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Cardano's van Rossem hard fork hits mainnet vote, first via Voltaire governance

The Protocol Version 11 hard-fork action was submitted to the Cardano chain on June 16, 2026. Earliest possible enactment: June 28.

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The van Rossem hard-fork initiation governance action was submitted to Cardano mainnet on June 16, 2026, opening the first DRep vote on a Cardano hard fork executed entirely through the Voltaire on-chain governance framework rather than by IO Global acting unilaterally. The action targets Protocol Version 11 — an intra-era step that lays groundwork for the next major era, Dijkstra, and the Leios scalability rollout. The primary source is Intersect's announcement; the on-chain action is gov_action13pzmlsmmktmfareqpl3gzj9nm63ugwvmp3y7urkjhd8rf89tn6msq95mp3f, viewable on the Cardano Foundation Proposal Examiner.

What happened

The Hard Fork Working Group convened a special session on June 15, 2026 and signed off on submission the following day, Epoch 637. The action carries a single change to the protocol parameter that gates the version transition: protocolVersion.major = 11. Under Voltaire, the action must be ratified by both DReps (Delegated Representatives, weighted by delegated ADA) and the Constitutional Committee before enactment.

The earliest epoch in which the upgrade can take effect, if DReps and the CC ratify quickly, is June 28, 2026. Subsequent epoch boundaries that fall inside the action's expiry window are July 3, 8, 13, 18, and 23. The governance action expires on July 18, 2026 — if it has not been ratified by then, it lapses and the process restarts.

A separate Plutus cost-model parameter update, ratified June 13 with 68.57% DRep approval and a 5-of-7 Constitutional Committee vote, was scheduled to enact on June 18, 2026 at 21:45 UTC. That update is distinct from van Rossem but ships into the same upgrade window.

What van Rossem changes

This is an intra-era hard fork: the chain stays inside the current Conway era after enactment, which keeps the disruption surface narrow for wallets, exchanges, stake pool operators, and dApp builders. The changes are mainly under the hood:

  • Plutus performance. Tightened evaluation paths and execution-cost adjustments for Plutus V3 scripts.
  • Ledger consistency. Fixes to edge cases in delegation accounting and reward calculation observed since the Voltaire activation.
  • Node-level security. Hardening that was tested across the preview testnet ahead of the mainnet action.

The fork does not ship Leios. Leios — the parallel-leader scheme that underpins Cardano's throughput roadmap — is a Dijkstra-era change. Van Rossem positions the ledger to receive it.

Numbers

- Hard fork                : van Rossem (Protocol Version 11)
- Era                      : Conway → Conway (intra-era)
- Submitted to mainnet     : 2026-06-16, Epoch 637
- Governance action ID     : gov_action13pzmlsmmktmfareqpl3gzj9nm...sq95mp3f
- Action expiry            : 2026-07-18
- Earliest enactment       : 2026-06-28 (epoch boundary)
- Plutus param update      : ratified 2026-06-13 (68.57% DRep, 5/7 CC)
                             enacts 2026-06-18 21:45 UTC (Cardano slot)
- Governance framework     : Voltaire (first hard fork ratified on-chain)
- Named for                : Max van Rossem, DRep and pool operator
                             (deceased October 2025)

The DRep approval threshold for a hard-fork initiation action under Voltaire is the Constitutional-Committee-approved security parameter; the Constitutional Committee threshold is a 5-of-7 majority of active members. SPOs no longer hold a separate veto on hard-fork actions submitted through the on-chain pipeline — that mechanic was Shelley/Byron-era.

Impact

  • Stake pool operators. New node binary will ship from IOG and the alternative implementations before the enactment epoch. SPOs that have not upgraded by the activation slot stop producing valid blocks in the new protocol version — same model as every prior Cardano fork.
  • Wallet and exchange operators. No address-format or signature-scheme changes. Light-client and exchange integrations need to update protocol-version checks but no migration of user balances. Adalite, Eternl, Lace, Yoroi each ship updates in step.
  • dApp developers on Plutus V3. Re-test scripts on preview/preprod after the relevant testnets activate Protocol Version 11. The cost-model changes from the June 13 ratification land before van Rossem and should be tested first.
  • DReps. Voting is open. The action becomes the most-watched governance event of Voltaire's first year — the precedent set here defines whether subsequent hard forks reliably route through DRep ratification.

What to watch

  1. DRep vote tallies. Live on the Cardano Foundation Proposal Examiner and on GovTool. Threshold for ratification under Voltaire is set per action type by the Constitution.
  2. Constitutional Committee disposition. Five of seven active members must vote yes. CC abstentions count as a no in the current threshold rules.
  3. Enactment epoch. If ratified before Epoch 638 transition (June 23), enactment falls in Epoch 639 (June 28). Each missed epoch boundary pushes activation by ~5 days.
  4. Node release. IOG's cardano-node repository will tag the version binding the new protocol version. The release lands on the cardano-node GitHub releases page before activation.

Context — Voltaire's first hard fork

Cardano's prior hard forks — Alonzo, Vasil, Valentine, Chang — were each initiated by IOG via the legacy hard-fork combinator with no on-chain ratification step. Chang (September 2024) shipped Voltaire itself: DReps, the Constitutional Committee, and the framework that now governs van Rossem. Every fork since then has had to pass through the same pipeline that van Rossem is now testing for real.

If van Rossem ratifies cleanly inside the action's expiry window, the precedent is set: Cardano hard forks ship via DRep vote. If it lapses or stalls, the network will need either to re-submit (resetting the clock) or to surface whatever procedural friction blocked ratification — a discussion that the Constitution leaves explicitly to the DRep body and the Constitutional Committee.

The hard fork is named for Max van Rossem, a Cardano community member, stake pool operator, DRep, and Constitutional Convention delegate, who died in October 2025. The name was chosen after broad DRep support during the Hard Fork Working Group's pre-submission consultation.

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