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Ethereum Foundation ships Kohaku Railgun SDK alpha-22 with ERC-4337 relaying

The Kohaku privacy SDK landed @kohaku-eth/railgun v0.0.1-alpha.22 on May 26 — brotli compression, ERC-4337 mempool relaying operational. Tornado Cash and Privacy Pools modules still in dev.

by 3 min read
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The Ethereum Foundation's Kohaku initiative published @kohaku-eth/railgun@0.0.1-alpha.22 on the ethereum/kohaku monorepo on May 26, 2026. The release follows alpha-21 (May 23), the first build to put ERC-4337 mempool relaying for shielded Railgun transactions into a usable state. Tornado Cash and Privacy Pools modules in the same SDK remain in development.

What shipped

Kohaku is the Foundation's wallet-side privacy toolkit. The monorepo exposes four packages:

  • @kohaku-eth/railgun — Railgun shielded-pool integration.
  • @kohaku-eth/privacy-pools — Privacy Pools protocol (Buterin-Diamandis-Sun design).
  • @kohaku-eth/provider — provider abstraction over ethers, viem, helios and colibri.
  • @kohaku-eth/pq-account — post-quantum ERC-4337 account implementation.

The Railgun package is the only one in active release cadence right now. The May 26 build switched the shielded-transaction transport to brotli compression, enabled structured logging, and fixed the Proof of Innocence (POI) caching and query path. The release-notes line in the GitHub releases tab is terse — three bullet points — but the underlying change is the first that wallet integrators can ship.

Why ERC-4337 relaying matters

Railgun's shielded transfers were already on mainnet through Railgun's own SDK. The constraint was the broadcast path: a shielded user transaction needs a non-shielded sender to pay gas, and that sender becomes a deanonymising relay if it's a single operator. Kohaku v0.0.1-alpha.21 wired the broadcast into the ERC-4337 user-operation mempool — the same set of bundlers that handle every other smart-account transaction. Privacy in: shielded payload. Privacy out: indistinguishable from any other 4337 user op being bundled.

For a wallet integrator (Ambire, Argent, Coinbase Smart Wallet, MetaMask Snaps), the SDK is what cuts the integration cost. Without Kohaku, every wallet team writes a Railgun adapter from scratch.

Reference wallet

Kohaku ships a companion reference implementation at ethereum/kohaku-extension — a browser extension forked from Ambire Wallet, currently wired to Sepolia testnet. It is not the product. The product is the SDK that other wallet teams consume. The extension exists to prove the SDK can be integrated and to give the team a place to dogfood the API surface.

Numbers block

Repo: github.com/ethereum/kohaku (358 stars, 59 forks)
Languages: Rust 45.6%, TypeScript 32.4%, Solidity 8.2%
Latest release: @kohaku-eth/railgun@0.0.1-alpha.22 (May 26, 2026)
Previous release: @kohaku-eth/railgun@0.0.1-alpha.21 (May 23, 2026)
Modules: 4 — railgun ✅, privacy-pools (in dev), provider ✅, pq-account ✅
Status: alpha, "not ready for production use" per README

What to watch

  1. Privacy Pools and Tornado Cash modules cutting their first alpha. The Railgun path is now usable; the other two shielded-pool integrations are still empty on the releases page. Whichever lands next sets the de facto wallet-side default for non-Railgun shielded transfers.
  2. First production wallet integration. No mainstream wallet has shipped a Kohaku-powered shielded flow yet. The first one to do so — and which shielded pool they pick — is the signal the SDK has moved past dogfood.
  3. Regulator stance on wallet-bundled shielding. Kohaku ships Tornado Cash as a named module alongside Railgun and Privacy Pools. The Foundation is making the bet that mainstream wallets can host shielded-pool flows inside a single SDK surface — a bet that depends on how regulators in the US and EU treat the wallet vendor's role in routing shielded transactions.

Context

Kohaku is the Foundation's first concrete piece of wallet-side privacy tooling since the Privacy Pools paper (Buterin, Diamandis, Sun, Wachs and Wahrstätter, September 2023) made the case for compliance-compatible shielded transfers. Vitalik Buterin's May 26 reply on X to the alpha-22 thread — that the ecosystem now has "enough privacy narratives" and needs production wallet shipping — is the public push toward integration.

The SRL (software readiness level) gap between alpha-22 and a mainstream wallet default is still large. What changed this week is that the gap is now measured in wallet engineering work, not in missing primitives.

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