Source code for Android P isn't available just yet but early release to OEMs for testing has now allowed XDA Developers to get a glimpse of the OS running on Huawei's Mate 10 and Mate 10 Pro. For now, the test only seems to be taking place on the Chinese variant of the Mate 10, bearing the model number ALP-AL00. It was also able to be seen running on the Huawei Mate 10 Pro thanks to some internal rebranding undertaken by the source using Funky Huawei. So there's not a lot that's new about it. Moreover, developer previews shouldn't be considered the end-all of any new Android version. There's still a pretty massive array of changes expected with Android P and most of that won't be present in the first preview. Huawei also has its own proprietary design language - shown on the device as EMUI 8.2 but expected to bump up to EMUI 9 by release. So some of the larger aesthetic changes associated with Android P, such as Material Design 2, probably won't be included when it does release officially.
Having said that, there are definitely some changes present from Huawei's current EMUI based on Android Oreo. In fact, there are even a few undisclosed developer options that hadn't made it out of AOSP by the time Developer Preview 1 was ready to release. Beyond that, apps are restricted that utilize non-SDK Java APIs, as are restrictions on third-party OMS overlays. New global actions for Accessibility Services have been turned on and that includes Android P's expected zoom on text selection feature. Since this is the first Developer Preview, it goes without saying that the Android P easter egg screen is onboard, too. That still doesn't seem to give away the treat name chosen for the new OS, however, and only shows a colorful "P," for now.
As of this writing, the preview doesn't seem to give away too much with regard to what can be expected in the final build. That shouldn't be too surprising since Google reportedly has no fewer than five Developer Previews planned for the upcoming version of Android. It's also not expected to officially launch until the third quarter. In the meantime, there will almost certainly be a lot more revealed at the company's I/O Developers Conference next month.