Solana Activates Alpenglow, Targeting 150ms Finality

150 milliseconds is the target time for finality under Solana’s new Alpenglow consensus protocol, which went live on mainnet on October 21. That is down from about 12.8 seconds under TowerBFT, meaning exchanges and merchants can treat transactions as irreversible much sooner.

The Solana Foundation’s upgrade guide says Alpenglow took over at the start of epoch 1064, at about 13:36 UTC. It replaced TowerBFT, the consensus protocol Solana had used since 2020. The network continued running through the change, carrying its existing ledger forward.

What changes when a Solana transaction becomes final?

Finality is the point at which a transaction can no longer be reversed. Under the previous system, a transaction could receive a quicker confirmation, but full finality took roughly 12.8 seconds. Alpenglow combines those steps, targeting about 150 milliseconds.

According to The Block’s report on the launch, the switch retired TowerBFT at slot 459,653,000. Solana’s guide says the handoff took about 900 milliseconds after a shared genesis block was certified by 446 of the network’s 654 validators.

How does Alpenglow reach finality faster?

Validators now send votes directly to one another instead of recording vote transactions in later blocks. They combine those votes into certificates, which confirm that enough stake has agreed on a block. Under the protocol, a block can become final after one or two rounds of voting.

The change affects how validators agree on blocks, not how applications execute transactions. Solana’s Foundation says the network’s transaction formats, fees, programs and execution environment remain unchanged. Wallets and apps should work as before.

Anza, Solana’s core engineering team, said the protocol is designed to continue operating when less than 20% of stake is acting maliciously and a further 20% is offline. The new voting method is called Votor. It is the first phase of Alpenglow’s rollout.

What still needs to change for validators?

Validator operators need compatible software and a fee balance in their vote accounts. Solana’s guide lists Agave v4.3.2, Jito-Solana and Harmonic Salsa as supported clients for the migration. It says operators must keep at least 0.8 SOL above the rent-exempt minimum to pay the Validator Admission Ticket each epoch.

That requirement is specific to validators. The Foundation says sending transactions and running onchain programs are unaffected. Operators who do not pay the fee will not vote or produce blocks in the following epoch.

Alpenglow’s second phase, Rotor, is still ahead. It is planned to replace Turbine, the system that spreads block data across Solana, with a relay layer. The Foundation has not scheduled its release. Anza has also discussed Quantumglow, a research design for post-quantum signatures, without setting a launch date.

Sources

• Solana Foundation’s upgrade guide — solana.com
• The Block’s report on the launch — theblock.co