Nitro is the latest iteration of the Arbitrum technology. It is a fully integrated, complete layer 2 optimistic rollup system, including fraud proofs, the sequencer, the token bridges, advanced calldata compression, and more.

The Nitro stack is built on several innovations. At its core is a new prover, which can do Arbitrum’s classic interactive fraud proofs over WASM code. That means the L2 Arbitrum engine can be written and compiled using standard languages and tools, replacing the custom-designed language and compiler used in previous Arbitrum versions. In normal execution, validators and nodes run the Nitro engine compiled to native code, switching to WASM if a fraud proof is needed. We compile the core of Geth, the EVM engine that practically defines the Ethereum standard, right into Arbitrum. So the previous custom-built EVM emulator is replaced by Geth, the most popular and well-supported Ethereum client.

The last piece of the stack is a slimmed-down version of our ArbOS component, rewritten in Go, which provides the rest of what’s needed to run an L2 chain: things like cross-chain communication, and a new and improved batching and compression system to minimize L1 costs.

Essentially, Nitro runs Geth at layer 2 on top of Ethereum, and can prove fraud over the core engine of Geth compiled to WASM.

Arbitrum One will be migrated seamlessly onto Nitro. More details will follow about the timeline and plans for the migration.

During the devnet period, we have licensed Nitro under a Business Source License, similar to our friends at Uniswap and Aave. Before mainnet launch, we will be re-licensing the code in a more permissive fashion to ensure that everyone can have full comfort using and running nodes on Arbitrum One.