Solana activates Alpenglow, targeting 150ms transaction finality

Since Solana launched in 2020, validators have used TowerBFT to agree on blocks; on Oct. 21, the network activated Alpenglow, replacing that consensus system and targeting transaction finality in about 150 milliseconds, according to the Solana Foundation’s Alpenglow upgrade page.

Faster finality could let exchanges, merchants and other services treat transactions as irreversible sooner.

The change took effect at the start of epoch 1064, at approximately 13:36 UTC, the Foundation said. Alpenglow consensus began at slot 459,653,000, following a genesis block certified by votes from 446 of the network’s 654 validators. The Foundation describes 150 milliseconds as a target; it is not a guarantee that every transaction will reach finality in that time under all network conditions.

How does Alpenglow change transaction finality?

Under TowerBFT, validators sent votes as on-chain transactions, and a block became final after enough votes accumulated over 32 slots. Alpenglow’s Votor protocol moves those votes off-chain: validators send votes directly to one another and aggregate them into certificates, allowing a block to become final after one or two voting rounds, according to the Foundation.

That cuts the time between a transaction appearing on the network and becoming irreversible. CoinDesk reported before activation that TowerBFT finality took about six seconds, while the Foundation’s upgrade page puts the previous time at about 12.8 seconds. The distinction is between an earlier confirmation and full finality: services waiting for the stronger guarantee may be able to act sooner.

For users, the Foundation says wallets and apps continue to work as before. Alpenglow changes how validators agree on blocks; transaction execution, programs and fees remain the same. The 150-millisecond target also refers to finality, not block production speed. Solana’s slot time was reduced separately, from 400 milliseconds to 200 milliseconds, in a rollout completed in October, according to the Foundation.

What changes for validators and Solana activity counts?

Validators no longer include vote transactions in blocks. That removes a source of on-chain transaction volume, so headline transaction counts can fall even if user activity does not. CoinDesk noted this effect ahead of the upgrade; it does not mean that every recorded transaction count will move in the same way, since metrics differ in whether they include votes.

Validator costs also change. The Foundation says validators pay a flat 0.8 SOL admission ticket per epoch from their vote accounts, replacing the per-vote fees under TowerBFT. The first ticket was charged at the start of epoch 1064 and covers participation in the following epoch. A validator that does not pay will not vote or produce blocks in that next epoch.

Alpenglow’s second phase, Rotor, is planned to replace Turbine, the protocol that distributes block data across the network, with a single relay layer. The Foundation says Rotor is not yet scheduled; the live activation covers Votor, the voting protocol.

Sources

• Solana Foundation’s Alpenglow upgrade page — solana.com
• reported before activation — coindesk.com