Will
Yin

Will Yin was the kind of student who, at sixteen, was presenting cardiovascular disease diagnostics at Nobel Prize ceremonies in Sweden. Not as an observer - as a researcher. Greenwich High School's class of 2017 valedictorian, U.S. Presidential Scholar, machine learning engineer before most of his peers had written their first for-loop. He enrolled at Stanford to study neuroscience, computer science, and mathematics, ran experiments at the Stanford School of Medicine, and crossed the country to do biochemistry research at MIT.

Then he quit. Sophomore year. Not from burnout and not from doubt. He looked at the thing he cared about - the healthcare system failing people who needed it most - and concluded that being inside a university lab was the slowest possible route to fixing it.

That clarity is the throughline. Every career move Yin has made runs on a single engine: what is the fastest path to impact? At 19, that meant joining Y Combinator and building Jupiter, a food-creator advertising network that raised $9M from Khosla, Canaan, NFX, and YC itself. By 2023, it meant pivoting entirely - watching family members navigate the nightmare of specialty drug approvals for cancer and Alzheimer's, and deciding that the 30-day wait between a life-saving prescription and the first infusion was not inevitable. Just unoptimized.

Specialty drugs are the future of medicine and the present dysfunction of healthcare administration. Treatments for cancer, multiple sclerosis, autoimmune conditions, rare diseases - these drugs now account for more than half of all U.S. prescription spending. They are also the most delayed. Not because the science is slow. Because the paperwork is.

Before a patient receives their first infusion of a biologic or specialty pharmaceutical, a clinic must verify insurance coverage, submit a prior authorization request, wait for a response (often by fax), handle appeals if denied, confirm reimbursement amounts, and manage billing. That process - done manually, by overwhelmed staff, across fragmented payer portals, with inconsistent information - routinely takes weeks. Patients with cancer. Patients with Alzheimer's. Waiting.

Will Yin watched this happen to people in his family. So did his co-founder Rohit Rustagi. They were not surprised. They were done waiting for someone else to fix it.

Mandolin launched its product in January 2025. The pitch is not "software that helps your staff work faster." The pitch is the staff. Mandolin's AI agents read, reason, and act across payer portals, fax systems, EMRs, and phone queues - completing entire workflows end-to-end, around the clock, with the judgment of an experienced biller and the throughput of a machine.

Benefits verification that used to take days: done in minutes. Prior authorization submissions that used to require three human handoffs: automated. Clinical notes parsed, payer policies analyzed, reimbursement amounts confirmed. The agents do not hand off to humans for the routine cases. They handle it.

Within months of launch, Mandolin was live across 700+ clinic locations and processing cases for 250,000+ new patients annually. Customers report converting days of administrative work into hours. Patients are getting on therapy weeks earlier. The outcomes are not theoretical.

Greylock, SignalFire, and Maverick led the financing alongside SV Angel. Jerry Yang - co-founder of Yahoo! - and Guillermo Rauch, CEO of Vercel, joined as individual investors. The $40M Series A announced in June 2025 brings Mandolin's total funding to $97M.

Before Mandolin, there was Jupiter. Before Jupiter, there was Palantir. Before Palantir, there was a Stanford sophomore who ran neuroscience experiments at the medical school and biochemistry research at MIT. Will Yin's career does not look like a straight line because it isn't one - it looks like a person who runs toward the hardest version of whatever problem he is currently obsessed with.

At Virtualitics, he worked on machine learning applications for large-scale data visualization. At Palantir, he was a Forward Deployed Engineer - the company's version of someone who goes into an organization, figures out what's actually broken, and builds something that works. That sensibility - operational, outcome-oriented, allergic to abstraction - carries through everything he's done since.

Jupiter (YC W19) was an advertising and commerce network for CPG brands and food creators. It raised $9M from Khosla Ventures, Canaan, NFX, and Y Combinator, and built infrastructure for a then-nascent grocery-delivery economy across the Bay Area. Yin served as Co-Founder, President, and CTO - the person who built the product and made it work at scale. When the company reached its conclusion, he did not take a break. He started paying attention to a different broken system.

The pivot to healthcare was not random. Both Yin and Rustagi had watched family members fight the administrative machinery around specialty drug access. They knew the workflows from the researcher's perspective - they had done neuroscience research on Alzheimer's and cancer treatments. They built Mandolin in 2024 because they ran out of reasons not to.

SignalFire described him as a "scrappy repeat founder" known for speed of learning and a customer-centric approach. Greylock noted his vision for AI-native platforms in physician-administered drugs. The investors who backed him twice - first at Jupiter, now at Mandolin - are not betting on the idea. They're betting on the person who executes it.

Mandolin's cap table reads like a dispatch from both traditional venture and founder-operator networks. The institutional lead is Greylock - one of Silicon Valley's oldest and most consistent healthcare and enterprise bets. The angels are instructive: Jerry Yang, who built Yahoo! into a category-defining company, and Guillermo Rauch, who built Vercel into the infrastructure layer under much of the modern web. These are people who recognize platform bets when they see them.