Which versions of the Apple Watch is Pokemon Go compatible with?

The update for Pokemon Go that integrates it with the Apple Watch has finally been released.

However, I cannot find any information about whether it is compatible with the first generation watches, or just the newest shiniest models.

Is Pokemon Go compatible with Series 1 Apple watches?

It seems that the game is compatible with every series of the Apple Watch. Looking at some commentaries on this Reddit thread, it looks like Series 1 users are able to play it too:

Q : It's only for Apple Watch 2 or the old watch can get it too?

A : All watches I presume. Works on my Series 1

And for original series:

Q : I'm hearing it is only for Apple Watch series 2 because of the built in gps can anyone confirm?

A : Works on the original Apple Watch. I have the first

A : Can confirm! You can even set the game as a complication on your watch face.

Series 4 won't allow the Pokémon Go app to appear as a complication on the face of the watch. No response from Niantic on this. I guess Apple watch owners are a very low priority to Niantic, even though this is the number one watch that is being sold today.