I'm surprised you have to ask but here we go.
There is always diffraction and CA in every image image past the diffraction limit. In lenses that have less than a pixel the odd colours from diffraction and CA tend to be overpowered by the light coming straight through the lens, as the diffraction and CA are always weaker than direct light. Until the diffraction becomes larger than a pixel it won't soften the edges. Once it becomes larger than a pixel it can soften the edges of the object photographed. That would be Klaus' from Optical Limits interpretation. The link I posted earlier in the thread suggested the 2 or 3 pixels is OK. But I'm going with Klaus' opinion since he actually measures the effects of diffraction with all the lenses he tests.
But to understand this all you have to do is ask yourself, what would be the effect of sending soft unfocussed light at the sensor during an exposure. Diffraction is a pattern of light created when the wave nature of light interacts with the aperture blades. Because of the wave characteristics the light hits the blades and scatters at odd angles. The smaller the aperture, the higher percentage of the light entering the lens is scattered. So diffraction becomes more pronounced as the aperture opening becomes smaller. However as pointed out in the thread above, long lenses are less affected because their apertures are bigger than wider lenses for the same ƒ-stop. So it's possible this lens (or any lens this long won't be much affected by diffraction even at ƒ11.
The charts where you can see the measured results that confirm these things are further up the charts.
Essentially if you understand Aperture, you know that resolution increases from wide open on a good lens very quickly. A good lens will hit maximum sharpness by ƒ2.8 or ƒ4. Because at it's level of sharpness, a bit of diffraction causes loss of resolution sooner, but normally, when you stop down the lens gets sharper until it hits the diffraction limit. For APS-c and FF it's between 5.6 and ƒ8. For my 1 inch sensor with it's much smaller pixels it's between ƒ2.8 and ƒ4.
If you think back to your grade 13 physics, if you're as old as I am, you actually did several experiments that demonstrate diffraction, both with light, and a simulation using marbles.
The other caveat here for photographers is that for the best lenses their maximum resolution comes sooner. If you go through the charts at Optical Limits you'll find every lens with a rep for great sharpness experiences it's resolution a wider ƒ stop, than the average lens which is between ƒ5.6 and ƒ8.
Here's an example Pentax 50 2.8 macro lens. Because of it's resolution it's diffraction limited by ƒ4.
The DA 50 1..8 on the other hand it's it's max resolution at ƒ5.6
Sharpness is affected by two things, making the aperture smaller increases resolution until you reach the diffraction limit (you can find diagrams on line explaining why.) Once the diffraction limit is reached even though the lens without diffraction would be sharper, the dulling effect of diffraction makes them softer. When you shut down your aperture you are always playing those two effects off one against the other.
You can see from chart of the DA 300 ƒ4
And yet it is buried by the DA 70 2.4 (not even a star lens)
So while the longer lenses are diffraction limited, in my limited search for examples, long glass would seem to be much softer than shorter lenses to begin with so possibly the diffraction , having less resolution to start with diffraction has less of an effect.
You only have to look at the charts of a typical 150-600 to see how these lenses perform at 600 mm. Or anywhere really.
I would expect this 800 to be similar.
Anyway, I'm having a discussion with myself here. Enough for now.