Solana’s Alpenglow consensus upgrade is live on mainnet

Solana activated Alpenglow on mainnet on Wednesday, Oct. 21, replacing its TowerBFT consensus system with a new process that moves validator votes off the blockchain and targets transaction finality in about 150 milliseconds. The Solana Foundation’s Alpenglow page says the change took effect at slot 459,653,000, after a transition period in epoch 1064.

How does Alpenglow change the way validators agree?

Validators are the computers that process Solana transactions and agree on which blocks count. Under TowerBFT, validators sent votes as on-chain transactions; enough votes had to accumulate before a block became final. Alpenglow’s first phase, called Votor, replaces that with direct messages between validators. They bundle votes into certificates, which record that enough stake has agreed on a block.

The protocol has a fast path and a second round. According to Solana’s technical description, a block can become final in one round if validators representing at least 80% of stake vote to notarize it. If that threshold is not reached, a second round uses certificates with 60% stake thresholds to determine whether the block is finalized or skipped. Solana’s page gives a target of roughly 150 milliseconds for finality, compared with about 12.8 seconds under TowerBFT.

The activation had two steps. The feature gate turned on at the start of epoch 1064, at about 13:36 UTC. TowerBFT continued for 5,000 slots while the network prepared the handoff. The last block in that window became Alpenglow’s genesis block; the new consensus took over from the next slot, at about 13:54 UTC. The CoinDesk report on the launch also describes the shift from on-chain votes to certificates.

What changes for transactions and apps?

The votes no longer appear in blocks, so transaction totals that included validator votes will change even if user activity does not. Solana says transaction execution, programs and fees remain the same. Wallets and apps can continue working as before, though developers who read network data may need to account for changes to block events and commitment labels.

Alpenglow’s 150-millisecond figure is a target, not a measured guarantee for every transaction. The upgrade changes how blocks are agreed on; it does not change how often blocks are produced. Solana separately reduced slot times to 200 milliseconds in four stages, completed in October.

What comes next for the upgrade?

Votor is live; the second phase, Rotor, is planned for a later release and is not yet scheduled. Rotor is intended to replace Turbine, the system that spreads block data across the network. The change now in effect is the consensus handoff from TowerBFT to Votor. The next points to watch are how finality performs on mainnet and when Solana schedules Rotor.

References

• Solana Foundation’s Alpenglow page — solana.com
• CoinDesk report on the launch — coindesk.com