When a self-driving car passes by, you tend to notice. The towering sensors whirling around on the top of the car more than stand out.

But Chinese autonomous vehicle company Pony.ai is reimagining the roofline for its next generation of autonomous taxicabs. As part of a partnership with autonomous vehicle sensor maker Luminar announced Monday, the Pony.ai robot-taxis will feature a flat roof housing the necessary cameras, radar, and LiDAR sensors, which use light to measure the distance between objects so the car can "see."

Typical LiDAR sensors like those from Velodyne, Intel's Mobileye, and Waymo's own Laser Bear Honeycomb are mostly cone-shaped to help pull in a full 360-degree view from the top and around the car. The Iris system relies on multiple sensors to capture that same 360-degree vantage point. (Tesla CEO Elon Musk is notoriously anti-LiDAR and doesn't include the "unnecessary" sensors on his partially autonomous vehicles, instead of relying on cameras and radar.)

Pony.ai already operates a self-driving taxi service in five cities in China and the U.S. and has 200 vehicles in its fleet. At a press reveal last week, the company showed what its future robot taxis will look like starting in 2023.

 The slimmer sensor system uses Luminar's new Iris LiDAR, which can "see" 500 meters ahead and projects an image with "camera-like" resolution. The whole roof unit is only about 10 centimeters high and integrated into the car instead of added on as a roof rack. Pony.ai will start testing with the Iris sensors next year.

It's a new look compared to cars from companies like Waymo, which runs a driverless taxi service in the Phoenix, Arizona, area. Waymo and others, like Ford's Argo AI cars or Baidu's robot-taxis in China, are visible from far away because of the tall and bulky LiDAR system on the roofs.

Luminar CEO Austin Russell called out other company designs without naming any brands, calling the new design a "stark contrast" to some of the "monstrosities that have been on some of the AV test vehicles."

Even Waymo's newer autonomous taxis, built into an electric Jaguar I-Pace (see below), are bulkier than your average car.

Luminar's CEO said the slimmer design is a signal that autonomous vehicles aren't just an experiment but a viable product here to stay.

At the very least, the sleeker design makes AVs more discreet.