Solana has activated Alpenglow, a new consensus protocol that reduces transaction finality on the network from roughly 12.8 seconds to about 150 milliseconds, in what core developer Anza calls the largest consensus upgrade since the blockchain launched in 2020.

Validators retired TowerBFT, the consensus protocol Solana had operated since March 2020, at slot 459,653,000 at around 14:00 UTC on Wednesday, Anza said. Independent operators coordinated a shared handoff point, switching systems while the running network carried its existing ledger forward.

The upgrade targets finality—the point at which a transaction can no longer be reversed, and the moment an exchange, bank, or merchant waits for before treating an asset as moved. Under TowerBFT, Solana gave a conditional confirmation within seconds but took about 12.8 seconds to reach full finality. Alpenglow condenses those two steps into one. Until full finality is reached, a transaction can still be reversed, so the compression from nearly 13 seconds to a fraction of a second correspondingly shrinks the window in which a payment remains exposed to a reversal.

"This is the largest, most ambitious blockchain upgrade since 'The Merge' and Anza took it from a white paper to running on mainnet in under 18 months," said Anza CEO Brennan Watt, referring to Ethereum's 2022 switch to proof of stake. Where The Merge moved Ethereum from proof-of-work mining to proof of stake, Alpenglow swaps only the protocol by which validators agree on blocks, with the chain's history running uninterrupted through the change.

From White Paper to Mainnet

Anza's research team, led by ETH Zurich professor Roger Wattenhofer alongside Quentin Kniep and Kobi Sliwinski, published the Alpenglow design in May 2025. Before reaching mainnet, the protocol went through public testing, including red teaming, penetration testing, repeated migration rehearsals and a security competition, followed by launches on Solana's testnet and devnet. Anza implemented the protocol in Agave, the validator software it maintains, and independent validators activated it.

Under Alpenglow, validators send their votes directly to one another instead of writing them into later blocks, and votes are weighted by stake. "If you have 80% of the votes say yes, then it's immediately done," Wattenhofer, Anza's head of research, said in an interview with Solana Foundation technology vice president Jacob Creech published last month. "You immediately know that the block is final."

A second route—two rounds of voting that each need 60% of stake—can be even quicker when validators are clustered close together, such as in Europe, he explainedn
The protocol is designed to keep working with less than 20% of stake acting maliciously and a further 20% offline. If the network goes 10 seconds without finalizing a block, validators gradually lengthen block times until messages get through. "Eventually, even a bad internet will give us a block again," Wattenhofer said.

Road to Mainnet Activation

Validators approved the upgrade in September 2025, voting 98% in favor of SIMD-0236, the proposal that implements it. "The biggest difference users will feel right away will be a reduction in confirmation latency approximately 150-200ms," Anza lead economist Max Resnick told Decrypt at the time.

Alpenglow went live on Solana's community test cluster in May 2026, when Resnick said the team was targeting a mainnet activation in late Q3 or early Q4. On October 13, Anza confirmed the October 21 date.

What Comes Next

Further upgrades are planned, though none has a committed date. Rotor will change how block data spreads across the network, and geographically aware leader rotation aims to cut delays as block production passes between validators. Quantumglow, a research design, would swap Alpenglow's elliptic-curve cryptography for hash-based signatures to make it secure against quantum computers while keeping the same finality speed.

The upgrade also opens the door to other changes. Developers at Jump Crypto's Firedancer team have proposed scrapping Solana's cap of 60 million compute units per block once Alpenglow is live, letting blocks grow as large as the fastest validators can handle while slower ones use its "skip vote" feature to abstain. Critics warned the change could favor well-funded operators and increase centralization. How that proposal advances will run through the same channel that activated Alpenglow—a validator vote, as SIMD-0236 showed. And with the protocol now live on mainnet, real-world data will show whether confirmation latency settles into the 150-200ms range Resnick described.

This article is based on reporting by Decrypt: Solana Alpenglow Goes Live in 'Most Ambitious' Upgrade Since Ethereum's Merge