More details from Ars Technica: This is part of a series of new campaign chapters, all developed by MachineGames "in collaboration with id Software." MachineGames is best known for making the games in the relatively recent Wolfenstein reboot series, as well as Indiana Jones and the Great Circle. The Quake maps are made by a team dubbed "Quake Club," which includes several MachineGames employees who work on Quake maps in their spare time.
The ambition and scope of some of these maps is beyond what was typical for Quake maps back in the late '90s, thanks in part to the team's use of TrenchBroom, a newer map editor that works well on modern systems and is easier to work with and more capable than what folks were using in those days. There are 19 new levels, and they have several new gameplay gimmicks, like a time loop mechanic and a disorienting-but-cool teleportation system that makes it look like the levels are changing on the fly — kind of similar to the multi-time-period levels we saw in Titanfall 2 or Dishonored 2, though in these Quake maps the time shifts happen without player input. There's also new music... The new maps have been added to the campaign list in the remastered version of Quake, and like that remaster, they're available free to anyone who already owns Quake on Steam, as well as Quake on current and last-gen PlayStation, Xbox, and Nintendo consoles.