On May 7, 2025, Eastern Time, GOAT Network officially released the GOAT BitVM2 white paper, proposing the first practical Bitcoin-native zkRollup protocol. This protocol builds on the advantages of the original BitVM2 protocol while introducing multiple innovations that systematically address key issues in security, challenge mechanisms, and economic incentives, laying the foundation for the scalability and programmability of the Bitcoin ecosystem.

The Potential and Real Bottlenecks of BitVM2

The BitVM2 protocol, proposed by Robin Linus and the ZeroSync team in 2024, is an innovative path that allows for on-chain verification of arbitrary computations without changing the Bitcoin mainnet protocol, creating possibilities for Bitcoin zkRollup and cross-chain bridges. However, there are still key issues to be addressed when moving towards practical applications and using BitVM2 for production-level cross-chain bridges:

• Operator Double-Spending Attacks: Currently, BitVM2 allows operators to submit verifiable but actually fraudulent states (e.g., sourced from forked chains), which may trigger the risk of double-spending attacks when users withdraw funds.
• Inefficient Challenge Process: The existing mechanism employs a one-to-one (staking, challenge) relationship, and the lengthy challenge cycle leads to high computation and coordination costs. Additionally, it does not support flexible withdrawal amounts, reducing fund utilization and user experience.
• Lack of Effective Incentive Mechanisms: The protocol lacks effective incentives to drive participation from various roles in the Rollup ecosystem, especially since challengers often do not receive rewards, leading to insufficient motivation to initiate challenges honestly and timely. In systems relying on crowdfunding incentives, there may also be issues with rewards being allocated to the wrong participants, further undermining the accuracy and effectiveness of incentives.

GOAT BitVM2: Three Major Mechanism Innovations

GOAT Network has launched the GOAT BitVM2 enhancement plan from an engineering perspective and has deployed it as the core execution system of GOAT Network, bringing Bitcoin zkRollup into practical application for the first time. This plan fundamentally improves upon three mechanisms:

1. Cryptoeconomic Security Layer

By combining Bitcoin's native Script verification with GOAT Network's dual penalty mechanism, the cost of malicious behavior by operators is significantly increased. This mechanism also maintains a reasonable scale of operator sets, ensuring high system activity under the "1-of-n honest node" assumption.

2. Accelerated Dispute Resolution

A multi-round challenger rotation mechanism is adopted, greatly shortening the challenge processing cycle and reducing effective finality time to less than one day.

3. Incentive-Aligned Challenge Economy

Successful challengers can receive a "fraud bounty" composed of the malicious proposer's staked funds. This mechanism increases challenge participation rates and aligns economic incentives between challenge behavior and the risk of operator malfeasance.

Universal Operator Model: Integrated Reconstruction of Economics and Architecture

To achieve the above mechanisms, GOAT Network has integrated and reconstructed the complex and separated role system in BitVM2.

In the traditional BitVM2 architecture, the Rollup system includes various roles such as sequencers, challengers, operators, and committee members. Due to significant differences in responsibilities and costs among these roles, designing a fair and efficient Rollup economic model and incentive mechanism becomes a highly challenging task.

The core innovation of GOAT Network lies in unifying these roles into a single identity—Universal Operator (referred to as Operator)—and through a role rotation mechanism, allowing all participants to take on different responsibilities at different times. All operators are required to stake in L2, and each round will be assigned to specific roles, bringing the following four major advantages:

• Balance of Revenue and Costs: GOAT Network ensures that income and expenses are relatively balanced in the long term by rotating operators between profit-generating and high-cost roles, avoiding the situation where some operators bear high computation costs for extended periods.
• Alignment of Incentive Mechanisms: The cross-subsidy mechanism between different roles smooths revenue fluctuations, incentivizing operators to maintain honest participation in any role.
• Lower Participation Threshold: Small and medium nodes do not need to continuously bear high-cost roles, allowing for easier participation and enhancing the system's decentralization and openness.
• Enhanced System Resilience: Even if individual operators go offline, the system can continue to operate through flexible role allocation, avoiding reliance on single points of failure.

In summary, GOAT Network unifies the behavioral roles of sequencers, computators, challengers, etc., into a role pool composed of staked operators, with all operators taking turns in responsibilities and subject to the constraints of the penalty mechanism. Proposers submitting fraudulent states will be penalized, and challengers who fail to fulfill their duties or engage in malicious challenges will also be penalized. This mechanism ensures that honest behavior is economically optimal while preventing the long-term concentration of roles in specific individuals through a clear rotation mechanism, thereby reducing centralization risks.

Protocol Architecture Overview: A Systemic Loop Built Around Universal Operators

This architecture not only needs to cover the cross-chain inflow and outflow processes (Bridge-In & Bridge-Out) but also to achieve trusted submissions from the sequencer set, on-chain coordination of the challenge process, and efficient generation and verification of zk proofs. The following are the core components of the GOAT BitVM2 protocol architecture:

Universal Operator Model

In GOAT BitVM2, each universal operator runs the same software and stakes BTC to gain participation eligibility. Through deterministic rotation or a random mechanism based on staking weight, these operators take turns fulfilling the following roles: sequencer (responsible for block production), prover (generating zkSNARK proofs), publisher (submitting state data to L1), and challenger (questioning fraudulent states). Each operator will experience both profit-generating and cost-bearing roles, thus avoiding role concentration and enhancing the system's fault tolerance through diversity.

Deposit and Withdrawal Processes

• Deposit: Users lock BTC and receive PegBTC in L2.
• Withdrawal (Peg-out): There is no need to rely on L1 to verify complex BitVM2 withdrawal scripts. Instead, GOAT uses an atomic swap mechanism to complete the withdrawal process directly with operators, while combining anti-fraud protocols to ensure security and reliability.

Sequencer Set Commitment

• Operators submit the Merkle Root of their public key set via OP_RETURN on the Bitcoin main chain.
• L2 utilizes transaction introspection to verify historical BTC states and matches them with the sequencer set on L1. This design does not require modifications to Bitcoin's consensus rules while achieving strong alignment with the native BTC state.

Efficient Dispute Resolution and zkMIPS Performance Boost

For Bitcoin-native zkRollup to be practical, it must have an efficient fraud detection and dispute resolution system. GOAT BitVM2 has made the following designs in challenge models and proof performance:

Multi-Round Random Challenger Selection

When a challenger is needed (e.g., during operator reimbursement), the system randomly selects a challenger from all staked nodes. If the selected challenger fails to initiate a challenge in a timely manner, the system will randomly select a new challenger as a substitute. If the new challenger successfully identifies fraud and initiates a challenge, all previous challengers who failed to fulfill their duties will be penalized (their stakes will be forfeited). Notably, anyone can initiate a challenge in any round, thus maintaining the security of the "1-of-n honest participant" assumption.

Additionally, random role assignment and fully penalizable staking mechanisms effectively prevent bribery attacks, ransom-style extortion, and malicious interference.

On-Chain and Off-Chain Execution

Most computational logic (such as ZKP generation, fraud verification, BitVM2 interaction scripts, etc.) is executed in L2, with only the final results (state submissions, challenge processing, penalty operations, etc.) uploaded to L1. This design significantly reduces on-chain gas costs while ensuring the verifiability of the entire system.

ZKP Performance Enhancement: Self-Developed zkMIPS

GOAT's self-developed zkMIPS is a zkVM compatible with the MIPS instruction set, optimized for STARK/SNARK backends. By batch processing multiple blocks and generating a unified proof periodically (e.g., hourly), GOAT's prover achieves extremely high cost efficiency. The "truth-table" method of BitVM2 can also be used in challenges to quickly locate dispute positions, facilitating rapid resolution of disputes.

Summary

Comparison with Original BitVM2: Faster, More Stable, More Practical

GOAT BitVM2 uses the Bitcoin network as the settlement layer and builds a decentralized sequencer network as the computation layer. Under the "1-of-n honest participant" assumption, this solution successfully addresses key issues in BitVM2 regarding flexible withdrawal amounts and insufficient challenger incentives. To accelerate optimistic verification, GOAT introduces a multi-round challenge mechanism, significantly improving the efficiency and effectiveness of fraud detection. Furthermore, combined with the efficient generation of ZK proofs by zkMIPS, GOAT BitVM2 has become the safest and most performant zkRollup protocol in the current Bitcoin ecosystem, with the potential to significantly accelerate the practical implementation of BitVM2 in the market.

Not only has it achieved breakthroughs in technical architecture, but GOAT BitVM2 has also built a robust economic system based on universal operator rotation. This system ensures that responsibilities such as sequencers, provers, challengers, and publishers are fairly distributed among all stakers. Through transaction fee sharing, fraud bounties, and penalty mechanisms, the protocol encourages honest behavior while economically penalizing malicious actions, thus creating a sustainable, fair, and resilient decentralized ecosystem.

As the first truly practical Bitcoin zkRollup protocol, GOAT BitVM2 achieves:

• Native security and compatibility without hard forks
• Rapid challenge mechanisms
• Reconstruction of economic incentives
• Efficient zero-knowledge proof engine
• Transition of BitVM2 from theoretical model to engineering practice

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