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Sandy Kory became BillionToOne's first outside investor in 2016, writing an…

2026-06-29 · 14:31 UTC ·@sandykory ·2 min read

Brief

Sandy Kory recounts becoming BillionToOne’s first outside investor in 2016 after meeting founders Oguzhan Atay and David Tsao in San Francisco and being convinced more by their communication and execution than by the science. Primed by a TechCrunch piece on YC’s inaugural Fellowship and a prior missed Benchling opportunity, she wrote an initial pre-seed check, doubled it a month later, added another a year on, then made seven further investments—ultimately making B2O her largest holding—and followed the company through every round to its IPO. Kory emphasizes the founders’ “fanatical” execution: detailed quarterly investor updates, consistent goal attainment, transparent handling of setbacks, plus her hands-on contributions (two partnerships and persuading 16 friends & family to invest). She warns against overlearning from single successes but treats B2O’s founder bar as a model for generational companies.

Why it matters

Sandy Kory became BillionToOne's first outside investor in 2016, writing an initial pre-seed check after meeting founders Oguzhan Atay and David Tsao in San Francisco and then following the company through every round until its IPO.

Key details

  • She increased her exposure early—doubling her initial check a month later, adding another check a year after that, and ultimately writing seven additional checks, which made BillionToOne her single biggest position.
  • Kory cites founder communication and relentless execution as the decisive signals: the company sent detailed quarterly investor updates, consistently hit (and often exceeded) stated goals, and publicly confronted and overcame setbacks.
  • She played an active support role between the A and B rounds by assembling two partnerships and convincing 16 friends & family investors to participate; her initial interest was primed by a TechCrunch write-up of YC’s inaugural YC Fellowship and a prior missed opportunity with Benchling.
Source evidence

In 2016, I became @BillionToOneInc's first outside investor when I wrote a check into their pre-seed round. I invested (and followed in every round until the IPO) because I saw exceptional potential in the founders. But my conviction had little to do with their science.

I'd been interested in the intersection of software and bio for a while. A couple years earlier, I'd looked at Benchling but took too long to pull the trigger. Big mistake. So when B2O showed up in TechCrunch’s write-up of YC’s inaugural YC Fellowship program, I was already primed.

I met the founders, Oguzhan Atay and David Tsao, for coffee in SF. I knew almost nothing about biotech diagnostics, so I asked newbie questions and paid close attention to how they answered them. In healthcare, you need to be able to communicate with people across different levels of background knowledge. These 2 could do that. By the end of the meeting, I felt like I really understood what they were building and why it had the potential to win a big market.

I wrote a very small check initially and helped them informally as they kept raising. I doubled my investment a month later after observing impressive intensity and coachability. I wrote another check a year after that as they raised a small pre-seed extension. It was bigger than before, but it still wasn’t a huge position at that point. I had a bit of an impostor complex investing as a biotech novice. But imposter syndrome be damned, I ended up writing 7 more checks into the business and made it my single biggest position.

The biggest signal of their potential was their almost fanatical level of execution. Every quarter, they sent out detailed investor updates. They always hit their goals, and usually extra ones. When they hit setbacks–no startup is immune to these slings and arrows–they always confronted them directly and overcame them. I can speak for other early investors: none of us ever saw another company with more consistently stellar performance.

I take most satisfaction in the number of follow-on checks I wrote. It’s one thing to write a small check backing impressive founders doing something you can’t understand. I also love that I was able to put together 2 partnerships and convince 16 friends & family members to invest in between the A and the B. Some investors will never look at a round extension or a bridge round. Not me.

I should be honest about the temptation to be overly deterministic about all of this. I made many other investments in 2016, all of which I was excited about. A few more became unicorns, and several others built strong businesses. But this is the best one, bar none.

It’s easy to over-learn from low-sample-size successes. So I don’t try to look for clones of B2O. But my understanding of the B2O founder’s absolutely remarkable technical and operational brilliance informs my approach today. It’s a great example of the extremely high bar that founders must clear if they want to build a truly generational company.