Google's Gary Illyes posted on Twitter this morning that he updated the crawl budget post from January 2017 to explicitly say that AJAX (i.e. XHR) calls were added to the list of things that will consume your site's crawl budget.
It now reads:
Q: Do alternate URLs and embedded content count in the crawl budget?A: Generally, any URL that Googlebot crawls will count towards a site's crawl budget. Alternate URLs, like AMP or hreflang, as well as embedded content, such as CSS and JavaScript, including AJAX (i.e. XHR) calls, may have to be crawled and will consume a site's crawl budget. Similarly, long redirect chains may have a negative effect on crawling.
Previously it read:
Q: Do alternate URLs and embedded content count in the crawl budget?A: Generally, any URL that Googlebot crawls will count towards a site's crawl budget. Alternate URLs, like AMP or hreflang, as well as embedded content, such as CSS and JavaScript, may have to be crawled and will consume a site's crawl budget. Similarly, long redirect chains may have a negative effect on crawling.
Here is how Gary announced this:
JFYI: based on @ajkohn 's recommendation, i added AJAX/XHR calls explicitly to the list of things that will consume your site's crawl budget.https://t.co/kVYj6XaNn0
— Gary "鯨理" Illyes (@methode) April 23, 2019
Forum discussion at Twitter.