Last month, Audi began a teaser campaign for three all-new concept vehicles, the Sky Sphere, Grand Sphere, and Urban Sphere. The Sky Sphere will debut first and that reveal is slated to happen this week in California. As the countdown clock continues to click down, the German automaker has released what are likely the last few teaser images. Based on last month's teaser image, the Sky Sphere looks like it'll be an all-electric coupe and Audi hinted it'll pack advanced autonomous capability.

Today's batch of images shows some close-up details including the wheel design and front grille. What's clear is that Audi's design team led by Marc Lichte paid extensive attention to the finest details.

Lichte previously said during a video presentation the concept takes inspiration from the Horch 853A, specifically the heavily stylized front and rear ends. Horch is a longtime defunct German car brand that later merged with Audi and two other companies to form the Auto Union in 1932.

It's too soon to know whether the Sky Sphere will advance to anything beyond the concept phase but we're certain much of its technology will. As for the other two concepts, the Grand Sphere is due to be unveiled at next month's Munich Motor Show while the Urban Sphere is due sometime in 2022.

Chances are the former is a preview of future Audi sedan design while the latter hints at a slick SUV. It'll be interesting to see how much the three concepts deviate (or not) from existing models, such as the Audi e-tron GT. Lichte has done wonders for Audi design since he assumed the chief designer spot in early 2014.

He's very successfully moved away from the so-called "Russian doll" design philosophy where all models, specifically sedans, look nearly the same except for their size. Lichte has also embraced electrification as many of the constraints involving combustion-engined models are gone, allowing him and his team to explore new design paths.