Across Protocol: Fast Intent-Based Bridging

Across Protocol is a cross-chain bridge that fills user transfers in seconds via a solver network, then settles slower on the back end. For same-token bridges (USDC on Base to USDC on Arbitrum), it is faster and often cheaper than canonical bridges.

How it works

1. User deposits USDC into Across contract on source chain and specifies destination + minimum received.
2. Solvers (professional relayers) monitor deposits.
3. Winning solver fronts USDC on destination chain from their own inventory.
4. Solver later reclaims deposit from source chain's Across pool.
5. UMA optimistic oracle verifies the fill was correct; challenge period backs the settlement.

Speed

Same-token bridges: 5-30 seconds destination fill. Cross-token bridges: comparable, with swap routing added.

Cost

Solver fee: 0.02-0.15% of transferred amount depending on chain pair and speed. Cheaper than most CEX withdrawals for L2-to-L2.

UMA optimistic verification

Solvers can only reclaim source funds after a challenge window (~2 hours). If a fraudulent fill is detected, anyone can dispute and slash the solver's stake. This is what makes trusting solvers safe.

ACX token

Airdropped 2022 to early users. Governs the protocol, distributes fees.

Where Across fits

• L2-to-L2 same-token bridging (USDC on Base → USDC on Arb).
• L1-to-L2 fast bridging (ETH from Ethereum to Base).
• Any bridging where sub-minute UX beats waiting 10 min for canonical.