Scaling Ethereum has turned into a two‑horse race between Optimistic and Zero‑Knowledge (ZK) rollups. Here’s the plain‑English breakdown.

1. Why Rollups?

They bundle (or “roll up”) scores of L2 transactions into a single L1 call—cutting gas and boosting throughput without sacrificing Ethereum’s security.

2. Optimistic Rollups

Feature Detail
Assumption Fraud‑proof unless challenged within the dispute window.
Challenge Period 7 days (Arbitrum), 24 hrs (Base).
Finality Lag Users wait to be sure funds won’t be disputed.
Projects Optimism, Arbitrum, Base, Blast

3. Zero‑Knowledge Rollups

Feature Detail
Assumption Validity proofs generated upfront.
Finality Lag Minutes—no challenge window needed.
Cryptography zk‑SNARKs, zk‑STARKs (Succinct Non‑interactive ARguments of Knowledge).
Projects zkSync, Starknet, Linea, Polygon zkEVM

4. Choosing the Right L2

  • TX Volume & Fees – Optimistic still cheaper today, but ZK costs are falling.
  • Withdrawal Urgency – Need instant exits? ZK wins.
  • Developer Tooling – EVM‑equivalence is improving across both camps.

5. Looking Ahead

EIP‑4844 (“Proto‑danksharding”) will slash calldata fees, super‑charging rollup economics. Expect UX to become chain‑agnostic by 2026.