Does the MERGE PARTITION functionality actually exist in PostgresSQL 17?

Is it possible to merge partitions in Postgres 17? There a a lot of blog posts on the internet suggesting that partition MERGE and SPLIT are (or will be) available in PostgreSQL 17 but there's no explicit mention of this in the release notes, nor have managed to get any of the commands to work. I have a table that's partitioned by date range. Initially the data is split by day, then it's merged into a monthly partition. This is the command I'm trying to run: alter table myTable merge partitions (myTable_202505, myTable_20250503) into myTable_202505a; And this is the error: >ERROR: syntax error at or near "merge" Have I got the command wrong, or did the SPLIT/MERGE functionality get pulled before release?