Are you referring to the big front subframe bolt?
Some builders have cut a hole thru the Cobalt floor sheet metal to gain better access to it.
Heat will win, but if you get the metal too hot, you loose its hardness.
You can combine the heat (expanding the outside of the threads) with cold (ice the inside bolt). Or even dry ice if you can get some.
Use a good penetrating oil: Kano Kroil, PB B'laster, Knock'er Loose Plus, etc.