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Arc’s consensus layer is built on Malachite, a high-performance, open-source implementation of the Tendermint Byzantine Fault Tolerant (BFT) protocol. BFT consensus ensures the network reaches agreement on a single history of transactions even if some validators behave maliciously or go offline. Arc uses a Proof-of-Authority (PoA) validator set to order transactions, produce blocks, and deliver deterministic finality — the guarantee that committed blocks are permanent and can never be reversed or reorganized — in under one second.

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How Malachite consensus works

For how this fits into the broader architecture, see the system overview. Each block passes through a four-step pipeline. A rotating proposer assembles transactions, and all validators participate in two rounds of voting before the block is committed.
  1. Propose — A validator selected as proposer for the current round bundles pending transactions into a block and broadcasts it.
  2. Pre-vote — Every validator evaluates the proposed block and broadcasts a vote on its validity.
  3. Pre-commit — Validators broadcast a second vote. If more than two-thirds of validators pre-commit to the same block, it proceeds to commit.
  4. Commit — The block is finalized and appended to the chain. Every transaction in the block is irreversible.
This two-phase voting process (pre-vote + pre-commit) guarantees that two conflicting blocks can never both be finalized, making reorganizations impossible.

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Proof-of-Authority validator set

Arc uses a permissioned Proof-of-Authority (PoA) model instead of anonymous economic staking. Validators are selected, known institutions with compliance obligations and operational guarantees. For details on operating a validator node, see running a node.
  • SOC 2 certified — Validators meet audited security and availability standards.
  • Geographic distribution — Nodes run across multiple global regions to reduce correlated downtime.
  • Rotating proposer — Block production rotates among validators to ensure fairness and liveness.
  • Uptime SLAs — Each validator commits to operational availability requirements.
This design replaces anonymous economic incentives with institutional accountability, providing stronger assurances for regulated finance.

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Performance characteristics

Performance also depends on the execution layer, which processes transactions within each block. Malachite delivers optimistic responsiveness: blocks are produced as fast as the network permits, with no artificial delays or extra timeouts.

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Security guarantees

Arc combines protocol-level safety with institutional safeguards: The deployment model provides additional detail on how validators are geographically distributed.

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Roadmap

The Malachite roadmap includes multi-proposer support (multiple validators propose blocks in parallel for higher throughput), a protocol optimization that reduces consensus from three rounds to two for lower latency, and a potential transition from Proof-of-Authority to permissioned Proof-of-Stake to broaden validator participation while maintaining compliance requirements.