Luckily, Google has said that Extreme Battery Saver will be coming to existing Pixels in a feature drop "very soon.".
Google claims that Extreme Battery Saver will let you keep your phone's battery going for up to 48 hours.
The new #Pixel5G phones feature Extreme Battery Saver to keep your phone going for up to 48 hours: https://t.co/c7Wpm04Sp1#LaunchNightIn pic.twitter.com/Nsck6RxbpL.