HRX2174VLA what does the 4 mean in the model number

Does anyone know what the 4 means in this model HRX217(4)VLA ?

I have been trying to determine thru Google but unsuccessful.

I originally planed to purchase the hrr but was offered the HRX from my local dealer at a really good price. It is old stock according to dealer but new and I did not find a recall on it. So, I have already paid for this and will pick up next week when my schedule clears up.

Thanks in advance for your help

Ok I may have just found the answer, the 4 represents K4. It has smart drive, which I happen to want anyway, and K5 has select drive.