- Joined Cognition
- Jul 2025
- How they joined
- With Windsurf
- Before Windsurf
- Develop HealthAI Engineering Consultant
- Status
- Current
Overlapped before Cognition
Details
LocationSan Francisco, California, United States
LanguagesEnglish, Portuguese
UniversityHarvard University, University of New Hampshire
Public SpeakingLeadershipTime ManagementTeamworkResearchAndroid DevelopmentJavaMicrosoft ExcelPythonFront-end DevelopmentMicrosoft OfficeJavaScript
Notes
- Joined Cognition as an Engineer in Aug 2024 (San Francisco Bay Area), per LinkedIn; Cognition's site later calls him a Member of Technical Staff.Aug 2024
- Codeium's Jan 2023 launch post for Vim/Neovim support says: 'We have made the Codeium.vim repo open source, and want to thank Sean Sullivan for building almost the entirety of this plugin.' The repo is now Exafunction/windsurf.vim.Jan 19, 2023
- SWE-1.5 (released Oct 29, 2025) is Cognition's fast agent model, served at up to 950 tok/s on Cerebras. Cognition calls it 'the product of a small and incredibly focused team'; the brief places him on it, but the public blog does not name team members.Oct 29, 2025
- Founding Engineer at Fig (YC terminal-autocomplete startup) from Apr 2021 to Mar 2023. On Fig's acquisition by AWS he wrote: 'Learned a lot in my time at Fig growing our products, building in open source, and innovating on one of the oldest dev tools.'Aug 28, 2023Could not be more excited to share Fig's acquisition by Amazon Web Services (AWS)! Learned a lot in my time at Fig growing our products, building in open source, and innovating on one of the oldest dev tools. Grateful for the powerhouse of a team I had the opportunity to work with and excited to see what comes next
- Was a Software Engineering Contractor at Codeium (Mountain View) from Aug 2023 to Jan 2024. Cognition acquired Codeium's Windsurf product in July 2025.Aug 2023
- Reposted Cognition's Devin GA launch with the caption 'Super excited to announce our GA launch today'.Sep 12, 2025
- Forbes (2018) says Summer Playbook cofounders Luke Heine and Raphael Rouvinov brought him on 'as their first full-time employee'. Heine is quoted: 'Sean's the best teammate I could ever ask for. He's unbelievable and works harder than anyone...'Jul 17, 2018
- TechCrunch corrected a 2018 story on YC W18 startup Playbook: Sean Sullivan was its first employee, not a cofounder. He was Lead Engineer there from Sep 2017 to Jan 2019 and built a platform 'used by students from 400+ universities to travel in 120+ countries'.Mar 9, 2018
- Public headline says "yeehaw".
- Cognition's 2026 team spotlight shows 'Sean Sullivan, Member of Technical Staff, teaching fellow Cog-leagues how to line dance at our 2026 Ranch offsite'.2026
- Consulted as an AI Engineering Consultant at Develop Health (SF) from Apr 2023 to Aug 2024, overlapping his Codeium contract, before joining Cognition.Apr 2023
- Software Engineer at Nuro on 'Autonomy Tools + Ground Truth Infrastructure' from Oct 2020 to Jul 2021, after a Sep-Dec 2019 Nuro internship.Oct 2020
Experience
Engineer at Cognition
Aug 2024 - Present
San Francisco Bay Area
Partner at Lower Haight Line Dancing
Jun 2024 - Present
San Francisco, California, United States
AI Engineering Consultant at Develop Health
Apr 2023 - Aug 2024
San Francisco, California, United States
Software Engineering Contractor at Codeium
Aug 2023 - Jan 2024
Mountain View, California, United States
Founding Engineer at Fig
Apr 2021 - Mar 2023
San Francisco, California, United States
Software Engineer at Nuro
Oct 2020 - Jul 2021
Autonomy Tools + Ground Truth Infrastructure
Associate Product Manager at Google
Jun 2020 - Sep 2020
Software Engineer at Nuro
Sep 2019 - Dec 2019
Mountain View, CA
Education
Harvard University
Jan 2016 - Jan 2020
Master's degree, Applied Mathematics
University of New Hampshire
Jan 2014 - Jan 2014
Mathematics
CATS Talent Program
Projects
Codeium.vim / windsurf.vim: Vim/Neovim AI completion plugin (built almost entirely by him)
chat-langchainjs
Fig autocomplete (founding engineer)
SWE-1.5 (Cognition)
Recent posts
August 2023
Could not be more excited to share Fig's acquisition by Amazon Web Services (AWS)! Learned a lot in my time at Fig growing our products, building in open source, and innovating on one of the oldest dev tools. Grateful for the powerhouse of a team I had the opportunity to work with and excited to see what comes next
Press
Profiles
Code
Repos46
Repos
Exafunction/codeium.vim (windsurf.vim)Sullivan-sean/chat-langchainjs
