# Sean Sullivan

![Sean Sullivan](/resources/cognition/portraits/sean-sullivan.webp)

Engineer at Cognition (SWE-1.5); built Codeium.vim; ex-Fig founding engineer  
Cognition  
San Francisco, California, United States

## At Cognition

- Role: Engineer (Engineering)
- Joined: Aug 2023
- How they joined: With Windsurf (https://www.autumn.ai/resources/cognition/acquisitions/windsurf)
- Before Windsurf: AI Engineering Consultant, Develop Health
- Overlapped before Cognition with other Cognition people at: Codeium (Windsurf); Nuro; Fig; Google; Harvard University (https://www.autumn.ai/resources/cognition/worked-together)

## Identity
- LinkedIn: https://www.linkedin.com/in/sullivan-sean
- GitHub: https://github.com/sullivan-sean

## 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. (https://www.linkedin.com/in/sullivan-sean)
- 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. (https://devin.ai/blog/codeium-copilot-alternative-in-vim)
- 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. (https://cognition.com/blog/swe-1-5)
- 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.' (https://www.linkedin.com/posts/sullivan-sean_fig-activity-7101987330370011136-tHBt)
- Was a Software Engineering Contractor at Codeium (Mountain View) from Aug 2023 to Jan 2024. Cognition acquired Codeium's Windsurf product in July 2025. (https://www.linkedin.com/in/sullivan-sean)
- Reposted Cognition's Devin GA launch with the caption 'Super excited to announce our GA launch today'. (https://www.linkedin.com/posts/sullivan-sean_devin-is-generally-available-today-just-activity-7272324404489945089-b9Yh)
- 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...' (https://www.forbes.com/sites/frederickdaso/2018/07/17/dropping-out-of-harvard-isnt-an-easy-choice-this-founder-did-it-three-times/)
- 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'. (https://techcrunch.com/2018/03/09/yc-backed-playbook-wants-students-to-make-plans-online-hang-out-offline/)
- Public headline says "yeehaw". (https://www.linkedin.com/in/sullivan-sean)
- 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'. (https://cognition.com/team-spotlights/alex-dengler)
- Consulted as an AI Engineering Consultant at Develop Health (SF) from Apr 2023 to Aug 2024, overlapping his Codeium contract, before joining Cognition. (https://www.linkedin.com/in/sullivan-sean)
- Software Engineer at Nuro on 'Autonomy Tools + Ground Truth Infrastructure' from Oct 2020 to Jul 2021, after a Sep-Dec 2019 Nuro internship. (https://www.linkedin.com/in/sullivan-sean)
- His GitHub has a fork of amazon-q-developer-cli ('Add autocomplete and AI to your existing terminal on macOS & Linux'), the open-source successor to Fig's CLI after the AWS acquisition. (https://github.com/sullivan-sean?tab=repositories)
- Built chat-langchainjs (TypeScript, about 294 stars), his most-starred original repo: a LangChain.js chat-over-docs app. (https://github.com/sullivan-sean?tab=repositories)
- Interned as an Associate Product Manager at Google (Jun-Sep 2020) and as a Software Engineer on the Integrity team at Instagram (May-Aug 2019, NYC). (https://www.linkedin.com/in/sullivan-sean)
- At Harvard's Developers For Development (2017) he 'Led a team of 8 in creating a predictive model of locust populations in Northern Africa for agriculture analytics firm Gro Intelligence'. (https://www.linkedin.com/in/sullivan-sean)
- Previous roles include AI Engineering Consultant at Develop Health; Software Engineering Contractor at Codeium; Founding Engineer at Fig; Software Engineer at Nuro; Associate Product Manager at Google; Software Engineer, Integrity at Instagram; Lead Engineer at Summer Playbook. (https://www.linkedin.com/in/sullivan-sean)
- Did a Product Consultant stint with Google's Business Inclusion team (Sep-Dec 2017); results were presented at the YouTube Creator Conference. (https://www.linkedin.com/in/sullivan-sean)
- Location is San Francisco, California, United States. (https://www.linkedin.com/in/sullivan-sean)

## Experience
- Engineer at Cognition - San Francisco Bay Area (Aug 2024 - Present)
- Partner at Lower Haight Line Dancing - San Francisco, California, United States (Jun 2024 - Present)
- AI Engineering Consultant at Develop Health - San Francisco, California, United States (Apr 2023 - Aug 2024)
- Software Engineering Contractor at Codeium - Mountain View, California, United States (Aug 2023 - Jan 2024)
- Founding Engineer at Fig - San Francisco, California, United States (Apr 2021 - Mar 2023)
- 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 - Mountain View, CA (Sep 2019 - Dec 2019)
- Software Engineer, Integrity at Instagram - Greater New York City Area (May 2019 - Aug 2019)
- Lead Engineer at Summer Playbook - Mountain View, CA (Sep 2017 - Jan 2019): - YCombinator W18 startup, couch surfing for college students, check out student stories below
- Created website platform used by students from 400+ universities to travel in 120+ countries
- Integrated frameworks including nginx, AWS, Docker, Flask, React Native, Postgresql, among others
- Developed mobile app for spontaneous hangouts with students nearby
- Product Consultant, Business Inclusion at Google - Cambridge, MA (Sep 2017 - Dec 2017): - Spearheaded data analysis with Google Business Inclusion team to create equitable access to digital resources
- Worked directly with Google Head of Communications to analyze market inequality for underpriveleged groups
- Developed methods to attenuate these discrepancies, results presented at Youtube Creator Conference
- Software Engineer at Developers For Development - Cambridge, MA (Aug 2017 - Dec 2017): - Led a team of 8 in creating a predictive model of locust populations in Northern Africa for agriculture analytics firm Gro Intelligence
- Improved on predictions by the United Nations FAO qualitative monthly writeups by linking ARTEMIS
satellite data to environmental data series
- Produced and presented python and machine learning workshops for my team members.
- Technical Analyst at CBE Consulting - Cambridge, MA (Jan 2017 - May 2017): - Conducted qualitative & qualitative analysis of industry data and trends to provide strategic decision advice and professional-standard development plans to a sustainability focused business; 
- Synthesized key considerations of the project (including market sizing, cost metrics, customer acquisition costs, and other descriptive variables such as industry structure and seasonality) into comprehensible presentations

## Education
- Harvard University - Master's degree, Applied Mathematics - (Jan 2016 - Jan 2020)
- Harvard University - Bachelor's degree, Neuroscience - (Jan 2016 - Jan 2020)
- University of New Hampshire - Mathematics - (Jan 2014 - Jan 2014): CATS Talent Program

## Sources
- https://www.linkedin.com/in/sullivan-sean
- https://devin.ai/blog/codeium-copilot-alternative-in-vim
- https://cognition.com/team-spotlights/alex-dengler
- https://www.forbes.com/sites/frederickdaso/2018/07/17/dropping-out-of-harvard-isnt-an-easy-choice-this-founder-did-it-three-times/
- https://techcrunch.com/2018/03/09/yc-backed-playbook-wants-students-to-make-plans-online-hang-out-offline/
- https://github.com/sullivan-sean?tab=repositories
- https://cognition.com/blog/swe-1-5
- https://github.com/sullivan-sean
- https://www.linkedin.com/company/cognition-ai-labs/posts
- https://www.linkedin.com/posts/sullivan-sean_fig-activity-7101987330370011136-tHBt
- https://www.linkedin.com/posts/sullivan-sean_devin-is-generally-available-today-just-activity-7272324404489945089-b9Yh


Researched with Autumn (https://www.autumn.ai) from public sources. Updated 2026-11-04. Profile: https://www.autumn.ai/resources/cognition/people/sean-sullivan · Everyone at Cognition: https://www.autumn.ai/resources/cognition/people