Should I trade my nikon d800 in for the new d850?

Should I trade my nikon d800 in for the new d850?

If you find that the D850 provides functionality that the D800 doesn't provide, then by all means get the D850. You'll get a few more pixels and 4k video. Otherwise, you probably won't notice any difference in your images unless you print large images.

No.

Why?

If you only want the new one because it's new then no need to upgrade. If you want a new feature on the D850 and can't live without it then yes, upgrade.