Cardano’s CAP-12 Draft Removes the Leios Off Switch

The fifth draft of Cardano’s CAP-12 constitutional amendment removes a mechanism that would let Cardano deactivate Ouroboros Leios through a protocol parameter change. Intersect reported that the draft leaves deactivation to the Dijkstra hard fork plan. On November 6, Kevin Hammond, chair of Intersect’s Technical Steering Committee, proposed restoring the mechanism under four conditions. The committee is scheduled to review his proposal on November 18.

How a Protocol Parameter Could Switch Leios Off

CAP-12 would add Dijkstra’s new protocol parameters to the Cardano Constitution and set limits on how they can be changed. One parameter, maxEndorserBlockTxsSize, caps the total size of transactions in an endorser block. Leios introduces these blocks as part of its design to increase Cardano’s transaction throughput.

An earlier draft would have allowed Cardano to deactivate Leios across the network by setting that parameter to zero. The fifth draft, published October 30, requires Leios parameters to have nonzero values. If adopted as written, that restriction would rule out the proposed method of deactivation through a parameter change.

What Hammond Wants Tested Before Restoring the Switch

According to a summary published by stake pool operator SIPO, Hammond wants the Leios team to confirm in writing that setting the parameter to zero would return nodes to behavior consistent with Ouroboros Praos. He also calls for testing both deactivation and reactivation on Cardano’s Preview and Preprod networks so that both transitions can be checked before the mechanism is used on mainnet.

The two other conditions are conformance tests across all node implementations and a change to the rules enforced by the Guardrails Script. The tests would check whether implementations behave consistently when the parameter changes. The guardrail change would allow a proposal setting the parameter to zero to pass the script’s checks.

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What Remains Open Before a CAP-12 Vote

Intersect’s November 6 update reported that about 30 values in CAP-12 still await feedback from the Parameter Committee and that a sixth draft is expected. DijkstraNet is already running protocol version 12, while Intersect is targeting cardano-node 11.3 as a release candidate that would combine the full Dijkstra feature set with Linear Leios.

Intersect has scheduled a public review of CAP-12 and other active amendments for November 12. At its November 18 review, the technical committee is due to consider whether to support restoring zero as the value that would deactivate Leios, subject to the proposed tests and guardrail change.