It looks like there will be something different about the navigation bar in Android P. In a Android Developers blog post discussing network security improvements, Google briefly slipped up and exposed the new layout in a screenshot. Since then, Google has cropped the navigation bar out, but not before the original image was captured.
According to the screenshot, it appears that the virtual home button will take the shape of a small pill, instead of a circle that we've been accustomed to. The triangular back button remains, though, 9to5Google states that the back button will auto-hide when not in use. In addition, the back button will not appear on the home screen due to it having no function there. Curiously, the multitasking button is gone and has been replaced by a swipe up gesture. This should be interesting on Pixel 2 devices since swiping up on the home screen currently brings up the app drawer.
More information regarding Android P and the new navigation bar will be found out next month at Google I/O. The conference will be held from May 8th to May 10th at the Shoreline Amphitheatre in San Francisco, California.
Source: Android Developers Blog via 9to5Google