I haven’t been able to find a clear quote in print, but a year-old article in Vox [1] reads:

> “Musk has been the visionary,” said Steve LeVine, a journalist at Axios who has written a book about the battery industry. “He has been willing to take the plunge all the way along, from the very beginning.” In contrast, he told me in a phone interview, “Detroit has approached this race so cautiously.”

I remember hearing Musk being quite adamant the scale of the factory was for batteries, but you have to understand, he can’t really publicly say that he’s leveraging Panasonic for now, but will drop them as soon as he can.

[1]: https://www.vox.com/new-money/2017/4/17/15293892/tesla-batte...

Everything that he has been saying lately implies that they won't drop them. They may add other suppliers (especially for the factory in China), but they will likely always rely on suppliers for the cells themselves. I can't really think of a good reason for this to change.

After all, they are by far the world's largest consumer of batteries. They have leverage.