TOKYO — Toyota Motor Corp. will deliver a fleet of hybrid next-generation Sienna minivans to Uber Technologies Inc. for development of Level 4 autonomous driving in what could become the first concrete output of the companies' 2-year-old partnership.

The minivans will be delivered to Uber in 2021 and are being modified to accommodate the U.S. ride-hailing company's array of sensors for self-driving vehicles, said Ken Koibuchi, chief technical officer of TRI-AD, Toyota's autonomous driving software development subsidiary.

Toyota's contribution to the project will be the vehicle interface with Uber's autonomous driving kit and the control computer that operates steering, braking, the motor and the battery.

Level 4 autonomy means the vehicle is capable of performing all driving functions under certain conditions.

Toyota will supply about 100 Siennas to the project, a source familiar with the plan said.