Basically? ... Yes.
Both Concentric design? ... Yes.
I heard someone at White's say they were in essence the same search coil, but without opening them up I can't measure the actual physical diameters of the Tx and Rx windings, but in-the-field they generally tend to perform quite similarly.
The differences? The 950 is a measures, physically, a bit over 9½" in diameter and the 9" spider coil is just a slight amount over 9" in diameter. The 9" coil is a 'spider' design, that is more open. Personally, I have grown tired of the early thin 950 and newer UFO shaped 950 coils, but I prefer smaller-sized coils anyway.
However, the 9" 'spider' coil does have a slightly smaller look about it and I find it to be a more durable looking and attractive search coil. Best of all, the 9" 'spider' has the rod mount point a little closer to the center of the coil and that helps give it a much better 'feel' and it is less likely to flop around or get bumped out of your desired position.
While it is 'basically' the same as the 950, I like using the 9" spider coil more, and in some moderate trashy sites it just seems to handle or work a little better than the 950 so, perhaps, is is just slightly smaller in internal winding diameter? Not sure, but I know it was a 'must have' coil in my arsenal after it came out and I used it twice. All of my 950 coils are gone with the exception of the one for my XLT that's sitting on shelf somewhere.
Monte