To provide review tools you need the code as well as its full history. An API is not going to cut it. However Git being the beautiful distributed system as it

To provide review tools you need the code as well as its full history. An API is not going to cut it. However Git being the beautiful distributed system as it is, you don't have to move your hosting. In fact you can push to multiple Git remotes, or use one for backup, or just for reviews. You can also push to multiple remotes at the same time by adding two urls for the origin. So if you like the idea of your source files residing on a particular provider then you can keep it there as well. Heroku works in a similar way, you may store your repo elsewhere but deploys happen when you push to their remote. The true API here is Git itself not some silly and constantly changing REST protocol over something as stable the Git Object Model.