The Content-Transform-Team uses parsoidtest1001 for weekly pre-train parsoid testing: we tag parsoid, then run round-trip tests on parsoid1001 against a read-only copy of the production database before releasing the tagged parsoid to mediawiki-vendor to ride the train.
Parsoidtest1001 is "almost entirely" a production mediawiki server.
As part of the PHP8.1 transition process, parsoidtest1001 should probably be switched to PHP 8.1 with the first group of test servers.