As documented API supports some search engines in list=search query. In Wikipedia it works good with default settings. But when you enable "New search" (CirrusSearch) in Beta features, "srbackend" parameter is no longer supported and generates an error:
"Unrecognized parameter: 'srbackend'" (XML) or
'{"servedby":"mw1190","error":{"code":"srunknown_srbackend","info":"Unrecognized value for parameter 'srbackend': LuceneSearch"}}' (JSON).

Example: https://ru.wikipedia.org/w/api.php?action=query&list=search&srbackend=LuceneSearch&srlimit=5&srprop=&srredirects=1&format=json&srsearch=Ubuntu* (need to enable "New search")

Version: unspecified
Severity: normal