If you look at the list of plugin maturities, say with:

SELECT plugin_name,plugin_version,plugin_maturity
 FROM information_schema.plugins
 ORDER BY plugin_name;

I notice that in 10.1, InnoDB/XtraDB is listed as Gamma (changed from Beta in 10.1.13), while in 10.0, with the same version of XtraDB, it's listed as Stable. What's the basis of the distinction between the two, especially since 10.1 itself is a stable release? It seems strange to have InnoDB listed as the same maturity as Spider :)