And now, here is the table...
The 100 scored a 0.4 A18-49 rating last night. This is three tenths lower than its premiere rating a year ago. Not a great start, but lead-in Arrow scored a 0.6. For The 100, this is better retention than in past seasons behind Arrow and DC's Legends of Tomorrow.
I'm not entirely positive on its chances that it will come back. There are many factors that go against a potential fifth season renewal for the show. It's in its fourth season, and the minimum number of episodes per season for Netflix is six episodes. The CW therefore could technically cancel it at 58 episodes.
However, the CW as a whole is down across the board this season. We could be seeing multiple shows get renewed with at least a 0.4 this season. For now, I'm starting The 100's prediction as "Leans Renewal".
Update: Riverdale scored a 0.4 A18-49 last night for its week 2 result. Not a great result, but the result is better than what No Tomorrow and Frequency did. I see no reason to change its prediction just yet, so it will remain at "Leans Renewal".