Probably not as long as the legendary Rodinal or HC-110 but still better than other developers I have used. I have had the last inch or so in a bottle last for a year. It got vary dark but still worked. Freshly made and in a stoppered PET bottle it is unchanged now for over 7 yrs. As with Rrodinal preparation it is important that there be no excess hydroxide present.
Now that sounds like excellent shelf life to me! After the holidays I'm going to mix a batch to play with. Jerry, I might be picking your brain for a little info when I start using it. Have a Merry Christmas! JohnW