It is wire-compatible with PostgreSQL clients, meaning that if you have a PostgreSQL client library for your favorite programming language, you can use that to connect to CockroachDB.

The database features and SQL dialect itself are not 100% compatible with PostgreSQL, and likely never will be.

Also, even if all the SQL you do want to use is supported, it is likely a sub-optimal idea to just port some SQL over to the CockroachDB platform without additional investigation. Some issues, like interleaving values from different tables, should be examined to ensure good performance on CockroachDB.

And even setting aside issues like that, the access patterns you'd use for a multi-region distributed database are going to be a bit different than a high-availability PostgreSQL cluster. Data locality and all that.

The wide availability of client drivers just means you can get started quickly on popular platforms.