If you own a Google Pixel (XL) or Pixel 2 (XL) you can flash what Google has been working on. Between the last DP and now are a few cosmetic changes as well as a (somewhat) theme mode. Beta 3 (or Developer Preview #4) provides a more stable build for developers to build on and users to test out.
Though this is likely stable enough to use as a daily driver, Google still recommends you use at your own risk. Meaning it may still have bugs in it as well as a few apps not working well with the new build. As this is designed to help app developers and manufacturers test and get their software up to date for when Android P goes live in a few months.
What are you noticing in the new P?