Solana has switched on Alpenglow, a major overhaul of how the network agrees on its own history.
Validators retired the old TowerBFT consensus system at slot 459,653,000, at around 14:00 UTC on Wednesday, according to Anza, the developer that built the upgrade. The switch happened on the live network, with the existing ledger carried forward.
What changes for users
The headline change is speed. Under TowerBFT, a transaction reached full finality, the point at which it cannot be reversed, in about 12.8 seconds. Under Alpenglow, that takes roughly 150 milliseconds.
Alpenglow also merges what used to be two stages, a quick conditional confirmation followed by full finality, into a single step.
“If you have 80% of the votes say yes, then it’s immediately done,” said Roger Wattenhofer, Anza’s head of research. “You immediately know that the block is final.”
How it works
Validators now send their votes directly to each other, rather than writing them into later blocks. Votes are weighted by stake.
A block is final once 80% of stake votes for it. Alternatively, it can be finalised through two faster voting rounds that each need 60% of stake, which can suit validators located close together.
The design is meant to keep working even if less than 20% of stake acts maliciously and another 20% is offline. If the network goes 10 seconds without finalising a block, validators gradually lengthen block times until messages get through.
“Eventually, even a bad internet will give us a block again,” Wattenhofer said.
From paper to mainnet
Anza’s research team, led by Wattenhofer, a professor at ETH Zurich, published the design in May 2025. Validators approved it in September 2025, with 98% of votes in favour of the proposal, SIMD-0236.
Testing included red teaming, penetration testing, repeated migration rehearsals, a security competition and launches on Solana’s test networks.
Anza chief executive Brennan Watt called it “the largest, most ambitious blockchain upgrade since ‘The Merge'”, Ethereum’s 2022 switch to proof of stake.
No launch problems had been reported at the time of writing.
What happens next
Anza plans further upgrades without fixed dates. They include Rotor, which will change how block data spreads across the network, and leader rotation that takes geography into account to reduce delays.
The real test is how Alpenglow holds up under heavy load over the coming weeks.
