Both Fedimint and Cashu give you ecash — blinded bearer tokens backed by bitcoin. But they make very different trust tradeoffs. This post breaks down when to use each and why ArxMint supports both.
The Trust Model Difference
Fedimint distributes trust across a federation of guardians. If you have 4 guardians, any 3 can process transactions. One guardian going offline or malicious doesn't affect the system. This is Byzantine fault tolerance applied to community custody.
Cashu is a single-mint model. One operator runs the mint server, issues tokens, and processes redemptions. Simpler to deploy, but the mint operator is a single point of trust (though not a single point of knowledge — blinded signatures mean the mint can't see who spent what).
When to Use Fedimint
- Community custody: 10+ people pooling bitcoin with no single trusted party
- Long-term savings: The federation model is more resilient to operator failure
- Guardian governance: You want rotation policies, uptime monitoring, quorum rules
- Larger communities: 30+ members where the coordination cost of multiple guardians is justified
Fedimint requires running fedimintd on each guardian node. ArxMint generates the Docker config for all guardians and handles the invite code flow.
When to Use Cashu
- Quick deployments: A single
nutshellor CDK mint on one VPS - Merchant payments: Low-latency token swaps for point-of-sale
- AI agent wallets: Ephemeral tokens with TTL and balance limits — agents don't need federation governance
- Interoperability: Cashu tokens follow the NUT spec and work across any compliant wallet
- Privacy-first: Even simpler privacy model — the mint literally cannot trace token flows
Cashu is also where the NUT-24 ecash paywall spec lives, which ArxMint uses for API access control.
Running Both
ArxMint's architecture supports both backends simultaneously:
- Fedimint handles community savings and high-value transfers
- Cashu handles daily spending, merchant payments, and agent commerce
- Lightning bridges the two and connects to the outside world
- The spend router automatically picks the best backend based on amount, privacy requirements, and recipient capabilities
This isn't theoretical — the wallet panel shows both balances and the privacy dashboard scores each transaction path.
Technical Comparison
| Feature | Fedimint | Cashu |
|---|---|---|
| Trust model | Federated (m-of-n) | Single mint |
| Setup complexity | Higher (multiple guardians) | Lower (one server) |
| Latency | Sub-second (consensus round) | Near-instant (single signature) |
| Privacy | Mint federation can't link spender to receiver | Mint can't link spender to receiver |
| Best for | Community custody, savings | Payments, agents, paywalls |
| SDK | @fedimint/core + @fedimint/transport-web (WASM) | cashu-ts v3 (pure TS) |
| ArxMint integration | Full wallet + peg-in/out | Full wallet + NUT-24 + NUT-26 |
The Bottom Line
Start with Cashu for speed. Add Fedimint when your community grows and needs distributed custody. ArxMint's community generator asks the right questions and configures both.
Next week: Building AI Agent Commerce with L402 and Ecash Paywalls