Solana Targets 150-Millisecond Finality With Alpenglow

Solana activated the Alpenglow upgrade on its mainnet on Oct. 21 at slot 459,653,000. The protocol replaces TowerBFT and targets finality in about 150 milliseconds. Under Alpenglow, confirmed and finalized refer to the same network state.

The upgrade changes consensus but leaves transaction execution, the Solana Virtual Machine and fee systems unchanged. Its first phase, Votor, lets validators exchange votes directly and combine them into certificates. Solana’s documentation says transactions can reach finality in one or two voting rounds. The second phase, Rotor, is intended to manage block propagation and has no launch date.

The main effect applies to applications that wait for irreversible transactions before releasing assets or recording settlement. Solana’s documentation lists TowerBFT finality at 12.8 seconds when slots lasted 400 milliseconds. The network reduced its slot duration to 200 milliseconds on Oct. 9. Applying TowerBFT’s documented 32-slot rule to the shorter interval produces a nominal 6.4-second baseline, not a measured end-to-end settlement time.

A sensitivity model estimates how faster consensus could affect the number of sequential settlements completed with the same funds. With instant reuse of funds and no other delays, reducing consensus time from 6.4 seconds to 150 milliseconds produces a theoretical 42.7-fold turnover increase. With two seconds of additional processing, the multiplier falls to 3.9 times; with five seconds, it falls to 2.2 times. Against the older 12.8-second baseline, the corresponding figures are 85.3, 6.9 and 3.5 times.

The model excludes custody checks, funding transfers, compliance reviews and signatures. It measures how often funds could cycle through serial settlements, not reductions in broker collateral, clearinghouse margin or total liquidity requirements.

The National Securities Clearing Corporation acts as a central counterparty for eligible equity trades and offsets purchases and sales among participants. The Depository Trust & Clearing Corporation reports that NSCC processed $608 trillion in equity transactions in 2025 and reduced payment obligations by an average of 98% through multilateral netting. The remaining net amount settles on the equity market’s T+1 schedule, one business day after the trade date.

The 98% figure measures payment obligations rather than transaction-processing time. Solana’s delivery-versus-payment design uses separate escrow accounts and a settlement authority that signs the exchange, allowing both sides to execute atomically. Network finality remains separate from the legal finality set by the parties’ agreements.

The Bank for International Settlements warned in a 2023 blueprint that settling transactions individually can increase liquidity needs when netting mechanisms are absent. A December 2025 BIS working paper found liquidity savings of 2.6% to 12.2% in simulations of an auction-based mechanism using payment data from Peru, South Africa, a Southern African regional system and Switzerland. The auction succeeded in 79% of cases on average.

DTCC announced on July 15 that tokenized securities held at the Depository Trust Company had completed live production transactions involving more than 30 firms. The transactions covered Treasury and equity delivery-versus-payment, securities lending, collateral pledging and central-counterparty margin workflows, using Besu and Canton. Future comparisons of Alpenglow will require observed mainnet finality, full settlement times, residual obligations after netting, peak prefunded liquidity and the legal treatment of completed transactions.