Excerpt:
Most major subreddits show a decrease of between 50 and 90 percent in average daily posts and comments, when compared to a year ago. This suggests the problem is way fewer users, not the same number of users browsing less. The huge and universal dropoff also suggests that people left, either because of the changes or the protests, and they aren’t coming back.
The figure is probably closer to 40% than 90%, subredditstats seems to be affected by the api changes too. However 40% at the low end of the range is still phenomenally bad. And every subreddit is definitely seeing a constantly declining amount of activity now.