I will be putting down 3/4" solid oak and recently read I can't put them down over particle board. I have a 1/2"ply sub with 3/4" particle on top. I've thought about every possible solution to not pull the particle board up but everything I read says it needs to come up. Can I use 1/2" OSB or does it have to be 5/8"-3/4". And my main question does the new sub floor need to acclimate as well? If the new OSB and floor moisture match can I proceed or should I wait a few days?

Good catch bm

Most people wouldn't think twice about it and there are more than just a few failed jobs due to high moisture content in plywood.

OSB and plywood will have different readings depending on moisture meters used. El cheapo's won't give an accurate reading. Not sure? Wait it out. Acclimate it. I couldn't even guess how long.

1/2" + 1/2" probably equals 7/8" the way plywood is graded.

Good enough if the floor joists aren't that far apart.