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Solana Alpenglow replaces TowerBFT with 150ms finality target

Solana activated Alpenglow on Oct. 21, replacing TowerBFT and targeting 150-millisecond finality; validator operators now face new software and vote-account requirements.

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Solana Alpenglow replaces TowerBFT with 150ms finality target

Solana activated Alpenglow on mainnet on Oct. 21, replacing its long-running TowerBFT consensus and targeting finality in about 150 milliseconds, down from 12.8 seconds. The Solana Foundation’s Alpenglow update says the change began in epoch 1064, while Alpenglow consensus took over at slot 459,653,000.

Anza, the engineering team that developed Alpenglow, said in its mainnet launch announcement that validators retired TowerBFT while carrying the existing ledger forward. The change affects how validators agree on blocks; Solana’s transaction execution and fees remain the same.

How does Alpenglow reach finality faster?

Alpenglow replaces validator vote transactions with direct votes between validators, which are combined into certificates. According to the Solana Foundation, a block can now become final after one or two rounds of voting, instead of waiting for votes to accumulate over 32 slots under TowerBFT.

The roughly 150-millisecond figure is a target for finality: the point when a transaction can no longer be reversed. It does not mean Solana produces blocks every 150 milliseconds. The Foundation says block time was reduced separately, from 400 milliseconds to 200 milliseconds, in stages that finished in October.

For you as a user, the Foundation says wallets and apps work as before. The Solana Virtual Machine, transaction formats and fee mechanics were not changed by Alpenglow.

What changed for validators and developers?

Validator operators need to run version 4.3.2 of an Agave-based client, such as Agave, Jito-Solana or Harmonic Salsa, and keep at least 0.8 SOL above the rent-exempt minimum in their vote account. The Foundation says that balance pays the Validator Admission Ticket fee each epoch; a validator that does not pay will not vote or produce blocks in the following epoch.

Developers who stream block data or count vote transactions may need to adjust their systems. Vote transactions no longer appear in blocks, and a slot can contain more than one candidate block, so the Foundation advises Geyser and gRPC users to track the bank associated with each event.

What comes next for Alpenglow?

The launch covers Votor, Alpenglow’s voting protocol. Rotor, a planned later phase, is intended to replace Turbine, which spreads block data across Solana’s network; the Foundation says Rotor has no scheduled release yet.

Watch for a release date for Rotor and for how the new finality target performs as validators and infrastructure operators adapt. The 150-millisecond figure is the protocol’s target, while the Foundation’s page describes the mainnet activation and its operator requirements.

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