Operators who became investors.

Marcus spent eight years in product and engineering at a large-scale consumer AI platform — building recommendation systems and AI-powered personalization features that served tens of millions of users. Between 2018 and 2020, he angel-invested in a dozen applied AI companies, backing founders working on LLM infrastructure before the term existed in that form.

In 2020, he co-founded Hearthstone with a thesis: that the tools enabling AI-native development were being systematically underfunded in favor of the applications built on top of them. Hearthstone Fund I was the result.

Marcus leads investments in LLM infrastructure, agent orchestration, and AI developer tooling.

Natalie was a founding engineer at a YC-backed AI research tools startup — one of the early companies building interfaces between researchers and foundation models. After two years helping that company scale from prototype to product, she joined a Series-B NLP company as Head of Product, where she led the development of enterprise LLM application builders.

She co-founded Hearthstone in 2020 to focus on the part of the stack she knew best: LLM orchestration, agentic interfaces, and the developer-facing tooling that makes AI application development tractable.

Natalie leads investments in agentic frameworks, applied AI platforms, and developer experience tooling.