Solana's Alpenglow Goes Live on Mainnet, Cutting Finality to 150 Milliseconds
Solana's new consensus protocol, Alpenglow, has gone live on mainnet beta, replacing TowerBFT. Anza, the core development team, said the switch took effect at slot 459,653,000, cutting the time for a transaction to become irreversible from roughly 12.8 seconds to about 150 milliseconds.
Validators retired TowerBFT — in use since Solana's network launched in March 2020 — at around 14:00 UTC, completing the largest consensus upgrade in the chain's history. The handoff took place on the running network with the existing ledger preserved, as independently operated parties coordinated a common switchover point. No outage was needed and no ledger state was lost.
The change targets finality: the moment a transaction can no longer be reversed, and the point at which exchanges, banks and merchants can treat an asset transfer as settled. Under TowerBFT, Solana confirmed transactions conditionally within seconds, but full finality took about 12.8 seconds. Alpenglow folds the two stages into one.
"This is the largest and most ambitious blockchain upgrade since 'The Merge,' and Anza turned it from a whitepaper into a live system on mainnet in less than 18 months," said Anza CEO Brennan Watt, referring to Ethereum's 2022 shift to proof-of-stake.
Before mainnet, Alpenglow went through public testing that included red teaming, penetration testing, repeated migration drills and a security competition, followed by deployment on Solana's testnet and devnet. Anza built the protocol into Agave, the validator software it maintains, and independent validators completed activation.
Anza's research team, led by ETH Zurich professor Roger Wattenhofer and including Quentin Kniep and Kobi Sliwinski, published the Alpenglow design specification in May 2025.
Under Alpenglow, validators no longer write votes into subsequent blocks. They send votes directly to one another, with vote weights calculated from staked amounts. "If 80% of the votes say yes, it's immediately finalized. You'll know right away that the block has been settled," Wattenhofer said last month in an interview with Jacob Creech, vice president of technology at the Solana Foundation. The second path runs two rounds of voting, each requiring 60% stake support; for validator clusters grouped closely together geographically, such as those in Europe, the process can run faster still.
The protocol is designed to keep operating even with less than 20% of stake malicious and another 20% offline. If finality is not reached within 10 seconds, validators gradually extend block times until messages get through. "Eventually, even a poor internet connection will get us another block," Wattenhofer said.
More upgrades are in the works. Rotor will change how block data propagates across the network, while geography-aware leader rotation aims to cut latency when block production passes between validators. Quantumglow, a research design, would swap Alpenglow's elliptic curve cryptography for hash-based signatures to resist quantum computers while holding finality speed. None of the three has a confirmed date.
Validators approved the upgrade in September 2025, passing the SIMD-0236 proposal with 98% support. Max Resnick, Anza's chief economist, told Decrypt at the time: "The most immediate change users will feel will be confirmation delays reduced to approximately 150–200 milliseconds." Alpenglow launched on Solana's community testnet in May 2026, when Resnick said the team was aiming for mainnet activation by the end of Q3 or early Q4. On October 13, Anza confirmed the October 21 date.
The upgrade also clears the way for other changes. Developers on Jump Crypto's Firedancer team have proposed scrapping Solana's current limit of 60 million compute units per block once Alpenglow is live, letting block sizes expand to whatever the fastest validators can handle while slower validators abstain through their "skip vote" feature. Critics warn the move could favor better-funded operators and deepen centralization.
