Updating the state root is crazily slow and is responsible for an up to 10x slowdown when building EVM blocks. SALT is MegaETH's solution to this problem. SALT is a brand new authenticated key-value store that replaces (instead of being a mere reimplementation of) EVM's Merkle Patricia Trie (MPT). It is optimized for just one thing: take as little space as possible so as to fit in computers' RAM. This goal is supposedly easy to achieve by tuning the MPT and making it wide and shallow, but to think so one overlooks a key issue: key sparsity. Our theory + experiments (lots of details in the talk) show that sparsity inflates the sizes of MPT and friends (such as the venerable Verkle Tries, unfortunately) by hundreds of times. Consequently, they have to overflow to slow and clunky hard drives which kills performance. (Remember the 10x slowdown?) By taming sparsity, SALT is able to get infinitely close to optimality. In fact, it is optimal in space and IO usage! The bottleneck of updating state roots has been solved once and for all. Check out the recording of the talk! The talk was presented at the Science and Engineering of Consensus workshop during SBC 25. Huge thanks to the Tse Lab at Stanford University for organizing the event, and to event sponsors @babylonlabs_io and @poddotnetwork!