Image stabilization panning detection in RF lenses

Duckman21 wrote:

Many "cheaper" EF or EF-S lenses have only one stabilizer mode, but Canon previously indicated these to have panning detection built in, so the horizontal axis would disable if you pan fast enough. I'm wondering if the same holds true for the RF lenses like the RF 100-400mm.

I will start with my impressions of the RF 800mm f11. The IS works very well for stationary subjects but not so much for slow panning at medium to low shutter speeds. Not sure if I'm panning too slowly to trigger a "panning mode" or there just isn't one to begin with. I've been photographing ducks and other waterbirds swimming leisurely and noticed considerable motion blur. Turning off gave me some sharper shots but most were prone to overall blur in both the vertical and horizontal axis. I had a similar issue with my Tamron 150-600mm G2 on DSLRs, and always do this for flying birds, but found swimming birds less of an issue. I also wonder how much of an effect IBIS is worsening this by "enhancing" the stabilization and if it fares better with non-IBIS bodies.

Great question. I'd like to know specifically about that for the RF100-400 f/5.6-8.0 and the RF85 f/2.0. Without knowing the answer, I imagine that if the lens doesn't show that it has the mode 2 stabilization, panning with stabilization just won't ever work correctly. With my EF, and now RF, lenses that have the mode 2, panning works very well.