This is achieved through differential delta-patching. The Egis software records only the changes made to the game state (e.g., "Health changed from 100 to 45," "Key item acquired"), storing them in a reversible ledger. If you decide you want that health back but want to keep the key item, the system reverses the health delta while leaving the item acquisition untouched.
ERGS does not prevent reloading old states, but logs each revert. Designers can detect excessive reversions and adjust difficulty or lock achievements – “temporal heat” mechanic. egis reversible game save
Furthermore, cloud-sync support is arriving. Imagine starting a game on your PC, playing for an hour, reversing a mistake on your laptop via cloud-synced deltas, and continuing seamlessly. The reversible ledger is no longer local—it is portable. This is achieved through differential delta-patching