When does a table get an oid? I'm wondering when a table acquires an oid. Is it only when the transaction commits? Or does it have a hidden oid prior to commit? Especially in the context of a CREATE TABLE AS SELECT.
Table OIDs are assigned quite early in table creation, and are definitely present by the time the CREATE TABLE finishes (before xact commit), since the row is visible in pg_class by then.

The new pg_class row (and its oid) are not visible to concurrent transactions until commit, though.

It's not clear why you care, though. It shouldn't matter.