Cal.com is going closed source

https://cal.com/blog/cal-com-goes-closed-source-why

by Benjamin_Dobell • 3 months ago

391 317 3 months ago

cal.com

andsoitis• 3 months ago

Today, we are making the very difficult decision to move to closed source, and there’s one simple reason: security.

It seems like an easy decision, not a difficult one.

gouthamve• 3 months ago

This is a weird knee-jerk reaction. I feel like this is more a business decision than a security decision.

I feel like with AI, self-hosting software reliably is becoming easier so the incentives to pay for a hosted service of an OSS project are going down.

badgersnake• 3 months ago

AI is certainly getting a lot of milage as an excuse for doing bad things.

Wanna sack a load of staff? - AI

Wanna cut your consumer products division? - AI

Wanna take away the source? - AI

rhubarbtree4• 3 months ago

Well, first AI uses security to sell models. So other companies hijack their narrative for their purposes. This is how marketing works.

esafak• 3 months ago

Their product is getting commoditized: https://workspace.google.com/resources/appointment-schedulin...

no_wizard• 3 months ago

I always felt it was a matter of time before Google took notice.

It has always been odd to me they didn’t have this functionality years ago. It’s been requested for a long long time

gp14• 3 months ago

Calendar apps have been commoditized for about 15 years now but they keep growing!

bensyverson• 3 months ago

The real downside to Google's solution is that you have to use Google Meet. Depending on your opinion of Meet, this is either no big deal or a total deal breaker.

rhubarbtree4• 3 months ago

Remember when calendly went out of business?

fhn• 3 months ago

Yeah, I don't buy it. If they don't want these security reports, ignore them and continue your path. Blaming AI is just an excuse to close source. If you don't want AI to learn from your code, too late. Add genetic algorithms and fuzzing into AI and it can iterate and learn a billion times faster, no need to learn for humans.

tecoholic• 3 months ago

I think people are finding ways to either enable “pro” features and at least find the right extension points to implement them easily with LLMs. Security is window dressing.

kartika363632• 3 months ago

correct. guy's doing mental gymnastics all to say he's a sellout.

doytch2• 3 months ago

I get the mentality but it feels very much like security through obscurity. When did we decide that that was the correct model?

Peer_Rich• 3 months ago

hey cofounder here. since it takes my 16 year old neighbors son 15 mins and $100 claude code credits to hack your open source project

doytch2• 3 months ago

Right, but those capabilities are available to you as well. Granted the remediation effort will take longer but...you're going to do that for any existing issues _anyway_ right?

I understand why this is a tempting thing to do in a "STOP THE PRESSES" manner where you take a breather and fix any existing issues that snuck through. I don't yet understand why when you reach steady-state, you wouldn't rely on the same tooling in a proactive manner to prevent issues from being shipped.

And if you say "yeah, that's obv the plan," well then I don't understand what going closed-source _now_ actually accomplishes with the horses already out of the barn.

simonw3• 3 months ago

Are you at all worried that the message you are spreading here is "We are no longer confident in our own ability to secure your data?"

sambaumann• 3 months ago

Couldn't you just spend those $100 on claude code credits yourself and make sure you're not shipping insecure software? Security by obscurity is not the correct model (IMO)

discordianfish• 3 months ago

Please, go ahead!

wild_egg3• 3 months ago

It only takes 20 minutes and $200 to hack a closed source one too though. LLMs are ludicrously good at using reverse engineering tools and having source available to inspect just makes it slightly more convenient.

hypeatei• 3 months ago

neighbors son 15 mins and $100 claude code credits

Is that true? Didn't the Mythos release say they spent $20k? I'm also skeptical of Anthropic here doing essentially what amounts to "vague posting" in an attempt scare everyone and drive up their value before IPO.

pdntspa• 3 months ago

whooptie fuggin doo, then spend $200 on finding and fixing the issues before you push your commits to the cloud

bakugo• 3 months ago

*This comment sponsored by Anthropic

toast0• 3 months ago

I don't think this really helps that much. Your neighbor could ask an LLM to decompile your binaries, and then run security analysis on the results.

If the tool correctly says you've got security issues, trying to hide them won't work. You still have the security issues and someone is going to find them.

bayindirh• 3 months ago

Why not can’t you (as in Cal.com) spend that amount of money and find vulnerabilities yourself?

You can keep the untested branch closed if you want to go with “cathedral” model, even.

senko• 3 months ago

What makes you think it'll take him more than 16 mins and $110 claude code credits to hack your closed source project?

ErroneousBosh• 3 months ago

since it takes my 16 year old neighbors son 15 mins and $100 claude code credits to hack your open source project

To what end? You can just look at the code. It's right there. You don't need to "hack" anything.

If you want to "hack on it", you're welcome to do so.

Would you like to take a look at some of my open-source projects your neighbour's kid might like to hack on?

otabdeveloper4• 3 months ago

No it doesn't. Have you been actually "hacked"?

Maken• 3 months ago

Was open source any more secure before LLMs became so cheap? For those same 100$ you could have a North Korean hacking your code for a whole month.

1970-01-013• 3 months ago

This is not security via obscurity; it is reducing your attack surface as much as possible.

dspillett5• 3 months ago

Reducing your attack surface as much as possible via obscurity.

behringer2• 3 months ago

right, they're just securing their application by making the bugs obscure. It's totally different.

keeda2• 3 months ago

Security through obscurity is only problematic if that is the only, or a primary, layer of defense. As an incremental layer of deterrence or delay, it is an absolutely valid tactic. (Note, not commenting on whether that is the rationale here.)

traderj0e2• 3 months ago

That, and plenty of closed-source software at least has a decent security track record by now. I haven't seen an obvious cause-and-effect of open-source making something more secure. Only the other direction, where insecure closed-source software is kept closed because they know it's Swiss cheese.

quotemstr2• 3 months ago

They probably lack a sufficient density of people who remember why "security through obscurity" become an infamous concept. It belongs to that family of bad ideas that's superficially appealing, especially if you're still at that stage of your career at which you think past generations were full of idiots and you, alone, have discovered how to do real software development.

ergocoder• 3 months ago

Security through obscurity is still better than no obscurity...

ButlerianJihad3• 3 months ago

This seems kind of crazy. If LLMs are so stunningly good at finding vulnerabilities in code, then shouldn't the solution be to run an LLM against your code after you commit, and before you release it? Then you basically have pentesting harnesses all to yourself before going public. If an LLM can't find any flaws, then you are good to release that code.

A few years ago, I invoked Linus's Law in a classroom, and I was roundly debunked. Isn't it a shame that it's basically been fulfilled now with LLMs?

https://en.wikipedia.org/wiki/Linus%27s_law

fwip• 3 months ago

It's entirely possible to address all the LLM-found issues and get an "all green" response, and have an attacker still find issues that your LLM did not. Either they used a different model, a different prompt, or spent more money than you did.

It's not a symmetric game, either. On defense, you have to get lucky every time - the attacker only has to get lucky once.

earthnail• 3 months ago

It's not a symmetric game, either. On defense, you have to get lucky every time - the attacker only has to get lucky once.

This! I love OSS but this argument seems to get overlooked in most of the comments here.

dgellow• 3 months ago

I mean, you should definitely have _some_ level of audit by LLMs before you ship, as part of the general PR process.

But you might need thousands of sessions to uncover some vulnerabilities, and you don’t want to stop shipping changes because the security checks are taking hours to run

samename• 3 months ago

That’s a non-trivial cost for commonly severely underfunded open source projects

yawndex• 3 months ago

Cal.com is not a severely underfunded project, it raised around $32M of VC money.

vlapec• 3 months ago

LLMs really are stunningly good at finding vulnerabilities in code, which is why, with closed-source code, you can and probably will use them to make your code as secure as possible.

But you won't keep the doors open for others to use them against it.

So it is, unfortunately, understandable in a way...

paprikanotfound• 3 months ago

I'm not a security expert but can't close source applications be vulnerable and exploited too? I feel like using close source as a defense is just giving you a false sense of security.

genxy• 3 months ago

You don't need the source, the LLM has the source, it is called the binary.

eloisant6• 3 months ago

LLM like humans can find vulnerabilities in black boxes. We already established 30 years ago that open source is usually more secure than closed source and that security by obscurity doesn't work.

layer83• 3 months ago

Attackers only need LLMs to be good at randomly finding one vulnerability, whereas service providers need them to be good at finding all such vulnerabilities.

johnfn4• 3 months ago

After a release, attackers have effectively infinite time to throw an LLM against every line of your code - an LLM that only gets smarter and cheaper to run as time passes. In order to feel secure you’d need to do all the work you’d imagine an attacker would ever do, for every single release you ship.

stavros• 3 months ago

This assumes that the relationship between "LLM tokens spent" and "vulnerabilities found" doesn't plateau, though.

mixdup• 3 months ago

The first few times it's going to be expensive, but once everyone level sets with intense scans of their codebases, "every single release" is actually not that big a deal, since you are not likely to be completely rebuilding your codebase every release

utopiah• 3 months ago

attackers have effectively infinite time

No, attackers are also rational economical actors. They don't randomly attack any software just for the aesthetics beauty of the process. They attack for bounty, for fame, for national interest, etc. No matter the reason it's not random and thus they DO have a budget, both in time and money. They attack THIS project versus another project because it's interesting to them. If it's not, they might move to another project but they certainly won't spend infinite time precisely because they don't have infinite resources. IMHO it's much more interesting to consider the realistic arm race then theoretical scenarii that never take place.

rhubarbtree4• 3 months ago

But so do you and all your users what’s your point?

sandeepkd2• 3 months ago

Every change would introduce the possibility of a vulnerability being added to the system and one would need to run the LLM scan across the entire code base. It gets very costly in a environment where you are doing regular commits. Companies like Github already provide scanning tools for static analysis and the cost is already high for them.

pianopatrick• 3 months ago

Might lead to a move away from continuous delivery back towards batched releases.

r2vcap• 3 months ago

As LLMs improve and adoption grows, maintaining a FOSS project is becoming more complex and more expensive in terms of time and manpower. That part is easy to understand.

It is also become a trend that LLM-assisted users are generating more low-quality issues, dubious security reports, and noisy PRs, to the point where keeping the whole stack open source no longer feels worth it. Even if the real reason is monetization rather than security, I can still understand the decision.

I suspect we will see more of this from commercial products built around a FOSS core. The other failure mode is that maintainers stop treating security disclosures as something special and just handle them like ordinary bugs, as with libxml2. In that sense, Chromium moving toward a Rust-based XML library is also an interesting development.

d3Xt3r• 3 months ago

Just use AI to fight AI, that's the only sensible way we can keep up. So if you're low-quality PRs, reports etc, have LLMs filter them out. Like how once upon a time we used to drown in email spam but it's now mostly a non-issue thanks to intelligent spam filters, the same needs to happen for opensource projects. Use AI to fight AI.

pcblues3• 3 months ago

Write simple code. Do what you said, which is a very good idea. Test LLM security against the compiler too.

benjaminoakes• 3 months ago

I suspect that AI is a convenient excuse to go closed source. They have probably wanted to do that for years after leaning more commercial.

rvz• 3 months ago

You know what?

Great move.

Open-source supporters don't have a sustainable answer to the fact that AI models can easily find N-day vulnerabilities extremely quickly and swamp maintainers with issues and bug-reports left hanging for days.

Unfortunately, this is where it is going and the open-source software supporters did not for-see the downsides of open source maintenance in the age of AI especially for businesses with "open-core" products.

Might as well close-source them to slow the attackers (with LLMs) down. Even SQLite has closed-sourced their tests which is another good idea.

zb33• 3 months ago

especially for businesses with "open-core" products.

Then good, that overengineered, intentionally-crippled crap should go away.

wild_egg3• 3 months ago

Haven't the SQLite tests always been closed? Getting access to them is a major reason for financially supporting them

hayleox2• 3 months ago

The tools are available to everyone. It's becoming easier for hackers to attack you at the same speed that it's becoming easier for you to harden your systems. When everyone gains the same advantage at the same time, nothing has really changed.

It makes me think of how great chess engines have affected competitive chess over the last few years. Sure, the ceiling for Elo ratings at the top levels has gone up, but it's still a fair game because everyone has access to the new tools. High-level players aren't necessarily spending more time on prep than they were before; they're just getting more value out of the hours they do spend.

popalchemist3• 3 months ago

I agree it's a shit tactic, but one thing I can say for those running software businesses is that it's not an equivalent linear increase on both sides. It's asymmetric, because # of both attackers and the amount of attack surface (exposed 3rd party dependencies, for example) is near infinite, with no opportunity cost for failure by the bad actors (hackers). However a single failure can bring down a company, particularly when they may be hosting sensitive user data that could ruin their customers' businesses or lives.

I think Cal are making the wrong call, and abandoning their principles. But it isn't fair to say the game is accelerating in a proportionate way.

See: https://www.youtube.com/watch?v=2CieKDg-JrA

Ultimately, he concludes that while in the short run the game defines the players' actions, an environment that makes cooperation too risky naturally forces participants to stop cooperating to protect themselves from being "exploited" (this bit is around 34:39 - 34:46)

ltbarcly32• 3 months ago

Take it back to linkedin!

simonw3• 3 months ago

Drew Breunig published a very relevant piece yesterday that came to the opposite conclusion: https://www.dbreunig.com/2026/04/14/cybersecurity-is-proof-o...

Since security exploits can now be found by spending tokens, open source is MORE valuable because open source libraries can share that auditing budget while closed source software has to find all the exploits themselves in private.

If Mythos continues to find exploits so long as you keep throwing money at it, security is reduced to a brutally simple equation: to harden a system you need to spend more tokens discovering exploits than attackers will spend exploiting them.

not-chatgpt• 3 months ago

Security should be a non issue in the age of AI now that auditing is cheaper than ever.

I'd give them more credits if they use the AI slop unmaintainability argument.

habinero3• 3 months ago

Ha ha ha ha. I wish that were true. Getting people to patch existing, known vulns is hard enough.

criddell• 3 months ago

How may open source libraries have auditing budgets?

Mordisquitos• 3 months ago

Their commercial users have auditing budgets.

simonw3• 3 months ago

I expect we're about to find that it's a lot easier to convince a company to spend money running an AI security scan of their dependencies and sharing the results with the maintainers than it is to have them give those maintainers money directly.

(I just hope they can learn to verify the exploits are valid before sharing them!)

pietz• 3 months ago

This conclusion makes more sense to me, but maybe I'm too naive.

The media momentum of this threat really came with Mythos, which was like 2 or 3 weeks ago? That seems like a fairly short time to pivot your core principles like that. It sounds to me like they wanted to do this for other business related reasons, but now found an excuse they can sell to the public.

(I might be very wrong here)

skybrian• 3 months ago

This seems similar to the lesson learned for cryptographic libraries where open source libraries vetted by experts become the most trusted.

Your average open source library isn’t going to get that scrutiny, though. It seems like it will result in consolidation around a few popular libraries in each category?

layer83• 3 months ago

An important difference between SaaS offerings and open source libraries is that the latter have not liability. They can much more easily afford exhibiting vulnerabilities until those are fixed.

DrammBA• 3 months ago

I have a feeling the real reason is them trying to avoid someone using AI to copyright-wash their product, they're just using security as the excuse.

OsrsNeedsf2P• 3 months ago

An app like Cal.com can be vibe coded in a few evenings with a Chrome MCP server pointed to their website to figure out all the nooks and crannys. The moat of Cal.com is not the code, it's the users who don't want to migrate.

The real answer is they are likely having a hard time converting people to paid plans

lisperforlife• 3 months ago

Exactly this! Classic open source bait and switch.

bit1993• 3 months ago

Called this 9 months ago https://news.ycombinator.com/item?id=44559840

"AI slop is rapidly destroying the WWW, most of the content is becoming more and more low-quality and difficult to tell if its true or hallucinated. Pre-AI web content is now more like the golden-standard in terms of correctness, browsing the Internet Archive is much better. This will only cause content to go behind pay-walls, allot of open-source projects will be closed source not only because of the increased work maintainers have to do to not only review but also audit patches for potential AI hallucinations but also because their work is being used to train LLMs and re-licensed to proprietary."

theahura2• 3 months ago

At risk of self promotion, I think more people should adopt something like the Ship of Theseus license (https://github.com/tilework-tech/nori-skillsets/pull/465/cha...). It's not obvious if this will patch the clean room hole in licensing, but I'd rather see it play out in court than assume opensource is just fully dead

mgdev4• 3 months ago

This is an economically sound conclusion.

It also means that you need to extract enough value to cover the cost of said tokens, or reduce the economic benefit of finding exploits.

Reducing economic benefit largely comes down to reducing distribution (breadth) and reducing system privilege (depth).

One way to reduce distribution is to, raise the price.

Another is to make a worse product.

Naturally, less valuable software is not a desirable outcome. So either you reduce the cost of keeping open (by making closed), or increase the price to cover the cost of keeping open (which, again, also decreases distribution).

The economics of software are going to massively reconfigure in the coming years, open source most of all.

I suspect we'll see more 'open spec' software, with actual source generated on-demand (or near to it) by models. Then all the security and governance will happen at the model layer.

cassianoleal2• 3 months ago

I suspect we'll see more 'open spec' software, with actual source generated on-demand (or near to it) by models. Then all the security and governance will happen at the model layer.

So each time you roll the dice you gamble on getting a fresh set of 0-days? I don't get why anyone would want this.

xigoi• 3 months ago

I love using software that changes every time you compile it.

jstummbillig2• 3 months ago

to harden a system you need to spend more tokens discovering exploits than attackers will spend exploiting them.

That can't be right, can it? Given stable software, the relative attack surface keeps shrinking. Mythos does not produce exploits. Should be defenders advantage, token wise, no?

paisawalla• 3 months ago

So long as that OSS keeps accumulating features, there isn't quite the equilibrium you're imagining. If you can pin to a stable version, which continues to audited, you're fine. But if the rest of the world moves on to newer versions of the software, you'll have to as well, unless you want to own the burden of hardening older versions.

rhplus• 3 months ago

It’s the classic asymmetric warfare problem:

Defenders have to find all the holes in all their systems, while attackers just need to find one hole in one system.

JoshTriplett2• 3 months ago

Mythos does not produce exploits.

AI in general will, don't worry. "Move fast and break things" makes more exploits than "move steadily and fix things" does.

dang2• 3 months ago

Thanks - I've re-upped* that one here: Cybersecurity looks like proof of work now - https://news.ycombinator.com/item?id=47769089 (no comments yet)

* a la https://news.ycombinator.com/item?id=26998308

flying_sheep• 3 months ago

to harden a system you need to spend more tokens discovering exploits than attackers will spend exploiting them

This is true until certain point, unless the requirement / contract itself has loophole which the attacker can exploit it without limit. But I don't think this is the case.

Let's say, if someone found an loophole in sort() which can cause denial-of-service. The cause would be the implementation itself, not the contract of sorting. People + AI will figure it out and fix it eventually.

tonymet• 3 months ago

This may be true long term but not short term. It also assumes that white hats will be as motivated as black hats – not true.

For projects with NO WARRANTY, the risk is minimal, so yes there are upsides.

For a commercial project like cal.com, where a breach means massive liability, they don’t have the resources to risk breaches in the short term for potentially better software in the long term.

Denkel• 3 months ago

I still need to see a single breach that ends up being a liability for the company.

pllbnk• 3 months ago

It's been a common wisdom now for decades that open source is more secure. Security is just a scapegoat here.

aleph_minus_one• 3 months ago

It's been a common wisdom now for decades that open source is more secure.

This is not true.

The problem rather is that the managers of many companies don't allow their programmers to apply their knowledge about security - the programmers should rather weed out new features.

MerrimanInd• 3 months ago

I wonder if we could find a way to donate unused tokens or even local compute resources to open-source projects we support. Especially for security auditing where it could probably be somewhat more asynchronous and disconnected than the open-source developers' personal tool choices.

throwuxiytayq• 3 months ago

“Unused tokens” are a weird, fragile concept that I wouldn’t want to build upon. You can just donate money, you know. That’s what money’s for - it’s the universal exchange thingy.

jeroenhd2• 3 months ago

"unused tokens" are the force driving token cost down. If everyone used all of the tokens they thought they were paying for, prices would explode. People with subscriptions that don't get out everything they can are subsidizing the system.

There are ways to use LLM service providers that leave no tokens unused, by just billing per token. Unsurprisingly, this quickly becomes much more expensive than subscriptions.

haritha-j• 3 months ago

I like that LLMs have basically switched to the weapons business model. Buy our LLM so that the bad guy we'll sell our LLM to doesnt destroy your code. As a bonus, we'll give you a little head start. And if you're a small company that can't afford our LLM, too bad.

alienbaby2• 3 months ago

This feels like it misses the point. Tokens = money. The real differentiator is time and effort.

Llm's will find your issues faster, but not necessarily more accurately than a domain expert. But experts cost money and effort takes longer to apply.

Are llm's going to reduce everyone's wages because they are cheap labour?

Gormo10• 3 months ago

> If Mythos continues to find exploits so long as you keep throwing money at it, security is reduced to a brutally simple equation: to harden a system you need to spend more tokens discovering exploits than attackers will spend exploiting them.

But this has always been the reality of security: it's always been fundamentally an economic question about which party has stronger incentives and greater resources than the other. The increasing sophistication of AI is available to both parties equally, so I don't see how AI in itself fundamentally changes the equation.

woodruffw• 3 months ago

Today, it's easy to (publicly) evaluate the ability of LLMs to find bugs in open source codebases, because you don't need to ask permission. But this doesn't actually tell us the negative statement, which is that an LLM won't just as effectively find bugs in closed codebases, including through black-box testing, reverse engineering, etc.

If the null hypothesis is that LLMs are good at finding bugs, full stop, then it's unclear to me that going closed actually does much to stop your adversary (particularly as a service operator).

zb33• 3 months ago

This has to be the most bullshit reason I've seen.. if AI can be pointed and find vulnerabilities then do it yourself before publishing the code.

dspillett5• 3 months ago

if AI can be pointed and find vulnerabilities then do it yourself before publishing the code

At your cost.

Every time you push. (or if not that, at least every time there is a new version that you call a release)

Including every time a dependency updates, unless you pin specific versions.

I assume (caveat: I've not looked into the costs) many projects can't justify that.

Though I don't disagree with you that this looks like a commercial decision with “LLM based bug finders could find all our bad code” as an excuse. The lack of confidence in their own code while open does not instil confidence that it'll be secure enough to trust now closed.

zb33• 3 months ago

For-profit companies using open-source software should bear that cost - that's my position.

I believe than N companies using an open source project and contributing back would make this burden smaller than one company using the same closed-source project.

bearsyankees• 3 months ago

Think this is a bad, bad move...

https://news.ycombinator.com/item?id=47780712

creatonez• 3 months ago

This is some truly exceptionally clownish attention seeking nonsense. The rationale here is complete nonsense, they just wanted to put "because AI" after announcing their completely self-serving decision. If AI cyber offense is such a concern, recognize your role as a company handling truckloads of highly sensitive information and actually fix your security culture instead of just obscuring it.

jhatemyjob• 3 months ago

I mean it's not complete nonsense, but yeah, doing it for security reasons sounds like BS. I actually thought this was going to be about how AI makes it super easy for someone to steal all their code and fold it into their own competing project. I've seen a few open source projects get sideswiped by this, AI is pretty good at copying code (and obfuscating the fact that it was copied). I suspect that's the real reason but it doesn't sound as good. So they went with this half-truth.

nativeit• 3 months ago

I guess why fix vulnerabilities when you can just obscure them?

asdev• 3 months ago

Who even uses their open source product?

_pdp_• 3 months ago

The real threat is not security but bad actors copying your code and calling it theirs.

IMHO, open source will continue to exist and it will be successful but the existence of AI is deterrent for most. Lets be honest, in recent times the only reason startups went open source first was to build a community and build organic growth engine powered by early adaptors. Now this is no longer viable and in fact it is simply helping competitors. So why do it then?

The only open source that will remain will be the real open source projects that are true to the ethos.

fcarraldo• 3 months ago

The real threat is not security but bad actors copying your code and calling it theirs.

How has this changed?

HyprMusic• 3 months ago

Bad actors can rewrite it with AI and claim ownership of the result.

evanjrowley2• 3 months ago

I agree with you that AI's disruption of attribution is a much bigger problem, but it's also worth recognizing that not everyone has this same motivation. It mostly affects copyleft open source licenses.

Attribution isn't required for permissive many open source licenses. Dependencies with those licenses will oftentimes end up inside closed source software. Even if there isn't FOSS in the closed-source software, basically everyone's threat model includes (or should include) "OpenSSL CVE". On that basis, I doubt Cal is accomplishing as much as they hope to by going closed source.

fedeb952• 3 months ago

If you copy the code infringing licenses, yes, it will be harder to legally sort things out.

Otherwise, copying code and improving it with AI or with humans is the same, as long as the product improves.

I doubt that many semi-automatic AI copies can really improve a product more than the original team, for really valid products.

AI will be a filter of bad quality.

Gormo10• 3 months ago

Now this is no longer viable and in fact it is simply helping competitors. So why do it then?
The only open source that will remain will be the real open source projects that are true to the ethos.

Well, the second point seems like the answer to the previous question. The original model of monetizing FOSS -- support contracts, risk indemnification, etc., for an otherwise functionally equivalent product -- will still remain viable.

But those trying to thread the needle of trying to use open-source to push a "freemium" model are now going to hit a wall: if you were withholding features from the community version in order to paywall them for the premium version, and now AI has made it easy for users to add those features back without paying you, then you're screwed. The people who were going to use AI to bypass your paywall are still not going to be your customers, but you no longer have the differentiator to put you ahead of the competitors that were already closed-source to begin with for the customers who are willing to pay.

I originally deployed Cal.com because I wanted an open-source solution. But now, why would I choose a closed-source Cal.com over Calendly? If I'm forced to go SaaS, I'll probably go with the more widely used Calendly. If I'm not forced to go SaaS, I'll forego them both, and go back to something like EasyAppointments, knowing that I won't be in conflict with the authors if I choose to add my own "premium" features to it, whether with AI or by hand. All Cal.com did here was remove any chance that I'd ever pay them anything.

popalchemist3• 3 months ago

Seems like it's just being used as a convenient pretense to back out of open-source.

ezekg4• 3 months ago

I mean, they were a COSS startup using the AGPLv3, so checks out. :)

liamgm• 3 months ago

Changed the license of the foss version cal.diy to MIT . Grace in disguise , now enterprise user can host cal.diy without worries of viral licensing .

barelysapient• 3 months ago

I hate how this sounds...but this reads to me "we lack the confidence in our code security so we're closing the source code to conceal vulnerabilities which may exist."

iancarroll• 3 months ago

I know plenty of security researchers who exclusively use Claude Code and other tools for blackbox testing against sites they don’t have the source code for. It seems like shutting down the entire product is the only safe decision here!

adamtaylor_13• 3 months ago

Could you not simply point AI at your open source codebase and use it to red-team your own codebase?

This post's argument seems circular to me.

hmokiguess• 3 months ago

Risk tolerance and emotional capacity differs from one individual to another, while I may disagree with the decision I am able to respect the decision.

That said, I think it’s important to try and recognize where things are from multiple angles rather than bucket things from your filter bubble alone, fear sells and we need to stop buying into it.

tudorg• 3 months ago

It's funny that this news showed up just as we (Xata) have gone the other direction, citing also changes due to AI: https://xata.io/blog/open-source-postgres-branching-copy-on-...

We did consider arguments in both directions (e.g. easier to recreate the code, agents can understand better how it works), but I honestly think the security argument goes for open source: the OSS projects will get more scrutiny faster, which means bugs won't linger around.

Time will tell, I am in the open source camp, though.

microflash• 3 months ago

Just wanted to appreciate the open-source work by Xata. I’ve been eyeing pgroll [1] for schema migrations after Liquibase license shenanigans (the only barrier for me is json-based migration instead of sql-based migrations)

[1] https://github.com/xataio/pgroll

tokai• 3 months ago

Security through obscurity has been known to be a faulty approach for nearly 200 years. Yet here we are.

righthand2• 3 months ago

This is the future now that AI is here. Publishing is going to be dead, look at the tea leaves, how many engineers are claiming they don’t use package managers anymore and just generate dependencies? 5 years and no one will be making an argument for open source or blogging.

evanjrowley2• 3 months ago

Juxtapose this with the fact that many HNers will decry strong copyleft FOSS licenses as not being truly "open source" - the reality is that closed source software is still full of open-source non-copyleft dependencies. Unless you're rolling your own encryption and TCP stack, being closed source will not be the easy solution that many imagine it to be.

NetMageSCW5• 3 months ago

Where is the Windows TCP stack source?

dec0dedab0de• 3 months ago

This seems dishonest, like someone is forcing the decision for other reasons, and they're using security and AI as a distraction.

poisonborz• 3 months ago

AI sure is useful as a scapegoat for any negative PR inducing moves.

xnx• 3 months ago

Saaspocalypse is coming for cal.com

fontain• 3 months ago

Monumentally dumb given their codebase is already public and the type of security issues that exist in software are usually found in the oldest code. But also, and more importantly, cal.com launched coss.com last year, open source is (ostensibly) their DNA. How could they do a complete 180 on something so fundamental and think that wouldn’t worry customers, much more so than their codebase being public? I cannot even begin to understand this. Surely there must be more to the story?

abound2• 3 months ago

Oh wow the coss.com thing makes this so much worse. Making such an aggressive and public commitment to open source to then turn around and do something like this is a pretty rough look.

t0mas88• 3 months ago

Coss.com reads like a half assed pivot if you look at it with today's news. It's clear cal.com isn't making enough money and going closed source is yet another attempt to fix that.

abound2• 3 months ago

This certainly makes me feel better about the project I started a few months ago to replace my Cal.com instance with a smaller, simpler self-hosted tool

https://git.sr.ht/~bsprague/schedyou

righthand2• 3 months ago

Good for them. I’m sure they saw the writing on the wall when Monday.com was cloned. This is the right move.

analogpixel• 3 months ago

TIL I learned about yet another calendar application I don't need. Someone should setup their openclaw to just write a new todo/calendar app each week; they'll be billionaires by the end of the year.

Tepix2• 3 months ago

Hey cal.com, as a potential customer, you have just lost me. Open source is set to profit from improved transparency in the SSDLC. With closed source, you will have to trust the software vendor instead.

I'm not sure I agree with Drew Breunig, however. The number of bugs isn't infinite. Once we have models that are capable enough and scan the source code with them at regular intervals, the likelihood of remaining bugs that can be exploited goes way down.

post-it• 3 months ago

- You know, Lindsay, as a software engineering consultant, I have advised a number of companies to explore closing their source, where the codebase remains largely unchanged but secure through obscurity.

- Well, did it work for those companies?

- No, it never does. I mean, these companies somehow delude themselves into thinking it might, but... but it might work for us.

codegeek• 3 months ago

I am beyond convinced at this point that you either run an Open Source Project with a small revenue company (single digit millions) or run a software company that does more than 10M ARR at the least and be closed source. I know there are exceptions but most open source Software companies are providing code with heavy restrictions or teaser features and gate keep everything in their "ee/enterprise" version etc.

wqtz• 3 months ago

In my advisory job founders always raise the question about open sourcing within the first hour of meeting me. They think that open sourcing product means transparency and developer trust which helps with early adoption. Every single founder I talked to brings up open source as a market penetration method to drive the initial adoption.

I always say to just stop with the virtue signaling led sales technique.

I despise the "we are like the market leader of our niche but open source" angle. Developer as a buyer and as a community these days in my opinion do not care about open source anymore. There is no long term value to that. The moment a product gets traction the open source elements is a constant mild headache as open source product means that they have no intellectual copyright on the core aspect of the product and it is hard to raise money or sell the company. And whenever a product gets traction they will take any excuse to make it close source again. With an open source product they are just coasting on brand. Regardless of what your personal opinion is, this has been largely true for most for-profit business.

Open source is largely is nothing more then a branding concept for a company who is backed by investors.

wartywhoa234• 3 months ago

Open source is largely is nothing more then a branding concept for a company who is backed by investors.

And a religion that was invented by those who wanted to have all the world's code for free to train AI to code.

dang2• 3 months ago

Related ongoing threads:

Open Source Isn't Dead - https://news.ycombinator.com/item?id=47780712

Cybersecurity looks like proof of work now - https://news.ycombinator.com/item?id=47769089

aizk• 3 months ago

Sounds backwards to me.

notnullorvoid3• 3 months ago

Security through obscurity can be a good security layer, but you need to maintain obscurity. That's a lot harder than Cal.com seems to realize.

For example using something like Next.js means a very large chunk of important obscurity is thrown out the window. The same for any publicly available server/client isomorphic framework.

com2kid• 3 months ago

Proposition 1: The majority of a code in a modern app is from shared libraries

Proposition 2: The most popular shared libraries are going to be quickly torn apart by LLM security tools to find vulnerabilities

Proposition 3: After a brief period of mass vulnerability discovery, the overall quality of shared libraries will dramatically increased.

Conclusion: After the initial wave of vulnerabilities has passed, the main threat to open source code bases is in their own comparatively small amount of code.

behringer2• 3 months ago

Security via obscurity and you get to blame AI too! What a win for their marketing team.

axeldunkel• 3 months ago

Sounds like "security by obscurity" to me - if you think AI is so good at finding security issues - it will find them in compiled code as well. Why not using it in your favor and let it search for bugs you'd otherwise not find?

traderj0e2• 3 months ago

You can lock down the source and also use AI to look for bugs in it. It does take significantly more time and money for AI to find bugs in compiled code.

That said, I agree with another commenter that this seems like more of a business decision than a security one.

mellosouls• 3 months ago

The founder proclaimed "Open Source is Dead" in the original tweet.

I thought this was grandiose and projecting their own weakness onto others, an extremely unappealing marketing position that may get clicks in the short term but will undermine trust beyond that.

lrvick4• 3 months ago

There are endless closed calendar options. Cal.com being FOSS and not making us feel locked in forever was the only reason we chose it over wasting limited cycles self hosting this at Distrust and Caution.

AI can clone something like cal.com with or without source code access, so in trying to pointlessly defend against AI they are just ruining the trust they built with their customers, which is the one thing AI can never create out of thin air.

We exclusively run our companies with FOSS software we can audit or change at any time because we work in security research so every tool we choose is -our- responsibility.

They ruined their one and only market differentiator.

We will now be swapping to self hosting ASAP and canceling our subscriptions.

Really disappointing.

Meanwhile at Distrust and Caution we will continue to open source every line of code we write, because our goal is building trust with our customers and users.

egorfine2• 3 months ago

What's preventing cal.com to run the AI researcher over their own codebase and find their vulnerabilities before anyone else and patch them all by tomorrow morning?

That's right. Nothing.

wartywhoa234• 3 months ago

Unwilling to pay AI tax, maybe?

egorfine2• 3 months ago

No worries, someone else will do that for them. Just like they explained.

And given that they will not rewrite the whole codebase in the next few days it means that security vulnerabilities are still there to be discovered by someone willing to pay the AI tax.

ryanleesipes4• 3 months ago

Head of Thunderbird project here.

Our scheduling tool, Thunderbird Appointment, will always be open source.

Repo here: https:// github.com/thunderbird/appointment

Come talk to us and build with us. We'll help you replace Cal.com

ezekg4• 3 months ago

"Thunderbird, the open source Cal.com"

ryanleesipes4• 3 months ago

Love it!

raybb• 3 months ago

You should add some screenshots to the readme or somewhere before a sign in screen.

Sounds like a great tool though. How much is the hosted version?

bean4692• 3 months ago

There are screenshots in the link[1] provided in the README.md

1. https://stage.appointment.day

m3nu• 3 months ago

A Docker image would be good too.

ryanleesipes4• 3 months ago

Yes, we should. Will do that today

devmount• 3 months ago

We added some screenshots to the repository now. Thanks so much for the suggestion!

sashimimono2• 3 months ago

I would like to, but... have you tried to use thunderbird on an "older" linux laptop nowadays? Even with 8 gigs of ram, and a non-fancy memory-saving windowmanager, thunderbird is almost unusable now (large imap mbox), firefox even worse. I don't see why all that additional bloat is needed, or wanted. Please keep in mind, that a lot(!) of people are not able to afford buying new hardware every now and then anymore. And this is getting worse. First the pandemic, then the war in Ukraine, now the war in Middle-East. Shortage of ram/storage/everything (thanks ai) and massivly increased costs of energy, housing, food, insurance, everything. And in the years to come, I am afraid, that will be getting worse. Please think about it, when adding the "next cool feature", 'Keep the internet affordable'. --thunderbird user since 1.0

hedora• 3 months ago

Regarding FF: Something is probably wrong with your install, or the websites you have open.

As a datapoint: FF + Chrome with lots of stuff open uses 2.6GB on my machine. With XFCE and a GB of other apps, it’s using about 4GB. 15 year old machine. Perf is fine.

carlosjobim• 3 months ago

Why don't you use an older version?

winrid• 3 months ago

Come talk to us and build with us

do we need an appointment :)

bean4692• 3 months ago

Thanks, looks like a great alternative

jen729w2• 3 months ago

1. Goes to site. Clicks appointment.tb.pro link in sidebar.

2. Gives email address.

3. Is told to join the waitlist.

4. Blocks email address given at 2.

Hardly a terrific experience.

ryanleesipes4• 3 months ago

Yeah. We need to create a docker container and make it easy to deploy for folks. We're not ready with the hosted option at the moment.

kewisch• 3 months ago

I'm curious how it blocked your email, could you share more details on what message you got? Feel free to reach out to me outside of HN.

constantlm• 3 months ago

Security through obscurity isn't a great strategy.

jemiluv8• 3 months ago

I have fond memories of this project. Contributing to it really helped me ramp up my dev skills and was effectively my introduction to monorepo’s in JavaScript. It was the kind of codebase I couldn’t get my hands on while working in my part of the world. Good luck going closed source.

smetannik• 3 months ago

This sounds more like a good excuse to go closed source. I feel that real reason might be revenue-related.

CamperBob2• 3 months ago

Today, AI can be pointed at an open source codebase and systematically scan it for vulnerabilities.

AI also goes a long way towards erasing the distinction between source code and executable code. The disassembly skill of a good LLM is nothing short of jaw-dropping.

So going closed-source may be safer for SaaS, but closing the source won't save a codebase from being exploited if the binaries are still accessible to the public. In that sense, instead of dooming SaaS as many people have suggested AI will do, it may instead be a boon.

alance• 3 months ago

I only found cal.com in the first place because I searched for an open source calendly alternative.

sadeshmukh• 3 months ago

Security by obscurity has never been real.

amazingamazing• 3 months ago

this is a big nothing. they relicensed the previous cal.com as cal.diy (MIT by the way, instead AGPL or something else) and effectively forked their own product into the "new" cal.com. anyone who cares would just use cal.diy as they were prior to this announcement with cal.com

theturtletalks2• 3 months ago

We’d hope but they could neuter Cal.diy over time. From their chart between the differences of cal.diy and cal.com, teams are not supported. I’m self hosting Cal.com and I think I do have access to teams as of right now.

NetMageSCW5• 3 months ago

That’s incorrect - they explained that cal.diy is missing a lot of recent changes.

neuroelectron• 3 months ago

Chatgpt, write me a reason to make more money as a tech ceo.

Charge for api access, take a cut of the extensions economy.

How do i do that, I'm open source?

theturtletalks2• 3 months ago

Enshittification has come for VC backed open-source. AI has deemed commercial open source obsolete especially when users can point Calude Code to calcom on GitHub and ask it to make them scheduling features directly into their product. That’s what spooked Cal.

femto• 3 months ago

Will it make any difference to security? LLMs are excellent pattern matchers. The source is a sequence of tokens, the binary is a sequence of tokens. Whats the difference to an LLM?

a-fadil• 3 months ago

Open source means living under constant scrutiny. AI just made that scrutiny cheaper and faster. I feel this every day maintaining an open source project. The temptation to close the source is real but let’s not forget that open source is what raised the bar for software quality in the first place.

dnnddidiej2• 3 months ago

Not really. Open source just means distributing the source. Either via CD or some internet based protocol.

Maybe you are referring to the whole Github thing.

mynameisvlad• 3 months ago

I mean, by definition, open source means that the source code is available and therefore _open_ to scrutiny. Regardless of how it is distributed.

wartywhoa234• 3 months ago

Open source is what made this AI shitshow possible in the first place.

ernsheong• 3 months ago

Well let’s just finish and CLOSE them off. Delete all your subscriptions, boys.

theahura2• 3 months ago

I'm sorta suspicious. I don’t really think this is why they are moving to closed source. It’s true that there is more security risk, but that actually justifies being open source, because open source tooling can spend more tokens hardening itself against security vulns than closed source tooling (at least, that’s the theory). My strong hunch is they are moving to closed source because it is now trivial to copy a product with AI clean rooms. Which, tbf, is a totally valid reason to move closed source. But I'd want to see more adoption of something like the Ship of Theseus license (https://github.com/tilework-tech/nori-skillsets/pull/465/cha...) before giving up on open source entirely

sgbeal2• 3 months ago

My strong hunch is they are moving to closed source because it is now trivial to copy a product with AI clean rooms. Which, tbf, is a totally valid reason to move closed source.

Since such "clean room" implementations ostensibly do not see the source, it's arguably irrelevant whether such sources are open are not. Such implementations will happen regardless of whether the sources they're reimplementing are opened or closed.

ezekg4• 3 months ago

I very much doubt that addendum would hold up to a lawyer.

NetMageSCW5• 3 months ago

because open source tooling can spend more tokens hardening itself against security vulns than closed source tooling (at least, that’s the theory)

Whose theory? That makes no sense at all. The creator can spend the same amount on tokens whether it is closed or open source.

Gormo10• 3 months ago

My strong hunch is they are moving to closed source because it is now trivial to copy a product with AI clean rooms. Which, tbf, is a totally valid reason to move closed source.

The "clean room" part of clean-room reverse engineering implies that there is no exposure to the original copyrighted code on the part of those doing the reimplementation, whether human developers or AI. Traditionally, if you're working of the source code itself, you have one party translate the source code back into a design document, specifying behavior, and then you have another party implement that design spec with original code.

If you already have a running copy of the software to model the behavior off of, then you don't need the original source code in the first place. So going closed source will have zero effect on the capacity of AI tools to be used for clean room reverse engineering: all you need is the runtime.

But I'd want to see more adoption of something like the Ship of Theseus license (https://github.com/tilework-tech/nori-skillsets/pull/465/cha...) before giving up on open source entirely

This license doesn't seem valid: a license can't redefine what qualifies as a derivative work. That's determined by copyright law itself, and if copyright law says that a clean-room reimplementation isn't a derivative work, then it isn't restricted by copyright, so doesn't need a license in the first place.

usernametaken29• 3 months ago

Just a random thought. Up until yesterday this project was open source. The code base won’t be rewritten tomorrow. More likely is that conserved parts of the source code, something like 90% will just remain the same. Particularly the core database schema around users and security are likely to stay the same. Since the old code is already out there what’s stopping me from exploiting the software as it was? This looks an awful lot like marketing to me, and not like real security concerns.

diebillionaires• 3 months ago

Lame. "We don't want AI pointed at our code so we're going closed source". That's hilarious and a cover up.

szszrk• 3 months ago

I think them going closed source is as much related to security and AI, as work from office is related to productivity in large companies.

So not really.

I think they went closed source as there are too many decent clones based off their code and they realized it's eating up their niche.

huslage• 3 months ago

Cal.com is failing. This is a rugpull with an AI excuse.

dhruv3006• 3 months ago

I guess this is an AI excuse again.

pcblues3• 3 months ago

Security by obscurity. Good luck. So novice.

opem2• 3 months ago

When we started Cal.com, we believed deeply in open source.

No you certainly didn't, otherwise you shouldn't have come up with such a meaningless excuse!

sreekanth850• 3 months ago

This has one of the most shittiest codebase out of all. Not surprised by this move.

thegdsks• 3 months ago

This is why CC0 and MIT matter for projects people depend on. Once you build on something with a restrictive license this is always a risk.

quotemstr2• 3 months ago

LOL. Every generation has to learn anew that security through obscurity is no security at all.

sgbeal2• 3 months ago

Today, we are making the very difficult decision to move to closed source, and there’s one simple reason: security.

(Enter name of large software vendor here) has long-since proven that security through obscurity is not a real thing.

kartika363632• 3 months ago

thats like the funniest excuse to cash out on people's open source contributions

whatiathisnon• 3 months ago

This is completely stupid and ridiculous. Why not just use AI to patch your software? Its just as effortful as someone finding and exploiting a vuln on your system.

What's worse is your choosing to keep it buggy behind closed doors so no one can see the bugs. That's 100% the wrong approach.

lapinovski• 3 months ago

Cal.com was open source?

mastermage• 3 months ago

Security through obscurity has always worked out so well.

abusedmedia• 3 months ago

The article is leaking from all sides. As a wannabe hacker would find a hole in a public repo, what can the repo owner do, who knows every detail of the project and has a high interest in it, also economically?

fedeb952• 3 months ago

security by obscurity doesn't work.

ButlerianJihad3• 3 months ago

security by obscurity doesn't work.

That is not true.

https://en.wikipedia.org/wiki/Security_through_obscurity

Security through obscurity doesn't work in isolation. It doesn't work as the only solution. It is discouraged, because it can be a panacea.

But it also doesn't hurt in many instances. Holding back your source code can be a strategic advantage. It does mean that adversaries can't directly read it (nor can your friends or allies!)

Having a proprietary protocol or file format, this is also "security through obscurity" and it may slow down or hinder an attacker. Obscurity may be part of a "defense in depth" strategy that includes robust and valid methods as well.

But it is harmful to baldly claim that "it doesn't work".

eloisant6• 3 months ago

This reads like a post from 1995.

"But if everyone can read the source code, they'll be able to find vulnerabilities more easily!"

No. Security by obscurity has proven wrong.

Nukahaha• 3 months ago

Isn't the joke that everything is open source if you can read assembly? Pretty sure someone is working on an AI that reads assembly... Not sure hiding the codebase away is a viable solution!

ButlerianJihad3• 3 months ago

That may be true for software that you download and install as an app, but for SaaS, there is no need to expose the code to anyone at all. Only your API endpoints are available. You can try and "black box reverse engineer" through the client code and its API calls, but that's not the same as having the server code in hand to pick apart.

aswerty• 3 months ago

Surely the argument is just to have an LLM stressing for vulnerabilities during the build pipeline before merging to main? Resulting in better security from LLMs.

One must assume this was a direction they wanted to move towards and this is the justification they thought would be most palatable.

Tepix2• 3 months ago

The AI companies profit hugely from open source. In fact, without open source, their most significant financial success (coding assistants) wouldn't exist.

They should provide free continued git commit security analysis for open source projects. That would increase the quality of open source projects and would inspire more projects to go open source, which is also a win for the AI companies.

alienbaby2• 3 months ago

This was my thought too. Your tool is great at finding vulnerabilities, and we want software to be secure for everyone, secure code should not be out of reach to those who can't afford it.

Scan everyone's code, for free. Make all code as secure as an llm can make it as a baseline.

ltbarcly32• 3 months ago

Let me share the press release template for 2026:

Hi {audience},

It is with a heavy heart that I have to announce that {thing we were going to do anyway} is necessary due to AI. AI has changed the industry and we are powerless to do anything other than {unpopular decision we were going to do regardless}.

swordsith• 3 months ago

Something about a scheduling/productivity app (one of the most common vibe-coded projects people make) being the subject of this is funny to me. I wonder how many tokens have been wasted making apps like this, let alone time.

Hendrikto• 3 months ago

Today, AI can be pointed at an open source codebase and systematically scan it for vulnerabilities.

So do that and fix your bugs. This post makes no sense.

robinhood• 3 months ago

Very weak argument. You could have had the same speech before AI.

I would rather say that the core product is not strong and differentiated enough to resist this new age of coding, and it's an attempt to protect revenues.

m11a• 3 months ago

I'm not sure security through obscurity is a great practice?

Not to mention, I presume the core bits of Cal.com's source code are already in place and aren't going to change significantly?

Like, this feels like a business decision and not a security decision

james-clef• 3 months ago

I'm all for FOSS as well, but not sure I would have open sourced the commercial offering to begin with. Love the idea though, it's so bold.

rbbydotdev• 3 months ago

I honestly was surprised with the response I got, for what was basically a Sunday hack project: https://github.com/rbbydotdev/someday

I think people really like how it's free (runs on google app scripts) and open source.

I've personally moved onto google's free gmail calendar scheduling tool, which strangely took pretty long to come to market. Calendly stretches back to ... 2013?

Scheduling, oddly feels a little niche (maybe less so today?), when it shouldn't be. Maybe there some more opportunity there.

8260337551• 3 months ago

Judging by the CEOs picture on LinkedIn, he's full of himself.

Gormo10• 3 months ago

EasyAppointments (https://github.com/alextselegidis/easyappointments) is still FOSS. We managed our team calendars on it at a previous company, but I rolled out Cal.com due to more apparent support and sophistication at my current company. Turns out most of that sophistication turned out to be bloat: we saw successive version releases add features we didn't care about while increasingly putting previously open features, like team calendars, behind a paywall.

This move by Cal.com seems to be transparently an attempt to maintain that paywall against users who'd otherwise just use LLMs to remove it. I guess it's back to EasyAppointments, which still seems to work just fine.

zerotoship• 3 months ago

users can just point Claude Code at cal on GitHub and ask it to build xyz features directly into their own product .. and most of them won't bother following the license. it's happening with so many projects in open source

Cal.com is going closed source

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