A transparent display is necessary for glasses based AR. The parts where stuff is displayed obviously aren't transparent, but when a pixel is off, the screen is transparent in that spot. There have been transparent displays for decades, and smart glasses for at least 5 years, but AR glasses are relatively new, yes. Smart glasses and AR glasses look relatively similar to regular glasses. AR glasses are a little more obvious when they are being actively used, as other people can see the section that isn't transparent. But smart glasses don't have the capability of advanced graphics and are more like a heads up display.

https://youtu.be/gElClXpg4J0?t=2m44s This is a partially pre-staged demo of the ones google is doing, but it does at least show the look of the glasses. And metas second gen ones after orion have slimmed down a bit too. What I have seen of apples looks like they are also going to be pretty slim. But I haven't seen anything past concept stage yet for them, so hard to say how close they'll get to what they are aiming for in the concept.