How Kilian Rausch Built Boltz, Bitcoin’s Cross-Layer Bridge

Kilian Rausch did not set out to build Bitcoin infrastructure. In early 2016, after the collapse of the Chinese company he worked for, he wandered into a Bitcoin meetup in Shanghai out of curiosity. “My Bitcoin journey was an accident,” he says. That night he met Samson Mow, agreed to an interview, and soon found himself working at BTC China (BTCC) while knowing almost nothing about Bitcoin.

At the time, Rausch was skeptical and pragmatic. He assumed Chinese authorities may shut operations down within weeks. “I figured it could be gone by next week, but I might as well have some fun in the meanwhile.” The ban did come, but about a year and a half later than he expected, and considering the network is still adding blocks every ~10 minutes, it clearly was not successful in the long run.

That detour pulled him deep into the Bitcoin ecosystem. Rausch explored mining pools, mobile wallets, and ultimately tried to build a decentralized exchange on the early Lightning Network in late 2017.

The timing was wrong, and the DEX failed. But out of that failure came a side project that solved a recurring pain point for Lightning users: keeping payment channels balanced so payments actually work.

That side project became Boltz, a non-custodial bridge that uses atomic swaps to move bitcoin between Bitcoin layers such as the main chain, Lightning, Liquid, and Rootstock. No accounts, no custody, no intermediaries. Cryptography ensures users retain control of their funds. Boltz launched on mainnet in April 2019 as a hobby project. When Rausch stepped back in 2021 for family reasons, it stayed online with minimal upkeep.

By 2022 it was clear Boltz was more than a curiosity. “We were barely doing anything except maintaining it, and still more and more people were using it,” Rausch recalls. He teamed up with his co-founders Michael and Karl, went full time, and incorporated the company in El Salvador in 2023.

They added Liquid swaps and professionalized operations. Today, Boltz underpins swaps in wallets and tools like Breez, BTCPay Server, and Aqua, and runs some of the largest Lightning nodes and operates without KYC or user accounts.

Rausch is unusually candid about Lightning’s evolution. In the early days it was a playground for hobbyists running command line nodes on Raspberry Pis.

After some years, reality set in. “The first people lost their money. Operating a Lightning node is actually pretty difficult,” he says. The notion that everyone would operate a node and earn routing fees faded quickly. Reliable routing became a professional game with capital and expertise advantages.

By 2022 and 2023, Lightning liquidity had consolidated around large players like Binance and Kraken. Later, entities like Lightspark brought Lightning functionality to exchanges and fintechs like Coinbase and Revolut. “The reliable Lightning Network is not as decentralized as we hoped,” Rausch observes.

What emerged instead was a familiar push and pull. In theory, the sovereign individual running their own node is the ideal. In practice, economies of scale matter. Running a high quality Lightning node takes capital, expertise, and constant attention. Those advantages compound quickly.

The pattern mirrors Bitcoin mining in many ways. Anyone can mine, and more people running lottery miners is a good thing, but over time, hashpower gravitates toward large operators with cheaper energy, better infrastructure, and tighter margins.

Lightning routing followed a similar path. The network remains permissionless, but reliability increasingly comes from professional operators. Rausch sees this not as a failure, but as an honest reckoning. “It’s now widely accepted that running a Lightning node is not for everyone,” he says. What matters is that users can still access Lightning in a non-custodial way with a good user experience.

That distinction becomes critical as custodial wallets are challenged via regulation. Apps like Wallet of Satoshi once dominated mobile Lightning because they were simple and worked instantly.

Regulation, especially in Europe, has made custody an unattractive risk for companies. Ironically, rules designed to increase control are pushing the ecosystem toward self custody. “Custodial wallets will all go away,” Rausch predicts, not because users demanded it, but because businesses no longer want the liability.

The transition is being smoothed by a new class of tools. Swap-based wallets like Aqua let users hold their own keys while outsourcing the hard parts of Lightning to professionals.

Channel management and liquidity are handled in the background, without giving up control of funds. Liquidity when you need it, sovereignty when you want it. It is great to see that regulation may end up accelerating the very self custody future it was never meant to encourage.

On tokenized assets, like say Apple stock issued on Bitcoin-related layers, Rausch is pragmatic. You still trust the issuer, so the settlement rail matters less. “It’s fine if USDT exists on Tether’s own chain,” he says. The real innovation is not token wrappers, but native Bitcoin functionality that does not require trusted intermediaries.

Nostr earns a cautious endorsement. Zaps, he says, are powerful. Boltz posts updates and receives instant feedback as micro payments. That dynamic could push other platforms to adopt Lightning. As a full social network, though, Nostr still struggles with relay reliability, delays, and long-term data storage. For short-lived, censorship-resistant messages like announcements, Rausch sees real potential.

What excites him most is the return of builder energy in Bitcoin. Wallets are getting better. Square is rolling out Bitcoin payments at millions of terminals. New layers promise significant improvements in user experience.

There is also the re-emergence of BTC finance. Lending markets and bitcoin-backed stablecoins built non-custodially on Rootstock or emerging rollups reduce the need to default to centralized exchanges for advanced financial products.

AI has quietly become Boltz’s force multiplier. With a self-funded five-person team, Rausch now writes pull requests, queries databases, and navigates large open-source codebases using tools like Cursor.

“Our engineers became several times more productive. A team this small could not operate something like Boltz otherwise.” He remains cautious about autonomous agents being handed private keys and handling funds, expecting slow progress there, but admits trading bots will likely dominate over time.

If Rausch could ask Satoshi one question, it would be simple: why? Beyond frustration with banks or broken money, what personal conviction justified years of unpaid work and the decision to write Bitcoin in C++? What inner drive sustains that level of patience and precision?

That question shapes how Rausch thinks about Bitcoin today. The protocol was not built to be admired from a distance. It was built to be used. His advice to Bitcoiners reflects that mindset: Use Bitcoin.

Try a Lightning wallet like Phoenix, Misty Breez, Bull or Aqua. Post a Lightning address on Nostr. Send and receive zaps. Feel what instant, permissionless value transfer actually means. Explore on-chain lending on Rootstock or emerging layers. “The earlier one starts tinkering around, the better,” he says.

What Boltz has built is more than a swapping tool. It is a core piece of Bitcoin’s multi-layer infrastructure that enables trustless, non-custodial atomic swaps between the main chain, Lightning, Rootstock and Liquid networks.

Users retain full control of funds throughout the process, preserving privacy and self-custody in a way traditional bridges do not. Boltz’s architecture enhances interoperability across layers, unlocks liquidity, and dramatically reduces risk for users while lowering fees and speeding up transactions.

The technology is recognized as critical infrastructure in Bitcoin’s layered ecosystem, with integrations that streamline access to smart contracts, faster settlements, and institutional adoption. Boltz’s role in increasing liquidity and connecting Bitcoin’s layers is a foundational development in scaling Bitcoin beyond the base layer.

Boltz fits naturally into the path Rausch describes. If your bitcoin is stuck on-chain and you need Lightning liquidity, you can swap without custody.

As regulation pushes more users toward self-custody, tools like Boltz quietly do the unglamorous work of making it practical. Rausch’s story is a reminder that many of Bitcoin’s most important tools began as side projects built by people who did not even plan to be there in the first place.