Zachary Rosen
About Zachary Rosen
Zachary (Zack) Rosen is co-founder and CEO of Pantheon, a venture-backed software company in San Francisco. Crunchbase lists him as CEO since August 2010. He attended the University of Illinois Urbana-Champaign. His first job was on Howard Dean's presidential campaign technology team.
Before Pantheon he co-founded the web agency Chapter Three (2006) and co-founded Mission Bicycle Company (2008), where he is listed as owner.
He also co-founded civic organizations. These include California YIMBY (2017), Covid Act Now (2020) and Abundance Network (2021). He sits on the boards of California YIMBY and Covid Act Now.
His AngelList profile lists him as an investor, incubator and advisor, based in San Francisco. We did not find a public list of his angel investments with dates, so only the deal below is confirmed. Crunchbase also has no investment list for him.
Zack Rosen is named as an angel investor in the $4.3M seed round of Mason AI, announced on March 30, 2026. The Urban Innovation Fund led the round, which the company described as oversubscribed.
Mason makes AI software that helps plan reviewers check building blueprints. The company says it uses a computer vision model built for blueprints. It also says reviewers report saving multiple hours per review.
He has not published a stage focus, sector list or check size that we could find, so none is stated here. His one confirmed AI investment is a seed-stage company in construction and permitting software. His own work centers on developer tools (Pantheon) and housing and civic policy (California YIMBY, Abundance Network). The Mason round is the only evidence of how this connects to his investing.
- Mason AI: AI platform that automates architectural blueprint review for plan reviewers. He joined its $4.3M seed round, announced March 2026, as an angel.
Investing activity
Zachary Rosen appears in 1 AI deal tracked by the Lounge deals desk. The rounds are mostly Seed, with a median round size of $4M. The most recent is Mason AI (Seed, $4.3M, Mar 2026).
Zachary Rosen most often invests alongside Urban Innovation Fund, Adam Cohen, Brian McClendon and David Braginsky, and the companies they back on Lounge are mostly in AI.
Deals
Frequently asked questions about Zachary Rosen
Who is Zack Rosen, the angel investor?
Zachary (Zack) Rosen is the co-founder and CEO of Pantheon. He also co-founded California YIMBY, Covid Act Now and Abundance Network. He is based in San Francisco.
Has Zachary Rosen invested in AI startups?
Yes. He is named as an angel in Mason AI's $4.3M seed round, announced March 30, 2026. The Urban Innovation Fund led that round.
What is Zack Rosen's check size?
He has not made a check size public, as far as we could find. Lounge does not estimate it.
What stage and sectors does Zack Rosen back?
He has no published thesis. His one confirmed AI investment is a seed round in AI for construction plan review. His operating background is in developer tools and housing policy.
How can founders contact Zack Rosen?
He is on LinkedIn at linkedin.com/in/zacharyrosen and on X as @zack. His AngelList profile also lists the site zacker.org.
Is this the same Zack Rosen who works at Ribbit Capital?
No. Zack Rosen at Ribbit Capital is a different person. This page covers the Pantheon co-founder who invested in Mason AI.
Is Zachary Rosen an angel investor?
Yes. Zachary Rosen invests personally as an angel.
What AI companies has Zachary Rosen invested in?
Zachary Rosen's AI investments include Mason AI. The 1 round on Lounge are listed on this page with amounts, dates and co-investors.
What stage does Zachary Rosen invest at?
In the rounds tracked on Lounge, Zachary Rosen has invested at Seed, with a median round of $4M.
Who does Zachary Rosen co-invest with?
Zachary Rosen's most frequent co-investors on Lounge are Urban Innovation Fund (1 deal), Adam Cohen (1 deal), Brian McClendon (1 deal), David Braginsky (1 deal) and Steve Bartel (1 deal).