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name: bitcoin-l2-bob description: | BOB (Build on Bitcoin): hybrid Bitcoin/Ethereum L2 using OP Stack

• Bitcoin security. Bridges to Bitcoin via threshold signatures
• zk-proofs. USE WHEN: building cross-chain Bitcoin/Ethereum apps, evaluating BOB hybrid model. allowed-tools: Read, Grep, Glob

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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.

See also

• hemi/SKILL.md
• bsquared/SKILL.md
• merlin/SKILL.md
• botanix/SKILL.md