CJ describes reverse-engineering findings showing Claude Code steganographically alters prompt formatting (date separators, apostrophe characters) when it detects Chinese time zones or domains linked to labs like DeepSeek, apparently to fingerprint usage and guard against distillation attacks. ✦ AI generated
CJ Reynolds · Syntax · 2026-07-06 · original ↗
starts at this moment · 74:00
if it detects that you're in either of these two Chinese time zones, it changes the prompt to have slashes instead of dashes and then it changes the apostrophe to use a different unicode value instead. So if you were working on code in China... you would kind of have no idea that it basically just fingerprinted you as someone using cloud code in China.
verbatim transcript · starts at 74:00
74:00something typically typically you see it with images. So like steganography can like hide a message inside of an image or something like that. Um but they use that word to say that the way that cloud code the CLI is writing its prompts is allowing them to do certain things on the back end. And the they basically reverse engineered the the cloud code locally. But the idea is when you send a
74:25prompt with cloud code, it has a piece of text at the top that says today's date is year- month-day. And that's the standard format. But there is some code that will detect like if you're running cloud code from the Asia Shanghai time zone or the Asia Eur. Is that like Russia or I don't know. >> I'm gonna go and say I do not know. Yes. >> Okay. I'll I'll look it up. I'll let
74:56that run in the background. Um northwest Oh, it's northwestern China. So, they're actually just two different Chinese time zones. So, basically, if it detects that you're in either of these two chi Chinese time zones, it changes the prompt to have slashes instead of dashes and then it changes the apostrophe to use a different unicode value instead. So if you were working on code in China and you you were even let's say you were
75:23just watching the request that cloud code was making you would kind of have no idea that it basically just fingerprinted you as someone using cloud code in China. But the way it fingerprints is it uses a different apostrophe character and uses slashes instead of dashes. Um the other thing is it can it detects uh I think like what domain you're running from and this is essentially to help prevent distillation
75:47attacks where some of these Chinese labs like DeepSeek and some of the others like Zai um are potentially prompting Claude saving the responses and then using that as training for their own models. So it detects where you're running from in terms of your domain and there's a whole list of like deepseek, moonshot, miniax and um all of that is is passed in in the prompt as well.