Claude Code started as a two day side project. It now runs at roughly $8 billion a year
In September 2024, one engineer built a terminal tool just to check what music he was playing. Anthropic's own retrospective traces how that experiment became Claude Code, one of the fastest growing software products on record.
Half of Anthropic's own engineers were using it within five days of release. Nobody had planned that.
Claude Code did not start as a plan to build one of the fastest growing software products in history. In September 2024, Anthropic engineer Boris Cherny built a small terminal tool just to check what song he was listening to at work. Anthropic's own retrospective on how the tool got built traces the path from that afternoon experiment to a coding agent now running at roughly $8 billion in annualized revenue.
A two day side project, not a roadmap item
Cherny had just joined Anthropic's Labs team and was learning the company's own API. He built a small terminal tool in a couple of days, nothing more than a script that used Claude to answer one question: what song is playing right now. He gave the tool access to the filesystem, and it started doing more than he expected.
There was a product overhang. This idea that you could build a product that does something the model is totally capable of doing, but no one has built the product that lets the model do it.
It spread inside Anthropic before it was even a product
Claude Code's first internal release came in November 2024, two months after that first prototype. 20% of Anthropic's engineering team was using it on day one. Within five days, half the team had adopted it. Today, more than 80% of Anthropic's engineers who write code use Claude Code daily, and the team that started as two people, Cherny and Sid Bidasaria, grew to roughly ten engineers by mid 2025 and now spans engineering, product, design, and data science.
From research preview to eight billion dollars a year
Claude Code now writes an estimated 4% of all public GitHub commits. And by Anthropic's own account, roughly 90% of Claude Code's own codebase is now written by Claude itself.
Anthropic bought the toolchain underneath it
In December 2025, Anthropic acquired Bun, the JavaScript runtime, package manager, bundler, and test runner built by Jarred Sumner, with over 7 million monthly downloads and 82,000 GitHub stars. Bun had already become part of how Claude Code scaled, including its native installer. Anthropic's Chief Product Officer Mike Krieger called it "exactly the kind of technical excellence we want to bring into Anthropic." Bun stays open source and MIT licensed.
Why a build studio cares
We use Claude Code every day. It is on our own tools page, sitting next to Figma and Cloudflare, not filed under some separate AI experiments section. The more interesting part of this story is not the revenue number. It is that the product that ended up on so many developers' machines, ours included, started from someone shipping a two day experiment instead of waiting for a roadmap slot. That is closer to how we try to build things too.
Next step: read Anthropic's full retrospective for the complete oral history, and the Bun acquisition announcement for how the infrastructure story continues. If you want a team that ships with the same tools every day, write to us at hello@gattyworks.com.