The very ending of Ex-Machina

On a concrete level, Ava simply went to the place she said earlier she wanted to visit - a busy intersection - to go people watching. On a deeper level, I believe the shot of the shadows relates to the Platonic description of real vs imagined experiences, which is a theme throughout. Until Ava is out in the real world, her experiences are like shadows against the wall, but when she goes to the intersection, the real world becomes the shadow, as her advanced ways of experiencing things are vastly superior to our own. In this moment, we the humans become the shadows. In the very last shot, we see her reflection in the window, but as she turns, she disappears out of that reflection altogether. This is no accident - it appears to have been digitally done in post-processing. I would interpret it as Ava literally going "through the looking glass", echoing Nathan's words at the beginning of the film.

If there's a message in the final scene, it's not very overt, and perhaps simply left up to our own personal interpretations. Mine is simply that she's now one of us. She's life.

If I recall correctly the scene begins with the camera angled upside-down at the ground, and bright low sunlight is casting long shadows of walking commuters. This is the busy Pedestrian and traffic intersection referred to in the Ava Sessions. We see a Girl walk into shot, wearing jeans and a top, which becomes a single stationary shadow in the centre of shot, which we are invited to believe is Ava, and this cuts to a complex multiply-reflected view of her watching the crowds pass close by her. She is expressionless, and after a beat, turns away, disappearing into the anonymous crowd. What I took away from that scene is that Ava fulfilled her wish to observe humanity, that 'concentrated but shifting view of human life', and without fanfare, disappeared without trace into that humanity.

I recently watched the movie as well, in my opinion ending scenes were reflection of the success of A.I designed by Nathan. The circumstances that he kept in mind for the A.I to truly succeed, were far more successful then he ever anticipated.

The movie ends by proving that machine objectivity is undeniable no matter what, 'She' made the best decisions for it's own survival, all the rest is just collateral damages, indifferent to 'her'.