Bitcoin Rollup Data Availability Choices

The Problem: Using a sidechain or external DA layer breaks the security model, reintroducing trusted assumptions. The Solution: Commit data directly to Bitcoin via Ordinals inscriptions or OP_RETURN, inheriting L1's full settlement assurance. This is the path of BitVM and Citrea.

• Key Benefit: Maximal security derived directly from Bitcoin's consensus.
• Key Benefit: Censorship resistance equal to base-layer transactions.

The Problem: Pure on-chain DA is prohibitively expensive and slow for high-throughput applications. The Solution: Post data to a high-throughput, cost-effective sovereign layer (like Celestia or Avail), then post a compact proof or hash commitment to Bitcoin L1. This is the model of Babylon and B² Network.

• Key Benefit: Cost efficiency for data (~$0.01 per MB vs. Bitcoin's ~$10).
• Key Benefit: Scalability to 100k+ TPS while maintaining a security anchor.

The Problem: Bitcoin's nascent ecosystem lacks the developer tooling and deep liquidity for complex DeFi. The Solution: Use Ethereum or an Ethereum L2 (like Arbitrum, Optimism) as the primary DA and execution layer, using Bitcoin solely as a sovereign asset bridge. This is the approach of Stacks sBTC and BOB.

• Key Benefit: Instant composability with the $50B+ DeFi ecosystem on Ethereum.
• Key Benefit: Mature infrastructure (wallets, oracles, indexers) accelerates development.

Native Bitcoin script cannot verify rollup state proofs. Publishing raw data to L1 is secure but cripplingly expensive and slow, creating a fundamental scaling bottleneck.

• Cost: ~$10-50 per transaction at scale
• Throughput: Capped at ~10 tx/s for data
• Finality: Hampered by 10-minute block times

Projects like BitVM and Citrea bypass Bitcoin's DA limit by posting only a tiny commitment (e.g., a 256-bit hash). Full transaction data is published off-chain, and clients enforce validity via fraud proofs.

• Security: Inherits Bitcoin's full security for settlement
• Cost: Reduces L1 footprint by >99%
• Trade-off: Introduces data availability risk and client operational burden

Architectures like Babylon and Bison split the trust model. Critical state proofs are anchored on Bitcoin, while high-volume transaction data is posted to a scalable external DA layer like Celestia or EigenDA.

• Performance: Enables ~10k TPS throughput
• Security: Compromise requires collusion across two systems
• Complexity: Adds modular stack risk and relayers

Leveraging Bitcoin's Taproot (Schnorr signatures) and OP_RETURN techniques popularized by Ordinals, projects embed rollup data directly into Bitcoin transactions as a sovereign chain. This maximizes Bitcoin's security but faces its inherent limits.

• Purity: 100% Bitcoin security, no external trust
• Capacity: Limited by block space auctions, leading to high fee volatility
• Ecosystem: Directly competes with Ordinals/BRC-20 for block space

Every Bitcoin rollup DA choice is a point on a spectrum. Pure Bitcoin DA offers maximal security but minimal scale. External DA offers scale but introduces new trust assumptions. The optimal choice depends on the application's threat model.

• Max Security: Sovereign client-side validation
• Max Scale: Hybrid external DA
• Market Reality: Most projects will adopt hybrid models for viability

Long-term solutions like Drivechains (BIP-300) propose a soft fork to allow Bitcoin miners to vote on sidechain state transitions, creating a native, miner-secured DA layer. This is the holy grail but faces significant governance and adoption hurdles.

• Potential: Native, miner-secured two-way pegs
• Timeline: Multi-year political process
• Impact: Would render most current architectures obsolete

Publishing rollup data directly to Bitcoin L1 is secure but cripplingly expensive and slow. A 1MB data batch can cost $50k+ and be confirmed only ~every 10 minutes, destroying scalability and user experience for high-throughput applications like DeFi or gaming.

Projects like Babylon and BitLayer use a hybrid model. Data is posted to a high-throughput off-chain network (e.g., Celestia, EigenDA, or a PoS sidechain), while a cryptographic proof or attestation of its availability is anchored to Bitcoin. This separates scalable execution from secure consensus.

• Key Benefit: Enables ~2s block times and <$0.01 tx fees.
• Key Risk: Introduces a weakest-link security dependency on the external DA layer.

Frameworks like BitVM 2 or rollups like Citrea propose optimistic systems where data is assumed available unless challenged. A successful challenge triggers a Bitcoin L1 fraud proof.

• Key Benefit: Maximizes Bitcoin's security for settlement without posting all data.
• Critical Unknown: The economic viability of the challenge mechanism. It requires bonded watchers with sufficient capital to be constantly online, creating a potential liveness-vs-censorship trade-off.

A sovereign rollup (e.g., potential Rollkit implementation) posts data to Bitcoin and lets its own nodes enforce rules. A smart contract rollup (e.g., Chainway's Citrea) has its bridge/settlement contract on Bitcoin. The DA choice dictates the model.

• Sovereign Risk: No forced tx inclusion on L1; relies on social consensus for upgrades.
• Smart Contract Risk: Bridge contract complexity becomes a single point of failure, as seen in hacks on Multichain and Wormhole.