Ok, I found it.
BTW, I tried very hard to research these filters and this company (they are only a distributor, I forget the manufacturer, but I posted it somewhere on here I think) a couple of years ago and found almost nothing... hadn't looked lately.
Anyway, it appears that these are indeed lifetime filters.
Along with the normal assurances for manufacturing flaws, they guarantee them for life (which I guess means the life of the company?).
From the Sawyer web site:
"All of the Sawyer® water filters and purifiers come with a MILLION GALLON GUARANTEE!"
Back flushing must be very efficient in this design (which appears to be the same technology as the Clean Stream and other MSR stuff).
I'm ordering one to test. Thanks for the heads up, Herman. How difficult is the back flushing, and is full flow restored?