Though the Gigafactory has been partially operational for months, Tesla hasn't yet officially "opened" its massive Nevada battery plant — but that'll change on July 29th, when some Tesla owners will gather with company officials for a ceremony at the facility.
Multiple publications, including Fortune and Tesla Central, have confirmed the July 29th date. So far, it appears that Tesla has only sent invites to certain VIPs, including those who "won" invites to the event through the company's Model S sales referral program by referring five buyers. Media outlets have not yet been invited, and it's not clear if they will be. (Tesla staged its Model 3 unveil in a similar fashion — owners were invited to the event before media were.) Tesla has generally not hosted media at the Gigafactory so far, although it brought Motor Trend onsite recently for a closer look at the Model 3 prototype.
Speaking of the Model 3, the Gigafactory is seen as a key element to affordable mass production of the Model 3 (or of any other Tesla vehicle). At peak output in 2020, it's expected to produce 35 gigawatt-hours of battery capacity per year, which Tesla claims is more than the entire world's lithium ion battery production in 2013.