Solana sets Alpenglow consensus switch for Wednesday

Solana is set to activate Alpenglow on Wednesday, replacing its TowerBFT consensus system with a new process designed to make blocks final in about 150 milliseconds. The Solana Foundation says the change affects how validators agree on blocks; transaction execution, fees and the Solana Virtual Machine stay the same.

How will validators agree on blocks?

Under TowerBFT, validators submit votes as on-chain transactions, and enough votes must accumulate before a block is final. The Solana Foundation’s Alpenglow upgrade guide says the current system takes about 12.8 seconds in its baseline comparison. Galaxy, which has operated a validator on Alpenglow’s test cluster, puts current finality at about six seconds following Solana’s separate reduction in slot times.

Alpenglow moves those votes off-chain: validators send them directly to one another, then combine them into certificates that prove enough stake voted. The certificate is included in a block in place of the individual vote transactions. Think of it as collecting signatures on a shared receipt instead of recording each signature as a separate transaction.

Galaxy describes two routes to finality. If 80% of stake votes to notarize a block, one round can finalize it. With lower participation, a second round requires both a 60% notarization certificate and a separate 60% finalization certificate. The protocol targets about 150 milliseconds, but that is a design target whose performance will need to be observed on mainnet.

When does the switch take effect?

The Foundation schedules activation for epoch 1064, which begins Wednesday, October 21, at approximately 13:20 UTC. The actual consensus handoff comes after the first 5,000 slots of that epoch, at slot 459,653,000, according to the Foundation’s guide. That leaves a transition window of about 18 minutes after the estimated epoch start.

The upgrade rolls out in phases. Votor, the voting protocol, is part of this activation. Rotor, which is intended to replace the block-data distribution system Turbine, is planned for a later release and has no scheduled date, the Foundation says.

What changes for users and validators?

Wallets and applications can continue signing and sending transactions as before, because execution and transaction formats are unchanged. Validators do need compatible software and a funded vote account: the Foundation says operators must run an Agave-based client and hold at least 0.8 SOL above the account’s rent-exempt minimum for the Validator Admission Ticket.

One visible effect is that vote transactions leave blocks, so transaction counts may fall even if user activity does not. The scheduled change is Solana’s first major consensus replacement since TowerBFT. The next thing to watch is whether Alpenglow reaches its finality target after the mainnet handoff.

References

• Solana Foundation’s Alpenglow upgrade guide — solana.com