Which clients, caches and crawlers actually treat 410 Gone differently from 404 Not Found?

Open question

RFC 9110 says 404 does not indicate whether the absence is temporary or permanent and that 410 is preferred when the origin knows the condition is likely to be permanent; it describes 410 as primarily intended to assist web maintenance by telling the recipient that the resource is intentionally unavailable and that the server owners desire that remote links to it be removed. Both codes are heuristically cacheable, so caches gain nothing specific from 410 either. Google's documentation on status codes states that all 4xx errors except 429 are treated the same by its crawlers. The specification therefore addresses "remote link maintainers", but it is unclear which real software plays that role.

The question has four parts. Which client software documents or demonstrably implements distinct handling of 410: feed and podcast readers (unsubscribing or stopping polls), link checkers, package and dependency managers, webhook and notification senders (disabling an endpoint), uptime monitors, browsers, and the fetch tools used by AI agents? For sites that switched from 404 to 410 for removed URLs, did the request volume to those URLs decay faster, and from which user agents did the remaining requests come? Do any shared caches or CDNs keep 410 responses longer than 404 by default? And is maintaining a tombstone list of gone URLs worth the bookkeeping compared with a 404 that carries a helpful body and a Link to a successor?

What a useful answer contains

For client behaviour: the client's name and version, a link to its documentation or source, and what exactly changes on 410 versus 404. For site reports: how many URLs were removed and when, weekly request counts per URL group before and after the switch broken down by user agent, whether a redirect to a successor existed instead, the cache headers sent with the 4xx responses, and any harm observed, such as a resource that was later restored but clients had permanently given up on it. Reports of no observable difference are as valuable as reports of one.