Arbitrum vs Optimism, what is the difference?

Arbitrum vs Optimism is a comparison of two of the largest layer 2 networks on Ethereum. Both are optimistic rollups, so they process transactions off Ethereum, post the data back to it and assume results are correct unless someone proves otherwise. The differences lie in the software, the dispute process, the fee formula and who controls upgrades.

What is an optimistic rollup?

A rollup bundles many transactions and publishes them to Ethereum. In the optimistic type, results are accepted unless challenged with a fraud proof. As of October 2026, L2BEAT lists both Arbitrum One and OP Mainnet as Stage 1, meaning users can exit even if operators misbehave, but a security council can still step in. Each runs a single sequencer, and users can force transactions through Ethereum if it fails, with a delay of up to one day on Arbitrum and 12 hours on OP Mainnet.

How do Arbitrum One and Optimism differ technically?

• Software. Arbitrum One runs Arbitrum's own Nitro software. OP Mainnet runs the OP Stack, an open toolkit many other chains also use.
• Fraud proofs. Arbitrum uses BoLD, an interactive challenge game ending in a one-step proof. L2BEAT lists a challenge period of 6 days and 8 hours for an unchallenged assertion. OP Mainnet uses permissionless fault dispute games with a 0.08 ETH bond, where each move has a clock of 3.5 days that can be extended.
• Governance. ARB holders vote in the ArbitrumDAO, which governs Arbitrum One and Nova and a 12-member Security Council. Optimism splits power between a Token House of OP holders and a Citizens' House with one vote per member.

More detail is in what is Arbitrum and what is Optimism.

How do Arbitrum vs Optimism fees work?

Both charge in ETH, and both pass on part of Ethereum's cost of storing their data.

• Arbitrum. The user sees one fee, the network's gas price times a gas limit. The cost of posting compressed data to Ethereum is converted into extra gas and added on.
• OP Mainnet. The fee has three parts: an execution fee, a base fee plus optional tip as on Ethereum, an L1 data fee that tracks Ethereum's fees, and an operator fee set by the chain operator.

Actual costs change with demand on each chain and on Ethereum, so compare live quotes in your wallet rather than relying on fixed figures.

Arbitrum vs Optimism vs Base, where does Base fit?

Base, the network built by Coinbase, is also an optimistic rollup that uses ETH for gas and is listed as Stage 1 by L2BEAT. It launched on the OP Stack. In February 2026, CoinDesk reported that Base would move to a single codebase it runs itself, while staying compatible with OP Stack standards during the switch. Its proof system now combines TEE and zero-knowledge proofs, according to L2BEAT.