BOB (Build on Bitcoin)
Hybrid L2 combining Bitcoin and Ethereum. Built on Optimism's OP Stack but with Bitcoin-anchored security mechanisms.
Architecture
- OP Stack for execution (Optimistic rollup style).
- Anchored to Ethereum for data availability + initial security.
- Bitcoin anchoring: state hashes also committed to Bitcoin via inscriptions / Taproot commitments.
- Bridges: native to Ethereum, with Bitcoin via federation + zk proofs.
Hybrid security
The "hybrid" model means BOB inherits both:
- Ethereum's data availability + fraud proofs.
- Bitcoin's PoW for state finality (via anchoring).
Trade-off: complex architecture, but potentially stronger long-term guarantees.
Use cases
- Cross-chain DeFi spanning BTC + ETH ecosystems.
- Apps that benefit from EVM tooling + Bitcoin anchoring.
- NFT bridges between Ordinals / Ethereum NFTs.
Comparison
| Aspect | BOB | Citrea | RSK |
|---|---|---|---|
| Execution | EVM (OP Stack) | zkEVM | EVM |
| Settlement | Ethereum + Bitcoin | Bitcoin only | Bitcoin merge mining |
| Bridge | Multi-asset | BitVM2 | Federation |
Limitations
- Complex security model — harder to audit.
- Dual-chain dependence — outages on either Ethereum or Bitcoin affect.
- Smaller community than EVM-only L2s.