Update: Tesla CEO Elon Musk has confirmed on Twitter that the Samsung batteries will be used in Tesla Energy's Powerwall and Powerpack products.

After ongoing reports and rumblings about Tesla looking at shaking up their battery supplier chain, Elon Musk took to Twitter to make it clear that "Tesla is working exclusively with Panasonic for Model 3" batteries, as well as the Model S and Model X:

This will not bring an end to the speculation, however, though it certainly muddies the waters. Panasonic has been a long-time battery supplier for Tesla, exclusively providing the cylindrical cells used in the Model S and every subsequent Tesla EV. Panasonic has also partnered with Tesla to build and operate the $5 billion Gigafactory in Nevada that will be vital to the Model 3 and Tesla's future growth.

But just recently Tesla took delivery of enough Samsung cells to make 200 battery packs and for a month now rumors have been swirling about negotiations with other suppliers like LG and SK Innovation. Just yesterday saw a report that Samsung SDI was making progress in talks with Tesla on supplying batteries. And Tesla has worked with other suppliers in the past — the battery pack in the upgraded Tesla Roadster 2.5, for example, featured cells sourced from LG.

Musk's comments should put an end to rumors and speculation about sourcing batteries for the Model 3, though it makes us wonder what that massive 120 ton shipment of Samsung batteries was for. Testing? Tesla Powerwall or Powerpack use? A goodwill overture from Seoul?

Shares of Samsung SDI are down more than 8% after Musk's tweets, knocking more than half a billion off the company's market capitalization. Panasonic, meanwhile, is up big, adding $800 million to its value.