Offchain Labs opposes Vitalik's RISC-V proposal, supports WASM for Ethereum L1

Offchain Labs, the main developer behind Arbitrum—a leading Layer 2 solution on Ethereum—has just presented arguments opposing Vitalik Buterin’s proposal to move Ethereum’s execution layer to a RISC-V architecture. In a technical article published on November 20 on Ethereum Research, the team argues that WebAssembly (WASM) is actually the choice that offers superior long-term benefits.

According to the four researchers from Offchain Labs—Mario Alvarez, Matteo Campanelli, Tsahi Zidenberg, and Daniel Lumi—while RISC-V currently has an advantage in generating ZK proofs, this does not mean it is the appropriate format for deploying and storing smart contracts on Ethereum.

Vitalik’s Controversial Proposal

Vitalik Buterin previously proposed replacing the Ethereum Virtual Machine’s bytecode with the open RISC-V instruction set in an article on Ethereum Magicians back in April. This idea aimed to drastically reduce the cost of generating ZK proofs, in some cases by up to 100 times.

However, Offchain Labs argues that the assumption “one ISA can optimally serve both proving and smart contract deployment” is unreasonable.

Separating “delivery ISA” and “proving ISA”

The team’s central argument is the need to separate:

• Delivery ISA (dISA): the format used to bring smart contracts on-chain.
• Proving ISA (pISA): the format used in the ZK virtual machine to generate proofs.

These two layers do not necessarily have to be the same.

Offchain Labs states that they have built a prototype demonstrating this approach: Arbitrum blocks—including Stylus smart contracts running on WASM—are ZK-proved by compiling WASM to RISC-V and then generating the RISC-V execution proof.

“We can ZK-prove actual blockchain blocks using WASM as the dISA via a RISC-V–based ZK-VM backend,” the team writes.

RISC-V May Not Be the Final Destination

The researchers also question whether RISC-V is actually the optimal endpoint for ZK-VMs, as the proving ecosystem is evolving rapidly. The recent shift from RISC-V 32-bit to 64-bit shows that this technology is still not stable.

If Ethereum “locks in” RISC-V at Layer 1, the blockchain could become stuck with outdated proving technology just as better solutions emerge. Meanwhile, WASM-based ZK-VMs—such as Ligero’s Ligetron—are showing advantages that pure hardware ISA architectures struggle to match.

Moreover, ZK-proving costs have dropped sharply to about $0.025 per Ethereum block and continue to fall, making extreme optimization for proving less urgent. “Even if L1 requires multiple ZK proofs per block, this cost is still very small compared to the gas fees and MEV a builder can earn,” the team notes.

Long-Term Advantages of WASM

Offchain Labs considers WASM superior due to:

• Clear structure, allowing optimization or modification without breaking existing contracts.
• Good performance on common hardware, without needing to emulate like RISC-V.
• Strong validation mechanisms, ensuring type safety and reducing security flaws.
• A mature tooling ecosystem, proven across billions of runtime environments.

The team concludes: “We believe WASM could become an Internet protocol for smart contracts—the ideal intermediary layer between diverse programming languages and various execution and proving backends.”

Thach Sanh