A slot-level finality protocol that concentrates validator votes through justifiability backoff, enabling fast finalization under good conditions and graceful degradation under adversity.
Each slot is divided into four 1-second intervals. Validators perform specific duties at each interval, orchestrating block production, attestation, and fork choice updates.
Not every slot is eligible for justification. The distance (delta) from the last finalized slot determines eligibility through three rules. This backoff creates fewer targets over time, concentrating votes to reach the 2/3 supermajority threshold.
Delta from finalized slot 0. Hover for rule. Note how gaps widen — forcing vote concentration.
Attestations flow through a two-stage pool before affecting fork choice. This batching prevents attestation-by-attestation recomputation of the head.
Validator signs & broadcasts attestation via P2P
new_attestations
Awaiting promotion
known_attestations
Fork choice active
Greedy heaviest subtree → head selection
Proposer includes aggregated attestations
Starting from the justified root, greedily descend the block tree always choosing the child with the highest attestation weight. Ties are broken by block hash.
A slot becomes justified when ≥2/3 of validators attest to it. It becomes finalized when two consecutive justifiable slots are both justified with no justifiable gaps between them.
Why unjustifiable slots matter:
Under network stress, validator votes scatter across many slots. By making most slots unjustifiable, 3SF-mini forces votes to concentrate on fewer eligible targets. The backoff pattern (close → squares → pronic) ensures rapid finalization in good conditions, while the widening gaps in bad conditions still eventually funnel enough votes to reach 2/3 supermajority.