Yohei Nakajima is building ActiveGraph with Cofounder

Yohei Nakajima is a venture capitalist at Untapped Capital and the creator of BabyAGI, one of the earliest and most influential autonomous agent projects. In May 2026, he used Cofounder to build ActiveGraph, his new open source runtime for building auditable, forkable AI agents.

Yohei occupies an unusual position in the AI ecosystem. His day job is venture capital, but his hobby is building. Over the past several years he has shipped a long string of experimental projects on nights and weekends, and one of them, BabyAGI, became a touchstone for the entire autonomous agent space. He approaches each new build with a single rule. If it stops being fun, he stops working on it.

That rule shapes how he picks projects. Yohei does not decide what he will work on until he sits down to build, and once he starts, he gives himself permission to abandon everything else if a more interesting idea shows up. The idea for ActiveGraph surfaced on a Saturday and pushed everything else out of the way. He started prototyping the same day, and once he had a working version, he decided he wanted to share it.

ActiveGraph rethinks how AI agents keep track of what they do. Most AI agents today work like a person making decisions out loud while a separate notetaker scribbles on the side, in case anyone wants to check the reasoning later. The notes are an afterthought, and they are usually incomplete. Yohei's approach flips that. In ActiveGraph, the notebook is the agent. Every decision, every action, every piece of evidence the agent uses gets written down permanently and in order, and the agent's current understanding of the world is nothing more than a faithful read of those notes. The result is that anyone can rewind a run from start to finish, branch off at any moment to see what a different choice would have produced, and trace any conclusion the agent reaches back to the exact step that produced it.

As soon as ActiveGraph started working, Yohei went to Cofounder, dropped in his GitHub repo, and asked it to build a marketing website and a newsletter sign-up around the project. Cofounder read the repo, picked up the branding cues, set up the site, and wired in Resend for email collection. When Yohei posted his first two project updates on Twitter, he asked Cofounder to spin up a blog and add those announcements to it. When subscribers started arriving, he asked Cofounder to draft a newsletter and send it out. He finished a second research push the following weekend, dropped the new blog post into Cofounder, and asked it to draft another newsletter and ship that one too.

Yohei does the research and Cofounder runs the website, the newsletter, the blog, and the announcements. Most successful teams pair a technical founder with someone who handles business and marketing. For ActiveGraph, Cofounder is the second person in that pairing.

When Yohei reflects on his earlier projects, the contrast is sharp. BabyAGI was a phenomenon, but he was too busy building to set up a website, a newsletter, or a real community presence around it. There was no easy way for people excited about the project to stay close to it.

"If I had Cofounder three years ago," Yohei says, "BabyAGI might have been a company."

The ActiveGraph rollout suggests what that alternative path could have looked like. Within two weeks of having the idea, Yohei had a working runtime, a published paper, a marketing site, a live newsletter, a blog with multiple posts, and a growing audience of researchers and engineers tracking the project. He spent his time on the research and the writing while Cofounder handled the rest.

For now, Yohei is heads-down on the research. ActiveGraph is open source under Apache 2.0, with full documentation, a reproducible quickstart, and a paper that lays out the architecture in detail. The marketing, the newsletter, the blog, and the announcements continue to run on Cofounder.

Start a project like Yohei's with Cofounder, and explore ActiveGraph at activegraph.ai.

Yohei Nakajima is a venture capitalist at Untapped Capital and the creator of BabyAGI. In May 2026, he used Cofounder to build ActiveGraph. He is also an investor in The General Intelligence Company of New York, the makers of Cofounder.