L2 Blockchain

L2 blockchains are built on top of L1 blockchains and they inherit finality from the L1 blockchain they rely on. There are several methods to achieve L2 finality:

1. Optimistic Rollups

   • Transactions are bundled and posted to the L1 blockchain as "commitments."

   • A "challenge period" allows for disputes if any fraud is detected. This period can last up to a week, delaying transaction finality.

2. ZK Rollups

   • Similar to Optimistic Rollups, but instead of a challenge period, transactions are validated using cryptographic proofs (validity proofs) before being finalized on L1.

   • This approach is faster but relies on specialized technology.

Note that, many L2 solutions, like rollups, use a centralized sequencer to order and bundle transactions before committing them to L1. While efficient, this method introduces trust dependency on the sequencer.