Hello,

I am looking to stain my wood floor. I am running into an issue. Most of the house is Red Oak from the 1940s the extension is also oak but it is of a much newer variety. I plan to sand both floors down and stain them dark. Is there any reason to worry that the stain may take on a different tone in the new part of the house?

The newer wood will likely be a little lighter than the older wood. The older wood will have more old growth type of wood with close growth rings which will absorb more color. The surface patina will have darkened, too, from the effects of light and moisture.
You could use a darker stain on the new wood and thin it down with neutral oil a little for the old wood.
I like to mix some rift sawn wood in to help blend the new wood to the older wood.
New wood has bigger growth rings from better managed forests. Bigger growth rings result in harder wood and harder wood absorbs less stain.