About the role
About River Markets
I’m Antonin, co-founder and CTO of River Markets. Oscar (CEO) and I spent 3 years as quants in HFT shops and hedge funds. At nights and weekends we started trading predictions markets for fun and built a ton of trading infrastructure. We are now using this to build the prime brokerage and execution layer for prediction markets: the infrastructure professional and institutional traders need to access, trade, and manage risk across venues like Kalshi and Polymarket at scale. We value ownership, speed, and a high technical bar. We expect to do more with fewer people than a team our size has any right to. We are currently fully connected to 3 exchanges, have 6 proprietary execution algorithms and already have paying users.
How we work: AI-native
AI is the operating model. Every engineer treats AI as a core part of how they work: writing and reviewing code with AI tooling, automating their own workflows, and building internal systems that lean on LLMs where it makes sense. The bar isn't "can you use Claude": it's "what did you stop doing by hand this week?" We're looking for people who instinctively reach for automation, who multiply their output rather than just grinding harder, and who are excited that the leverage per engineer here is genuinely uncapped. We expect engineers to still understand every line they ship, AI-generated or not.
What you'll do
As a founding engineer, you'll own core systems end to end, scoping features directly with the founders, designing the architecture, building backend and frontend, integrating with exchange APIs, and watching it run in production. Concretely, you'll:
· Build and maintain the systems behind our order book, execution stack, exchange connectivity and portfolio management.
· Integrate with external exchanges and APIs where reliability and latency matter
· Write high-quality, testable code and raise the bar on everyone else's through review
