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Y Y Combinator · the world's leading startup accelerator

Garry Tan built an AI second brain. Then open-sourced it.

The CEO of Y Combinator built a personal AI knowledge system — a knowledge graph, 74 MCP tools, and a nightly consolidation loop. Then he published it so anyone can run it.

74
MCP tools in GBrain
66
nightly cron jobs (memory consolidation)
23
tools in gstack Claude Code setup
The problem

Most AI feels like it forgets you the second you close the tab.

Out-of-the-box LLMs are stateless. They re-meet you every session, lose context across days, and can't track the entities, relationships, and history that make your judgment yours. For someone like Garry Tan — running an accelerator, talking to hundreds of founders — that's a non-starter.

What he built

A graph, a toolbelt, and a nightly loop.

GBrain is three layers stacked on top of an off-the-shelf model. The model didn't get smarter — the context around it did.

GBrain stack
Layer 01 · Knowledge
Graph + entities
A knowledge graph of people, companies, and relationships, captured from notes, conversations, and reading. Persistent across sessions. The AI knows what you know.
Layer 02 · Tools
MCP tools (74)
A library of tools the AI can call: graph search, entity sweeps, citation lookups, file reads. Each tool is a thin wrapper around a real function. Composable, observable.
Layer 03 · Loop
Nightly dream cycle
66 cron jobs run between you and the next morning: memory consolidation, citation fixing, entity sweeps, dedup. The AI wakes up cleaner than it went to sleep.
The result

An AI that gets sharper overnight.

GBrain runs 24/7. The knowledge graph compounds. Citations get fixed. Entities get merged. By morning, the AI knows more — and more accurately — than it did yesterday. And because it's open source, you can run the same thing.

Garry also published gstack — his 23-tool Claude Code configuration. Same posture: keep the model fixed, sharpen the context and tools around it.

The model can do most of what I need. The hard part is giving it the context, the memory, and the tools to actually do it. — Garry Tan, President & CEO, Y Combinator
What you can steal

You don't need bigger models. You need better infrastructure around them.

Garry didn't fine-tune anything. He didn't train his own model. He gave the model persistent memory, real tools, and a nightly consolidation loop. That's the gap between AI that forgets you and AI that gets sharper every day.

Sources

GBrain (github.com/garrytan/gbrain)
gstack (github.com/garrytan/gstack)