I have spent the last four years building Halcyon with Marcus Chen, and in that time I have never once questioned whether we had the right technical leader. That sentence may sound casual. It is not. Founders know how rare it is to mean it. I am writing to recommend Marcus for YC's Visiting Partner program without reservation, and with the specific belief that he will be unusually good at the job.
When Marcus and I started Halcyon in late 2020, we had a rough thesis, a Figma file, and a single enterprise pilot that had not yet paid us. He wrote the first version of our orchestration engine alone, over a six-week stretch, and made architectural decisions during that period that are still load-bearing today — decisions that allowed us to scale without a rewrite as we grew.
What distinguishes Marcus is not raw technical talent, though he has plenty of it. It is his judgment about when to apply it. He is the rare engineer who will argue against his own instinct to build, who will tell a founder to delay a migration, who will push back on a customer commitment that sounds good in a meeting but breaks the roadmap. Twice in our history he has quietly prevented me from making an expensive strategic mistake — once by refusing to greenlight an acquisition integration, and once by walking me through why a prospective Series A term sheet was structured badly for us technically.
He also builds teams that other engineers want to join. Our retention on the engineering side is 94% over four years, in a market where that number is usually catastrophic. Senior engineers at Stripe, Anthropic, and Ramp have taken our offers specifically because Marcus interviewed them. He coaches well, writes feedback carefully, and has a temperament that I would describe as patient without being passive.
"The YC Visiting Partner role is, at its core, a founder-whisperer job. You need someone who has felt the weight of every decision a technical founder is about to make. Marcus has. And he is unusually generous with what he learned."
I know what YC is evaluating with this program. You need a partner who can sit across from a founder at 11pm the night before Demo Day and be useful — who can read an architecture diagram, diagnose team dynamics, and deliver difficult feedback without losing the person on the other side of the table. Marcus does all three of those things for me every week. I expect I will miss it.
I am recommending him knowing that his acceptance is, in the short term, costly to me personally. I am doing so because I believe the best technical founders in your next batches will be materially better off having him in their corner. You will not regret this one.