They removed the CAPTCHA, I'm not surprised.
We’re experimentally removing CAPTCHA and using other methods for spambot detection.
We know it’s annoying for humans, and are starting to worry the bots are actually enjoying it.
Plus, our visual CAPTCHA was failing on accessibility for non-visual redditors.1) High percentage posts flagged as 'reported'
2) High percentage posts flagged as 'spam'
3) High volume of posts containing URLs
4) Posts containing identified spam messages (like how an email spam filter may work)
5) Multiple accounts from similar/same IPs
Almost all spam in a subreddit I mod for is from accounts < week old. (I believe there may already be a limit on how much you can post after registration though)
It catches some false positives from people who sign up just to post something, but it's also drastically decreased the spam. Most spambots are still at the "sign up and then blast shotgun-loads of posts before the algorithms catch you" level of behavior.
It can be rough on a brand-new account that wanted to jump into a discussion right away, but at the same time the quantity of spam hitting your subreddit once you pass the 100k mark is just ludicrous, and this is by far the most effective way to stop it.