Alpenglow is designed to continue operating with up to 20% of stake acting maliciously and another 20% offline

From the articleSolana Alpenglow Goes Live in 'Most Ambitious' Upgrade Since Ethereum's Merge - DecryptAlso in Solana Activates Alpenglow on Mainnet, Swapping Out TowerBFT for a Faster Consensus Engine - Unchained, Solana's Alpenglow upgrade set to cut finality to 150ms