Valve's Steam Achievement Sets broke bulk unlocks in third-party tools

On October 15, 2026, Valve added Achievement Sets to the Steam Client Beta, letting developers split achievements into up to 40 groups with separate progress bars. Steam servers now reject unlocks from DLC sets the account doesn't own or from archived sets, so batched "unlock all" writes fail entirely with EResult.InvalidParam.

• Up to 40 achievement sets per game, each with its own progress bar
• DLC sets count toward completion only after the DLC is owned
• Archived achievements stay on profiles and stop blocking 100%
• One unowned DLC achievement rejects the whole batch with InvalidParam