Alpenglow went live on Solana today: finality drops from 12.8 seconds to about 150ms, and to get there Solana deleted the two ideas it launched with. The problem it solves is the one Solana got mocked for the longest: validators voting with on-chain transactions. Votes were about three quarters of the ledger, finality needed 32 slots of them, and every validator paid about 1 SOL a day just to vote. Votes had to be on-chain because they needed a place on the Proof of History clock, the hash chain that was the whole pitch in 2018. So PoH went out of consensus, replaced by local timeouts, and a vote became a UDP packet sent to every validator directly. Any node collects 80% of stake, bundles it into one BLS signature, one round, done. In hindsight PoH was holding the door open until BLS aggregation was production-ready. The novel part of Solana turned out to be the part they could remove. Credit where due: it takes a serious team to delete its own founding idea on a live network with tens of billions on it. Tower BFT and PoH did their job for six years, and what replaced them is textbook BFT with a very good engineering story. The price: Byzantine tolerance drops from 33% to 20%, and votes are no longer visible on-chain. Probably worth it for 100x finality.