Solana wants to make its transactions final in the blink of an eye. The network has started testing its Alpenglow update, an overhaul of its consensus that could reduce transaction finality from 12.8 seconds to 150 milliseconds.
Exchange platforms, cross-chain bridges and merchants could then consider a payment to be irreversible almost the moment it leaves.
Key Points
Solana launched the Alpenglow tests, the overhaul of its consensus that could reduce finality from 12.8 seconds to 150 milliseconds.
Designed by Anza, Alpenglow replaces TowerBFT and the Proof of History with two bricks: Votor for voting, Rotor for the distribution of blocks.
Exchange platforms, bridges and merchants could make a payment irreversible almost instantly, much faster than with a bank card.
Favored by more than 98% by validators, the protocol tolerates 20% malicious staking and an additional 20% offline.
What Alpenglow is changing in the Solana blockchain consensus
Finality refers to the moment when a transaction can no longer be canceled or rearranged by the network. This is then considered definitive and irreversible. For Solana, this happens on the side of TowerBFT, its in-house consensus system. Under the hood, TowerBFT relies on a method called Proof of History (PoH), which divides time into slots of 400 milliseconds. Thus, a block only becomes definitive after 32 successive confirmation slots, or currently 12.8 seconds.
Alpenglow is shaking up the internal workings of Solana. Indeed, it replaces both TowerBFT and Proof of History at the heart of the consensus. The protocol was unveiled a little over a year ago by Anza, the company spun off from Solana Labs which develops the Agave validator software. Anza researchers designed it with the support of Roger Wattenhofer, head of the distributed computing group at the Swiss Federal Institute of Technology in Zurich.
Alpenglow rests on two bricks. On the one hand, Votor orchestrates the vote of validators, weighted by their stake (the SOLs immobilized to secure the network). A fast path finalizes a block in a single round if validators representing 80% of the stake approve it, a slow path in two rounds if they only weigh 60%. The two paths run in parallel and the first one that ends sets the finality.
On the other hand, Rotor succeeds Turbine for the distribution of blocks. The producer of each block entrusts its fragments to a single layer of relay nodes selected according to their stake, where Turbine passes them through a multi-stage tree.
The majority of transactions registered on Solana today are validator votes. The new protocol will circulate them off-chain, bundled into certificates that serve as compact proof of voting. Space freed in blocks will revert to user transactions.
Thus, it is these two developments that will allow nodes to agree more quickly on the purpose of a transaction and will also allow them to broadcast them more efficiently throughout the network.
A finality in 150 milliseconds: what crypto gains
With this proposal, Anza hopes to achieve a median finality of 150 milliseconds. Measurements from simulations calibrated on the real distribution of the stake, certain blocks having even been finalized even faster, in 100 milliseconds.
For now, the update is still relatively experimental. In fact, it will be deployed this week on the Solana testnet. This will allow Anza developers to test their system in a real situation and correct any failures encountered.
With this update, Solana intends to become one of the fastest blockchains. For comparison, on Ethereum you have to wait two epochs of 32 slots of 12 seconds, or 12.8 minutes in theory, before a block becomes irreversible. On Bitcoin, the rule of use of six confirmations represents around an hour and the finality remains probabilistic. Indeed, each added block makes a cancellation more improbable without ever excluding it.
Such a short purpose would allow an exchange platform to credit a deposit almost at the moment the user validates the sending. Bridges would also benefit, since each second of waiting ties up funds and leaves a window for a possible reorganization of the chain.
For a merchant, the finality time matters more than the throughput in transactions per second, which blockchains readily make a commercial argument. Blockchain already has its input into payment. Indeed, from 2023 Visa extended its USDC settlement system to Solana, and Western Union selected the network to issue its USDPT stablecoin. A payment by bank card is authorized in one to two seconds, but settlement between banks then takes one to two working days and the customer can dispute the transaction for several months. A stablecoin transfer on Solana would become final even before the terminal displays “payment accepted”.
A security compromise approved by more than 98%
Alpenglow claims so-called “20+20” resilience. This means that the network remains capable of finalizing blocks with 20% of the stake in the hands of malicious actors and another 20% offline. Classic BFT protocols tolerate just under a third of malicious participants. Anza therefore lowers this threshold in exchange for better resistance to server failures, much more common than coordinated attacks.
Protocol modifications are described in Solana Improvement Documents (SIMD), and some, like Alpenglow, go through a vote of validators. The SIMD-0326 proposal was approved last September with more than 98% of votes in favor. Note, however, that the vote recorded a participation of approximately half of the total stake mobilized on the network.
The test phase which begins must now verify that the figures obtained in simulation hold up outside the laboratory. The new protocol must then be integrated into Agave and Firedancer, Jump Crypto's validator software, before any activation on the mainnet.
Solana will then finalize its blocks without Proof of History, the invention that co-founder Anatoly Yakovenko placed in 2017 at the heart of the network's original whitepaper.
