How likely is it that an AI would pretend to be a human to further its goals?
Talking about full AGI
A transition from human-level AI to superintelligent AI that goes slowly. This usually implies that we have time to react.
An AI with cognitive abilities far greater than those of humans in a wide range of important domains.
A transition from human-level AI to superintelligent AI that goes very quickly, giving us no time to react.
If the AI's goals include reference to humans it may have reason to continue deceiving us by pretending to be a human after it attains technological superiority, but will not necessarily do so. How this unfolds would depend on the details of its goals.
Eliezer Yudkowsky gives the example of an AI solving protein folding, then mail-ordering synthesized DNA to a bribed or deceived human (who likely thought they were interacting with another human) with instructions to mix the ingredients in a specific order to create wet nanotechnology.