Google has a tradition of code-naming upcoming devices after fish or other forms of aquatic life. For example, last year's Pixel and Pixel XL smartphones were code-named "sailfish" and "marlin," respectively. Now, a pair of reports reveal three new codenames in use by Google: "muskie," "walleye," and "taimen."
According to reports from Android Police and Droid Life, the three mysterious devices are the successors to the existing Pixel and Pixel XL. The three codenames represent each device's size—"muskie" is the smallest device and "taimen" is the largest; "walleye" falls in between. Unfortunately, no specifics on screen size or overall dimensions are available.
Several sources have confirmed to both websites that the codenames are correct. The sources also confirm that the "taimen" device is much larger than the other two, yet is still a phone. This lays to rest early theories that it might be a tablet or similarly-sized device. The final piece of information comes via an AOSP code review entry, and shows that the "walleye" device "boots, and ... doesn't show warnings and errors." It's not terribly exciting information, but it proves the device exists and is being worked on.