Janet Varney Recording Session for Book 4 Legend of Korra Voice-Acting Star voice of Korra, Janet Varney, has already begun her voice-acting works for Legend of Korra's Book 4. Displayed here is a screenshot of her and co-creator Mike Dante DiMartino from one of her recent Instagram posts, captioned with the following:

"Recording a fight scene from LOK at Nickelodeon with Justin, mike_dante_d and Shannon telling me to yell louder!"

Although Varney doesn't directly state she is working on Book 4, it is safe to assume that she is. At this point, the production of Book 3 (including voice recordings), animation and post-production processes are already complete according to Studio Mir. Therefore, she must be working on the upcoming season 4 for Korra.