Across Protocol (ACX) is a cross-chain token bridge that strives to facilitate efficient transfers between different blockchain networks. It leverages UMA's optimistic oracle to verify transfers, ensuring a balance between speed and security. The protocol is designed to optimize capital efficiency through a single liquidity pool, a competitive relayer landscape, and a no-slippage fee model. Across Protocol intends to provide a bridging experience for users, eliminating the need for users or liquidity providers to bear protocol or finality risk.

Across Protocol operates by using third-party relayers who facilitate the bridging of assets. These relayers can choose to move funds faster than the origin or destination chain's finality times, allowing for quick transfers. The protocol uses UMA’s optimistic oracle to confirm that transactions on all chains are correct. If a transaction is incorrect, it will be disputed and resolved by UMA tokenholders. Across Protocol also employs a smart strategy of keeping funds on the chain they are already on if they are about to pass in opposite directions, and it rebalances automatically every 4-8 hours.

Across Protocol is designed to facilitate efficient and secure cross-chain transfers, making it a valuable tool for users who need to move assets between different blockchain networks. It can be used by individuals who want to bridge assets between Layer 2 solutions and the Ethereum mainnet. Additionally, liquidity providers can use Across Protocol to receive compensation from transfers, and third-party relayers can receive compensation by facilitating the bridging of assets. The protocol also includes a referral program and a locking program, providing additional ways for users to receive ACX.

Across Protocol was developed with the aim of creating a more efficient and secure bridge for Ethereum. It was designed to optimize capital efficiency and provide a bridging experience for users. The protocol has been audited by OpenZeppelin, a security audit firm in the blockchain space, to ensure its robustness and reliability. Over time, Across Protocol has evolved to include features such as a single liquidity pool, a competitive relayer landscape, and a no-slippage fee model, all of which contribute to its goal of providing efficient and secure cross-chain transfers.