Cashu

Cashu is a Chaumian ecash protocol built for Bitcoin. Wallets use a mint's Lightning node to deposit funds, and receive ecash tokens in return. The mint does not know who you are, what your balance is, or who you are transacting with. Payments between users are private and cannot be censored.

Cashu powers Bitcoin communities worldwide, and is already at the heart of multiple companies' products. This momentum is only possible thanks to our incredible grassroots community and the freedom-driven contributors who make Cashu what it is today.

—Calle

The protocol is defined by a set of specifications called NUTs (Notation, Usage, and Terminology). Client libraries exist in Python, TypeScript, Rust, and Kotlin. The reference mint implementation is Nutshell, and Cashu.me is the main web wallet. Other wallets include Nutstash, Minibits, and eNuts.

Recent protocol work introduced authentication for mints (NUT-21/22), cached responses (NUT-19), shared custody via SIG_ALL (NUT-11), and payment requests (NUT-18) that work over HTTP and nostr. Other tools include a mint auditor for verifying reserves and the Cashu Decoder for inspecting tokens.

Why fund it?

Ecash gives Bitcoin capabilities it doesn't have on its own. Cashu tokens enable true micropayments, streaming payments, and pay-per-use API calls at amounts that would be uneconomical on-chain or even over Lightning. They can also be sent offline, transferred over Bluetooth or NFC, and they bring real privacy to everyday payments: the mint cannot trace who spent what.

Cashu is free, open-source software with no business model. Protocol work, the reference mint, the web wallet, and ecosystem coordination all depend on grants.

OpenSats has been supporting Cashu since the first wave of Bitcoin grants in July 2023. A long-term support grant followed in June 2024. Separate grants went to Nutshell (8th wave), Nutstash (9th wave), and OpenCash for broader ecosystem coordination.

What's next?

Nutshell 0.20.0 shipped in Q1 2026 with improved P2PK/HTLC validation and expanded test coverage. Keyset V2 derivation is rolling out across implementations. Bolt12 support for Cashu.me is close to done, and security audits across the Cashu ecosystem are a priority for the coming months.

For a detailed look at recent progress, see the Advancements in Ecash impact report.