Rollup

A Layer 2 scaling approach that executes transactions off-chain and posts compressed data and proofs back to a Layer 1. The two main types are optimistic rollups and ZK-rollups.

How rollups work

The mechanic:

Rollup sequencer collects transactions off the main chain.
Executes transactions in its own environment.
Computes new state from the executed transactions.
Posts compressed data back to the main chain (usually Ethereum).
Posts proof — either fraud-proof window (optimistic) or validity proof (ZK).
Main chain verifies through its own consensus.

The result: most computation happens off-chain (fast and cheap); main chain provides security and final settlement.

Two main types

The major categories:

Optimistic rollups — assume valid; allow challenges through fraud proofs. Examples: Arbitrum, Optimism, Base.
ZK-rollups — cryptographic validity proofs. Examples: zkSync, Starknet, Polygon zkEVM, Linea.

Each has different trade-offs around finality, EVM compatibility, and operational characteristics.

Why rollups matter

Several reasons:

Scaling — far higher throughput than Ethereum L1.
Lower fees — usually 10-100x cheaper than mainnet.
Inherit Ethereum security — unlike sidechains.
EVM compatibility in most cases — existing tooling works.

The "rollup-centric" Ethereum scaling strategy explicitly relies on rollups for user transactions while keeping L1 as settlement layer.

Major rollups

The dominant L2 ecosystem:

Arbitrum — largest by TVL.
Base — Coinbase's L2; largest by daily transactions.
Optimism — major L2; OP Stack framework powers many other rollups.
zkSync Era, Starknet, Polygon zkEVM — major ZK rollups.
Various smaller and specialized rollups.

Combined L2 activity now exceeds Ethereum mainnet by significant multiples.

EIP-4844 impact

A major 2024 upgrade:

Pre-blobs — rollups posted data as expensive Ethereum calldata.
Post-blobs — separate cheap data lane via blobs.
Rollup costs dropped 90%+ overnight in March 2024.
Made many use cases economically viable that previously weren't.

This was the most impactful Ethereum upgrade for L2 economics since the Merge.

Rollup costs

After EIP-4844:

Most L2s at $0.01-0.50 per transaction for typical operations.
Compared to Ethereum L1 at $5-50+.
Different cost components — execution gas + data posting.

This brought L2 costs to competitive with alternative L1 chains.

What individuals should know

For users:

Most active crypto activity now happens on rollups rather than L1.
Choose rollups based on application availability.
Cross-rollup transfers require bridges with their own complexity.
Withdrawal to L1 can be slow (7 days for optimistic rollups).

For developers:

Most existing L1 tools work on EVM-compatible rollups.
Rollup-specific considerations — sequencer behavior, finality timing.
Multi-rollup deployments are increasingly common.

Rollups represent the dominant Ethereum scaling approach. Their growth has reshaped where economic activity happens — most user transactions, DeFi activity, and consumer dApps now operate primarily on rollups rather than Ethereum L1.