How River Markets raised an $8.5M seed round

River Markets is the prime brokerage for prediction markets. The company gives professional traders one account and one API to trade across Kalshi, Polymarket, Polymarket US and Novig, with smart order routing, risk management and the order types institutional desks actually need.

In August 2026, River Markets announced an $8.5 million seed round led by Haun Ventures, with Y Combinator, Coinbase Ventures and Qube Research & Technologies participating, alongside angels from Google, Nvidia, JPMorgan and Citadel. The round closed in August 2026.

• Raised $8.5M seed led by Haun Ventures
• Founded by CEO Oscar Levy and CTO Antonin Parrot, who met at UC Berkeley
• Used by three of the top ten traders on Kalshi and Polymarket
• More than $50M moved on the platform

Before the raise started, Oscar did something most founders skip. He benchmarked the tool he would use to share the deck.

I signed up for 10 data rooms, uploaded the same document set to each one, and shared it the way you'd share it with a real investor. This is what I found.

The Challenge

Oscar and Antonin spent two years writing prediction market trading algorithms on nights and weekends before going full time. When they started raising, the problem was not the story, it was running the process.

1. A long investor list to sequence – Funds, strategics and angels all needed different materials at different moments.
2. No signal after sending – A PDF sent over email disappears. There was no way to tell interest from politeness.
3. Sensitive materials – Execution logic, venue relationships and volume numbers could not sit in an open link forever.
4. Two founders, no ops help – Every hour spent on document logistics was an hour not spent on product or on calls.

The Solution

One structured data room

Instead of a folder of attachments, River Markets built a single Papermark data room containing the deck, the model, the metrics and the diligence materials. Each investor got their own link, so access could be tailored and revoked without re-sending anything.

Slide-level engagement data

Papermark's page-by-page analytics showed the founders how long each investor spent on each slide. Slides that consistently held attention stayed in the deck. Slides that were skipped got cut or rewritten.

Papermark helped us structure, send and monitor investor interest. Extremely good to see which slides were eye catching or boring.

— Oscar Levy, CEO and co-founder, River Markets

Follow-ups timed to real interest

Real-time notifications told the team the moment a deck was opened, and repeat views flagged the investors worth calling first. Follow-ups went out while the material was still fresh instead of on a fixed weekly cadence.

Oscar's tips for founders raising now

1. Be clear in the pitch and the use of funds. Investors decide fast. Ambiguity about what you do or where the money goes is the most expensive thing in a deck.
2. Investor sequencing is extremely important. The order you talk to people in changes the outcome of the round, not just its speed.
3. Small angel checks can lead to bigger intros. A modest check from the right person often matters more for the round than its size suggests.
4. Track what happens after you send. Knowing which slides landed is the difference between guessing and iterating.

The Results

• $8.5M seed round closed in August 2026, led by Haun Ventures
• Deck iterated on real data, with weak slides identified from engagement rather than opinion
• Follow-ups prioritized by actual investor engagement instead of guesswork
• Sensitive execution and volume data kept under link-level control throughout the process

Use Case

Fundraising — River Markets used Papermark data rooms and analytics to run a multi-investor seed process with a two-person team.

Document Types Shared

• Pitch deck
• Financial model
• Platform and volume metrics
• Diligence materials

Conclusion

River Markets is building institutional infrastructure for the fastest-growing asset class in trading. Running a seed round the same way, on data rather than instinct, is what let two founders close $8.5 million while still shipping product.