So, in blender 2.8, you would jump to Transparent view by hitting z > 2. But in blender 2.81 beta, there's no such option and every build I get, there isn't either so it's not a bug.
The shortcut Z to show the shading pie menu still exists in Blender 2.81 and 2.82. However it's 4 to enable Wireframe mode, 2 is for the Material Preview mode.
You can also enable Wireframe mode by clicking on its icon.
If you're referring to the X-ray mode, it can either be toggled through Alt+Z or by clicking on its icon.