The lineage of Ouroboros variants reflects different operational regimes:
- Classic introduced provably-secure PoS with synchronous, semi-trusted setup.
- Praos moved to a private leader election via VRFs, removing the need for committee coordination. This is the protocol Cardano mainnet runs today.
- Genesis adds a chain-density rule so a brand-new node can join the network and pick the honest chain without external checkpoints. It is implemented in the node and is the default on the Preview and Preprod testnets, but on mainnet it is opt-in and Praos remains the running consensus.
- Chronos (research) tightens the protocol's reliance on external time sources.
Two extensions are on the way with the Dijkstra era. Peras adds a voting layer in which stake pool committees vote on recent blocks, so transactions settle in roughly two minutes instead of waiting for many confirmations, and is planned for the second Dijkstra phase in 2027. Leios raises throughput by adding larger endorser blocks next to the Praos chain, runs on a public testnet since June 2026 and is the headline feature of the first Dijkstra phase targeted for late 2026.
See Ouroboros for the longer write-up.
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- SlotEach slot represents an opportunity for a block to be produced by an elected slot leader.View term
- Slot LeaderThe stake pool selected by Ouroboros to produce a block in a given time slot.View term
- VRFA cryptographic function that produces a verifiably random output; Cardano uses it inside Ouroboros as a private per-slot lottery, letting each pool check whether it won the right to produce a block, fairly and unpredictably.View term
- KESKey Evolving Signatures. Block-signing keys that move forward in time to limit the damage of a key compromise.View term
- Stake PoolA server node that participates in the Cardano network by validating transactions and producing blocks.View term
- Proof of StakeA consensus mechanism where validators are selected to create blocks based on the amount of cryptocurrency they hold and stake (commit) to the network.View term
- Proof-of-Stake AttacksThe set of known attack categories against proof-of-stake blockchains and how Cardano's Ouroboros family defends against each.View term
- LeiosAn Ouroboros extension that raises Cardano throughput by letting block producers publish larger endorser blocks next to regular Praos blocks. Linear Leios is the variant headed for mainnet with the Dijkstra hard fork.View term
- DijkstraThe next Cardano ledger era and hard fork, named after Edsger Dijkstra. Its first phase, targeted for late 2026, brings Linear Leios and nested transactions, a second phase adds Peras.View term