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Sean Pennino

Sean Pennino

Product engineer at Y Combinator — ex-USDS, ex-Instagram

San Francisco Bay Area
wellfound+1
Joined February 2026
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Summary

Product-focused engineer who supports founders and internal YC tooling — Sean currently works as a Product Engineer at Y Combinator, contributing to the internal and founder‑facing platform and tooling that power YC batches and operations. ycombinator
Has public‑sector engineering experience — his public profile and social bio list a stint at the United States Digital Service, indicating experience building government digital services and working on high‑impact, mission‑critical software for public programs. x
Background in scaling product and marketplace e‑commerce — earlier roles include early‑employee and data/team manager responsibilities at Teespring and product/full‑stack engineering at Castle, showing experience across e‑commerce, data, and product engineering in startups. entercastle+1
Maintains public engineering work and side projects — GitHub account (spennino) hosts projects such as 'sleeper‑agent', demonstrating full‑stack web development (Next.js/React/TypeScript) and an interest in shipping public apps and tooling. github+1
STEM foundation with entrepreneurship training — holds a B.S. in Physics (University of Notre Dame) and an M.S. in Innovation Management & Entrepreneurship (Brown University), a combination that suggests strong quantitative problem‑solving plus formal training in startup and product strategy. nd+1
Active online presence and approachable personal brand — maintains social profiles (X/Instagram) with a personable bio ('i make pizza, jokes') and mentions hobbies like pizza‑making and climbing, which appear across company and social bios. x+2

Work

Education

Projects

Hobbies

Rock climbing and making pizza from scratch; mentions of pizza and outdoor/racing involvement appear in public bios. entercastle+1

Notes

GTGarry Tansaid
SPSean Pennino
is one of the most impressive product engineers they've worked with.

Aug 27, 2025