The Google Pixel and Pixel XL phones are structured differently than the current Android devices on the market. The phones feature multiple slots for system, boot, vendor and other partitions, and if you’re into flashing and stuff on these devices you might run into trouble with the current ADB and fastboot installers since the multi slots system isn’t supported on the older files.
Thanks to xda user romracer who took the matter in his own hands and compiled frsh files of Fastboot from the AOSP (Android Open Source Project) source. You can download his Fastboot files from the link below.
The zip file also contains freshly compiled ADB files. Although, the previous ADB files work just fine with the Pixels, but you can use the new ones just to make sure you’re updated.
If you’re looking update your current installed Fastboot files, just take the libwinpthread-1.dll file from the zip and paste/replace it into the directory where Fastboot is installed on your PC.
Image source: The Verge