How do you headshot a Bastion in Sentry or Tank configuration?

Configuration: Recon mode:

• His headshot hitbox is the entirety of his head. He has no vulnerabilities in the front or the back.

Configuration: Sentry mode:

• His headshot hitbox is this cyan-colored box sticking out of his back. Shooting this deals the same damage as a headshot.

Configuration: Tank mode:

• He has no headshot hitbox in Tank mode; in fact the opening that's exposed in Sentry mode is completely covered up in Tank mode

Great News! Bastion does in fact actually have a critical hit point (headshot) while he is in turret mode. On the back of the turret you will see a blue-like box, that is his weak spot that acts as a headshot point. So, to answer, yes, you can headshot Bastion in turret mode, though we don't think there is a Critical Hit Point on his Tank Form, thankfully though he can only stay in tank form for a short while. Hope this helped!