Amusing new observation due to today’s outage [0]: apparently GitHub never bothered to do the obvious optimization to the /pulls page: when you load it with the default “is:pr is:open”, they seem to be depending on their heavyweight search service, despite the fact that their normal API can enumerate open PRs just fine (and probably at dramatically lower cost to them). Sometimes the common case of a webpage should be simple instead of a relying on something fancy.

[0] Which has been ongoing for hours but hadn’t started when I wrote my comment. https://www.githubstatus.com/incidents/x69zbgdyfzg0