Earlier quoted context omitted.
I have never in RL heard anyone call it "OS ten"
Just curious what age range you are in. From what I've personally noticed, younger folks tend to almost all pronounce it "O-S-ecks" and most in my generation (~40) tend to pronounce it "O-S-ten".
Plus, "O-S-ecks" gets too close to "O-S-sex". I was a kid...