http://www.pcgamer.com/assassins-creed-origins-loot-boxes-can-only-be-bought-with-in-game-money/

Some fans have been worrying about loot chests that have been appearing in Assassin's Creed: Origins screenshots. The chests are sold by a special merchant who sells mystery items and rare crafting materials for large chunks of gold, leading to speculation that AC:O will join the growing line of current releases that include a loot box microtransaction element.

Speaking to Eurogamer, game director Ashraf Ismail clarified that these loot chests can only be purchased with in-game currency. They are designed to be a gold sink for players that successfully max out the economy. You can still acquire these high level items by infiltrating high level military locations if you prefer a more combative play style.