Rugs, Carpets and Carpeting - sealing spaces between underlay?

Hi! We have just laid a new wooden subfloor in our new master bedroom. The bedroom is in our basement and the house is 52 yrs old. However, our slab is extraordinarily thick (about 14"!)and has no cracking or heaving. We put down vapour barrier, framed the floor, insulated and installed 3/4" tongue and groove OSB. We were instructed to leave 1/8" between the sheets of OSB. We plan to install 9 lb underlay and carpet on top. However, we are wondering if we have to fill the 1/8" gaps before we put down the underlay. Can you please tell us? Thanks in advance for your help! Much appreciated!

You don't want to fill the expansion area you left! 1/8" isn't very much. With stretch in carpet, I would have left a 1/4". You will never feel or see it. If you are worried you can tape them with duct tape, before rolling out the padding.

Thanks Perry! Appreciate the advice, we'll just leave it as is.