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Sarah Guo became Greylock's youngest general partner in 2018 at age 28 and left…

2026-07-21 · 05:14 UTC ·@shuooo ·2 min read

Brief

Sarah Guo left Greylock (youngest GP, 2018, age 28) to found Conviction, focusing exclusively on AI. She seeded Baseten and Harvey (each now >$11B) and backed Sierra, Cognition, and Mistral (combined $54B). Betting frontier labs will try to own the entire stack, she actively funds, mentors, and recruits founders to ensure independent startups can build on top.

Why it matters

Sarah Guo became Greylock's youngest general partner in 2018 at age 28 and left four years later to found Conviction, a venture firm staked entirely on AI.

Key details

  • Conviction seeded Baseten and Harvey before ChatGPT; each is now worth over $11 billion, and Guo's early checks into Sierra, Cognition, and Mistral are now worth a combined $54 billion.
  • Guo warns frontier labs (worth close to a trillion dollars apiece) are trying to own the stack; in Q1 2026 $300 billion in VC deployed, with 65% going to Anthropic, OpenAI, xAI, and Waymo — she recruits, mentors, and funds founders (Karpathy worked from Conviction until Anthropic hired him in May) to prevent that.
Source evidence

Sarah was one of the first investors I ever spoke with, and she remains a huge inspiration to me 💜

Colossus (@colossusmag)

In 2018, Sarah Guo became the youngest general partner in Greylock's 60-year history. She was 28. Four years later, she quit to launch Conviction, a firm staked entirely on AI.

Before ChatGPT shipped, she seeded Baseten and Harvey; each is now worth over $11 billion. In Conviction's first year, she wrote early checks into Sierra, Cognition, and Mistral; those three companies are now worth, together, $54 billion.

Andrej Karpathy worked out of Conviction's office until Anthropic hired him in May. Guo has been close to Jensen Huang for over a decade. Her first two calls after starting the firm were to Sam Altman and Nat Friedman.

And yet the investor closest to the AI frontier is betting against its biggest companies.

The two big frontier labs, worth close to a trillion dollars apiece, no longer just want to build the models. They also want to build every product and company on top of them, leaving nothing for anyone else.

The market is paying as though they might succeed. Of the $300 billion in venture capital deployed in the first quarter of 2026, the biggest quarter in the history of the trade, 65% went to only four companies: Anthropic, OpenAI, xAI, and Waymo.

Guo is betting the labs can't build everything, and she spends her days making sure of it. She won Harvey its first client. She flew across the country to take a single Baseten candidate to a four-hour lunch. On one wedding anniversary, she spent the whole weekend on back-to-back calls, keeping two founders on the line so they couldn't speak to rival firms. Twice a year, she flies the world's brightest young founders to San Francisco and inducts them into the fight.

In the months @domcooke spent reporting this piece, @saranormous had her fourth child, walked the Met Gala in 45 pounds of chainmail, and still answered her founders' texts within minutes.

Guo's parents arrived from China in 1987 with $50, built a company, and took it public at $1.2 billion. Then it went bankrupt. Guo grew up inside that startup. She built its first website, did her homework in a cubicle, and slept over for bug bashes. She loved it.

If two labs build everything, no one gets to do that again.

Welcome to Sarah's Wager. Read it below.

— https://nitter.net/colossusmag/status/2079169545705525510#m