Solana's biggest upgrade gets a date: Alpenglow goes live October 21 and cuts finality from 12.8 seconds to about 150 milliseconds

Solana has put a date on the most consequential change to its network since it launched. The Solana Foundation's upgrade page says Alpenglow, the consensus protocol that replaces TowerBFT, will activate at the beginning of epoch 1064, which is expected to start around 15:00 UTC on October 21, and it advises operators to track the epoch rather than the clock, because epoch start times drift. Anza, the developer of the Agave client, announced the schedule on Tuesday, Solana Compass reported.

The switch happens in two steps. The feature gate turns on at the epoch boundary, but TowerBFT keeps running for the first 5,000 slots; Alpenglow takes over at slot 459,653,000, roughly 18 minutes into the epoch. Under the old system, every validator vote is a transaction recorded on-chain, which is why votes make up a large share of Solana's reported transaction count. Under Alpenglow, validators exchange votes directly and combine enough of them into a certificate that finalises a block after one or two rounds. CoinDesk noted that the network's headline transaction figures may therefore fall sharply on activation day even if real activity is unchanged.

The prize is speed and certainty. Solana transactions already look confirmed almost instantly, but deterministic finality today takes about 12.8 seconds. The Foundation's target is about 150 milliseconds, with the caveat that the number depends on the stake distribution and on whether a block finalises in one round or two. The design is also meant to be sturdier: the Votor voting component tolerates 20% of stake acting maliciously plus a further 20% being offline.

For validators the to-do list is short but unforgiving. They must run Agave, Jito-Solana or Harmonic Salsa built on Agave 4.3.0, and fund their vote account with at least 0.8 SOL above the rent-exempt minimum, because a flat admission fee of 0.8 SOL per epoch, charged in advance and burned, replaces the roughly 1 SOL per epoch they now spend on vote transactions. A validator that cannot pay produces no blocks in the next epoch and forfeits its rewards. Firedancer and Frankendancer, the alternative clients, are not supported during the migration; Solana Compass estimates that validators running Firedancer-family software held about 15.8% of stake among the top 500 as of Tuesday, which gives them eight days to switch.