least amount of trust assumptions baked into their architecture, which makes them near-perfect building blocks for liquidity networks to build on top of.
However, canonical bridges, by design, are only available for L2s at the moment, so this type of configuration restricts Across from expanding to chains that don’t have canonical bridges (Across supports Ethereum and Ethereum L2s (Arbitrum, Optimism, and Polygon) at the moment). Thus, to expand to multiple EVM chains without compromising security, Across is launching its Universal Bridging Adapter (UBA).
What’s UBA? Brace yourselves because it has all the right keywords ;)
The Universal Bridging Adapter (UBA) enables Across to connect to any EVM bridge using zk messaging by Succinct and optimistic verification by UMA.
Let’s break look at each component here:
zk messaging — To send messages from Ethereum to any EVM Chain, Across has partnered with Succinct, a project aspiring to bring trust-minimized interoperability to Ethereum via proof of consensus (using zero-knowledge proofs). Together, the teams are building zk-powered tech that allows unidirectional message passing from Ethereum to any EVM chain.
Optimistic verification — Across is powered by UMA’s Optimistic Oracle. The Optimistic Oracle is used to resolve disputes on Across — meaning that it is in charge of deciding whether or not the details posted by a Relayer about the transaction coming from an L2 to L1 is correct. The Optimistic Oracle allows any Relayer to dispute transaction details reported by another Relayer. Once disputed, the Optimistic Oracle funnels the transaction through a data verification system that relies upon UMA token holders to decide whether or not a transaction is valid or not. Any Relayer that successfully disputes transaction details of another Relayer may then claim the original Relayer’s bond.
Dynamic pricing — Currently, Across uses canonical bridges to rebalance its pools. To overcome this hurdle for chains without canonical bridges, Across is developing a novel pricing mechanism that rewards or penalizes bridging flows to particular chains based on the current state of the pools at a specific time. For instance, if Across’ pool on Polygon is running low on liquidity, users bridging to Polygon will be rewarded for essentially re-filling liquidity on that pool. Similarly, users who bridge away from Polygon at that time will be penalized for draining the pool further.
2. Enabling messaging + token bridging in the same transaction via Composable Bridging.
Bridging tokens from one chain to another is great, but it’s only the beginning of what is possible with bridges. The ability to send a message along with tokens across chains in the same transaction makes it possible to execute more complex cross-chain flows. Message passing opens up new possibilities and that’s exactly what Across aims to unlock: allowing users to bundle instructions for what to do with the tokens once they are bridged.
This is essentially the functionality offered by arbitrary messaging bridges (AMBs). However, Across argues that unlike AMBs, messages sent via this approach don’t have the economic security issues associated with an unbounded value of messages since the message is only as valuable as the funds being bridged in that specific transaction and not all the funds moving through the system at any given time. In other words, Across is making a bet that the only message that users will want to send across chains will come with some type of token action on the destination chain.
3. Capital recycling.
Across’ current approach for bridging tokens essentially involves Relayers providing upfront capital for user transfers which the LP reimburses after UMA’s Optimistic Oracle verifies a transaction's validity. As the optimistic verification process is permissionless, i.e., anyone can propose and dispute proofs, the current repayment cycle takes 3 hours (2 hours challenge period + ~1 hour for repayments to settle). This repayment cycle is relatively long and creates an inefficiency in the system where Relayer capital cannot be utilized for approx. 3 hours, which also caps the maximum fast transfer throughput of the bridge.
To overcome this inefficiency, Across is introducing a concept called Capital Recycling, which will allow the DAO to elect Proposers responsible for submitting valid relay proofs. This will significantly reduce the challenge period, allowing Relayers to recycle their capital almost continuously and increasing the capital efficiency of the protocol.
With the current approach, the relayers had to provide upfront capital for user transfers and wait for reimbursement from the LP. This resulted in inefficient use of capital and limited the maximum fast transfer throughput of the bridge. However, with the new Capital Recycling approach, the relayers can recycle their capital almost continuously, allowing for much more efficient use and higher transfer throughput.
That being said, improved capital efficiency will have trade-offs (and kudos to the Across team for pointing this out themselves) – the change to a permissioned proposer opens up the risk of censorship, but Across believes that this risk can be mitigated by the DAO replacing the Proposer if it suspects censoring behavior. It’s important to point out that this is an assumption made on Across’ part that the DAO can effectively and timely replace a Proposer in such a manner.
4. More capital efficiency through predictive rebalancing.
As a protocol with a hub and spoke model, Across can rebalance its pools via canonical bridges. However, canonical bridges lock capital for 7 days making the capital unavailable for that period. To overcome this locking issue, Across is introducing the concept of predictive rebalancing.
Predictive rebalancing of pools uses historical data to predict how much money will need to be moved between pools and sets a target threshold. This allows Across to selectively not rebalance certain pools (based on historical user flows), given the high probability of the pool rebalancing on its own in the future. As a result, it makes the protocol more capital efficient since the capital doesn’t need to be locked in for 7 days and instead can be used for fulfilling existing transactions.
In addition to platform-level improvements, Across is also making overall improvements to the protocol by offering:
Optimistic governance and community – integrating decentralized governance via oSnap which empowers the DAO to execute the results of Snapshot votes on-chain independently.
Community and growth initiatives – using community NFTs to incentivize deeper ACX liquidity and improving the bridging user experience by working on brand and UI enhancements.
Closing Thoughts
This guy said it best :)
Across Protocol deserves praise for its innovative approach to developing its platform. Rather than simply building another messaging bridge, the team has taken a unique approach to address the challenges of the cross-chain ecosystem. We’re excited to support Across in their journey.
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