Earlier quoted context omitted.
Strange...I thought it was pretty clear by the end (without going into spoilers) that Ava is sentient. Interesting that there is another interpretation of what happened.
it was clear by the end she was acting like a machine programmed to do a specific thing that happens to look exactly like what a human would do. that tells me nothing about sentient.
just wanted to observe and imitate humans (on a street corner, where the density of observable humans is very high).
I still think it's left as an open question to the viewer, though. After all, humans spend their whole lives trying to imitate and improve upon the actions of their ancestors.