What is Arbitrum Nitro?

Nitro is the engine Arbitrum runs on. It went live on 31 August 2022, exactly one year after Arbitrum One launched, and replaced the network's original custom-built virtual machine. The old design worked, but it used a bespoke language and prover that were slow to maintain and held performance back. Nitro swapped that out for something far closer to Ethereum itself, rebuilt around standard tools. The result was a big jump in capacity and a sharp drop in fees, which is the main reason Arbitrum pulled ahead of rival Layer 2s and became the largest by value locked.

Geth integration and full Ethereum equivalence

The core move was putting Geth at the centre. Geth is the most widely used Ethereum execution client, the same software that runs much of the Ethereum mainnet. Nitro runs Geth directly at Layer 2, which means Arbitrum follows Ethereum's rules almost exactly. For developers, this is the whole point. Any Solidity contract, any Ethereum tool, any wallet works on Arbitrum with no code changes. You are not building for a lookalike chain. You are building for something that behaves like Ethereum but settles cheaply, and that compatibility is why so many established projects ported across without a rewrite.

Advanced calldata compression

Fees on a rollup are dominated by one thing: the cost of posting data back to Ethereum. Every batch has to be recorded on L1, and L1 space is expensive. Nitro attacks that directly use advanced calldata compression, squeezing each batch so it takes up far less room on Ethereum. Less data posted means less paid in L1 fees, and those savings pass straight through to users. This is the unglamorous plumbing that makes cheap transactions possible, and it is doing more work than any flashy feature on the surface.

Put the pieces together, and you get the headline.

How Nitro reduced fees by 50%

When Nitro shipped, user-facing fees on Arbitrum fell by roughly half, and throughput rose sharply. Compression cut the L1 data bill, and the Geth-based engine processed transactions far more efficiently than the old stack. Fees then dropped again across every Ethereum rollup in March 2024, when Ethereum's Dencun upgrade introduced blob storage and cut L2 data costs by a further 80% to 90%. Arbitrum transactions now routinely cost a few cents or less, which is what makes everyday activity like swaps, mints and games practical on the network.

Stylus the Rust C C++ contract upgrade on Nitro

Nitro also set up Arbitrum's next leap. In September 2024, the network added Stylus, which runs a WebAssembly engine alongside the existing EVM. Developers can now write contracts in Rust, C or C++, not only Solidity, and the two environments are fully interoperable, so a Rust contract and a Solidity contract can call each other freely. For heavy computation, Stylus contracts can run up to 70 times faster and use far less gas. It opens Arbitrum to millions of developers who have never touched Solidity.

Arbitrum Nitro: The Upgrade That Cut L2 Fees in Half