Consensus
How nodes agree on the chain: the state they track, how work is measured, how outputs are tracked, and how blocks are validated and applied.
Consensus is the set of rules every node applies to decide which chain is valid. A block is checked against the state left by its parent, and applying it produces the next state.
These pages cover what that state contains, how proof of work is measured, how outputs are tracked in the accumulator, and how the rules have changed through hardforks.
- StateThe values every node must agree on to validate and apply the next block, and why Sia keeps them small and explicit.
- WorkHow Sia measures proof of work, and how the Oak algorithm adjusts difficulty to hold a 10-minute block time.
- OutputsAmounts of siacoins or siafunds that can be spent once, how they mature, and how they are identified.
- AccumulatorThe Merkle structure that replaces the UTXO database, so a node stores proofs only for the outputs it cares about.
- ValidationThe checks a block and each of its transactions must pass against the parent state.
- ApplicationHow a valid block is applied to its parent state to produce the next state, and how blocks are reverted.
- HardforksEvery change to the consensus rules since 2015, including the v2 hardfork in June 2025.
- Instant SyncingHow a new node can start fully validating blocks from a recent checkpoint instead of replaying the whole chain.