Valve has added a new achievements system to the Steam client beta, letting developers keep base-game, DLC and seasonal achievements in separate sets.
It is beta-only for now, so most Steam users will not see it until it reaches the standard client. Developers can build custom sets around their game, such as mastering a specific character class or finishing a singleplayer campaign. The achievements page has been redesigned too. Overall completion and progress on individual achievements now share one page, and players can compare achievements with up to three friends at once.
The change targets a long-standing irritation. Until now, a player who unlocked every achievement in a game saw 100%, but a DLC with new achievements dragged that figure back down. With DLC in its own set, skipping an expansion no longer costs anyone their completion number. Seasonal sets follow the same logic. Valve's example is a "Halloween Event Achievements" set that is valid for a limited period and leaves the base game's count alone.
The catch is that nothing changes for a game until its developer sorts the achievements into sets. Several titles have done so already, including Portal 2, Left 4 Dead 2, Team Fortress 2, Forza Horizon 5, Crusader Kings III and Call of Duty: Modern Warfare 4. Valve's own older games on that list show that existing releases can adopt the system, but it still takes work from someone.
Valve is also matching an existing standard here rather than setting a new one. PlayStation consoles have offered friend comparison and separate DLC achievement sets for a while. The open question is how many older games with long-finished DLC will ever be updated, since the completionist payoff depends on studios that may have moved on.