Microsoft acquired Beam, a live streaming service, back in August 2016. After the acquisition, Microsoft rebranded the service as Mixer and started adding new features based on audience feedback. Few months back, Mixer said that it had surpassed 10 million monthly active users last December and has continued to grow ever since. At E3 2018, Mixer yesterday announced that it is seeing continued growth with viewership doubling in just six months to more than 20 million.
Microsoft also highlighted that the majority of this is growth from viewers on mobile, thanks to its new mobile apps. You can read about the new Mixer mobile apps here.