Toyota is in the early stages of development of a next-generation Sienna minivan, which is expected on the market in 2020 as a 2021 model.

A test mule has been spotted, and while it's still wearing the body of the current Sienna various modifications hint at what we can expect on the redesigned version.

Modifications to the front fenders suggest a longer wheelbase, and the protruding tires suggest the width will be bumped up slightly. The rear overhang has also been stretched meaning Toyota may be looking to increase space in the rear, too. It also appears that Toyota will move the side mirrors to the doors instead of at the base of the A-pillar like on the current model.

Residing underneath the makeshift body is thought to be a stretched version of the modular platform underpinning the latest Camry and Avalon. The platform should result in improved rigidity and potentially less weight for the redesigned Sienna. An 8-speed automatic and available hybrid powertrain should also be part of the package.

Examples of the redesigned Sienna will eventually be fitted with self-driving technology being developed separately by Toyota and Uber. The self-driving Siennas will operate on a trial basis in Uber's ride-hailing fleet starting in 2021, though specific details on the deployment are yet to be provided.