In this episode, Calle introduces Numopay, an open-source Bitcoin payment terminal that enables tap-to-pay experiences similar to fiat systems. We explore its technical foundations, privacy features, future developments, and the broader ecosystem of Bitcoin payment solutions.
Takeaways:
🔸Numopay’s open-source payment terminal
🔸Tap to pay Bitcoin using NFC and QR codes
🔸Privacy features of Cashu’s eCash system
🔸Auto withdrawal to Lightning addresses for security
🔸Future developments including BIP321 and integrations
Timestamps:
(00:00) – Intro
(00:38) – What is Numopay?
(03:29) – Numopay’s UX, tap-to-pay & offline NFC payments
(08:30) – Unified QR codes (BIP 321)
(10:21) – Auto withdrawal to lightning address
(13:51) – Evolution of Bitcoin payment infrastructure
(20:08) – What is the future of Numopay?
(22:47) – The Cashu ecosystem in 2026
(27:34) – Where should people be using Cashu systems today?
(30:48) – Privacy in Bitcoin
(34:34) – Future of Bitcoin development with AI
(42:06) – Closing thoughts
Links:
Stephan Livera links:
- Follow me on X: @stephanlivera
- Subscribe to the podcast
- Subscribe to Substack
Transcript:
Stephan Livera (00:00)
Hi everyone and welcome back to Stephan Livera podcast. Today we’re rejoined by our friend Calle. Calle is known for a bunch of things, probably mostly known for his work on Cashew, but also working on Bit Chat. And I know Calle recently put out this new thing, it’s called Numopay. And I wanted to chat about that because I thought it’s fascinating. had a quick chance to play around with it. First off, welcome back to the show Calle.
Calle (00:22)
Hey, thanks for having me, Stephan.
Stephan Livera (00:25)
So let’s just start with the obvious, like why, why NUMO Pay? What’s the story behind it?
Calle (00:30)
So NumuPay is a payment terminal that we’ve been working on.
for quite a while in the background in stealth mode in the last couple of months or so. And it’s a payment terminal, open source payment terminal that anyone can download and install on their Android phone. And you can use it to receive Bitcoin in your brick and mortar store basically. So you can run it on any Android phone out there or on a typical POS device, these open source, open hardware POS devices that are basically everywhere. And the differentiating factor
the reason why we’ve been working on Numopay was because we wanted to see tap to pay in Bitcoin. We’re all kind of jealous about the fiat payment experience with, you tap your phone and the payment goes through instantly and takes maybe a second or two. And with Bitcoin, we kind of achieved good UX over the last couple of years, but we stagnated a little bit in terms of, you know, we all converge to QR codes and scanning, showing QR codes. And that is pretty common in
many parts of the world, but all across the world people are using more more tap to pay using their credit cards and with Numopay that’s our approach to bring that kind of experience into the Bitcoin world. And how we were able to achieve this is by leveraging the features or the properties of Cashew itself. So Cashew is a Charmin eCash system that is built on top of Bitcoin. It kind of gives you a private, instant, cheap way to make Bitcoin payments.
using payment rails that are built on top of Bitcoin. It is a custodial system. That means you have to trust a mint operator with the Bitcoin when you deposit Bitcoin and receive an E-cash for it. The E-cash itself is highly privacy preserving and it’s a…
It’s a bear asset that you store on the device that you hold it on. So for example, that could be your phone. And because the eCache is stored on the payer’s phone, we can now build these experiences where if you…
tap that phone onto a NUMO terminal, the eCash can travel from one phone to another using the NFC chip. And that is exactly kind of the ingredients that you need in order to build this tap to pay UX flow for Bitcoin. But now with the twist that we have an open protocol that supports this, it can be built on top of basically anything. Obviously we choose to build on Bitcoin and it is highly privacy preserving. That means kind of
⁓ we have this rare occurrence where UX and privacy are perfectly aligned where the best privacy option basically also can give you the best UX option and I think that’s not typical. Usually you kind of have to make a trade-off between the two but not in the case of eCash.
Stephan Livera (03:13)
Excellent and so yeah, there’s a lot in there We’re gonna dive into some of those things But I guess we’ll talk through what it looks like now. I had I just played around with it on my phone I found it very simple basically I mean I could probably pull it up just on the screen But basically the gist of it is you download you install this app
And it allows you to very quickly show a QR. That QR can show a cashew, basically like a terminal. So listeners can see if you’re watching on the video. basically, looks like just think about you’re at the farmer’s market, you’re the guy selling meat or whatever. You can literally type in, I want to receive whatever, 1,100 cents or whatever it is, and it shows a QR. I guess, to your point, Callei,
The difference is here you can also not just scan to pay like we’re used to in Bitcoin with lightning, but you can also tap to pay. So just elaborate a little bit on what that looks like for listeners.
Calle (04:09)
Yeah, so the setup is extremely easy. You download the app, you install it and during the setup process, that’s it. You don’t need any additional software. You don’t need to run a server somewhere in the cloud. You don’t need to get a BPS or anything. So that was very important for us that the setup is super seamless. The only thing that you need to decide at the beginning and we help you with that is to choose a mint. That means where the Bitcoin is going to flow into and then you can withdraw it from there. So once you’ve done that and it takes you like five seconds to set it up,
You’re greeted with this, you you were showing it into the camera. Basically a super simple checkout POS flow where you enter the amount. And ⁓ as you said, you’re then, you know, once you enter the amount, you see a QR code and there are two QR codes there. First of all, there is a cashier QR code, which is a cashier payment request. And you can also flip on lightning. And we do both. Basically it supports.
cashier payments directly or lightning payments for everyone else who doesn’t have a cashier wallet yet. So it presents you both and you can scan those with a camera. But on top of that, there’s also the tab to pay experience that we’ve implemented for both cashier and lightning. So that means in the case of cashier, if you have a cashier wallet and your customer has a cashier wallet,
they instead of scanning the QR code, they can just tap their phone onto your phone and their cash or wallet will automatically detect that this is a cash payment request and then select some eCash from their device and send it over via NFC to the receiver’s POS device. So that is a purely offline payment. Your customer’s phone doesn’t really doesn’t even need to be online for it. As long as there is some eCash in the phone, the eCash will travel directly from one phone to the other.
without even touching the internet and that has a couple of very cool features or you know gives ⁓ first of all it is instant so you don’t have this delay that you need to connect to the internet second of all it it is
independent of internet connectivity, so it always works. As long as the POS device, the receiver, has internet, the customer will always be able to pay and that is also the case for credit card tap-to-paste, by the way. And third of all, because you don’t touch the internet and coupled with the incredible privacy that eCash already gives you,
And you don’t even touch the internet that means you have kind of like twice the amount of privacy even if you want Because your device doesn’t even register, you know on any server that it’s making this payment right now the only thing that the mint sees is that the receiver POS has done a swap so that E-cash came in and E-cash went out kind of like the receiver takes the E-cash swaps it with the mint for new E-cash and that’s it the mint doesn’t see Whether there was a sale who paid for it
and like any other personal information of the pairs and so I was saying there’s this ecash part there’s also the lightning part
So for anyone with just a Lightning wallet, they can still pay at any NUMO terminal because we create invoices automatically. there’s also a kind of Phoenix is the only wallet that supports this. There’s also a push to support Tap to pay with Lightning. So what your terminal does is basically it offers the Lightning invoice via NFC. So any device that can read NFC from the device and that could be a
Phoenix wallet for example, can read that Bolt 11 invoice and then make a payment over the internet to the terminal using Lightning. Unfortunately, so far I’m only aware of Phoenix really supporting this and
there’s definitely more interest in the ecosystem. This is also our goal to increase interest in tap to pay and hope that more wallets will follow up and follow soon and integrate tap to pay into their wallets as well, especially if it’s just Lightning Wallets. Obviously we have, I think…
eight or so cash dollars that support this out of the box right away. So we hope that we’ll see also more penetration and lightning for this kind of payment experience and we’re also pushing for the adoption of a BIP. That’s BIP 321. I think at least that’s unified QR codes. Someone needs to correct me on the BIP number but unified QR codes or unified payment
humanified payment addresses are a way for a Bitcoin wallet to offer you, for example, if you want to pay to it, an on-chain address, a Bolt 11 address, and also now a cash-through payment request all in a single QR code, all in one.
payload and so for QR codes this was kind of a problem because the QR code used to get larger and larger which makes scanning harder and harder but for NFC this is really ideal because for NFC you don’t really care about the payload size that much it will it will work so you just tap to tap your phone to the POS device and it could receive like this beep
3-2-1 unified QR code payload and then the wallet itself could decide I’m an on-chain wallet so I’ll pay an on-chain, I’m a lightning wallet so I’ll pay with lightning or I’m a cash wallet so I’ll pay with cashew. So we’re trying to kind of raise the bar in the expectation of what good UX should look like and hope that everyone else will also see this and we’ll see more more adoption of tap to pay in bitcoin.
Stephan Livera (09:31)
Yeah, and I just quickly checked just for listeners. It is bit 321 came out in November 2024 looks like it’s by Matt Corrella relating to the URI scheme and it’s kind of like an advanced or maybe an update or kind of a Upgrade to bit 21 which some listeners may know
historically, which was similarly about unified QR codes. The other big thing that we should mention for listeners, Carly, if you can explain this idea of auto withdrawing to a lightning address, because I think that’s also really handy, because a common fear people may have is, what if I get rugged by this mint? Well, now it’s going to be a different context, or it’s going to work in a different way. Can you explain the rationale on how this works in Numopay?
Calle (09:59)
Mm-hmm.
Yeah, absolutely. So the eCache that you receive as a POS device, as a NUMO POS lives on the device itself. And as we said before, Cashew is a custodial system. So as a user of Cashew, you want to limit your exposure risk to this custodial risk of the Mint operator.
Obviously, the mint itself could be operated by, let’s say, the restaurant owner themselves. So you don’t really have this trust issue there because the payment infrastructure itself could be run by the same people that also use the POS. But in general, this will not be true. There will be many more people who just want to use the POS and fewer people who will run the infrastructure. Right. So there is this risk scenario. And again, as I said, the eCash itself lives on the device. So that also means, you know, although you have a seed phrase and you can back up,
everything. You eventually want to withdraw the funds from the POS to some other centralized place where, for example, you have a restaurant and you have a single big wallet where all the payments should flow in. So you want to handle ⁓
you know, your 10 different POS devices, should all withdraw to the same address. That’s kind of the goal. So for this, we have built in the auto withdrawal with Lightning Address. And what this looks like is very simple. When you set up the wallet, you can go into the settings and you say, enable auto withdrawal, and then you can set a threshold, an amount threshold. For example, it could be 50,000 Satoshis and enter a Lightning Address from your non-custodial Lightning node or any other wallet that provides
lightning address and with that you basically have everything now you can give this POS to your let’s say your workforce and your you know people working in your store for example and they could collect payments for all the things that they sell over the during the day and as soon as the wallet reaches that threshold that you’ve set so the balance of the wallet the POS
reaches, let’s say, 50,000 SATs, it will automatically execute a withdrawal to the lightning address that you’ve set so that the exposure risk per device can be perfectly controlled and kept in a safe range, basically. So that way you can make hundreds of thousands of SATs per day without risking too much to either the individual POS devices being lost or being stolen or something like that, or the Mint operator who could run
you anytime by turning off the mid.
Stephan Livera (12:39)
Yeah, it’s fascinating and it’s just really interesting to see how quickly these ideas are kind of all evolving now. If I think back to earlier years, in order to do this, people had to use BTC pay server and set it all up that way and have quite an involved setup. Or maybe they had just one guy with an app kind of thing. But then when you go to the shop, that guy has to be there and know how to use it, otherwise you can’t pay. Whereas now, it’s like there are all these ways that people can just have different apps.
and
it can just be auto withdrawn, let’s say, to the owners, the merchants, lightning address, or even if he needs it, let’s say he’s a restaurant owner, he needs to send it to his lightning address that’s on an exchange because he has to sell some for fear. Like it can just be kind of automatically, programmatically done. And so that’s like, it’s just enabling all these new things that allow, obviously, people to use Bitcoin peer to peer. So I think it’s a really fascinating and a really, just kind of an interesting evolution that we’re seeing. Now, of course, I’m still a founder
I’m not saying it’s obviated, but it’s just there are lots of different options now aren’t
Calle (13:40)
No, that’s the most important thing. And it’s good that we have a diversity of options. There will be a solution for every skill level, knowledge level, how deep you are already in the tech, obviously. But the biggest blocking factor for Bitcoin today, I think, is not kind of the existence of the tech. It’s more the UX side and kind of convincing people to stay on board. And I’ve…
noticed or experienced this multiple times myself that I go into a store and as you said there’s like there’s the Bitcoin Bitcoin enthusiast owner of the store who set up a POS device like
months ago and then as other workers join or know another cashier works at the counter today and they might not know how to use bitcoin and so on that day you cannot pay with bitcoin but you have to come back when the owner is back in the store then you can pay with bitcoin like i’ve experienced exactly this this scenario many times before so this shows you what the real problem is it’s not
that Bitcoin is off on every Thursday so you can’t pay with Bitcoin anymore is because the workers themselves haven’t learned how to use the device, although it could be very easy or someone could show them. So we just wanna lower the bar that makes Bitcoin useful for people. And in Fiat, and you can see how…
Much work has gone into making sure that Fiat is as seamless and simple as possible. So this is what credit card experiences today mimic. It’s basically, you know, no thinking. just take out your phone. In most phones, you don’t even need to unlock your phone anymore to pay. You just hold it to the device and it’s done. You don’t need to use your fingerprint or anything. They have like thresholds for small payments where you don’t even need to confirm anything. So, and obviously the POS market for Fiat is well,
established and has lots of different options for people to use and in Bitcoin we haven’t seen that much of a push in that realm with super simple UX yet. So most of the solutions either, you know…
require you to understand how Bitcoin works, which is a big problem for all these people who are not Bitcoiners but are supposed to use Bitcoin in the store when they work in there, or set and run and manage your own infrastructure, which is something that I can do, no problem, but I know that 98 % of people won’t be able to achieve that kind of knowledge because they want to focus on something else. They want to run a business. They don’t want to take care of the POS infrastructure to actually
do their business. I think as a developer community in Bitcoin we need to be much more thoughtful about what you know where our users are and who we want to to actually use our software. If we just built
software for each other, for all the nerds and all the people who really deep into Bitcoin, that will just limit the way that Bitcoin can grow, whereas other payment rails, especially fiat and stablecoins, are really pushing super hard to make their experience as seamless and intuitive and simple as possible.
Stephan Livera (16:52)
there has been a massive investment in making these things as slick as possible because hey, they wanna make sure they can take payment in a slick way. And of course it’s like the Fiat payment rails. What we’re starting to see in a lot of places now and especially kind of post or the lockdown era, we were starting to see when you go to a restaurant, you scan the QR to see the menu. And nowadays it’s quite common. I mean, even for me, I live in Dubai, I live in UAE. We go to restaurants, oftentimes when you go to pay, they will literally be like, oh, hey, you scan the QR on your table and you pay through that.
And again, it’s a fiat payment and it might be like Google Pay or something like this or typing in your credit card details. But that’s the direction things are going. And so if we can’t get Bitcoin and Lightning payments built in to that, it’s just gonna be a very difficult uphill battle.
Calle (17:39)
Yeah, it’s getting harder and harder to catch up, which is not the situation that we want to be in. you know, the…
Bitcoin gave us the possibility to build payment systems outside of this fiat system, where you have huge companies pushing for adoption and they have been lagging behind for years before. If you think back 10 years or so, fiat payments still sucked on the internet. There was kind of only PayPal and Google Pay, Apple Pay, all those weren’t either not round or not really popular.
especially the situation that you just painted where you use a web checkout in the restaurant although you’re physically present the web checkout itself is more efficient because you don’t need to get up stand in line there is no you know not a worker doesn’t need to take care of you you just you do everything on your table and you finish the job on your table you go out that is an efficiency gain and that is also why these technologies spread because the
The more efficient, the easier, the less manual work is necessary to achieve a goal. That is typically something that gains popularity and is being pushed. These companies obviously have financial incentives to push these technologies because they also make a profit from seeing it being adopted. There is no issue with that. It’s just like an additional incentive. Whereas in Bitcoin, our incentive is mostly, you know,
We work in open source, we collaborate across different projects because we have all a singular goal, which is to push Bitcoin adoption. So that also means that it requires a bit more coordination and working together in pushing it into the same direction. That is also why, know, BIBs like BIB 321 exist because we want a unified experience that everyone can adopt so we can all march forward together. Sometimes that’s a bit slower, but I believe that is ⁓ longer last
We have a better foundation to build on and because I know that we’ll be working and improving Bitcoin over decades and decades to come, I’m pretty confident that we will be able to make that gap between Bitcoin experiences and fiat experiences ⁓ narrower and smaller over time.
Stephan Livera (19:57)
So if I were to think about, if I were to ask you, where are you going with Numopay in the future? Like what kinds of features or direction are you going to take that project?
Calle (20:08)
So it is fully open source and it’s free. Anyone can download it, modify it, use it as they like. It is built on top of the Cache protocol. And so it gives you as an operator many different options to actually deploy it and experiment with it. We are working on a BTC-Pace server integration as well. So we want…
to be able to not only use a Cashroom Mint as a backend, but also a BTC Pay Server as a backend. Because the UI and the UX that we’ve built is super slick, it can be also useful for other Bitcoin projects. Numo, for example, has a tipping feature where the customer can leave a tip to the worker. It has a basket feature where you can manage multiple, let’s say, tables in a restaurant and then add items and check out later. It has a
receipt feature where you can print out receipts that you can give to your customers. So there’s a bunch of really useful features that we’ve thought hard about and we’ve, you know, considered what is necessary for a good experience in a store when you actually work there. And so all of these features we also want to be able to provide to other platforms. So we’re working on a BTCPay server integration that is already working. It’s just not released yet, but it’s open source. You can find it online if you look for it. And we also
have a dashboard in the works where a singular computer let’s say in the store you can observe the activity of all the numeral terminals in your store so let’s say you have five of these terminals that you give to your workers then a single place where you can you know there will be a single place where you can see how many items are sold across all the devices who has made how much money and
time series and so on and so forth. So working on more analyticals, analytic software to make operations easier and improve integrations with existing Bitcoin wallets. As I said, also, we’re also pushing the adoption of BIP321. So we want more unified payment payloads, ⁓ unified QR codes across the space. And just want to be contributing towards our larger goal. And that is our North Star goal is to push Bitcoin
as money and as push the adoption of Bitcoin as a payment system. That is the most important thing for us and it’s kind of the highest reason, the biggest reason why we work on Casio and why we put out NIMO.
Stephan Livera (22:36)
Excellent, and so with Cashew, just kind of more generally, give us a bit of an overview on where the ecosystem is at nowadays. Like as I understand it, I mean there’s a bunch of mint people running the underlying mints, there are a range of Cashew wallets, you’re trying to show ways that it can be built, obviously with Numopay, that it can be like a merchant tool. Give us an overview, where is the Cashew ecosystem at nowadays?
Calle (22:58)
So the project itself has been around for I think around three years now and in that time we’ve seen
quite astonishing growth. We started with just a very few projects. At the beginning was just me and another guy who joined and we’ve been building out ⁓ wallets and software. At some point it became a protocol. So we kind of intentionally tear down everything and rebuild everything as a specification with documents where everything is documented. So anyone else can also join the protocol and build their own software. And we’ve succeeded with that. Today we have
it’s really hard to even keep track of it there is a awesome cashew repository on github where we’re trying to collect all the different projects that we encounter but there are dozens of different wallets that are being maintained built by different projects and there are you know maybe somewhere between 50 and 100 mints that I’ve
I was able to find that are running and operating from small size to bigger size from personal means for a single family to large mint of regulated company. So there’s the whole bandwidth of individual tinkers and hackers to actual serious company deployments where people even make money by running infrastructure. so the
There’s been astonishing adoption across the board for Bitcoin payment systems. And then there is kind of a completely separate layer of ⁓ users or consumers of Cashew, which just basically focuses on their token and bear asset nature of E-Cash itself. And that was also one of the goals when we built the protocol is to show and…
make it easy and possible for everyone to just use the eCash part without having to hook it up or connect it to a monetary based system. And so you can just use the eCash without Bitcoin. so projects like Tolgate come to mind where they literally sell not Satoshi eCash tokens, but
denominated in megabytes for a internet router. So it’s like a community internet router where you can become an ISP yourself and you can sell internet access to your router, to your neighborhood, for example. And so they use Cashew in order to coordinate the payments in the system or you could call it credits for using the system. Another project that I’m thinking of is Portal, for example.
Portal is a new Bitcoin inspired…
kind of a wallet and identity management app. And they’re partnering also with a Bitcoin conference in this year where they are selling the tickets as cashier tokens. So you will have kind of privacy preserving tickets for a conference, for a Bitcoin conference that cannot be double spent. So you can also sell them or give them to someone else. It’s a big problem in the ticketing world is double spending because, you know, when you go online and you buy a ticket, which is just a PDF file, for example, how do you know that the same ticket
hasn’t been sold to three other people, right? So there is no way to verify that. With eCash, it’s just a simple transfer of that token from one person to another and then the ticket is transferred. even, you know, the nice part about it is that you have perfect privacy, the operator of that conference doesn’t know who bought which ticket. So
There’s a lot of adoption in Bitcoin. ⁓ Everyone is talking about Cashew. I go to conferences, there’s always a Cashew talk. are dozens and dozens of people working on the Cashew main protocol. Probably hundreds of people working around Cashew or with Cashew. So in that sense, it’s a great success and a fundamental part now of the Bitcoin ecosystem. At least that’s how I perceive it and that’s how…
the activity and conferences and so on. And then there is like this ⁓ interesting experimental adoption that basically just uses the eCash part itself and tries to improve the privacy and properties of other non-monetary systems such as internet use, ticketing and so many more.
Stephan Livera (27:18)
Yes, fascinating, because I think it’s grown so quickly. okay, let’s put it this way. Where do you think people should be using a cashier system where they are currently not using it? Especially in web or corporate environments. I think that would be useful for listeners.
Calle (27:32)
Clear.
So, Casio is not a replacement for non-custodial systems because you do not hold the keys for the Bitcoin that is denominated with Casio in most cases. how we see Casio play a role is to improve existing custodial systems of which there are tons and tons around. We want to improve, first of all,
the ability to run these systems on yourself. So you don’t have to rely on a third party operator company that runs, let’s say, know, wallet of Satoshi or something, or an exchange like Kraken or anything where your Bitcoin is not secured by yourself. That’s where Cashew comes in. So you can run them in yourself and ⁓ all the users of those systems.
their privacy is greatly enhanced. I want to say the best possible privacy that you can get with
with any type of cryptocurrency used today is probably is using eCash. So that’s why we’re so passionate about it because it allows you as a user to be uncensorable and untrackable even when you’re using a custodial system. So in that sense, it’s a big level up. And for the organizational case, we’ve seen interest from people expressing their needs about ⁓ internal organizational funds.
There is like cross
cross-company payments, if you have a multinational for example, where there’s one project where someone told me about this idea is they want to set up a mint for their multinational organization because they have this big problem of sending funds around internally and making sure that everything is accounted for internally. And for internal payments, it’s perfect because you could set up a mint for your international organization and then send around funds between different
branches of that organization, for example, as eCash and you don’t need to account for it because the eCash itself is already, the flow of eCash itself is basically accounted for. There is no double spending risk. As long as you receive the funds, you know that the receiver has them and you don’t need to make sure that you keep track of all the payments in a ledger, for example. for, and another thing where people were interested in is payouts.
of
salaries within an organization so you know that you’re paying your employees let’s say you know I don’t know a hundred K per month or something and that’s the total sum of the salaries that you pay out and maybe you don’t want to know what their on-chain address is and what their public key is the lightning public key so if you want to preserve
privacy and anonymity within your organization. It is also useful for that because you could, in that case, just pay your employees in eCash and let them withdraw it to their Lightning node, to their Bitcoin on-chain address without having to keep track of who has which address.
Stephan Livera (30:38)
Yeah, so it’s just interesting to point out that there are these scenarios where it could be used now to provide more privacy because sometimes in, you know, even in quote unquote crypto world, they all sometimes attack Bitcoin and say, Bitcoin is not private while neglecting some of these privacy techniques that can be used inside that already can be used in Bitcoin. Obviously things like PayJoin, Silent Payments, Lightning, and as you mentioned, Cashew, because these all combined can actually provide privacy, but it’s just more like
the world today hasn’t quite set up to use that, right? So for example, if exchanges started to use PayJoin, if more people had, you know, Lightning users instead of defaulting to just doing things on chain with a static donation address, if we started to use like that kind of best, the best that’s available already today, Silent Payments, PayJoin, Lightning, Cashew, some combination of these things, we actually would have some level of privacy in our Bitcoin use.
Calle (31:35)
Yes, so as a advanced user of Bitcoin, you can achieve great levels of privacy already today with all the tools that you’ve mentioned, but here’s that is no, it’s related to the point that we were making earlier is the UX of these individual privacy methods really plays an important role in the adoption. So I believe that
Privacy needs to be a default and you you
You should not have to decide or research or figure out how to improve your privacy if you want everyone to use it. So we should be working on solutions where the user even doesn’t need to care whether it’s a private method or not. They should be just basically thrown into a privacy preserving system by default. And that’s why also using privacy preserving systems must be as smooth as using any other system.
out there because it just requires too much effort for most users to even climb over that hill. And you know it’s not in everyone’s interest to be perfectly private because most people don’t even know what the risks are. So why should they care about being private? And that’s what you will hear when you have these conversations with normies. They will say like I have nothing to hide. It’s the most common thing that most people say. Obviously you don’t have anything to hide until it’s too late. So
And the other part is that the more people use privacy preserving systems, the better for everyone else because privacy lives off numbers. The more people are part of an anonymity set, the better for everyone inside that anonymity set.
That is why UX is so fundamentally important. It is almost as important or maybe even more important than the actual technical solution to the problem itself, because if it’s too hard, then it will only reach a very limited number of people. And for privacy, that is a fundamental loop. For privacy, we fundamentally want…
everyone to use it. So we just have to be a lot more cognizant about these trade-offs and how real people with completely different ⁓ goals than you should be using these technologies as well. As I said before, the shop owner probably doesn’t care about privacy but cares about their sales, right? And that is what they should care about. But we can give them solutions.
that have incredible privacy built in even without having to make that cognitive decision themselves.
Stephan Livera (34:11)
The other topic that I know is obviously very relevant nowadays with AI, vibe coding and so on. I know you’re working on a bunch of different projects and I know you are also using a lot of this AI tooling to amplify your productivity. So can you give us some thoughts, where are you at on the use of AI, vibe coding and these tools to be more productive?
Calle (34:34)
Yeah, so I hope that there is probably no developer out there anymore who hasn’t already figured that things are fundamentally changing and especially for developers.
Everything has changed in the last year or two maximum, although the development of AI and the evolution of AI models has been a much longer story. The penetration into the actual productive world has maybe started to materialize in one or two years ago. And it seems like in the last six months it is really picking up. And at this point,
Everyone is understanding that software development will never go back to what it was before. ⁓ so I’m talking about AI assisted coding or agentic coding or wipe coding in where you.
Instead of writing most of your code manually, you let an AI agent to write the code and what you do as a software developer is you describe your intent or the goal that you want to reach to the machine and you do that in a way.
that you expect the machine to understand you in the best way and then the machine executes and you review the code or you accept whatever the machine does or not. And so the flow or the method of how we’re writing software has fundamentally changed and with that the…
productivity and output that a single motivated person can produce has increased by many folds and within a very short period of time. Personally, I would have never thought that ⁓ I would ever witness this in course of my lifetime.
because although I’ve been following AI developments for a very long time, very closely, and seeing this happen in real time with every single model along the way, and even, you know, before GPT and everything was around, where people have been already demonstrating that these models can produce text really well, it wasn’t clear really that they will also be able to produce really good code. And even I, so deep,
I would consider myself so deep into the space, didn’t expect a year ago that we will come to a point that fast, that quickly, where you don’t even really have to look at the code that much anymore. And you as a professional developer will…
most of the time not be able to produce better code than the machine itself. So like ⁓ one year ago, my conversations with developers were…
often along the lines of, hey, are you using these tools? And if you do, if you don’t do, why not? And the answers that I would get most of the times were that these agents are still too bad. They make mistakes. They’re not good enough for my expectation. And that’s why I’m not using them. And within a single year that has completely changed, there are still people who are incredibly good at what they’re doing and AI agents will not be able to match them yet. Obviously, they will be able to match them soon
because that’s the only direction that we’ve been moving towards. But for most developers, and it’s probably like above 95 % of developers, AI agents today produce already better code than them. And they’re not only producing better code, but they’re also producing it 100 times faster than any developer can do. So if you’re a developer…
then it’s almost already, you you’re already too late if you haven’t adopted this, but you still have a chance. You still have a chance to save yourself because the output efficiency that you gain from using these tools correctly is just mind blowing. And it’s hard to compare it to anything else because I really can’t compare it to anything else. Maybe, you know, the horse buggy against the car even, but not even that makes, you know,
that much of a jump. Not even that was like a 10 to 20x improvement. if you’re a developer who… Yes, probably, but it’s probably that. you know, there’s even with walking, you can get to places where you cannot go with driving. You’d just be slower, but you will get there. With AI tooling and agents, you can get to places where…
Stephan Livera (38:47)
Yeah, so it’s basically like the difference between walking and driving.
Calle (39:06)
you will never be able to go as a person. it’s, yes, it knows the things that you don’t know.
Stephan Livera (39:09)
Right, because you can learn things as well. So,
for listeners who are interested, maybe the developers or builders themselves, do you have any tips on the best ways to leverage this AI or leverage AI tools? What tools are you using? Any tips for listeners who want to build Bitcoin stuff with AI?
Calle (39:29)
Yeah, so whatever I say right now will be obsolete in two months, so I won’t be able, won’t give you like specific tips. Or maybe, you know, I can tell you what my pipeline is today, but I use all the models. I don’t care about which models it is. I just switch around. You need to figure out which model is good at what, right? That is something that…
is your job as a developer. And then you use a coding agent, there’s this kind of a harness that contains the brain, which is the AI model, and gives it legs and arms, which is reading files, writing files, searching the web, and doing kind of actions in the real world. I heavily use OpenCode today. I also use Goose from time to time, and I use other agents, Codex and Cloud Code and all of these different things as well. So my tip to developers is
first of all if you haven’t tried it yet then it’s time now you need to start learning these things and then you need to keep learning for the next couple of years.
maybe less than that, your job is basically staying on top of this technology because it’s changing so fast that things that I’ve been doing that I was doing six months ago I don’t do anymore. just try to whenever there is a new release of something new fundamental fundamentally new I try to get on top of it as quickly as I can because I know that there’s a bunch of people doing exactly the same thing and I just want to know whether this is useful for me or not whether I can ignore it or whether I should invest more time in figuring it out. So right now I think
we’re in kind of the most turbulent of times, which is, know, the ecosystem will settle in six to 12 months to some, you know, specific form of using these tools. But right now, anything that is out there could be kind of revolutionary and new. So what you should be doing is to invest more time in learning to use these tools and understanding what these different tools are, how they’re built and how you can make use of them. That’s the thing to focus on right now.
is try everything, figure out what works for you, and keep trying until this transformation has settled.
Stephan Livera (41:32)
Yeah, it’s a really very quickly changing time, right? I think a few years ago, it was almost like you really had to have something to be a programmer. You sort of had to think a certain way to do it. Whereas now it’s almost like it’s just opened up the access so much more that now you can learn and do things that previously, you know, it’s like…
Calle (41:50)
Yes.
Stephan Livera (41:51)
It’s like, know previously you were handicapped but now with AI tools you’re not handicapped you can Think better or learn faster. So really fascinating times. I think we’ll leave it there though But listen is make sure you check it out as as Kyle said, it’s a really slick UX I was playing around with it like if you have You know family or friends who are looking at you know could benefit from using Bitcoin payments check out Numa pay I think the UX is really really slick. It’s very like just click simple, you know, very guided process
very similar UX that normies will be used to from their fiat perspective. So Karli, where can people find you and find Numopay?
Calle (42:28)
So for Numopay you can go to numopay.org. It’s fully free and open source, download it and try it out. You need an Android device to receive, but any iOS and Android app can pay to it. So that’s Numopay. You can find me on socials where you’ll probably see me shitposting somewhere. So I’m not gonna have to point you towards my profile. I will find you. And if you’re a developer out there who is kind of looking for purpose and figuring out what to do in the next couple of months, I ⁓ urge
you to ⁓ consider joining the Bitcoin open source development.
space. We are working as a very large group of people all around the world with a strong purpose into a singular direction, which is pushing Bitcoin as a global monetary system on the internet. We need your help. We need more people working on open source Bitcoin tech. we are the fundamental kind of building the fundamental layer of making sure that Bitcoin will prevail in the next 10, 20, 30, 200 years.
please join us ⁓ reconsider if your job is boring and you work in a stupid tech startup that you never supported then just quit start contributing to Bitcoin look for grants look for companies that can help you support that and and join us
Stephan Livera (43:48)
Fantastic. Thank you, Calle.