Aztec upgrades to V5 in alpha, adding full private execution environment to decentralized Ethereum L2

Quick Take

• Aztec v5 is a full execution environment for the Ethereum scaling layer that Vitalik Buterin said has entered Stage 2 decentralization.
• V5 focuses on supporting "client-side proving," enabling computation-heavy ZK proofs on simple devices like phones and laptops.

Crypto privacy project Aztec has released its v5 upgrade in alpha, taking a step toward making fully private transactions "the default" in the Ethereum ecosystem, Aztec co-founder Zac Williamson told The Block in an interview.

The update, passed by token-holder governance and executed onchain on Tuesday, enables users to generate end-to-end private transactions directly on their own devices, like their phones and consumer laptops, while retaining the censorship resistance and decentralization of crypto.

This "client-side proving" process differs from the approach used by most other ZK projects, where zero-knowledge proofs are generated in centralized data centers, Williamson said.

"We've been ruthlessly saying we need to prove things on phones, on consumer laptops, on some random $500 Lenovo piece of junk, if this technology is going to actually have an impact," Aztec co-founder Zac Williamson told The Block in an interview.

According to a press release on Tuesday, the upgrade reduces private transaction proving times by more than 2x, cuts the average cost of a fully private transaction by roughly 50%, and shortens average block production time from 14 seconds to six seconds.

The network is now "the fastest system in the world for proving a fully private transaction entirely on a user's own device," Williamson said.

"The goal is really to be completely seamless and unnoticeable from the user's perspective," he said, noting that for now, Aztec's private transactions will take a little longer to complete than, say, interacting with Ethereum normally via MetaMask. "We've made massive improvements and we're going to continue as we have future releases."

The upgrade also lowers the cost of verifying rollup proofs on Ethereum by about 40%, bringing the average fee for a fully private token transfer to under $0.05, according to the release.

Tuesday's release comes with a package of use cases, most notably a way to privately earn yield on Aave via wallet project Nyx. Shield and TRAIN are also providing bridges to Ethereum.

"We've designed Aztec to enable, effectively, a privacy shield for all of crypto," Williamson said. "Initially with Ethereum, but also using bridges elsewhere."

On Monday, Ethereum founder Vitalik Buterin launched a demo for an anonymous message board on Aztec, noting the scaling solution has reached "Stage 2" decentralization by his own classification standards for Layer 2s. Buterin is a financial backer of Aztec, which has raised over $119 million in total funding, per The Block Pro's Funding Dashboard.

V4 vulnerabilities

Notably, the release comes just months after Aztec warned users from interacting with its previous v4 version, which was deprecated after vulnerabilities were discovered in March.

"V4 was our very first launch, and it coincided with the dramatic acceleration of AI, which impacted the network as well as many others in the ecosystem," Williamson said. "V4 does have active vulnerabilities that we are aware of, so that's why we're not recommending people use it."

Williamson noted the team has thrown resources into "an enormous amount of security work" for v5 and that Tuesday's release remains in alpha. According to the announcement, 234 security researchers participated in Aztec's bug bounty program.

"Obviously we're also very aggressively exploring formal methods and formal verification," he said, referring to mathematical proofs that rigorously prove that a system behaves exactly as intended. "We're going to be releasing a security roadmap described in some more detail."

By most accounts, Aztec has been considered at the leading edge of ZK cryptography. Williamson and his team, including distinguished cryptographer Ariel Gabizon, created the PLONK zero-knowledge proof system in 2019, which has since developed into a whole family of frameworks, like Plonky2 and Plonky3 used by Polygon.

Aztec launched its Ignition Chain consensus and sequencing layer --- which serves as the foundation for the new v5 execution environment --- in mid-November 2025 after years of R&D. The Ignition Chain launched after v4 and ran empty blocks to test its decentralization.

The project raised $100 million in Series B funding in December 2022, with backing from Paradigm and a16z. It also raised $60 million in ETH from 16,741 participants through an AZTEC token sale on Uniswap in December.

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