Harmonic

Harmonic

Harmonic is an AI company building Aristotle, a mathematical-reasoning model designed to return answers that are formally checked rather than merely plausible. Instead of producing free-text reasoning like a typical chatbot, Harmonic outputs proofs in the Lean 4 language, which a verifier can confirm step by step. The company calls this approach Mathematical Superintelligence and argues it sidesteps the hallucinations that plague language models on hard math. Aristotle reached gold-medal level on the 2025 International Mathematical Olympiad, producing formally verified solutions to five of six problems. Harmonic ships Aristotle as a consumer app and a public API for students, researchers, and mathematicians.

Production credibility: Founded in 2023 by Tudor Achim (CEO, previously co-founder and CTO of self-driving company Helm.ai) and Vlad Tenev (Executive Chairman, co-founder and CEO of Robinhood). Harmonic has raised about $295M across three rounds in roughly 14 months: a $75M Series A (September 2024), a $100M Series B (July 2025) at a reported ~$900M valuation, and a $120M Series C (November 2025) at a $1.45 billion valuation. The Series C was led by Ribbit Capital, with Sequoia Capital, Kleiner Perkins, Index Ventures, Paradigm, and Laurene Powell Jobs' Emerson Collective participating. Aristotle delivered formally verified solutions to five of six 2025 IMO problems and reported 96.8% on the VERINA code-verification benchmark (December 2025). Its proofs are written in Lean 4 so results can be machine-checked for correctness.

Key Features

• Outputs solutions as Lean 4 proofs that a formal verifier can check line by line
• Aristotle consumer app (iOS) for step-by-step math problem solving
• Public Aristotle API for mathematicians, researchers, and students
• Mathematical Superintelligence (MSI) approach aimed at hallucination-resistant reasoning
• Gold-medal-level result on the 2025 International Mathematical Olympiad (5 of 6 problems)
• Reported 96.8% on the VERINA code-verification benchmark
• Flags inconsistencies and unproven steps instead of asserting unverified answers
• Trained substantially on synthetic, formally checked math proofs

Ideal Use Case

Students, researchers, and engineers use Aristotle to solve and verify math problems where a wrong step is unacceptable, getting a machine-checked proof rather than a plausible-sounding explanation.

How Harmonic differentiates

General chatbots like ChatGPT and Gemini answer math in natural language and can state confident but wrong steps. Harmonic's Aristotle instead emits Lean 4 proofs that are formally verified, so a correct answer is provable rather than merely likely. The cost is scope: Aristotle targets formal mathematics and verifiable reasoning, not open-ended writing, coding chat, or general knowledge. Against research efforts like Google DeepMind's AlphaProof, Harmonic ships a public app and API rather than a closed lab system. Coverage is still narrower than a generalist model, and problems that resist formalization fall outside its strengths.

FAQ

Q: What is Harmonic's Aristotle? A: Aristotle is Harmonic's math-reasoning model. It answers questions by producing proofs in the Lean 4 language that a formal verifier can check, aiming for results that are provably correct rather than just plausible.

Q: Who founded Harmonic? A: Harmonic was founded in 2023 by Tudor Achim (CEO, previously co-founder and CTO of Helm.ai) and Vlad Tenev (Executive Chairman and co-founder/CEO of Robinhood).

Q: How much has Harmonic raised? A: Harmonic has raised about $295M across three rounds. Its November 2025 Series C added $120M at a $1.45 billion valuation, led by Ribbit Capital with Sequoia, Kleiner Perkins, and others participating.

Q: Harmonic vs ChatGPT for math: what's the difference? A: ChatGPT answers in natural language and can produce confident but incorrect steps. Harmonic's Aristotle outputs Lean 4 proofs that are formally verified, so it targets provable correctness on formal math rather than general-purpose chat.

Q: Is Aristotle free to use? A: Harmonic offers the Aristotle app and a public API to students, researchers, and the general public, with free access available; check Harmonic's site for current limits and paid tiers.

tl;dr

Harmonic builds Aristotle, a math-reasoning AI that writes formally verified Lean 4 proofs to avoid hallucinations. Co-founded by Robinhood's Vlad Tenev and ex-Helm.ai CTO Tudor Achim, it raised $120M at a $1.45B valuation in late 2025 and hit gold-medal level at the 2025 IMO.

Related

Looking for more options? Browse the AI/ML Models directory or read our best AI models listicle. Harmonic is also tracked on Crunchbase.