Fast bridge (liquidity bridge)

Withdrawing from an optimistic rollup through its canonical bridge takes about a week because of the challenge period. A fast bridge, also called a liquidity bridge, skips that wait. The user deposits tokens on the source chain, and a relayer or solver who already holds funds on the destination chain sends the equivalent amount straight away, minus a fee. The relayer is repaid later, once the deposit is verified, often through the slower canonical route.

Most cross-chain transfers by retail users today go through this model, because it turns hours or days into seconds or minutes. Many such bridges are built around intents: the user states what they want to receive and competing fillers race to deliver it, which keeps fees tight.

Speed comes with dependencies. Users rely on relayers having enough liquidity, on the bridge's own contracts and on the system that settles repayments, which may use an oracle or its own security assumptions rather than the rollup's. Large transfers can face higher fees or delays when liquidity on one side runs thin. A fast bridge is not the same as the canonical bridge, even when both move the same token.