BTC++, Berlin, and breakthroughs in advancing Bitcoin custody.

Bitcoin's ecash community has moved quickly to address a core weakness in decentralized custody: software monoculture. In the span of weeks, the Fedimint team brought a single federation online across three independent code implementations at Ecash Hackday in Berlin, while developer Calle unveiled Federated Cashu at bitcoin++, a design in which no single operator stands alone behind a user's funds.

The advances respond directly to an argument made a few weeks earlier by Fedi and Fedimint co-founder Obi Nwosu, who wrote in a guest post for Bitcoin Magazine that the Bitcoin ecosystem kept asking the wrong question, tending to frame everything as “trusted” or “trustless.” Instead, he urged people to ask: “How many independent things have to go wrong before you lose your money?”

Nwosu pointed to Liquid and, weeks before that, Coldcard as cases in point, citing the most succinct formulation of the issue from Matt Corallo: run the same software, suffer the same bugs. The critique applied to Fedimint as well, and Nwosu was the first to say so. Fedimint was built to remove single people and single institutions as points of failure, he wrote, yet there was just one implementation of the protocol — a software monoculture below federations of humans. In his words: “Not secure enough.”

Fedimint developers have already responded. At Ecash Hackday in Berlin, the Fedimint team got a single federation running across three independent implementations, with Cashu's thesimplekid building one of them. Eric Sirion, who posts as elsirion, announced the milestone on X.

Had a great time at Ecash Hackday in Berlin, got a Fedimint running with 3 different implementations by @thesimplekid , me and the Fedimint team! Already got 3 Fedimint implementations now, who will build the 4th one? pic.twitter.com/2MPdtlaJqt
— elsirion (@EricSirion) September 30, 2026

Three separate codebases, one federation, holding funds together. In Nwosu's view, developers have begun to build a solution to the monoculture he called out weeks earlier — and the team's choice to ask who will build the fourth implementation captured exactly the spirit he had hoped to see.

Calle took the same principle and ran with it in his own direction. At bitcoin++ he unveiled Federated Cashu, which is designed in a way that no single operator stands alone behind a user's funds. Any four or five keep the federation going, on a new blind signature scheme.

. @callebtc unveils “Federated Cashu” at @btcplusplus “You don’t need to trust the operator with your privacy, but you do need to trust the operator with your security” “Any combination of 4/5 continues the federation” A new Blind BLS signature scheme is involved. pic.twitter.com/S8iL9Qaa9u
— Matthew Vuk (@matthewvuk2) October 1, 2026

Two teams. Two approaches. One shared goal: ecosystem resilience, advanced within weeks.

For Nwosu, fault tolerance does not come from trustworthiness alone, however good the audits, formal verifications, and security culture may be. It comes from independent failure domains — no single bug, no single vendor, no single jurisdiction able to take everything at once.

He drew a clear line between the project's layers, because the distinction matters: Fedimint is the open-source protocol, while Fedi is what his team builds on top of it. When the protocol grows a second and a third implementation, every federation gets more resilient, and no member has to change anything about how they use their wallet. Guardians can run different software while serving the same people.

Nwosu laid out five layers where independence has to hold, and said he would hold himself to them:

• Multiple implementations of every protocol that holds funds.
• Multiple wallet implementations.
• Keys generated on hardware from different vendors.
• Multiple independent, trustworthy people, whose privacy is protected, behind every system that holds money.
• Distribution across geographies and jurisdictions, because a jurisdiction's rules can change overnight.

According to Nwosu, the developers who worked on this in Berlin moved those five layers closer to reality. He thanked everyone who continues to focus on building and sharing their proof-of-work, while adding that the rest of the community — himself included — is not done. The ecosystem, he argued, needs to start demanding independence at every layer: software, hardware, humans, jurisdictions, all the way down.

That, in his view, is how users' confidence in Bitcoin can be maintained as the ecosystem enters what he described as a new age of AI-assisted threats.

This is a guest post by Obi Nwosu, Co-Founder of Fedi and Fedimint. Opinions expressed are entirely his own and do not necessarily reflect those of BTC Inc. or Bitcoin Magazine. The article first appeared on Bitcoin Magazine.