Solana switches mainnet to Alpenglow at slot 459,653,000

Solana switched its mainnet to Alpenglow on Oct. 21, replacing TowerBFT and aiming to cut the time for transactions to become irreversible from about 12.8 seconds to roughly 150 milliseconds. The Solana Foundation’s upgrade page says the new system took over at slot 459,653,000.

The change affects how validators agree on blocks, rather than how transactions run. The Foundation says the switch happened in epoch 1064, which began at about 13:36 UTC. Alpenglow’s faster finality could let services treat a payment as settled sooner.

What replaced TowerBFT on Solana?

Alpenglow’s Votor voting protocol replaced TowerBFT, Solana’s previous consensus system. Consensus is how validators agree on transaction order and when a transaction can no longer be reversed. According to the Foundation, TowerBFT gathered validator votes as transactions over 32 slots; Alpenglow has validators send votes directly to one another and combine them into certificates.

The transition took place on the live network. The Foundation says TowerBFT continued for the first 5,000 slots of epoch 1064. The last block under the old system was slot 459,652,999, which became Alpenglow’s genesis block. A certificate for that block drew votes from 446 of the 654 validators participating in the network. Alpenglow consensus began on the next slot.

How does Alpenglow aim to finalize blocks faster?

Under Alpenglow, a block can become final after one or two rounds of voting. The Solana Foundation gives roughly 150 milliseconds as the target, compared with about 12.8 seconds under TowerBFT. That is a target for finality, not the interval between blocks.

Decrypt’s report on the launch says the first voting path needs 80% of stake to agree in one round; another path uses two rounds, each requiring 60%. Stake is the SOL validators have committed to help secure the network. The report says the protocol is designed to keep working if up to 20% of stake acts maliciously and another 20% is offline.

What changes for users and developers?

The Foundation says sending transactions, running programs and paying fees work as before. The changes are in how blocks are finalized and how some infrastructure reads them. Vote transactions no longer appear in blocks, so tools that count or analyze those transactions may need to adjust.

Decrypt reports that validators activated the change while carrying the existing ledger forward. The Foundation says Alpenglow’s next phase, Rotor, is planned to change how block data spreads across the network, but it has no scheduled date.

Sources and documents

• Solana Foundation’s upgrade page — solana.com