Withdrawing from an L2: why the native bridge holds your money for a week and how people get around it

The first withdrawal from Arbitrum or Optimism through the native bridge greets the user with a surprise: funds will arrive in ~7 days. That is not a broken interface - it is the challenge window, the security foundation of optimistic rollups.

Why a week is needed

An optimistic rollup publishes the network's state to Ethereum without proofs - "optimistically". Network watchers can challenge a fake record by presenting a fraud proof, and a window of several days is reserved for that. While the window is open, the withdrawal is not final: if money were released instantly, a malicious sequencer could withdraw other people's funds before being exposed.

How fast bridges work

Third-party bridges pay out at the moment of the request from their own liquidity pool on the destination network, and collect your "slow" withdrawal themselves a week later. They charge a fee for this - effectively interest on a one-week loan. The risk moves to the bridge: if its pool or contract gets hacked, the fast withdrawal turns into a loss. Bridge hack stories are a genre of their own - we have a section for it.

In practice: large amounts with no rush - the native bridge; small and urgent - a proven fast bridge; and never keep more in bridges than you are ready to lose.