I spent a month reading Reddit. Not posting, not replying, just reading. Different subs, different times of day, all looking for the same thing. Where do AI replies stand out, and why.
The pattern wasn't what I expected. It wasn't the em-dashes or the “Hope this helps!” or the bulleted lists. Those are surface tells, the kind of thing you can grep for. The deeper signal was simpler. The AI replies sounded the same in every room.
Reddit isn't one website
It's a few thousand rooms, each with its own voice. r/AITA is therapy-blunt. People show up annoyed and want a verdict. r/cscareerquestions is dry and slightly grumpy. Allergic to vibes. r/AskReddit goes for jokes first, content second. r/relationship_advice is somehow gentler than therapy and more brutal than your friends in the same breath.
The same person posting in three of these rooms writes three different ways without thinking about it. They have to. The replies that go anywhere are the ones that already speak the local language.
Where the AI gets caught
AI replies don't do that. They sound like a moderately polite person who has never been to Reddit, walking into every room with the same voice. Measured, slightly LinkedIn. In r/AITA it explains the situation back to you in your own words before answering. In r/cscareerquestions it offers “considerations.” In r/AskReddit it's missing the joke. The actual register is wrong everywhere, even when the words aren't.
You can see it in the votes too. Natives spot the off-register reply before they've consciously read it. “Sounds like AI” is the modern “sounds like a cop.” Once your nervous system has the pattern, it fires before your brain does.
What we changed
The takeaway, for us at least, is that AI-sounding isn't a property of a sentence. It's the gap between the sentence and the room. The thing we ended up building isn't a slop filter or a humanizer. It's a model that's been told, very clearly, that it's standing in a specific room before it opens its mouth. Most of the work is teaching it to notice the room.
I don't think any of this is solved. The texture of online voice keeps drifting. Twitter killed em-dashes. AI brought them back. Now everyone is suspicious of them again. New rooms appear. Old rooms shift. The move that keeps working is the same one every time. Notice where you are before you write a word.
If you've ever posted a reply that technically answered the question and still made the thread weirder, you know what I mean.
It's at rawreply.com.