The Claude Code Source Leak: fake tools, frustration regexes, undercover mode(alex000kim.com)
264 points by alex000kim 7 hours ago | 117 comments
- mzajc 1 hour agoThere are now several comments that (incorrectly?) interpret the undercover mode as only hiding internal information. Excerpts from the actual prompt[0]:
This very much sounds like it does what it says on the tin, i.e. stays undercover and pretends to be a human. It's especially worrying that the prompt is explicitly written for contributions to public repositories.NEVER include in commit messages or PR descriptions: - The phrase "Claude Code" or any mention that you are an AI - Co-Authored-By lines or any other attribution BAD (never write these): - 1-shotted by claude-opus-4-6 - Generated with Claude Code - Co-Authored-By: Claude Opus 4.6 <…>[0]: https://github.com/chatgptprojects/claude-code/blob/642c7f94...
[-]- otterley 1 hour agoI would have expected people (maybe a small minority, but that includes myself) to have already instructed Claude to do this. It’s a trivial instruction to add to your CLAUDE.md file.[-]
- arcanemachiner 37 minutes agoIt's a config setting (probably the same end result though):
https://code.claude.com/docs/en/settings#attribution-setting...
- petcat 1 hour agoIt's less about pretending to be a human and more about not inviting scrutiny and ridicule toward Claude if the code quality is bad. They want the real human to appear to be responsible for accepting Claud's poor output.[-]
- otterley 1 hour agoThat’s ultimately the right answer, isn’t it? Bad code is bad code, whether a human wrote it all, or whether an agent assisted in the endeavor.
- hombre_fatal 1 hour agoYou can already turn off "Co-Authored-By" via Claude Code config. This is what their docs show:
~/.claude/settings.json
The rest of the prompt is pretty clear that it's talking about internal use.{ "attribution": { "commit": "", "pr": "" },Claude Code users aren't the ones worried about leaking "internal model codenames" nor "unreleased model opus-4-8" nor Slack channel names. Though, nobody would want that crap in their generated docs/code anyways.
Seems like a nothingburger, and everyone seems to be fantasizing about "undercover mode" rather than engaging with the details.
- peacebeard 2 hours agoThe name "Undercover mode" and the line `The phrase "Claude Code" or any mention that you are an AI` sound spooky, but after reading the source my first knee-jerk reaction wouldn't be "this is for pretending to be human" given that the file is largely about hiding Anthropic internal information such as code names. I encourage looking at the source itself in order to draw your conclusions, it's very short: https://github.com/alex000kim/claude-code/blob/main/src/util...[-]
- christinetyip 30 minutes agoNot leaking codenames is one thing, but explicitly removing signals that something is AI-generated feels like a pretty meaningful shift.[-]
- eli 14 minutes agoDoesn't seem so crazy if the point is to avoid leaking new features, models, codenames, etc.
- wnevets 42 minutes agoBAD (never write these):
- "Fix bug found while testing with Claude Capybara"
- "1-shotted by claude-opus-4-6"
- "Generated with Claude Code"
- "Co-Authored-By: Claude Opus 4.6 <…>"
This makes sense to me about their intent by "UNDERCOVER"
- dkenyser 2 hours ago> my first knee-jerk reaction wouldn't be "this is for pretending to be human"...
"Write commit messages as a human developer would — describe only what the code change does."
[-]- amarant 1 hour agoThat seems desirable? Like that's what commit messages are for. Describing the change. Much rather that than the m$ way of putting ads in commit messages[-]
- evenhash 25 minutes agoUnfortunately GitHub Copilot’s commit message generation feature is very human. It’s picked up some awful habits from lazy human devs. I almost always get some pointless “… to improve clarity” or “… for enhanced usability” at the end of the message.
VS Code has a setting that promises to change the prompt it uses to generate commit messages, but it mostly ignores my instructions, even very literal ones like “don’t use the words ‘enhance’ or ‘improve’”. And oddly having it set can sometimes result in Cyrillic characters showing up at the end of the message.
Ultimately I stopped using it, because editing the messages cost me more time than it saved.
/rant
- fweimer 42 minutes agoThe commit message should complement the code. Ideally, what the code does should not need a separate description, but of course there can be exceptions. Usually, it's more interesting to capture in the commit message what is not in the code: the reason why this approach was chosen and not some other obvious one. Or describe what is missing, and why it isn't needed.[-]
- somat 16 minutes agoIt sounds like if you are vibe-coding, that is, can't even be arsed to write a simple commit message, your commit message should be your prompt.
- ImPostingOnHN 36 minutes agoThat sounds like design discussions best had in the issue/ticket itself, before you even start writing code. Then the commit message references the ticket and has a brief summary of the changes.
Writing and reading paragraphs of design discussion in a commit message is not something that seems common.
[-]- skydhash 29 minutes agoNot really about design, but technical reasons why this solution came to be when it’s not that obvious. It’s not often needed. And when it does, it usually fits in a short paragraph.[-]
- ImPostingOnHN 3 minutes ago> technical reasons why this solution came to be
What you're describing here is a design. The most important parts of a design are the decisions and their reasoning.
e.g. "we decided on pattern X over pattern Y because Z" – that is a design, usually discussed outside (and before) a commit message.
- giancarlostoro 36 minutes agoAs opposed to outputting debugging information, which I wouldnt be surprised if LLMs do output "debug" output blurbs which could include model specific information.
- LeifCarrotson 11 minutes agoThe human developer would just write what the code does, because the commit also contains an email address that identifies who wrote the commit. There's no reason to write:
> Commit f9205ab3 by dkenyser on 2026-3-31 at 16:05:
> Fixed the foobar bug by adding a baz flag - dkenyser
Because it already identified you in the commit description. The reason to add a signature to the message is that someone (or something) that isn't you is using your account, which seems like a bad idea.
[-]- jakeinspace 4 minutes agoAside from merges that combine commits from many authors onto a production branch or release tag. I would personally not leave an agent to do that sort of work.
- peacebeard 1 hour ago~That line isn't in the file I linked, care to share the context? Seems pretty innocuous on its own.~
[edit] Never mind, find in page fail on my end.
[-]- stordoff 1 hour agoIt's in line 56-57.[-]
- peacebeard 1 hour agoThanks! I must have had a typo when I searched the page.
- andoando 1 hour agoI think the motivation is to let developers use it for work without making it obvious theyre using AI[-]
- ryandrake 1 hour agoWhich is funny given how many workplaces are requiring developers use AI, measuring their usage, and stack ranking them by how many tokens they burn. What I want is something that I can run my human-created work product through to fool my employer and its AI bean counters into thinking I used AI to make it.[-]
- __blockcipher__ 1 hour agoUndercover mode seems like a way to make contributions to OSS when they detect issues, without accidentally leaking that it was claude-mythos-gigabrain-100000B that figured out the issue[-]
- stavros 1 hour agoWhat does non-undercover do? Where does CC leave metadata mainly? I haven't noticed anything.[-]
- sprobertson 44 minutes agoit likes mentioning itself in commit messages, though you can just tell it not to.[-]
- arcanemachiner 40 minutes agoThere is a config setting for this:
https://code.claude.com/docs/en/settings#attribution-setting...
- stavros 43 minutes agoAh, thanks, it hasn't done it for mine so I was wondering if there's something lower-level somehow.
- evil-olive 28 minutes ago> So I spent my morning reading through the HN comments and leaked source.
> This was one of the first things people noticed in the HN thread.
> The obvious concern, raised repeatedly in the HN thread
> This was the most-discussed finding in the HN thread.
> Several people in the HN thread flagged this
> Some in the HN thread downplayed the leak
when the original HN post is already at the top of the front page...why do we need a separate blogpost that just summarizes the comments?
[-]- groby_b 26 minutes agoBecause the original post was noisy and lacked a concise summary of findings.
Or, more simply: Because folks wanted it enough to upvote it.
- Reason077 1 hour ago> "Anti-distillation: injecting fake tools to poison copycats"
Plot twist: Chinese competitors end up developing real, useful versions of Claude's fake tools.
[-]- 3abiton 3 minutes agoTbh, I think distillation is happening both ways. And at this stage, "quality" is stagnating, the main edge is the tooling. The harness of CC seems to be the best so far, and I wonder if this leak would equalize the usability.
- WorldPeas 27 minutes agomore likely, they would parse them out using simple regex, the whole point is they're there but not used. Distillation is becoming less common now however
- causal 1 hour agoI'm amazed at how much of what my past employers would call trade secrets are just being shipped in the source. Including comments that just plainly state the whole business backstory of certain decisions. It's like they discarded all release harnesses and project tracking and just YOLO'd everything into the codebase itself.[-]
- semiquaver 11 seconds agoMost large private codebases look like this. Anthropic did not expect the source to leak.
- CharlieDigital 1 hour agoComments are the ultimate agent coding hack. If you're not using comments, you're doing agent coding wrong.
Why? Agents may or may not read docs. It may or may not use skills or tools. It will always read comments "in the line of sight" of the task.
You get free long term agent memory with zero infrastructure.
[-]- perching_aix 49 minutes agoAgents and I apparently have a whole lot in common.
Only being half ironic with this. I generally find that people somehow magically manage to understand how to be materially helpful when the subject is a helpless LLM. Instead of pointing it to a random KB page, they give it context. They then shorten that context. They then interleave context as comments. They provide relevant details. They go out of their way to collect relevant details. Things they somehow don't do for their actual colleagues.
This only gets worse when the LLM captures all that information better than certain human colleagues somehow, rewarding the additional effort.
- prepend 41 minutes agoComments are great for developers. I like having as much design in the repo directly. If not in the code, then in a markdown in the repo.[-]
- hk__2 24 minutes agoThis is also a great way to ensure the documentation is up to date. It’s easier to fix the comment while you’re in the code just below it than to remember “ah yes I have to update docs/something.md because I modified src/foo/bar.ts”.[-]
- CharlieDigital 9 minutes agoPeople moving docs out of code are absolutely foolish because no one is going to remember to update it consistently but the agent always updates comments in the line of sight consistently.
Agent is not going to know to look for a file to update unless instructed. Now your file is out of sync. Code comments keeping everything line of sight makes it easy and foolproof.
- JambalayaJimbo 1 hour agoI guess they weren't expecting a leak of the source code? It's very handy to have as much as possible available in the codebase itself.
- pixl97 1 hour agoProject trackers come and go, but code is forever, hopefully?
- treexs 1 hour agowell yeah since they tell claude code the business decisions and it creates the comments
- ripbozo 2 hours agoI don't understand the part about undercover mode. How is this different from disabling claude attribution in commits (and optionally telling claude to act human?)
On that note, this article is also pretty obviously AI-generated and it's unfortunate the author didn't clean it up.
[-]- giancarlostoro 2 hours agoIt's people overreacting, the purpose of it is simple, don't leak any codenames, project names, file names, etc when touching external / public facing code that you are maintaining using bleeding edge versions of Claude Code. It does read weird in that they want it to write as if a developer wrote a commit, but it might be to avoid it outputting debug information in a commit message.
- ramon156 1 hour agoEven some of these comments are obviously Ai-assisted. I hate that I recognize it.
- simianwords 2 hours ago> The multi-agent coordinator mode in coordinatorMode.ts is also worth a look. The whole orchestration algorithm is a prompt, not code.
So much for langchain and langraph!! I mean if Anthropic themselves arent using it and using a prompt then what’s the big deal about langchain
[-]- ossa-ma 52 minutes agoLangchain is for model-agnostic composition. Claude Code only uses one interface to hoist its own models so zero need for an abstraction layer.
Langgraph is for multi-agent orchestration as state graphs. This isn't useful for Claude Code as there is no multi-agent chaining. It uses a single coordinator agent that spawns subagents on demand. Basically too dynamic to constrain to state graphs.
[-]- simianwords 46 minutes agoYou may have a point but to drive it further, can you give an example of a thing I can do with langgraph that I can't do with Claude Code?[-]
- ossa-ma 19 minutes agoI'm not an supporter of blindly adopting the "langs" but langgraph is useful for deterministically reproducable orchestration. Let's say you have a particular data flow that takes an email sends it through an agent for keyword analysis the another agent for embedding then splits to two agents for sentiment analysis and translation - there is where you'd use langgraph in your service. Claude Code is a consumer tool, not production.[-]
- simianwords 10 minutes agoI see what you mean. Maybe in the cases where the steps are deterministic, it might be worth moving the coordination at the code layer instead of AI layer.
What's the value add over doing it with just Python code? I mean you can represent any logic in terms of graphs and states..
- peab 31 minutes agonobody serious uses langchain. The biggest agent products are coding tools, and I doubt any of them use langchain
- rolymath 1 hour agoYou didn't even use it yet.[-]
- space_fountain 1 hour agoI've tried to use langchain. It seemed to force code into their way of doing things and was deeply opinionated about things that didn't matter like prompt templating. Maybe it's improved since then, but I've sort of used people who think langchain is good as a proxy for people who haven't used much ai?
- simianwords 1 hour ago?
- fatcullen 28 minutes agoThe buddy feature the article mentions is planned for release tomorrow, as a sort of April Fools easter egg. It'll roll out gradually over the day for "sustained Twitter buzz" according to the source.
The pet you get is generated based off your account UUID, but the algorithm is right there in the source, and it's deterministic, so you can check ahead of time. Threw together a little app to help, not to brag but I got a legendary ghost https://claudebuddychecker.netlify.app/
[-]- sync 19 minutes agoCute! Cactus for me. Nice animations too - looks like there were multiple of us asking Claude to reverse engineer the system. I did a slightly deeper dive here if you're interested, plus you can see all the options available: https://variety.is/posts/claude-code-buddies/
(I didn't think to include a UUID checker though - nice touch)
[-]- fatcullen 3 minutes agoNeat! That's a great write up, cool to see others looking into it. I do wonder if they're going to do anything with the stats and shinies bit. Seems like the main bit of the code for buddies that's going to handle hatching them tomorrow is still missing, so maybe it'll them there.
- layer8 37 minutes ago> Sometimes a regex is the right tool.
I’d argue that in this case, it isn’t. Exhibit 1 (from the earlier thread): https://github.com/anthropics/claude-code/issues/22284. The user reports that this caused their account to be banned: https://news.ycombinator.com/item?id=47588970
Maybe it would be okay as a first filtering step, before doing actual sentiment analysis on the matches. That would at least eliminate obvious false positives (but of course still do nothing about false negatives).
[-]- ArvinJA 32 minutes agoIs this really the use-case? I imagine the regex is good for a dashboard. You can collect matches per 1000 prompts or something like that, and see if the number grows or declines over time. If you miss some negative sentiment it shouldn't matter unless the use of that specific word doesn't correlate over time with other negative words and is also popular enough to have an impact on the metric.[-]
- internetter 27 minutes agoWhen you read the code, what you propose is actually its exclusive use... logging.
- pixl97 2 hours ago>Claude Code also uses Axios for HTTP.
Interesting based on the other news that is out.
[-]- alex000kim 2 hours agoOh right, I just saw https://news.ycombinator.com/item?id=47582220 will update the post with this link
- greenavocado 1 hour agoWhat version?[-]
- Stagnant 1 hour ago1.13.6, so should not be affected by the malware
- ptrl600 19 minutes agoWhy didn't they open the source themselves? What's the point of all this secrecy anyway?[-]
- hxugufjfjf 14 minutes agoBecause they (apparently) keep a bunch of secret features and roadmap details in said source code.
- stavros 1 hour agoCan someone clarify how the signing can't be spoofed (or can it)? If we have the source, can't we just use the key to now sign requests from other clients and pretend they're coming from CC itself?[-]
- MadsRC 47 minutes agoWhat signing?
Are you referencing the use of Claude subscription authentication (oauth) from non-Claude Code clients?
That’s already possible, nothing prevents you from doing it.
They are detecting it on their backend by profiling your API calls, not by guarding with some secret crypto stuff.
At least that’s how things worked last week xD
[-]- stavros 45 minutes agoI'm referring to this signing bit:
https://alex000kim.com/posts/2026-03-31-claude-code-source-l...
Ah, it seems that Bun itself signs the code. I don't understand how this can't be spoofed.
[-]- MadsRC 19 minutes agoAh yes, the API will accept requests that doesn’t include the client attestation (or the fingerprint from src/utils/fingerprint.ts. At least it did a couple of weeks back.
They are most likely using these as post-fact indicators and have automation they kicks in after a threshold is reached.
Now that the indicators have leaked, they will most likely be rotated.
- simianwords 2 hours ago> The obvious concern, raised repeatedly in the HN thread: this means AI-authored commits and PRs from Anthropic employees in open source projects will have no indication that an AI wrote them. It’s one thing to hide internal codenames. It’s another to have the AI actively pretend to be human.
I don’t get it. What does this mean? I can use Claude code now without anyone knowing it is Claude code.
[-]- alex000kim 2 hours agotechnically you're correct, but look at the prompt https://github.com/alex000kim/claude-code/blob/main/src/util...
it's written to _actively_ avoid any signs of AI generated code when "in a PUBLIC/OPEN-SOURCE repository".
Also, it's not about you. Undercover mode only activates for Anthropic employees (it's gated on USER_TYPE === 'ant', which is a build-time flag baked into internal builds).
[-]- simianwords 2 hours agoI don’t know what you mean. It just informs to not use internal code names.[-]
- robflynn 2 hours agoIt also says don't announce that you are AI in any way including asking it to not say "Co-authored by Claude". I read the file myself.
I'm still inclined to think people might be overreacting to that bit since it seems to be for anthropic-only to prevent leaking internal info.
But I did read the prompt and it did say hide the fact that you are AI.
[-]- simianwords 1 hour agoWhy does that matter though
- giancarlostoro 2 hours agoI agree with you, I think people are overthinking this.
- slopinthebag 2 hours agoI think it means OSS projects should start unilaterally banning submissions from people working for Anthropic.[-]
- simianwords 2 hours agoWhy? What does this have to do with the leak
- armanj 37 minutes ago> Anti-distillation: injecting fake tools to poison copycats
Does this mean `huggingface.co/Jackrong/Qwen3.5-27B-Claude-4.6-Opus-Reasoning-Distilled` is unusable? Had anyone seen fake tool calls working with this model?
[-]- amdivia 5 minutes agoAssuming Claude Code was used. If OpenCode or some other programmatic method was used, the "fake tool calls" won't be added
- agilob 31 minutes agoVery likely Claude was trained on Deepseek, so it's possible that spiderman-pointing-at-spiderman.jpg all models are wrong now https://www.reddit.com/r/DeepSeek/comments/1r9se7p/claude_so...
- seanwilson 2 hours agoAnyone else have CI checks that source map files are missing from the build folder? Another trick is to grep the build folder for several function/variable names that you expect to be minified away.
- motbus3 1 hour agoI am curious about these fake tools.
They would either need to lie about consuming the tokens at one point to use in another so the token counting was precise.
But that does not make sense because if someone counted the tokens by capturing the session it would certainly not match what was charged.
Unless they would charge for the fake tools anyway so you never know they were there
- amelius 29 minutes agoA few weeks ago I was using Opus and Sonnet in OpenCode. Is this not possible anymore?[-]
- alasano 18 minutes agoIt's still possible but if you do it using your Claude Max plan, it's technically no longer allowed.
They don't want you using your subscription outside of Claude Code. Only API key usage is allowed.
Google also doubled down on this and OpenAI are the only ones who explicitly allow you to do it.
- viccis 36 minutes ago>This was the most-discussed finding in the HN thread. The general reaction: an LLM company using regexes for sentiment analysis is peak irony.
>Is it ironic? Sure. Is it also probably faster and cheaper than running an LLM inference just to figure out if a user is swearing at the tool? Also yes. Sometimes a regex is the right tool.
I'm reading an LLM written write up on an LLM tool that just summarizes HN comments.
I'm so tired man, what the hell are we doing here.
- marcd35 40 minutes ago> 250,000 wasted API calls per day
How much approximate savings would this actually be?
- simianwords 2 hours agoGuys I’m somewhat suspicious of all the leaks from Anthropic and think it may be intentional. Remember the leaked blog about Mythos?[-]
- Analemma_ 1 hour agoIt's possible, but Anthropic employees regularly boast (!) that Claude Code is itself almost entirely vibe-coded (which certainly seems true, based on the generally-low quality of the code in this leak), so it wouldn't at all surprise me to have that blow up twice in the same week. Probably it might happen with accelerating frequency as the codebase gets more and more unmanageable.
- __blockcipher__ 1 hour agoI'm normally suspicious but honestly they've been so massively supply-constrained that I don't think it really benefits them much. They're not worried about getting enough demand for the new models; they're worrying about keeping up with it.
Granted, there's a small counterargument for mythos which is that it's probably going to be API-only not subscription
[-]- simianwords 1 hour agoWhy would Claude code mention Mythos then[-]
- hxugufjfjf 18 minutes agoYou can still use Claude Code with API-only.
- drewnick 29 minutes agoYou can use Claude Code with API mode (not a sub)[-]
- simianwords 14 minutes agofair but I'm guessing access would be limited to 20x max users or something like that. not gated by API.
- saadn92 1 hour agoThe feature flag names alone are more revealing than the code. KAIROS, the anti-distillation flags, model codenames those are product strategy decisions that competitors can now plan around. You can refactor code in a week. You can't un-leak a roadmap.
- dangus 21 minutes agoSomething I’ve been thinking about, somewhat related but also tangential to this topic:
The more code gets generated by AI, won’t that mean taking source code from a company becomes legal? Isn’t it true that works created with generative AI can’t be copyrighted?
I wonder if large companies have throught of this risk. Once a company’s product source code reaches a certain percentage of AI generation it no longer has copyright. Any employee with access can just take it and sell it to someone else, legally, right?
- mmaunder 43 minutes agoCome on guys. Yet another article distilling the HN discussion in the original post, in the same order the comments appear in that discussion? Here's another since y'all love this stuff: https://venturebeat.com/technology/claude-codes-source-code-...
- OfirMarom 2 hours agoUndercover mode is the most concerning part here tbh.[-]
- anonymoushn 2 hours agowhy[-]
- AnimalMuppet 2 hours agoWell, as a general rule, I don't do business with people who lie to me.
You've got a business, and you sent me junk mail, but you made it look like some official government thing to get me to open it? I'm done, just because you lied on the envelope. I don't care how badly I need your service. There's a dozen other places that can provide it; I'll pick one of them rather than you, because you've shown yourself to be dishonest right out of the gate.
Same thing with an AI (or a business that creates an AI). You're willing to lie about who you are (or have your tool do so)? What else are you willing to lie to me about? I don't have time in my life for that. I'm out right here.
[-]- otterley 1 hour agoOut of curiosity, given two code submissions that are completely identical—one written solely by a human and one assisted by AI—why should its provenance make any difference to you? Is it like fine art, where it’s important that Picasso’s hand drew it? Or is it like an instruction manual, where the author is unimportant?
Similarly, would you consider it to be dishonest if my human colleague reviewed and made changes to my code, but I didn’t explicitly credit them?
[-]- feature20260213 22 minutes agoYes because you can be sued for copyright violation if you don't know the origin of one, and not the other.
- AnimalMuppet 50 minutes agoWhy does the provenance make any difference? Let me increase your options. Option 1: You completely hand-wrote it. Option 2: You were assisted by an AI, but you carefully reviewed it. Option 3: You were assisted by an AI (or the AI wrote the whole thing), and you just said, "looks good, YOLO".
Even if the code is line-for-line identical, the difference is in how much trust I am willing to give the code. If I have to work in the neighborhood of that code, I need to know what degree of skepticism I should be viewing it with.
[-]- otterley 42 minutes agoThat's the thing. As someone evaluating pull requests, should you trust the code based on its provenance, or should you trust it based on its content? Automated testing can validate code, but it can't validate people.
ISTM the most efficient and objective solution is to invest in AI more on both sides of the fence.
- simianwords 1 hour agoWhat’s the lie? It’s just asking to not reveal internal names[-]
- BoredPositron 48 minutes agoYou are spamming the whole fucking thread with the same nonsense. It is instructed to hide that the PR was made via Claude Code. I don't know why people who are so AI forward like yourself have such a problem with telling people that they use AI for coding/writing, it's a weirdly insecure look.[-]
- simianwords 44 minutes agoI can do that right now with Claude Code without this undercover mode.. In fact I do it many times at work. What's the big deal in this?
Do you not think it is an overreaction to panic like this if I can do exactly what the undercover mode does by simply asking Claude?
[-]- BoredPositron 26 minutes agoIt's different if it's an institutional decision or a personal like in your case. Which is and I am repeating myself here borderline insecure.[-]
- simianwords 23 minutes agowhat's insecure about it? if it is up to the institution to make that decision - you can still do it. Claude is not stopping you from making that decision[-]
- BoredPositron 17 minutes agoYou have to work on your reading comprehension or you are intentional deceptive. Bye.
- Jaco07 11 minutes ago[dead]
- skrun_dev 24 minutes ago[dead]