Atomic swaps: BTC → XMR with UnstoppableSwap (now eigenwallet)
Guide · research-based, September 2026 · not financial advice.
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What an atomic swap is
An atomic swap exchanges coins across two blockchains with no intermediary at all — no exchange company, no order book operator, no escrow agent. Cryptography does the job instead: the protocol links a Bitcoin lock to a Monero lock so that either both sides complete or both sides get refunded. It is "atomic" because you cannot end up in the losing half of a trade as long as you follow the protocol.
For BTC → XMR this uses adaptor signatures and zero-knowledge proofs to bridge Bitcoin's and Monero's different cryptography. The practical upshot: your Bitcoin goes into a lock that only releases when the Monero side releases too — and the Monero side is, like all Monero transactions, opaque on-chain. There is no company that can freeze the swap, demand ID, or get hacked mid-trade, because there is no company.
How UnstoppableSwap / eigenwallet works
UnstoppableSwap is the protocol and desktop app that made BTC↔XMR atomic swaps practical. In 2026 the project rebranded to eigenwallet (eigenwallet.org; docs still at docs.unstoppableswap.net) and is on version 4.12.0 — the software has been live for over three years and is under active development.
The roles:
- Taker (you): you sell BTC and buy XMR. You install the desktop app, browse offers, pick one, and deposit Bitcoin.
- Makers: volunteers/entrepreneurs who run the maker software (ASB), hold XMR liquidity, and buy your BTC in return for XMR. Each maker sets their own exchange rate, minimum/maximum amounts, and fee policy — you choose whom to swap with.
Makers discoverable through the app's rendezvous points publish quotes with their price, min/max swap size, and refund terms. A recent third-party liquidity scrape found typically 3–6 active makers holding roughly $300K–$500K+ of XMR liquidity in total (estimate, September 2026). Anyone can become a maker by running the open-source ASB software — the network has no gatekeeper.
What it costs
- Maker markup: each maker prices XMR at a spread above centralized-exchange rates. The docs use a 3% markup as the example; in practice expect roughly 1–3% (estimate — varies by maker and market conditions). A lower markup means more XMR for your BTC.
- Anti-spam deposit: makers may require a small deposit (the docs' example is 2%) that is refunded when the swap completes normally — it exists to deter spam, not as a fee.
- Network fees: you pay the Bitcoin transaction fee for the lock transaction, plus the (tiny) Monero fee on the receiving side.
- Minimums: the first-swap guide suggests having at least ~0.0003 BTC (around $30); individual makers set their own minimums and maximums per offer.
There is no protocol-level fee and no account. Compare the final XMR amount against the market rate the same way you would with an instant exchange — the markup is the maker's margin.
Doing your first swap
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Install the app
Download eigenwallet (formerly UnstoppableSwap) for Linux, macOS or Windows from the official site or GitHub (eigenwallet/core). Verify checksums/signatures before running — this is privacy software; downloading it from a random mirror defeats the purpose.
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Browse maker offers
On the Swap page, view the offers. Compare each maker's markup, min/max amounts, and anti-spam deposit. Pick the best combination, not just the headline rate.
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Enter your addresses
Provide your own Monero receiving address and a Bitcoin refund address (used if the swap doesn't complete). Double-check both — same irreversible-address rules as everywhere in crypto.
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Deposit Bitcoin and keep the app online
Send BTC to the lock address shown. The swap then executes automatically, but historically you needed to keep the app online until it finished (recent versions added the Hermes protocol, which lets a swap complete without a persistent peer connection after setup). Confirmations on both chains take time — be patient.
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Start small
The original developers' advice still holds: test with a small amount first. A failed or stalled swap doesn't lose your funds (timelock refunds kick in), but it can leave them locked until the timeout expires.
Prefer a lighter-weight start? unstoppableswap.net offers a web UI where you pick a swap provider and run the swap from a guided CLI flow — same protocol, less app to install.
Honest trade-offs vs instant exchanges
- Trust: atomic swaps win outright — no custodian, no AML screening, no account, no company that can disappear with deposits.
- Privacy: excellent. No identity is ever collected, and the Monero leg is opaque by design.
- Speed and convenience: instant exchanges win. A swap service takes minutes with no software to install; an atomic swap needs a desktop app, offer-hunting, and patience for on-chain confirmations on both sides.
- Liquidity: instant exchanges win for larger amounts. Atomic-swap liquidity is real but thin — a handful of makers, each with their own limits.
- Cost: roughly comparable for small amounts (a 1–3% maker markup vs 0.4–1% exchange fees plus spreads), but always compare the final quote.
- Failure mode: an instant exchange can freeze your funds pending review; an atomic swap can stall and lock funds until a timelock refund. Neither failure loses money by itself, but the swap's failure mode demands more technical patience.