Solana Activates Alpenglow, Targeting 150-Millisecond Finality

Solana activated Alpenglow on Oct. 21, introducing a consensus system designed to shorten the wait before payments and trades become irreversible. Developer Anza said the upgrade targets finality of roughly 150 milliseconds.

Solana Replaces TowerBFT on Its Live Network

Anza said validators activated Alpenglow on mainnet-beta at slot 459,653,000, around 2 p.m. UTC. The migration replaced TowerBFT, which Solana had used since its March 2020 launch, while preserving the existing ledger.

Finality is the point at which the network considers a transaction irreversible. Galaxy estimated finality at roughly six seconds before Alpenglow, following earlier reductions in block intervals. Anza said shorter finality could reduce waiting times for exchanges crediting deposits and merchants accepting payments.

Earlier upgrades shortened block intervals, while Alpenglow changes how quickly blocks become final. Its roughly 150-millisecond finality figure remains a design target rather than a guaranteed time for every transaction.

Alpenglow Moves Validator Votes Off-Chain

Under TowerBFT, validators submitted votes as transactions on the blockchain. Alpenglow instead lets them exchange signed votes directly and combine signatures into compact certificates showing that sufficient stake supports a block.

Galaxy said the protocol can finalize a block in one voting round when 80% of stake supports notarization. The alternative path requires two voting rounds, with certificates showing that 60% of stake supports notarization and 60% supports finalization. Both paths operate concurrently, and whichever finishes first determines finality.

Alpenglow Replaces Per-Vote Fees With Flat Charge

Alpenglow replaces fees paid for individual votes with a flat admission charge. Galaxy said the charge at activation would be approximately 0.8 SOL per epoch, with an epoch lasting about 24 hours, while staking-reward mechanics remain unchanged.

The change does not produce an equal saving for every operator. Galaxy noted that validators also lose revenue from including vote transactions in blocks, so the net effect depends on their block-production activity.

Anza said the rollout followed security testing, migration rehearsals and deployment on testnet and devnet. Further work includes Rotor, which changes how block data spreads across the network, and faster leader handoffs; those additions have no committed release date.