Solana activates Alpenglow, targeting 150ms transaction finality

Solana has relied on TowerBFT for consensus since its launch in 2020. On Oct. 21, it activated Anza’s Alpenglow upgrade, which targets transaction finality in about 150 milliseconds.

• Activation: epoch 1064, at about 13:36 UTC on Oct. 21
• Alpenglow consensus began at slot 459,653,000
• Previous TowerBFT finality: about 12.8 seconds
• Target under Alpenglow: about 150 milliseconds

The Solana Foundation’s Alpenglow upgrade page says the change replaces TowerBFT and leaves transaction execution, fees and the Solana Virtual Machine unchanged. The 150-millisecond figure is a target for finality, the point when a transaction can no longer be reversed.

How does Alpenglow change validator voting?

Validators now send votes directly to one another and combine them into certificates, rather than recording votes as on-chain transactions. A block can become final after one or two voting rounds, according to the Foundation.

CoinDesk reported that the starting block was certified by 446 of Solana’s 654 participating validators. The handover itself took about 900 milliseconds, according to the Solana Foundation; that measures the switch between consensus systems, not the time for every transaction to reach finality.

What does the upgrade change for users?

The shorter target could let services settle payments or credit exchange deposits sooner. CoinDesk reported that wallets, fees and applications remain unchanged, so users do not need to switch wallets or alter how they send transactions.

Apps may be able to rely on finality sooner. That could matter when a merchant releases goods or an exchange makes deposited funds available, but the protocol upgrade does not itself confirm that services have changed their policies.

Is 150 milliseconds guaranteed?

No. The Foundation describes roughly 150 milliseconds as the target, and CoinDesk says it applies under normal network conditions. Actual time to finality can vary; the target is not a guarantee for every transaction or user.

The upgrade changes how Solana reaches consensus, not how quickly blocks are produced. The Foundation says block time was reduced separately, from 400 milliseconds to 200 milliseconds, in stages completed in October. Another Alpenglow phase, Rotor, is planned to change how block data travels across the network, but it has no scheduled release date.

Source material

• Solana Foundation’s Alpenglow upgrade page — solana.com