Current game stage: 1
Alpha 18 is an upcoming major update to the game. Experimental builds became public early October. Currently, the latest experimental build is A18 B155.
Many changes have been made and are being added as new bugs are being patched. Most of these notable changes involve texture changes, mechanic rebalances, new weapons, the new zombie; The Demolisher, the return of classic schematics (where you read them and permanently learn the recipe), new perk books, new skill tree, and the dyes becoming purely cosmetic.