I have a oak wood floor that is approx. 1 year old, and is 1400 sq. ft. It has major gaps EVERYWHERE. I can fit in 2 quaters in between some of them, but they are mostly about 2 dimes wide. My builder wants to repair them with filler is this okay? We do have a humidifier in our home.
Thanks for any info.

The wood was not acclimated at all and installed without a running HVAC unit. to climatize the interior. The wood was installed "wet" and now it has lost moisture content, and shrunk.

In this instance, filler is not going to be acceptable, from my house, looking at yours. Did you pay for a third rate floor, or a work of art?

We just tore up and replaced a Beech hardwood floor with the same problem. You cannot let him fill the gaps with filler. Your floor needs to be replaced at the expense of the installer.

Here where I live, the flooring is usually at 6%, and the subfloors are 9-14 percent. Higher in new construction, as they don't like to fire up the central heat until the floors are in. The dry flooring equalizes with the wetter subfloor, THEN shrinks back to a point of equalibrium, resulting in the gaps. I see lots of gapped floors up here that never close up, and they are 2 1/4 inch red oak. With all the wide plank going in now, the thought of what those floors will look like a year or two after the install is pretty scary...