I'd like to believe Chrome* users are usually up to date on version numbers. We could update the library cache on a different schedule from browser updates. Finally, we could fall back to a CDN (with further fall back to your own server?) if the server requests jQuery 2.0.1 and the browser says sorry, best I can do is 2.0.0.

My fear was more on the server-side. Can we accomplish this without further butchering the head from the standard? I can't see all browsers adopting this or it becoming a standard without a major sponsor. And like someone else mentioned, we can get about the same benefits from aggressive caching. I agree for the most part.

Don't get me wrong. I love Google. I love what they do to make the web faster with their hosted libraries[1]. Correct me if I am wrong but caching the libraries from Google only helps if the the server specifies they want that particular file from Google (I'd imagine it would be a gaping security hole any other way). My thought is whether it is possible to just declare something like 1.9.1.min.jQuery.com and have the browser just recognize it and say "Oh yes I have that. No need for a server round trip. You're welcome." or "No, I don't understand what you're talking about. Give me an address so I can fetch it."

Is it even worth it? jQuery 1.9.1 minified is ~90 kB, so we're probably just trying to shave off tens of milliseconds at the most. I bet we all have fruits hanging lower than this to worry about it. Another thing is that it will probably have to be a vendor-specific meta tag (as I don't see everyone getting aboard this, if anyone) in the header which I don't know is a good thing.

[1] https://developers.google.com/speed/libraries/

*I believe Mozilla Firefox has also started silent updates. It'd be nice to see how quickly users update when a new build gets pushed out.