A layer-2 scaling solution that executes transactions off-chain and posts compressed transaction data back to the main chain. Rollups inherit the security of the underlying layer 1 while dramatically increasing throughput. The two main types are optimistic rollups and zero-knowledge rollups.
Rollups are the dominant approach to scaling Ethereum, processing transactions off-chain and posting compressed data or validity proofs to the base layer. By bundling hundreds or thousands of transactions into a single L1 submission, rollups dramatically increase throughput while inheriting Ethereum's security. This approach is central to Ethereum's modular scaling roadmap.
The two main types are optimistic rollups, which assume transactions are valid unless challenged via fraud proofs (7-day dispute window), and ZK-rollups, which generate cryptographic proofs of validity for each batch (no dispute period needed). Optimistic rollups are simpler to implement and currently dominate by TVL, while ZK-rollups offer faster finality and better long-term scaling potential.
Optimistic rollups assume validity and use fraud proofs with a 7-day challenge period. ZK-rollups generate mathematical proofs of validity for each batch. ZK-rollups offer faster finality but are more complex to implement. Both inherit L1 security.
Yes, rollups are central to Ethereum's scaling roadmap. The Ethereum Foundation has explicitly stated that rollups are the primary path to scaling Ethereum. Future upgrades like full danksharding will further reduce rollup costs.
Rollups batch many transactions together, amortizing the cost of L1 data posting across all transactions. A batch of 1,000 transactions costs only slightly more than a single L1 transaction to post, making each individual transaction 100-1000x cheaper.
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The base blockchain protocol that processes and finalizes transactions on its own network. Examples include Bitcoin, Ethereum, Solana, and Avalanche. Layer 1 blockchains provide the fundamental security and consensus that other layers build upon.
Layer 2A secondary protocol built on top of a layer-1 blockchain to improve scalability and reduce transaction costs. Layer 2 solutions process transactions off the main chain and periodically settle them on layer 1 for security. Examples include Arbitrum, Optimism, and the Lightning Network.