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I don't intend to ask whether AMPs (hard to resist calling them 'AMP pages') exist somewhere on non Google servers. Obviously third party content that Google is presenting exists somewhere off Google. And obviously it has to be formatted in a way that's compatible with AMP, and it makes sense that that is going to be done off Google domains. I at least knew the gist of that already, and I regard the detour into that explanation to have been a non sequitur. The point is that Google presents AMPs and it serves it's cached version of them from Google servers, on a Google domain. The beginning, middle, and end of the experience of searching for finding and consuming that news never has to involve leaving a Google domain. It's not open in the sense of involving interaction between servers that aren't controlled by Google, until you make that extra click to go from a cached Google version of an AMP to the version that sits on the domain controlled by a third party, at which point going to the third party has been rendered optional and largely unnecessary from the point of view of the user.

This next part is super important: the fact that I'm asking about openness and interoperability, or the lack thereof, in this sense doesn't mean that I'm failing understand the technical advantages with caching and optimization. I regard those as derails that don't wrestle with the issue of openness that's being raised. The point is that the connection between consumers of content who start on Google, and the third party content provider, increasingly depends on Google in a way that shifts nearly the entire experience of consuming content onto Google's infrastructure.

>All of them (100%) are delivered by non-Google domains to Google, Bing, and other caches.

This is the starkest example of a question not being answered but replaced with a different question. I asked 'what percentage of total amps are delivered by non Google domains' and you replied by answering a different question, what percent of non-Google amps were delivered TO Google and other caches, noting that it was 100%. Which of course it is, but that's because that's a tautology.

By contrast, it is helpful to note that there are caches other than Google, like Bing and 'others', which, in contrast to much of the rest of your comment, I feel actually is a pertinent and fair response to the question I'm actually asking. But those aren't content providers, so unless Bing or Google are content creators that were delivering content to themselves, it's tautologically true that 100% of that is going to be delivered to them by third parties, which has absolutely nothing to do with openness. If I'm using magic words correctly, I guess what I want to ask is what percentage of AMP traffic to cached pages is served to users by Bing and others that aren't Google.