Is there a 4 year option when enlisting as a navy nuke?

According to my ASVAB scores I am Alpha qualified for the navy nuclear program and as such I have received significant pressure from my recruiter to join the program. I am very interested in the program but the required minimum enlistment of 6 years has made me apprehensive. Upon learning this, my recruiter made me aware that there is also a 4 year option available when enlisting as a navy nuke. However, every person I've talked to, even another recruiter, told me that there is only the six year option. And yet when I chatted with a navy recruiter on the navy website, he said that the 4 year option DID exist but he did not offer detailed information as to how the two vary. Does anyone know who is right and who is wrong in this situation as it is all getting very confusing. Detailed information would be appreciated.