Ethereum L1 and L2

Ethereum L1 is the base chain — the thing every node validates — with hard limits on throughput (~15 TPS) and brutally high fees at peak. L2 is the family of solutions built on top that batch many transactions off-chain and post compressed proofs back to L1, inheriting its security but with 10-100x lower fees and much higher throughput. Two main flavours: optimistic rollups (Arbitrum, Optimism, Base) assume transactions are valid and let anyone challenge fraudulent ones within a 7-day window; zk-rollups (zkSync, Starknet, Polygon zkEVM) prove validity cryptographically, no challenge window needed. The mental model: L1 is the settlement court of last resort, L2 is where the day-to-day trading and DeFi actually happens now. Most DEXes and apps are already multi-chain across L2s.