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Arc’s consensus protocol provides deterministic finality in under one second. It is built on Malachite, a high-performance implementation of the Tendermint Byzantine Fault Tolerant (BFT) protocol, and uses a Proof-of-Authority (PoA) validator set. As a developer, you don’t interact with consensus directly, but it defines the guarantees you can rely on when building payment, trading, or settlement applications.

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Core properties

Arc consensus is designed for institutional-grade performance and trust:
  • Deterministic finality: A transaction is either unconfirmed or final. Once finalized, it cannot be reversed or reorganized.
  • Low latency: Blocks finalize in less than one second under normal conditions.
  • High throughput: Benchmarks show 3,000+ TPS with 20 validators and sub-second latency. Smaller validator sets can reach 10,000+ TPS.
  • Validator accountability: Validators are regulated institutions with operational and compliance obligations.
  • Optimistic responsiveness: The Tendermint protocol implemented by Malachite ensures block production and transaction confirmation proceeds as fast as the network permits, with no extra timeouts or artificial delays.

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Proof-of-Authority validator set

Arc uses a permissioned Proof-of-Authority (PoA) model.
  • Validators are selected, known institutions with reputations, compliance requirements, and operational guarantees (such as uptime SLAs and SOC 2 certification).
  • Geographic distribution ensures resilience. Validators run across multiple global regions.
  • Block production is rotated among validators to ensure fairness and liveness.
This design provides stronger assurances for regulated finance by replacing anonymous economic incentives with institutional accountability.

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How Tendermint consensus works in Malachite

To order and finalize transactions, Arc uses the Tendermint BFT consensus protocol, implemented in the Malachite consensus layer. At a higher level, Tendermint works as follows:
  1. Propose
    • One validator is chosen as proposer for a round.
    • The proposer bundles transactions into a block and broadcasts it.
  2. Pre-vote
    • Validators broadcast votes indicating whether they consider the block valid.
  3. Pre-commit
    • Validators broadcast a second round of votes.
    • If more than two-thirds of validators pre-commit to the same block, it is locked in.
  4. Commit
    • The block is finalized and appended to the chain.
    • Transactions inside the block are now irreversible.
This two-phase voting process ensures consensus safety: two conflicting blocks cannot both be finalized. As a result, block reorganizations are impossible, and each block is finalized quickly and deterministically. The diagram below illustrates the high-level concept behind this process.

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Deterministic finality

Unlike probabilistic models (like proof-of-work), Arc provides certainty about finality.
  • Once a block is finalized, it cannot be reverted without collusion of at least two-thirds of validators.
  • There is no need for developers to wait for multiple confirmations.
  • Applications can release funds or complete trades immediately after confirmation.
For developers, this reduces complexity since you don’t need rollback logic, and you can provide users with instant settlement guarantees.

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Performance characteristics

Arc is engineered for low latency and high throughput. In testnet environments, you can expect performance characteristics similar to the following:
  • 3,000 TPS with 20 globally distributed validators.
  • <350 ms finality under benchmark conditions.
  • >10,000 TPS with reduced validator counts (for example, 4 validators).
  • Future roadmap includes multi-proposer support (see below), which can increase throughput by ~10X, and consensus optimizations that can cut latency by ~30%.
These metrics make Arc suitable for high-frequency payments, trading, and settlement systems.

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Multi-proposer

The Malachite roadmap includes a planned upgrade called multi-proposer. This feature allows multiple validators in the network to propose blocks in parallel, rather than sequentially. By enabling concurrent block proposals, multi-proposer can significantly increase network throughput and improve overall scalability.

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Security guarantees

Arc combines protocol-level safety with institutional safeguards:
  • Safety: With <1/3 faulty validators, consensus guarantees no conflicting blocks can be finalized.
  • Liveness: The system continues to make progress as long as ≥2/3 of validators are online and honest.
  • Accountability: Validators are regulated institutions with compliance obligations, making malicious behavior costly in the real world.
  • Resilience: Geographic distribution reduces correlated downtime and attack risk.

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Developer implications

For developers, consensus guarantees that:
  • Your transactions settle instantly and irreversibly.
  • You don’t need to design around chain reorganizations or probabilistic confirmations.
  • Arc can handle institutional workloads with high TPS and low latency.
  • Validator accountability ensures the network remains secure and compliant, even at scale.

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Roadmap

Malachite continues to evolve:
  • Multi-proposer support: Multiple proposers per height increase overall throughput.
  • Latency optimizations: New protocol variant reduces consensus rounds from three to two.
  • Permissioned Proof-of-Stake transition: Over time, Arc may evolve from PoA to a permissioned PoS model, allowing broader validator participation while maintaining compliance.
These upgrades will further strengthen Arc as infrastructure for global financial applications.