Solana activates Alpenglow, cutting transaction finality to 150 milliseconds

Core engineering team Anza said Solana activated the Alpenglow consensus protocol on mainnet-beta on Wednesday, reducing transaction finality from about 12.8 seconds to roughly 150 milliseconds. Alpenglow is Solana's biggest consensus upgrade since the network began operating in 2020. Validators replaced TowerBFT at slot 459,653,000, around 14:00 UTC. TowerBFT had served as Solana's consensus protocol since March 2020. Independent operators coordinated the transition on the running network and preserved the existing ledger.

Finality means a transaction has become irreversible, allowing an exchange, bank or merchant to regard an asset transfer as complete. TowerBFT provided conditional confirmation within seconds, followed by full finality after about 12.8 seconds. Alpenglow combines those stages into a single step. Anza CEO Brennan Watt called Alpenglow the biggest and most ambitious blockchain upgrade since Ethereum's 2022 transition to proof of stake, known as the Merge. Watt said Anza brought Alpenglow from a white paper to mainnet operation in less than 18 months.

Alpenglow underwent public testing that included red teaming, penetration testing, multiple migration rehearsals and a security competition before deployment on Solana's testnet and devnet. Anza incorporated Alpenglow into Agave, the validator software Anza maintains. Independent validators activated the protocol. Anza's research team, led by ETH Zurich professor Roger Wattenhofer alongside Quentin Kniep and Kobi Sliwinski, released the design in May 2025.

Alpenglow validators exchange votes directly rather than recording votes in subsequent blocks, with voting power determined by stake. Wattenhofer, Anza's research head, said approval from 80% of votes makes a block final immediately. Wattenhofer described the mechanism in an interview with Solana Foundation technology vice president Jacob Creech published last month. Wattenhofer said another route requires two voting rounds, each supported by 60% of stake, and can be faster for geographically concentrated validators, including those in Europe. Alpenglow is designed to continue operating when malicious participants control less than 20% of stake and another 20% of stake is offline. Validators progressively extend block times if the network fails to finalize a block for 10 seconds, allowing messages more time to arrive. Wattenhofer said the adjustment would eventually allow a block to finalize even with poor internet connectivity.

Planned upgrades include Rotor, which will alter the distribution of block data across the network. Geographically aware leader rotation aims to reduce delays when block production moves between validators. Quantumglow, a research design, would replace Alpenglow's elliptic-curve cryptography with hash-based signatures to provide security against quantum computers without changing finality speed. None of those upgrades has a committed date.

Validators approved SIMD-0236, the proposal implementing Alpenglow, in September 2025 with 98% voting in favor. Anza lead economist Max Resnick said at the time that users would immediately notice confirmation latency falling to approximately 150 to 200 milliseconds. Alpenglow reached Solana's community test cluster in May 2026. Resnick said then that the team was aiming for mainnet activation in late Q3 or early Q4. Anza confirmed on October 13 that activation would occur on October 21.

Developers on Jump Crypto's Firedancer team have proposed eliminating Solana's limit of 60 million compute units per block after Alpenglow becomes operational. The proposal would allow blocks to expand to the capacity of the fastest validators, while slower validators could abstain through Alpenglow's skip vote feature. Critics warned that the proposal could benefit well-funded operators and make the network more centralized.