HotStuff / HotStuff-2

Origin: implements, designed by others; Solidus wrote its own Rust implementation. Solidus status: testnet, live (3-chain version) on a small dev committee; a faster HotStuff-2 core is built and benchmarked but not yet deployed publicly.

HotStuff is a family of Byzantine Fault Tolerant (BFT) consensus protocols built around one core idea: a chain of "quorum certificates." Each time a validator committee agrees on a block, it produces a quorum certificate (QC), a compact, aggregated proof that at least two-thirds of the committee signed off. A block becomes irreversible ("final") once enough further QCs have been built on top of it. The original HotStuff needs three consecutive QCs to finalize a block (the "3-chain" rule); the newer HotStuff-2 variant simplifies this to two ("2-chain"), cutting a round of network communication out of every block without weakening safety.

What made HotStuff influential wasn't the QC-chain idea alone, earlier BFT protocols like PBFT already had something similar: it was that HotStuff's leader-based, pipelined structure keeps communication linear in the number of validators, instead of the quadratic message complexity that made classic PBFT hard to scale past a few dozen nodes. That's why it's the consensus family behind several production blockchains, not just an academic curiosity.

Where it comes from

HotStuff was published in 2019 by Maofan Yin, Dahlia Malkhi, Michael K. Reiter, Guy Golan Gueta, and Ittai Abraham. It was picked up almost immediately by Meta (then Facebook) for LibraBFT, the consensus engine behind the Diem project, and later became the basis for Aptos's consensus layer. HotStuff-2, a tighter, two-phase version of the same idea, was described by Dahlia Malkhi and Kartik Nayak in 2023.

Solidus did not invent any part of this. It implements the published protocol from scratch in Rust, rather than forking an existing HotStuff codebase (Diem's, Aptos's, or otherwise).

What Solidus actually runs today

This is where precision matters, because there are two different things both loosely called "Solidus's HotStuff":

1. The shipped engine, live on the public testnet. rpc.solidus.network runs the original three-phase HotStuff: a VRF-elected leader proposes a block, the committee BLS-signs votes, and a block finalizes once two further quorum certificates have formed on top of it (round + 2 ≤ highest QC round). This is real, running code, on a small, team-operated validator committee, not an independent, adversarial network of external validators.
2. A HotStuff-2 core, built and benchmarked, not yet public. Separately, a from-scratch HotStuff-2 (2-chain) implementation has been written, TLA+-model-checked (963,033 states explored with zero safety violations, plus a larger simulated run), and benchmarked, but the benchmark ran on a single Apple M4 machine over local loopback, not a real network. It has not replaced the live testnet engine.

Conflating these two would be exactly the kind of overclaim this Lexicon exists to avoid. The honest sentence is: the live network runs 3-chain HotStuff; a faster 2-chain core exists as tested-but-undeployed engineering work.

Check it yourself

The public solidusnetwork/protocol repository is the place to look, no account or trust required. The solidus-consensus crate is the shipped engine; docs/v2-benchmarks.md and docs/bench/2026-07-13-apple-m4/ contain the raw logs and exact commands behind the HotStuff-2 single-machine numbers, including the TLA+ model-check output.

Related terms: HotStuff → BFT · Finality · Committee Election · Validator · Slashing · Proof-of-Identity · BLS Signature