Rollups: Optimistic, ZK, and the Dencun Upgrade
Understand how rollups work, the difference between optimistic and ZK rollups, and how EIP-4844 (March 13, 2024) cut rollup fees by approximately 90 percent.
14 min · intermediate · part of Layer 2 Solutions & Scaling
What you'll learn
- What a Rollup Actually Is
- Optimistic Rollups vs ZK Rollups
- EIP-4844 (Dencun): The 90 Percent Fee Reduction
- Today's Rollup Ecosystem: Arbitrum, Base, Optimism, zkSync, StarkNet
- Using Rollups: Bridging, Networks, and Direct On-Ramps
Key terms
- Rollup
- A Layer 2 that executes transactions off the main chain and posts compressed data and proofs back to the main chain. Inherits the base chain's security through these commitments.
- Optimistic rollup
- A rollup that assumes batches are valid and uses a fraud-proof challenge window (typically 7 days) to handle disputes. Arbitrum and Optimism are the leading examples.
- ZK rollup (validity rollup)
- A rollup that posts a cryptographic proof (SNARK or STARK) demonstrating correct execution of every batch. Withdrawals can finalize within hours rather than the 7-day optimistic window. zkSync Era and StarkNet are examples.
- EIP-4844 (proto-danksharding)
- Activated March 13, 2024 in the Dencun upgrade. Introduced blob-carrying transactions (max 6 blobs per block) for cheap, temporary rollup data storage. Cut rollup fees by approximately 90 percent.
- Arbitrum One
- The leading optimistic rollup, mainnet launched August 31, 2021 by Offchain Labs. ARB token launched March 23, 2023 (10 billion supply, 11.5 percent airdrop). Approximately 16 billion dollars TVL in late 2025.
- Base
- Coinbase's OP Stack rollup, mainnet launched August 9, 2023 ("Onchain Summer"). No native token. Approximately 15 billion dollars TVL in late 2025.
- OP Stack / Superchain
- Optimism's open-source rollup framework. Powers Base, World Chain, Mode, Ink, Unichain, opBNB, and others, with shared security primitives.
- zkSync Era
- Matter Labs' EVM-equivalent ZK rollup, mainnet launched March 24, 2023. The first production-grade zkEVM rollup at scale.
- StarkNet
- StarkWare's ZK rollup, mainnet alpha launched November 29, 2021. Uses Cairo language and STARK proofs. Co-founded by Eli Ben-Sasson.
- Polygon zkEVM sunset
- Polygon announced in June 2025 that the zkEVM sequencer would shut down July 1, 2026 due to sluggish adoption and reported annual losses of over 1 million dollars.
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Open lessonEducational only — not financial advice.