Solana switches on Alpenglow, its biggest consensus overhaul since 2020, aiming for 150-millisecond finality

Summary

Solana validators activated the Alpenglow consensus upgrade on the live network on Wednesday, Oct. 21, retiring TowerBFT, the protocol Solana had run since its March 2020 launch, at slot 459,653,000 around 14:00 UTC, core engineering firm Anza said, according to The Block and Decrypt; Cointelegraph, citing the Solana Foundation's dashboard, put the switch at about 1:54 pm UTC.

Alpenglow targets transaction finality of roughly 150 milliseconds; The Block, Decrypt and Cointelegraph say that is down from about 12.8 seconds, while CoinDesk described today's lock-in time as about six seconds.

Instead of writing votes onto the chain as transactions, validators now send stake-weighted votes directly to each other and bundle them into certificates that can finalize a block in one or two rounds, CoinDesk and Decrypt reported.

Anza CEO Brennan Watt called it "the largest, most ambitious blockchain upgrade since 'The Merge'," per The Block and Decrypt, and further changes such as Rotor block propagation and the post-quantum Quantumglow design have no committed dates.

Updates

• Update, Thu, 22 Oct 2026 13:12:08 UTC: Oct. 22: CoinDesk's explainer said the new voting system targets settlement in about 150 milliseconds, which could shorten waits for payments and deposits, and that users can keep their existing wallets.

Key facts

• Validators approved the upgrade in September 2025, voting 98% in favor of proposal SIMD-0236, Decrypt reported. (Decrypt)
• Validators currently spend about 2 SOL a day on vote fees; Alpenglow replaces them with a flat "validator admission ticket" of 0.8 SOL per roughly 24-hour epoch, about 60% cheaper, according to CoinDesk. (CoinDesk)
• The test network was wiped and restarted six times since early May and one migration attempt failed network-wide and was rolled back before a later one succeeded, CoinDesk reported, citing Galaxy Digital. (CoinDesk)
• At press time the Solana Foundation dashboard showed 6.6-second finality and 4,721 transactions per second, Cointelegraph reported, which has asked the foundation about real-world finality measurements. (Cointelegraph)
• Active Solana validators fell to 659 at the end of September from 696 three months earlier, roughly 30% below a year ago, CoinDesk reported, citing Bitwise. (CoinDesk)
• The protocol is designed to keep working with less than 20% of stake acting maliciously and a further 20% offline, Decrypt reported. (Decrypt)
• Jump Crypto's Firedancer team has proposed (SIMD-0370) removing Solana's 60 million compute-unit block limit after Alpenglow, The Block reported; Decrypt said critics warned the change could favor well-funded operators. (The Block)

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