No, it has 2.8, because the pupil is magnified by the front element moving relative to the pupil.
If they could make the blades open to 71mm in the same form factor, they sell it as a 70-200f/1-2.8.
Zooming a lens doesn't mechanically widen the pupil. It optically magnifies it.
There is a lot of mis-information on the Internet about how "constant aperture" zooms work, but the most lucid explanation comes from Bob Shell:
Comments from Bob Shell (January 8, 2003):
"An f-stop is the ratio between the focal length of the lens and the *apparent* size of the lens opening as viewed through the front. It must take into account the magnification factor of all lens elements in front of the diaphragm, because it is the size of the opening that the light "sees" as it passes through the lens, not the actual physical diameter of the diaphragm opening.
It is this fact that allows companies to make constant aperture zoom lenses which maintain a constant f-stop when the focal length changes, because such lenses are designed so that the magnification factor (diopter value) of all elements in front of the diaphragm changes as focal length is changed to hold the aperture value constant."
Learn something new every day.
Yet, Canon's teleconverter are connected behind the diaphragm (between the lens and the camera body), so the bottom line is this TC would make the lens 2.8x longer & three stops slower.