https://www.vice.com/en_us/article/5d99pn/reddit-api-apollo-app-controversy-explained

Dozens of major subreddits say they will temporarily shut down to protest a change Reddit is making that would effectively kill third-party Reddit apps by making it financially unviable for them to operate. Last week, the developer of the hugely popular Apollo app said it would cost him $20 million annually to keep his app operational with the new API fees, which were announced earlier this spring and are set to go into effect on July 1. 

“It went from $0 to effectively $20 million a year if I kept the app as it is currently,” Christian Selig, the developer of Apollo, told me. Apollo and other third-party apps like Reddit Is Fun, Narwhal, BaconReader, and dozens of others are essentially apps that let users browse, post on, and interact with Reddit without using the official app. When I asked him if other third-party app developers are “freaking out,” he said “very much so. I think that’s apt language. We were expecting bad, but when we saw [the pricing] we were like, ‘This has to be a joke.’”