last night, the Chieftain in HD was introduced to the supertest. Strangely enough nobody leaked it yet, very unusual. It would be nice if someone did.
Here's a catch: the Chieftain is introduced as a tier 10 PREMIUM (as in, CW event tank). Don't worry, it's not intentional - the developers (due to some internal client issues) decided to test is a premium but it WILL be a regular tank (the FV215b replacement). So no panic.