No, it is not optional. If you publish a valid AMP page and Google finds out about it, it will be cached.
https://developers.google.com/amp/cache/faq
> Can I stop content from being cached?
> No. By using the AMP format, content producers are making the content in AMP files available to be cached by third parties. For example, Google products use the Google AMP Cache to serve AMP content as fast as possible.
Re:Google May Be Stealing Mobile Traffic
by spiderfarmer on Thursday October 20, 2016 @06:32AM
(#12751115)
So cache-busting Javascript will be needed, which will kind of defeat the purpose.
Re:Google May Be Stealing Mobile Traffic
by spiderfarmer on Thursday October 20, 2016 @06:31AM
(#12751111)
> Small sites usually dont use CDNs so there it is.
I think it's easier to use a CDN like CDN77 than to convert the average site to AMP.
The problem isn't that Google "steals" traffic in the sense it's going against the wishes of the site publisher, but that the author didn't know what he was buying in to and thus was surprised.
There is the other thing which is the AMP Cache is probably more local and faster than your site. Small sites usually dont use CDNs so there it is.