Solana (SOL) will apply its next major network upgrade, Alpenglow, to the mainnet on Oct. 21. The upgrade is expected to shorten transaction finality to about 150 milliseconds from about 12.8 seconds. A key goal is to replace the existing consensus system to speed up finality and improve efficiency in areas where real-time processing matters, such as DeFi and trading.

Blockchain outlet Decrypt reported on Oct. 14 that Alpenglow is set to be applied when epoch 1,064 begins on Oct. 21. The Solana Foundation expects the epoch to start at about 1500 UTC that day.

The existing system will not stop immediately when the upgrade begins. Even after the feature gate is activated, the existing consensus system, TowerBFT, will keep running for about 5,000 slots, or about 18 minutes. Alpenglow then takes over consensus leadership at slot 459,653,000. Solana plans a phased transition to secure network stability and prevent problems that could arise during migration.

A core element of Alpenglow is replacing TowerBFT with a new consensus structure. In the first stage, it introduces Votor, a protocol in which validators exchange and certify votes.

Under TowerBFT, validators submit votes as on-chain transactions, and a block is finalized only after votes accumulate over 32 slots. Vote transactions take up block space and the structure takes time to reach finality.

Votor adopts a method in which validators directly exchange messages and bundle votes into certificates. It is designed so a block can be finalized in 1 voting round, or at most 2 rounds.

Specifically, if more than 80 percent of total stake supports a particular block in the first round, it is finalized immediately. If support is 60 percent or more but less than 80 percent, a second round follows, and finality is decided based on the 60 percent threshold. The Solana Foundation explained the structure is designed to tolerate 20 percent malicious stake plus an additional 20 percent stake being offline.

Transaction finality is expected to fall to about 150 milliseconds from about 12.8 seconds. At 0.15 seconds, that is about 85 times faster than the existing finality time.

Alpenglow is also expected to affect key performance metrics of the Solana network. Under the current system, validators' consensus votes are recorded as on-chain transactions, but the new structure removes these vote transactions from blocks. As a result, the total number of transactions displayed externally and transactions per second (TPS) may drop sharply.

This does not mean actual user transactions or network activity will decline. It is a statistical change because votes needed for consensus will no longer be tallied in the same way as ordinary on-chain transactions.

Regular users do not need to take any special action. They can keep using existing wallets and applications, and the Solana virtual machine (SVM), transaction formats, programs and fee system will remain. For developers, the existing commitment levels of "confirmed" and "finalized" are expected to become effectively the same.

Validators' cost structure will change. Each vote account must prepare an additional 0.8 SOL as a validator entry ticket cost, beyond the rent-exempt balance. The fee is charged each epoch and burned. This replaces the structure under TowerBFT in which validators spent about 1 SOL per epoch on vote transaction fees. Validators that cannot pay will be unable to participate in voting and block production from the next epoch.

Developer Anza said on Oct. 13 on X, formerly Twitter, that Alpenglow will go live on mainnet beta on Oct. 21. Anza said the migration will occur in a single slot after about 18 months of work, and stressed that transaction finality will drop from seconds to about 150 milliseconds.

Alpenglow has also gone through a validator approval process. The related proposal, SIMD-0326, passed with 98.27 percent approval in a vote in September 2025. Anza chief economist Max Resnick had suggested late third quarter or early fourth quarter as the timing for mainnet deployment in May, and the current schedule falls within that expected range.

What will be applied on Oct. 21 is Votor, which represents half of the full Alpenglow package. Rotor, which will replace the existing Turbine system responsible for propagating block data among validators, is set to be introduced later. The specific timetable for Rotor has not yet been set.

Alpenglow is an upgrade focused not only on increasing throughput but on reducing the time it takes for transactions to reach an irreversible state. Key points to watch are whether Solana's finality speed improves in practice with Votor and how much overall network performance changes as Rotor is implemented later.