http://www.pcgamer.com/warframes-open-world-plains-of-eidolon-confirmed-for-next-week/

Earlier this week, Digital Extremes hinted that Warframe's Plains of Eidolon update might be with us sooner than expected. Now, the developer has confirmed it's coming next week. 

And when it does, it'll bring with it the much-anticipated open world 'Open Zone'—a non-procedurally generated, hand-crafted environment said to offer "exploratory daytime activities and towering night-time battles"—as well as new weapons and a new warrior, among others things.