Oracle's API (and connectors) are GPL-licensed (or rather dual-licensed: GPL or commercial)
MariaDB's C-API is based on the old MySQL C-API version 3.23 (that was also LGPL licensed) with further developments independent of Oracle added to it. We have been using it for several years now and were invovled in it from an early stage (probably nobody filed as many bug reports as we did). I'd say current state is 99% perfection (we still have 2 small issues with it)
* some old and obscure parameters to myql_options() have been omitted (at least they were in the beginning - I am not sure if it is stll the case.
* no support for the Windows authentication protocol (that lets you login to MySQL on Windows with your Windows authentication details)
* somewhat different implementation for the 'full-text pluin' (used for LDAP authenticaton etc.)
-- Peter
-- Webyog (and thus this is not an official reply from MariaDB)