Arbitrum Nitro and Stylus

Arbitrum's Position in the L2 Landscape

Arbitrum, run by Offchain Labs and now governed by the Arbitrum DAO, is the largest L2 by TVL — generally $15-20B depending on the cycle, ahead of Base, OP Mainnet, zkSync, and others. It's an optimistic rollup: transactions are assumed valid unless someone submits a fraud proof during a 7-day challenge window. The 'optimistic' label captures the trust model; the architecture has gone through multiple major redesigns since launch in 2021.

Arbitrum One vs Arbitrum Nova vs Arbitrum Orbit

Three distinct things called 'Arbitrum.' **Arbitrum One**: the main rollup, security from Ethereum, where most TVL and dApps live. **Arbitrum Nova**: an AnyTrust chain (DA via a Data Availability Committee instead of Ethereum) — much cheaper but with weaker trust assumptions. Used for gaming and high-frequency apps. **Arbitrum Orbit**: open framework for launching new chains using Nitro stack. Multiple production chains run on Orbit, similar in concept to OP Stack.

What 'Nitro' Brought

Nitro (deployed August 2022) was a major rewrite that replaced Arbitrum's original custom execution architecture with Geth (the most common Ethereum client) compiled to WebAssembly (WASM). This made Arbitrum much more EVM-compatible — anything that runs on Ethereum runs on Nitro essentially unchanged. It also made the fraud-proof system simpler: instead of proving custom execution, fraud proofs prove WASM execution, which is well-understood.

• Largest L2 by TVL — $15-20B sustained
• Arbitrum One = main optimistic rollup; Nova = AnyTrust variant; Orbit = chain framework
• Nitro (Aug 2022) = Geth-on-WASM architecture, dramatically improved EVM compatibility
• 7-day fraud-proof window applies to all withdrawals