CDK Besu is live on Ethereum mainnet for private chains

Polygon's CDK Besu is live on Ethereum (ETH) mainnet, and the clause that matters is what the proof refuses to say. On October 19, 2026, Polygon said a bank or market infrastructure provider can launch a private Hyperledger Besu chain, keep transaction data on its own infrastructure, and move assets to any other chain connected to Agglayer. Those transfers settle against a zero-knowledge proof on ETH. The proof checks the bridge balance. It does not attest the private transactions behind it. That is the tokenised-deposit problem, not a public rollup: the asset that leaves an institution is not the book that stays inside.

The proof checks the bridge, not the book

The October 19 post adds Besu to the Chain Development Kit (CDK) beside the OP Stack path. CDK Besu runs the standard Besu client with QBFT, which Polygon's documentation calls Besu's Byzantine fault tolerant proof-of-authority consensus. The institution, or a consortium, runs the validators and sets account permissioning. Bridge and Global Exit Root contracts sit in the genesis, so the connection exists from the first block. A separate node keeps the validators off the public network. Aggkit packages bridge activity into certificates. Agglayer requests a pessimistic proof, generated on the Succinct Prover Network, and the verified certificate settles on ETH. Polygon says the path is ready for production on ETH mainnet, with testnet and devnet setups in the public runbook.

The proof shows a chain cannot withdraw more than it deposited, and it does not prove internal state transitions. CDK Besu posts no transaction data to ETH. Polygon calls that the intended design. No bank is named, and the post has no volume and no revenue figure. The bank example is a sketch: tokenised deposits for treasury clients, then part of the balance moving to a fund on another chain as one canonical asset, not a new wrapper per bridge. Teams that want every state transition proved are sent to CDK on op-reth, which can post data to ETH. Existing Besu networks can connect, Polygon says, but not through the new-chain runbook. Open Money Stack ramps and wallets are offered alongside, not as a live CDK Besu flow.

"Financial institutions have been using Hyperledger Besu for years. It has worked well for them, except that they are all disconnected. With Polygon CDK Besu, financial institutions can now connect their Besu chains with all other chains on Agglayer, providing the most secure form of cross-chain asset transfers."

Marc Boiron, chief executive at Polygon Labs, posted that on October 19, quoting Polygon's launch post. The blog draws a narrower line. Each connected chain has a running balance of what it has received and what it has sent. A withdrawal above that balance fails the proof. Polygon says no signer committee can approve a transfer that does not balance, and a compromised neighbour can lose its own deposits but cannot reach yours.

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None of those Besu names is a CDK Besu customer. The post says Besu is open source under the Linux Foundation, and that DTCC's collateral platform, Clearstream's digital securities infrastructure, Citi Token Services, Project Agorá and Swift's shared ledger run on it. It cites 80 institutional platforms on the foundation's decentralised-trust technologies. That report treats the ledger choice as the smaller decision and puts interoperability above it. CDK Besu is Polygon's answer, not a sign that any of the 80 has taken it. The same split is already in JPMorgan and Citi's tokenised-deposit plans, in Japan's tokenised-deposit test, which still used a stablecoin between banks, and in Partior's attempt to settle stablecoins against tokenised deposits. Circle's permissioned Arc validators are the other piece, a known set of institutions producing blocks. Polygon also says a bridged token has one canonical version on every connected chain, and the post calls the lack of a revenue share "no rent."

Where several firms share a chain, each member runs its own QBFT validator and keeps its own key. Membership changes go through a validator vote, and no certificate settles until M of N members have signed it against their own view of the chain. No single member can produce blocks or settle withdrawals alone. Polygon's account wrote on October 19 that a private Besu chain "no longer has to be an island." If counterparties accept the pessimistic proof, value can move without the books being posted. If they still want a contract over the unproved ledger, CDK Besu sits beside agreements they already sign. Polygon has not named a bank that has chosen.

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