[xxpor]

>up-to-the-fraction-of-a-second updates.

I don't think that's true. I believe the comment pages are cached for 1 min.

[_delirium]

I've anecdotally noticed an increase in stale pages lately as well, which I would guess is from more aggressive caching. For example, new submissions used to show up instantly, but on popular subreddits may now take a few minutes to show up on the New tab.

[xxpor]

If someone really wants to figure it out:

https://github.com/reddit/reddit