What's more, Shimano have mixed up their groupsets and their nomenclature with the latest versions. For example, up until recently, Deore had M6xxx in the code, Alivio M4xxx, Acera M3xxx, Altus M2xxx. Now the newest Deore 12speed RD is M6100, Deore 11speed RD is M5100/M5120, Deore 10/11speed RD is M4120. Meanwhile Alivio RD has been demoted to M3100, and furthermore, as far as I can tell from pictures, it is the exact same RD as Altus M2000.