PeopleofSuperintelligence

Researcher

Sebastian Ullrich

Sebastian Ullrich is a programming-languages researcher whose work on Lean links formal proof with AI-assisted theorem proving. He became a core contributor to Lean in 2015, coauthored formal-verification research in 2017, presented a redesigned Lean 4 parser in 2018, and published work on hygienic macros in 2020. He completed a PhD on Lean 4 and co-founded the Lean Focused Research Organization with Leonardo de Moura in 2023. Lean received the ACM SIGPLAN Programming Languages Software Award in June 2025, with its citation highlighting the system’s use in AI-based mathematical reasoning. In June 2026, he presented a demonstration in which a general-purpose AI converted zlib into Lean and proved it correct after passing the library’s test suite; as of October 2026, he is Head of Engineering at the Lean FRO.

Works
45
Citations
708
h-index
14
Badges

Publication numbers from OpenAlex, as of 22 October 2026.

Timeline

  1. Since 2015

    Joining Lean's development

    He becomes a core contributor to Lean in 2015, helping develop the programming language and theorem prover.

  2. 2017

    A formal-verification paper

    At Karlsruhe Institute of Technology, he coauthors “A Metaprogramming Framework for Formal Verification” in 2017.

  3. October 2018

    A new Lean 4 parser

    In October 2018, he presents a new Lean 4 parser at Microsoft Research Redmond as part of a redesign to make the language's frontend easier for users to extend.

  4. 2020

    Hygienic macros for Lean 4

    In 2020, he and Leonardo de Moura describe a hygienic macro system for theorem-proving languages and report its integration into Lean 4.

  5. 2023

    A PhD and Lean FRO

    He completes a PhD on Lean 4’s design and co-founds the Lean Focused Research Organization with Leonardo de Moura in 2023. Lean FRO works to make formal verification more accessible across mathematics research, software and hardware verification, and AI-assisted theorem proving.

  6. June 2025

    Lean receives a SIGPLAN award

    Lean receives the ACM SIGPLAN Programming Languages Software Award in June 2025; its citation highlights Lean’s use in AI-based mathematical reasoning.

  7. June 2026

    AI verifies zlib in Lean

    In June 2026, he presents a demonstration in which a general-purpose AI converts zlib, a C compression library, into Lean, passes its test suite, and proves the code correct.

  8. As of October 2026

    Head of Engineering at Lean FRO

    As of October 2026, he is Head of Engineering and co-founder of the Lean FRO.

Career

  1. Since 2023Lean Focused Research OrganizationCo-founder, Head of Engineering
  2. 2016–2021Schmalkalden University of Applied Sciences
  3. 2016–2023Karlsruhe Institute of Technology
  4. 2010–2013German University of Administrative Sciences
  5. 2006–2010RWTH Aachen University

From the biography and OpenAlex affiliations (the years of papers that list the organization), so some years are approximate.

Most-cited works

  1. Strategic Development of Business Models: Implications of the Web 2.0 for Creating Value on the Internet2010 · 113 citations
  2. Negative online consumer reviews: effects of different responses2015 · Journal of Product & Brand Management · 88 citations
  3. A metaprogramming framework for formal verification2017 · Proceedings of the ACM on Programming Languages · 79 citationsWith Leo de Moura
  4. DETERMINANTS OF SOCIAL MEDIA WEBSITE ATTRACTIVENESS2013 · Journal of electronic commerce research · 75 citations
  5. eHEALTH IN THE PUBLIC SECTOR: AN EMPIRICAL ANALYSIS OF THE ACCEPTANCE OF GERMANY'S ELECTRONIC HEALTH CARD2011 · Public Administration · 40 citations

From OpenAlex, as of 21 October 2026.

  1. Google has the highest combined h-index among AI organizationsIncludes Convergent Research. We estimate that Google holds the highest combined h-index at 8,016, while universities account for 73% of the deduplicated total across AI organizations.
  2. More people shaping AI studied at Massachusetts Institute of Technology than at any other institutionIncludes Karlsruhe Institute of Technology. We estimate where the people shaping AI studied and where their careers led. Massachusetts Institute of Technology leads with 467 former students, including 291 recorded doctorates.
  3. The company share of AI researchers’ top papers was 31% in 2020–2024 and 8% in 1970–1974Includes Karlsruhe Institute of Technology. We estimate where the people shaping AI worked when their most-cited papers appeared: the company share was 31% in 2020–2024 and 8% in 1970–1974, and Google led all organizations in 2020–2024.
  4. The Massachusetts Institute of Technology trained or employed 44 of the 187 AI major-prize winners, more than any other universityIncludes Karlsruhe Institute of Technology. The Massachusetts Institute of Technology trained or employed 44 of the 187 AI major-prize winners, more than any other university. We compare doctorate and 5+ year employment links, career timing and current workplaces for 187 major-prize and 1,111 best-paper winners.

Colleagues

People with dated positions at the same organization in the same years.

Sources and credits

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  1. About me - Sebastian Ullrich sebasti.a.nullri.ch. Checked 20 October 2026.
  2. Sebastian Ullrich, Head of Engineering and co-founder | Convergent convergentresearch.org. Checked 20 October 2026.
  3. Dr. Sebastian Ullrich pp.ipd.kit.edu. Checked 20 October 2026.
  4. Lean 4: Reimplementing Lean in Lean lean-lang.org. Checked 20 October 2026.
  5. Beyond Notations: Hygienic Macro Expansion for Theorem Proving Languages arxiv.org. Checked 20 October 2026.
  6. Programming Languages Software Award sigplan-www.sigplan.hosting.acm.org. Checked 20 October 2026.
  7. About — Lean Lang lean-lang.org. Checked 20 October 2026.
  8. Theorem Proving in Industry with Lean lean-lang.org. Checked 20 October 2026.