Layer 2 (L2)
Networks built on top of L1 (mainly Ethereum) for scalability and lower fees.
L2: bundle tx off-chain, periodically post proofs to L1. Types: Optimistic (Arbitrum, Optimism, Base: 7-day fraud proof window) and ZK (zkSync, Starknet, Linea: crypto proofs, faster withdrawal). Fees 10-100x lower. Top L2 TVL >$50B (2025). Base (Coinbase) growing fast.
In plain words
Networks built on top of Ethereum that bundle many transactions and post only the summary to the main chain. Fees are 10-100x lower and tx faster. Most popular: Arbitrum, Optimism, Base (Coinbase). Most DeFi activity is moving here.
Example
Top L2: Arbitrum ($18B TVL), Base ($15B), Optimism ($5B), zkSync ($1B). Swap on Arbitrum: ~$0.30 vs $10 on ETH. Tokens: ARB, OP. Base no token (Coinbase strategy).
Also known as: L2, Layer 2, rollup