Nexus launcher is a polished version of the Google Now Launcher, which is exclusive to the device. The launcher was leaked shortly after the news of Google Pixel surfaced and has been available to all Android users ever since.
Download Google Pixel Launcher:
The launcher has been picked up by third-party developers, it is not officially available on the Google Play Store for downloading, so you need to download the app in its APK format and manually install it.you can download Google Pixel Launcher APK file from this link:
PixelLauncherPrebuilt.apk
Also, You can download Pixel Launcher Wallpaper Add-On from here:
WallpaperPickerGooglePrebuilt.apk
How to Install Google Pixel Launcher:
After downloading Google Pixel Launcher apk file and Wallpaper Add-On (if you need) using the link given above, make sure you have Unknown Sources enabled from Settings->Security. if all right, just go ahead and tap on the downloaded .APK files to install them on the device easily.