One of the most notable things is that of its hands, as Tesla wants them to be nimble enough to thread a needle. This has proven to be very difficult. Scaling production and refining manufacturing are also likely challenges. Musk says Tesla is "working hard on scaling Optimus," something that is a crucial issue to solve as the project is a major contributor to the company's future.
It was then no surprise that some in the Tesla community had the impression that the refined version of the prototype featured in the new images was Optimus V3. With its more advanced hands, forearms, and sleek new paint job, after all, the unit could very well be a whole new evolution of the humanoid robot. As per Musk, however, this was not the case.