The July 16 episode of The 100 is called “Matryoshka” and The CW has released an official description to promote it.
Here’s the write-up:
REUNITED – Russell (guest star J.R. Bourne) seeks justice. Meanwhile, Gabriel (guest star Chuku Modu) must make a difficult choice. Lastly, the Blake siblings reunite. Eliza Taylor, Bob Morley, Paige Turco, Marie Avgeropoulos, Lindsey Morgan, Richard Harmon, Tasya Teles and Shannon Kook star. The episode was directed by Amanda Tapping and written by Drew Lindo (#610). Original airdate 7/16/2019.
UPDATE: We now have some preview images which you can find below! Try and find some new spoilers within the gallery slide show.