Hello, The PHP response format [1] has been deprecated in favor of json format for more than ten years https://www.mediawiki.org/w/index.php?title=API:Data_formats&diff=prev&oldid=1937805now. The usage of it is extremely low (0.17% which mostly are scrapers loading links or examples). In comparison, The xml format that was also deprecated for more than ten years now still gets 18 times more requests than the PHP format.
It is now time to pull the plug. We will drop the format in a month (around May 1, 2026). You can follow the work or comment (for example if you need more time) in T118538 https://phabricator.wikimedia.org/T118538.
[1] for example: https://meta.wikimedia.org/w/api.php?action=query&meta=siteinfo&sipr...
Best