We have just shipped an updated Steam Client to the Preview/Beta channel.
Steam Achievement Sets
A new way to organize, track, and complete a game's achievements. Read more details in the announcement.
Games can now organize and group achievements for base game and DLC content
DLC achievements can be added via sets without breaking game completion
Completed achievement sets remain completed when new sets are added
Achievements and sets can be archived if they are seasonal or can no longer be achieved
Updated Achievements page and achievement rollup displays

General
Notifications settings layout has been changed to be easier to work with on all screen sizes
Fixed multiple edge cases that could cause memory leaks in game streaming and controller code
Multiple general stability improvements and fixes for rare crashes affecting small numbers of users
Fixed an error displaying dates for users in British Columbia
Library
Linux
The Steam client is now a 64bit application.
The Steam client now runs inside a Steam Runtime container.
Fixed a case where Steam updater UI would fail to show for some users.
Remote Play
Steam Controller Firmware
Accessibility