NEXUS-Bitcoin

NEXUS-Bitcoin launches after Zcash. Zcash is the first live chain. Bitcoin support is fully designed and implemented — this page documents what Bitcoin integration will look like at launch.

Overview

NEXUS-Bitcoin brings smart contracts to Bitcoin without changing Bitcoin itself. Your BTC stays in a Bitcoin vault. NEXUS runs programs on top. What NEXUS adds to Bitcoin:

Smart contracts (written in Rust/WASM)
Fungible tokens (NEP-20)
Decentralized trading (AMM pools)
BRC-20 token bridging

New to NEXUS? Start with the Introduction for plain-English context. See the Glossary for any unfamiliar terms.

How Trust Works on Bitcoin

NEXUS-Bitcoin is trustless — you don’t need to trust any individual operator. Here’s how: Step 1 — Cryptographic proofs Every time NEXUS processes a batch of transactions, it generates a ZK-STARK proof — a mathematical certificate proving all transactions were handled correctly. Step 2 — Anyone can challenge Proofs are posted to Bitcoin along with a financial bond (deposited by the operator). If the proof is wrong, anyone in the world can challenge it using BitVM2:

Challenger posts a bond and opens a dispute
A bisection game narrows to the single bad computation step
That step is verified on Bitcoin itself
Wrong party loses their bond to the correct party

No permission needed. No special access. Anyone can be a challenger. Step 3 — Your escape hatch Even without any challenge process, you always hold a pre-signed exit transaction. If NEXUS stops working, wait ~2 weeks and your BTC returns to you automatically.

Bitcoin Vault Details

Property	Value
Address type	Taproot (P2TR) — Bitcoin’s modern address format
Vault structure	2-of-2 multisig (you + protocol)
Escape hatch	2,016 block timelock (~2 weeks)
State commitments	OP_RETURN outputs every N blocks
Deposit confirmations	6 blocks (~60 min)

Supported Features (V1)

Feature	Status
Smart Contracts (WASM)	✅
Taproot Vaults	✅
State Commitments on Bitcoin	✅
BitVM2 Fraud Proof System	✅
SPV Transaction Proofs	✅
Cross-Contract Calls	✅
BRC-20 Token Bridge	✅
BTC ↔ ZEC Swaps	🔄 V2 (intent exchange)
BTC ↔ DOGE Swaps	🔄 V2 (intent exchange)
Unified Liquidity Pools	🔄 V2
Runes Bridge	🔄 Coming soon
Ordinals	🔄 Coming soon

Smart Contract Capabilities

NEXUS-Bitcoin supports the full WASM smart contract system:

Capability	Description
Full WASM execution	Any logic expressible in Rust
Cross-contract calls	One contract calling another
Delegate calls	Run another contract’s code in your storage context
Contract-from-contract deployment	Factory patterns
Persistent storage	Key-value data that survives between calls
Event emission	Notify off-chain indexers
Reentrancy guard	Built-in protection against reentrancy attacks
Bitcoin SPV proofs	Verify Bitcoin transactions inside a contract

Deposit Guide

1. Get your vault address

const vault = await client.getVaultAddress(2016); // 2,016-block timelock (~2 weeks)
console.log('Send BTC to:', vault.vaultAddress);

Or via CLI:

nexus wallet vault-address --chain bitcoin

2. Send Bitcoin

bitcoin-cli sendtoaddress <VAULT_ADDRESS> 0.01

3. Wait for 6 confirmations (~60 minutes) 4. Check your NEXUS balance

const balance = await client.getBalance();
// Balance shown in satoshis (vSAT)

Withdrawal Guide

// Returns: { success, txid, status, path, confirmed? }
const result = await client.withdrawFunds(
  'bc1p...',  // your Bitcoin destination address
  100000,     // amount in satoshis
);
console.log('Withdrawal txid:', result.txid);

Withdrawals are processed in batches for efficiency. You receive BTC in your Bitcoin wallet within a few minutes of processing.

State Commitments

NEXUS posts a summary of all state changes to Bitcoin periodically:

Bitcoin Block 100:  State Root 0xabc... (stored in OP_RETURN)
Bitcoin Block 200:  State Root 0xdef... (stored in OP_RETURN)
Bitcoin Block 300:  State Root 0x123... (stored in OP_RETURN)

Anyone can verify NEXUS is behaving correctly by:

Downloading the full NEXUS state from any node
Computing the Merkle root of that state
Comparing it to the value posted on Bitcoin

Configuration Reference

[bitcoin]
rpc_url = "http://localhost:8332"
rpc_user = "user"
rpc_password = "password"
network = "regtest"  # mainnet | testnet | signet | regtest

[bitcoin.vault]
escape_timelock = 2016  # ~2 weeks in blocks

[bitcoin.state_commit]
interval_blocks = 100   # post state every 100 Bitcoin blocks
bond_amount_sats = 100000

Comparison with Bitcoin Alternatives

Feature	NEXUS-Bitcoin	Spark (Lightning)	OP_NET	Arch Network
Smart Contracts	✅ Full WASM	❌ Payments only	✅ WASM	✅ WASM
Trust Model	Trustless (ZK+BitVM2)	Federated	Optimistic	BitVM
Multi-Chain	✅ BTC+ZEC+DOGE	❌ BTC only	❌ BTC only	❌ BTC only
Self-Custody	✅ Always	✅ Channels	Partial	Bridge-based
DeFi	✅ AMM, tokens, etc	❌	✅	✅

Roadmap

V1 (Live)

✅ Full WASM smart contracts
✅ Cross-contract calls & delegate calls
✅ Taproot vaults with escape hatch
✅ ZK-STARK + BitVM2 verification
✅ BRC-20 bridge
✅ Stealth addresses & encrypted mempool (via NEXUS protocol layer)

V2 (Planned)

🔄 Unified liquidity with ZEC/DOGE via intent exchange
🔄 Cross-chain swaps (BTC/ZEC/DOGE)
🔄 Runes bridge
🔄 Ordinals support

Getting Started

Supported Chains

Core Concepts

Smart Contracts

Guides

Reference

Overview

How Trust Works on Bitcoin

Bitcoin Vault Details

Supported Features (V1)

Smart Contract Capabilities

Deposit Guide

Withdrawal Guide

State Commitments

Configuration Reference

Comparison with Bitcoin Alternatives

Roadmap

V1 (Live)

V2 (Planned)

​Overview

​How Trust Works on Bitcoin

​Bitcoin Vault Details

​Supported Features (V1)

​Smart Contract Capabilities

​Deposit Guide

​Withdrawal Guide

​State Commitments

​Configuration Reference

​Comparison with Bitcoin Alternatives

​Roadmap

​V1 (Live)

​V2 (Planned)

Overview

How Trust Works on Bitcoin

Bitcoin Vault Details

Supported Features (V1)

Smart Contract Capabilities

Deposit Guide

Withdrawal Guide

State Commitments

Configuration Reference

Comparison with Bitcoin Alternatives

Roadmap

V1 (Live)

V2 (Planned)