PostgreSQL plan cache and variable number of arguments

Query: select * from table where col in ( values (?), (?), (?) ) The query text is generated, and number of (?) is variable and up to 10000. It works just fine, just wondering, whether Postgres caches same plan instance for different number of args? In other words: what is the _key_ for plan cache in Postgres? And how does it apply for the query above?