You enable amp, like maybe you started using png over just gifs - and then Google takes your search hits hostage by rewriting the url, adding a banner - and forcing you to keep the amp version if it turned out to fit you and your users or not.
The amp spec looks friendly and harmless - a good use of html5's flexibility. On the surface the only odd bit is the reliance of js to get the "new" image tags to work (with resulting reduced flexibility wrt Web user agents, like w3m).
And suddenly Google controls your page design for everyone that finds your site through Google!
This is not open, there is no source, because AMP is a hosted service.