Earlier this month our spy photographers captured a McLaren 720S test mule sporting hybrid technology. Two stickers on the vehicle were visible (if you zoom in) confirming this, stating "hybrid" and "hybrid prototype." It was, therefore, a fair assumption McLaren is testing a new powertrain for what will likely be the 720S successor.

The Supercar Blog, however, is claiming its McLaren sources have revealed this prototype's powertrain is not all-new but rather from something already familiar: the Speedtail. There's also an orange decal on the windshield that reads "MVY04-BP23", the Speedtail's internal codename. So McLaren is further testing the Speedtail's hybrid powertrain in the Super Series 720S? Yes, exactly.

Why bother developing an entirely new hybrid powertrain when the Speedtail already exists? Its twin-turbo 4.0-liter V8 alone produces 746 hp and 590 lb-ft of torque while the electric motor contributes an additional 309 hp and 258 lb-ft. Why not continue with this setup in future vehicles, as tech like this have a way of "trickling down." Makes complete sense to us. So what's are the main takeaways from this? Either McLaren is simply continuing to test the Speedtail's powertrain and/or it wants to see how it functions in a different body.

We've reached out to McLaren for additional comment and we'll be sure to update this space if we receive a relevant response. In the meantime, it's hard to reason why McLaren would continue work on the Speedtail's engine in a vehicle that's not the Speedtail. Considering the Speedtail has already been revealed, what's there to hide?

A more likely scenario is what we've already speculated: the beginning of the future Super Series, aka the 720S successor. The 720S, more than likely, will not spawn a hybrid variant. As part of McLaren's Track25 business plan, a total of 18 new models will arrive by 2025, including a successor to the P1. The next-generation Super Series, it seems, is in early development its hybrid inspiration comes directly from the Speedtail. Good things are happening over in Woking.