Finality

Finality is the moment a block becomes permanent. Before it, a transaction is a claim; after it, the transaction is history that no honest validator will roll back. Chains differ in how they reach that point. Probabilistic designs such as proof-of-work only make a block less and less likely to be replaced as more work accumulates on top of it, which is why exchanges and bridges wait for many confirmations. BFT consensus takes the other route: a block signed by a supermajority of known validators is final the instant it is committed, and honest validators never reorganize it.

Chain 2800 takes the second route. It runs QBFT with ten validators and a quorum of seven: once seven commit signatures exist for a block, that block is final. Blocks target 500 ms and arrive roughly every 0.62 s (0.620 s measured on 2026-10-15), so for a validator inclusion and finality arrive together, in well under a second. Since 2026-09-11 every validator refuses a commit without a valid post-quantum seal of its author (the nine Besu-derived validators since block 17,250,000); since block 24,300,000 (AIP-22 stage 4), every vote counts only with the verified post-quantum seal of its author, and a commit still carries the ECDSA commit seal of its validator as an additional check, and since block 25,080,000 (AIP-22 stage 5) headers no longer carry ECDSA commit seals; chain 2800 calls that post-quantum consensus, with three limits: the transport between nodes is still authenticated by secp256k1, the ten validators are run by one operator, and no third party has audited it yet. A node that does not take part in consensus admits a header between anchors on the Falcon-512 seal of its proposer alone, so the post-quantum key of one validator can serve such a node a branch up to the block before the next anchor (below block 25,080,000 that took the ECDSA keys of a quorum), and the next anchor ends it for a node that requires the seals of a quorum in its certificate (the published follower, with its seal ceiling at 1, is not such a node: for it one leaked or misused post-quantum key of a validator makes the rewrite depth unbounded, section 6.4 of the aere-node SPEC).

Two further mechanisms guard finalized history. A second client, an independently implemented Nethermind fork, validates every block alongside the first, Besu-derived client, and since 2026-09-11 it also proposes and seals blocks as the tenth validator (nine of the ten run the first client; corrected 2026-10-28: this sentence called the first client the producing client), which is the point of client diversity. And since block 13,014,000, every anchor block header (every 32nd block; every 128th from 17,225,968 to 20,746,736) carries a post-quantum anchor: a certificate of post-quantum signatures (Falcon-512 at every anchor and, since 2026-09-04, SLH-DSA-SHA2-128s as a second, hash-based scheme, every 128th block since 2026-09-29) from the validators over the parent block, at least 7 for each scheme today (3 until 2026-08-21, 6 until block 20,715,632 on 2026-09-29) and seals from 8 to 10 validators in practice, whose 32-byte digest sits inside the data covered by the block hash.