Flat Capital is a publicly traded family office based in Stockholm, Sweden, founded in 2013 by Nina and Sebastian Siemiatkowski. It invests long-term capital in entrepreneur-led companies globally, with notable positions in OpenAI, SpaceX, Klarna, DeepL, and Figma, operating with a flat cost structure of no fees and no carry.
Deal activity increased 200% year-over-year (3 deals in the last 12 months). Average disclosed round size is $47.2M (across 4 rounds with reported amounts).
Portfolio
7
Fund Size
—
Top Stage
Series B
Last 12 Mo
2
Team
SS
Sebastian Siemiatkowski
Partner
Portfolio Breakdown
Stage Distribution
Sector Distribution
Investment Activity
DealsAvg Round Size
Portfolio
7 investments
Top Co-Investors
Kraken Ventures2 shared
MUFG Innovation Partners2 shared
Opera Tech Ventures2 shared
DRW Venture Capital2 shared
Industrifonden2 shared
Aster Capital1 shared
Earlybird Venture Capital1 shared
Endeavor1 shared
General Catalyst1 shared
Thrive Capital1 shared
DAG Ventures1 shared
Creandum1 shared
Index Ventures1 shared
Diagram1 shared
Portage Ventures1 shared
Horizons Ventures1 shared
Social Leverage1 shared
Unbound1 shared
Last updated: 8 September 2026