Even an XML-U3 running at 1.5 amps will only give you 624-663 lumens (and that’s theoretical max) – which is 2 hours of run time from a 3100 mah cell. So if you really mean >900 lumens for >2hrs then you will have to be running multiple torches, or a bike light powered by a battery pack.
But 900 real lumens is pretty bright. I run 2 XML-T6 torches (£10 ea)on medium – I’m guessing that gives me 2 x 200 lumens for >3 hours, supplemented by an SSC P7 (now an XML-U3) on full beam for sections when I need more light… so a boost of 500, now up to maybe 800+ lumens