Solana Activates Alpenglow Consensus Upgrade, Reducing Finality to 150 Milliseconds

• Solana activated the Alpenglow consensus upgrade on mainnet-beta at slot 459,653,000 around 14:00 UTC on Oct. 21, retiring TowerBFT after more than six years.
• The protocol cuts transaction finality from approximately 12.8 seconds to about 150 milliseconds by condensing confirmation into a single step.
• Anza CEO Brennan Watt described it as the largest, most ambitious blockchain upgrade since Ethereum’s Merge, completed in under 18 months from white paper to mainnet.

Solana completed its largest consensus overhaul since the network’s March 2020 launch when core engineering firm Anza activated the Alpenglow protocol on mainnet-beta at slot 459,653,000 around 14:00 UTC on Wednesday, Oct. 21, according to a statement shared with The Block and Anza’s own announcement.

The upgrade retires TowerBFT, the consensus mechanism Solana has used since genesis, and reduces the time for a transaction to become irreversible from about 12.8 seconds to roughly 150 milliseconds. Anza’s Alpenglow page confirms the mainnet-beta status as completed, with the migration feature gate (SIMD-0384) activating at an epoch boundary followed by a 5,000-slot window before the handoff to the new Votor voting system.

In a post on X, @anza_xyz announced that “Alpenglow is live on mainnet-beta,” noting finality reduced from 12.8 seconds to 150 milliseconds. The official Solana account echoed the news, calling it “the biggest consensus upgrade in Solana’s history, built by @anza_xyz.”

“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,” Anza CEO Brennan Watt said in a statement reported by The Block and Decrypt. The design was first published in May 2025 and underwent red teaming, penetration testing, migration rehearsals, and a security competition before activation.

Alpenglow moves validator votes off-chain as BLS-signed messages aggregated into a single certificate, freeing block space previously used for on-chain votes. It tolerates up to 20% of stake acting adversarially and another 20% offline simultaneously, a higher threshold than TowerBFT’s under-33% adversarial limit. Under normal conditions, blocks can finalize in one round with 80% stake participation or two rounds at 60%, per Anza’s technical documentation.

The change is particularly relevant for exchanges crediting deposits and merchants processing payments, where sub-second deterministic finality reduces settlement risk. Anza has indicated further protocol work, including Rotor for improved block propagation and a post-quantum research design called Quantumglow, though neither has a committed timeline. Actual observed finality on mainnet will depend on network conditions and will be tracked by RPC providers and dashboards in the coming days.