Solana Activates Alpenglow, Cutting Finality to 150 Milliseconds

Solana activated its Alpenglow consensus protocol on mainnet on Oct. 21, replacing TowerBFT and targeting transaction finality in about 150 milliseconds, according to the Solana Foundation’s upgrade page. Finality is the point when a transaction can no longer be reversed. The previous system took about 12.8 seconds to reach it.

• Activation: epoch 1064, at approximately 13:36 UTC
• First Alpenglow consensus: slot 459,653,000
• Previous finality time: about 12.8 seconds
• Target finality: roughly 150 milliseconds

The change replaces how Solana validators agree on blocks; it does not change how transactions execute, or the network’s programs and fees, the Foundation said. Anza, Solana’s core engineering team, told Decrypt that the live handoff carried the existing ledger forward as validators switched systems.

How does Alpenglow change transaction settlement?

Under the old TowerBFT system, validators sent votes as transactions, and a block became final after enough votes accumulated over 32 slots. Alpenglow’s Votor protocol sends votes directly between validators and bundles them into certificates, so a block can become final after one or two rounds of voting, the Foundation said.

For you as a user, the intended effect is quicker settlement in wallets and apps. The 150-millisecond figure measures finality, not how often Solana produces blocks. Slot times were reduced separately, from 400 milliseconds to 200 milliseconds in a change completed in October.

Faster finality may matter to services that wait for a transaction to become irreversible before acting on it. Decrypt reported that Anza cited exchanges, banks and merchants as potential beneficiaries. The timing is a target, however; the sources do not establish that every transaction will finalize in exactly 150 milliseconds under all network conditions.

What did validators have to change, and what comes next?

Validators had to run an Agave-based client to vote and produce blocks after the migration. The Foundation lists Agave v4.3.2, Jito-Solana and Harmonic Salsa as supported clients for the transition; it says Firedancer and Frankendancer were not supported for the migration.

Validators also need at least 0.8 SOL in their vote account for a Validator Admission Ticket fee. The fee charged at the start of an epoch pays for the validator’s inclusion in the following epoch. A validator that does not pay will not vote or produce blocks in that next epoch, according to the Foundation.

Alpenglow’s live phase is Votor. A second phase, Rotor, is planned for a later release and would change how block data spreads across the network, but it is not yet scheduled. The Foundation says transaction execution remains unchanged; the upgrade changes consensus and, later, block data propagation.

The rollout followed validator approval of the upgrade in September 2025, with 98% voting in favor of the proposal, Decrypt reported. Before mainnet, the protocol ran on Solana’s testnet and devnet. The activation marks a major change to how the network reaches agreement, while the planned Rotor phase remains ahead.

Sources and documents

• Solana Foundation’s upgrade page — solana.com
• Decrypt — decrypt.co