Sebastian Siemiatkowski
Angel Investor · Co-Founder at Flat Capital
Stockholm, Sweden
Sebastian Siemiatkowski is a seed investor at Flat Capital in Stockholm focused on Software and Internet. Sebastian Siemiatkowski is based out of Stockholm, Stockholms Lan, and is the Co-Founder and CEO of Klarna. Sebastian Siemiatkowski attended the Stockholm School of Economics.
- Total investments:
- 22
- Last investment:
- Lead investor:
- 9%
Last updated:
For AI agents: llms.txt
Industries Sebastian Siemiatkowski invests in
Stages Sebastian Siemiatkowski invests in
Countries Sebastian Siemiatkowski invests in
Round sizes
Contacts
| Type | Contact | Validation |
|---|---|---|
| Work email | ||
| Personal email | ||
| Work phone | ||
| Personal phone | ||
| Socials |
Round size
- Seed
- $1.1M–$8M
- Series A
- $10M–$200M
- Venture - Series Unknown
- $798k–$800M
Investment Focus
Industry
- Software 8 (36%)
- Internet 4 (18%)
- E-Commerce 4 (18%)
- SaaS 3 (14%)
- FinTech 3 (14%)
Stage
- Seed 4 (18%)
- Series A 4 (18%)
- Venture - Series Unknown 3 (14%)
- Pre-Seed 2 (9%)
- Series C 2 (9%)
Country
- Sweden 7 (32%)
- United States 3 (14%)
- Poland 1 (5%)
- Germany 1 (5%)
- United Kingdom 1 (5%)
Investments
| Company | Description | Round | Links |
|---|---|---|---|
| Introducing nexos.ai — a powerful model gateway that delivers game-changing AI solutions. With advanced automation and intelligent decision making, nexos.ai helps simplify operations, boost productivity, and accelerate business growth. | $35.2M / Series A / Sep 29, 2025 | ||
| Lovable builds software that builds software. Lovable vision is to unlock human creativity by enabling anyone to create software. | $200M / Series A / Jul 17, 2025 | ||
| Introducing nexos.ai — a powerful model gateway that delivers game-changing AI solutions. With advanced automation and intelligent decision making, nexos.ai helps simplify operations, boost productivity, and accelerate business growth. | $8M / Seed / Jan 17, 2025 | ||
| Talentium is an AI-powered platform revolutionizing the way you discover and connect with top talent. Engineered specifically for recruitment, Talentium is your go-to platform for finding top talent in seconds globally.Talentium has an AI Search that can find the exact persons companies are looking for in seconds, an automated communication andoutreach system connected with your mail & calendar. A jobs dashboard to manage all your candidates, and to finalize it, complete statistics on performance where you can see your actual results. | $3.7M / Pre-Seed / Dec 04, 2024 | ||
| Klarna is an eCommerce payment solutions platform for merchants and shoppers.The platform gives customers the freedom to choose how and when to pay. They also offer direct payments, pay after delivery options, and installment plans. Klarna is a regulated bank known for its “buy now, pay later” model that offers shoppers interest-free financing onretail purchases over a period of installments.Klarna was founded in 2005 in Stockholm, Sweden by Sebastian Siemiatkowski, Niklas Adalberth, and Victor Jacobsson. | $800M / Venture - Series Unknown / Jul 11, 2022 | ||
| Discord operates as a voice, video, and text communication service to talk and hang out with friends and communities. It was originally created for people who loved to play games, but these passionate people realized it could be enjoyed for more purposes. Discord is now used by everyone from local hiking clubs, to art communities, to study groups. | $2M / Secondary Market / Mar 03, 2022 | ||
| Violet is a Commerce API Platform enabling any app to integrate universal checkout in weeks instead of years. Through its headless API, any app maintains control of their own checkout, while ensuring product and order data is always in sync and seamlessly integrated with the original Merchant’s system.Violet is creating a more open, distributed,and collaborative version of e-commerce, where shoppers can buy products directly inside social, livestream, sms, voice, AR, VR, or any other experience developers and app companies decide to build. | $10M / Series A / Oct 12, 2021 | ||
| Nylas provides an API platform that enables developers to quickly and securely access and process user data from any email, calendar, and contacts provider in the world. The solution allows developers to integrate complex, unstructured communications data into their applications in days, providing secure pre-built integrations that are SOC 2certified, GDPR compliant, Privacy Shield certified, and HIPAA and FINRA-ready. | $120M / Series C / Jun 17, 2021 | ||
| Prion makes it quick and easy for the preschool staff to give parents insight into what happens at preschool - together with the children. The app is available free for iPhone, Android and iPad. | $412K / Pre-Seed / Sep 23, 2019 | ||
| Mollie is a payments platform that offers an easy-to-implement process for integrating payments into a site or app.It is a technology-based company processing payments for more than 50.000 clients with local payment methods such as Mastercard, VISA, Amex, PayPal, iDEAL, Bancontact, Bitcoin, SEPA Direct Debit, Cartes Bancaires, ESP, Giropay,SOFORT Banking, and more. Mollie aims to make online payment simple for merchants by taking away the complexity from payment methods and offering a simple, but powerful API.Mollie has a strong focus on technology, innovation, and reliability. The company was founded in 2004 and based in Amsterdam, Noord-Holland, The Netherlands. | $26.5M / Series A / Jul 02, 2019 | ||
| See all 22 investments → | |||
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FAQ
What does Sebastian Siemiatkowski invest in?
Sebastian Siemiatkowski invests primarily in Software, Internet and E-Commerce startups, most often at Seed and Series A stage. Most of the 22 investments tracked by Shizune back companies in Sweden. The Investment Focus section breaks down every industry, stage and country in the portfolio.
What round sizes does Sebastian Siemiatkowski invest in?
Sebastian Siemiatkowski typically joins rounds of $1.1M–$8M at Seed, $10M–$200M at Series A and $798k–$800M at Venture - Series Unknown. These are whole funding-round sizes, not Sebastian Siemiatkowski's own check, which is rarely disclosed: the 10th–90th percentile of the confirmed public funding rounds Sebastian Siemiatkowski took part in.
How do I contact Sebastian Siemiatkowski?
Public channels for Sebastian Siemiatkowski include LinkedIn, X (Twitter) and Facebook. For a verified work email and phone number, create a free Shizune account — contact data is searched across 20+ sources and validated before delivery, so your outreach lands in the right inbox.
When did Sebastian Siemiatkowski last invest?
The most recent investment recorded for Sebastian Siemiatkowski closed in Sep 2025. Shizune tracks 22 investments in total for this profile, including round sizes, stages and portfolio companies, all sourced from confirmed public funding rounds and refreshed monthly.
Is Shizune's investor data accurate?
Yes — every stat on this profile is calculated from confirmed public funding rounds monitored across hundreds of sources since 2020. This profile was last refreshed in Oct 2026 and is updated monthly. Spotted something off? Use the “Suggest an edit” link near the top of the page.
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