API Token Length

We've got four Big-IP pairs, two running 11.6.1 and two running 12.1.3.2. When we connect to the API we get a token in the response but the they're different lengths. The 11.6.1 Big-IPs return a 128 character token while the 12.1.3.2 boxes return a 26 character token.

Searching hasn't helped. Does anyone know why the token is shorter or if there's a setting somewhere that I can tweak to make my security folks happy?

Thanks