Arbitrum

How it works

Arbitrum batches Ethereum transactions and executes them off-chain, then posts a compressed summary back to Ethereum along with cryptographic data sufficient to reproduce the result. Validators on Ethereum don't re-execute every transaction; instead, they assume the rollup's claim is correct ("optimistic"), with a 7-day window during which any observer can submit a fraud proof if the claim was wrong. If the fraud proof succeeds, the bad state is reverted; if no challenge appears, the rollup state finalizes on Ethereum.

This is the optimistic rollup design, which Arbitrum and Optimism both use. The seven-day window is the trade-off: it inherits Ethereum's security guarantees but introduces a long delay for trustless withdrawals back to L1. Most users withdraw faster through third-party "fast bridges" that take on the timing risk in exchange for a fee.

Why it succeeded

Arbitrum was one of the earliest and most aggressively adopted L2s. Three reasons stuck:

• Full EVM compatibility. Existing Ethereum contracts could be deployed to Arbitrum with no code changes, and existing tooling (MetaMask, Hardhat, ethers.js) just worked. This made migration nearly free for developers.
• Lower fees, retained security. A typical Arbitrum transaction costs a small fraction of the equivalent Ethereum mainnet transaction, while still settling to Ethereum.
• Strong DeFi presence. Aave, Uniswap, GMX, Camelot, and others deployed early and brought meaningful TVL with them.

By 2023, Arbitrum routinely ranked first or second in L2 total value locked.

Tokenomics and governance

The ARB token launched in March 2023 via an airdrop to historical Arbitrum users — over 600,000 wallets received tokens. ARB is a governance token; it lets holders vote on protocol upgrades, treasury spending, and parameter changes through the Arbitrum DAO. ARB does not pay for gas — gas on Arbitrum is paid in ETH, like Ethereum mainnet.

The DAO controls a multi-billion-dollar treasury, making it one of the largest funded treasuries in crypto. Spending decisions have included grant programs, ecosystem incentives, and infrastructure funding.

The Arbitrum stack

Beyond the main "Arbitrum One" chain, Offchain Labs (the team behind Arbitrum) ships a broader stack:

• Arbitrum Nova — a separate chain with cheaper fees but slightly weaker security, aimed at gaming and consumer use cases.
• Arbitrum Orbit — framework for launching custom L3 chains that settle to Arbitrum One.
• Stylus — VM upgrade letting developers write contracts in Rust, C, or C++ alongside Solidity.