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<p>Solana replaced TowerBFT with Alpenglow on its mainnet on October 21, in its most significant consensus change since launch. The new protocol targets a finality close to 150 milliseconds, compared to about 12.8 seconds previously, but part of the planned architecture is still to be deployed.</p>
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  <h2 class="in-brief--title" id="in-brief">In Brief</h2>
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   <li>Solana activated Alpenglow on October 21, replacing TowerBFT on its mainnet.</li>
   <li>The new consensus targets a finality of 150 milliseconds, compared to 12.8 seconds previously.</li>
   <li>The transition occurred without a network-wide outage, with participation from 654 validators.</li>
   <li>The Votor mechanism speeds block validation through new voting procedures and BLS signatures.</li>
   <li>Alpenglow promises faster final transactions and better fault tolerance.</li>
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<h2 id="alpenglow-replaces-towerbft-on-the-mainnet">Alpenglow Replaces TowerBFT on the Mainnet</h2>
<p><a href="https://www.cointribune.com/en/solana-prepares-alpenglow-upgrade-in-push-for-nasdaq-like-speed/" rel="noopener noreferrer nofollow">The activation began</a> at the start of epoch 1064. However, the network retained TowerBFT for the first 5000 slots of this epoch, about 18 minutes, to prepare the transition to the new system.</p>
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<p>The transition completed at slot 459653000. The validators then formed the cryptographic certificate marking the birth of the Alpenglow consensus. Anza, the lead developer of the Agave client, <a href="https://decrypt.co/381484/solana-alpenglow-goes-live-in-most-ambitious-upgrade-since-ethereums-merge" rel="noopener noreferrer nofollow">described</a> this operation as the <em>“greatest upgrade in Solana’s history”</em>.</p>
<p>The key elements of the activation illustrate the magnitude of the change :</p>
<ul>
 <li>Alpenglow replaces the TowerBFT consensus used since Solana’s inception ;</li>
 <li>The targeted finality goes from 12.8 seconds to about 150 milliseconds ;</li>
 <li>654 validators participated in the transition ;</li>
 <li>The switch from one consensus to the other lasted about 900 milliseconds ;</li>
 <li>Validator votes are no longer recorded as on-chain transactions ;</li>
 <li>BLS signatures allow multiple votes to be aggregated into a single certificate ;</li>
 <li>Each admitted validator must pay a ticket of 0.8 SOL per epoch.</li>
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<p>The transfer occurred without a full network halt. During the critical phase, blocks temporarily stopped including user transactions and carried only the necessary votes. This precaution was to allow a rollback without invalidating a user-signed operation.</p>
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<p>Once the genesis certificate was formed, nodes handed the consensus over to the new Votor algorithm. Transactions then resumed under the Alpenglow regime.</p>
<h2 id="votor-dramatically-reduces-final-confirmation-delay">Votor Dramatically Reduces Final Confirmation Delay</h2>
<p>The consensus allows validators to agree on the order of transactions and when a block can no longer be reverted. With TowerBFT, Solana produced blocks quickly, but their full finality required about 12.8 seconds.</p>
<p>Votor uses two voting procedures in parallel. The first can finalize a block in one round when 80% of tokens staked staking respond. The second can conclude after two rounds with 60% participation. The protocol adopts the path that finishes first.</p>
<p>Votes are no longer recorded as ordinary transactions. Validators exchange signed messages directly via the BLS system. Multiple signatures can then be aggregated into a compact certificate, freeing block space for user operations.</p>
<p>Alpenglow also targets better fault tolerance. Its design allows simultaneous tolerance of 20% of tokens staked on offline validators and 20% on hostile actors. TowerBFT relied on a limit of less than one-third malicious participation.</p>
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<p>For users, the expected effect mainly concerns payments, decentralized exchanges, and applications demanding quick certainty. A finality near 150 milliseconds would reduce the wait before an operation is considered irreversible. However, this gain doesn’t mean all applications will respond that fast, as their interfaces, servers, and controls add their own delays.</p>
<h2 id="h-part-of-the-upgrade-is-still-to-come">Part of the Upgrade Is Still to Come</h2>
<p>The activation on October 21 mainly concerns Votor, the new consensus mechanism. It does not yet deploy all the components described in the Alpenglow project.</p>
<p>Rotor, the future block propagation system, is set to replace Turbine in a later phase. It plans to distribute data shards via a single relay and to use the network’s full bandwidth. Its activation schedule is not yet set.</p>
<p>The economic operation of validators is also changing. Off-chain votes remove the old fees paid for each vote transaction. Instead, the protocol charges a validation ticket of 0.8 SOL per epoch on the vote account. An operator lacking the required amount cannot vote or produce blocks during the following epoch.</p>
<p>The comparison with Ethereum’s <em>“The Merge”</em> mainly illustrates the technical significance of the change. Ethereum abandoned proof-of-work for proof-of-stake in 2022. Solana keeps its general model but directly replaces the engine organizing agreement among its validators.</p>
<p>The coming weeks will verify whether the observed finality remains near 150 milliseconds during high activity periods. Network stability, validator participation, and the future deployment of Rotor will determine if <a href="https://www.cointribune.com/en/solana-to-deploy-alpenglow-upgrade-on-october-21/" rel="noopener noreferrer nofollow">Alpenglow lives up to its promises</a>.</p>

Solana Targets 150ms Finality With Alpenglow Upgrade

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