Currently yes, only assembling Panasonic cells. They’re building the factory to change that, by making their own cells. Panasonic only owns about 35% of the factory, the rest is TSLA.

Panasonic owns the cell development side of the factory.

Tesla has no plans to make their own cells. This is a simple fact.

Panasonic invested $1.6B while the total project cost is about $5B. E.g. here: http://mashable.com/2016/01/16/panasonic-tesla-gigafactory-i... While 32% if significant share, it’s less then half. I don’t see how the cells manufactured by a Tesla-branded factory, where TSLA owns more than 50% of the factory, aren’t Tesla’s own.

You've never been in an office building with more than two different companies inside?

I mean, serious question. In the office building I work in, my company only owns two floors. The next floor is another company, and the floor above that is yet another company. My company owns more than half the building (the bottom floors has more space for various reasons), but the stuff made upstairs isn't made by my company.

Different modes of co-ownership. In the building you’re talking about, each company has/rents some distinctive piece of real estate. Not the case with gigafactory. E.g. read there: http://fortune.com/2015/11/03/tesla-grid-batteries-gigafacto... As you see, Tesla’s saying they will be producing cells, not Panasonic.