Top Anthropic engineer says Claude now writes 'literally all' her team's code

• Anthropic platform engineering head Katelyn Lesse said that Claude now writes all her team's code.
• Lesse shared ways that Claude Code has helped the company become more efficient.
• Anthropic nears an initial public offering at a potential $2 trillion valuation.

A top Anthropic engineer says that Claude Code has already wiped out all human coding at one of the AI lab's central teams.

Katelyn Lesse leads the AI startup's platform engineering group, which handles the company's core services, developer tools, and product infrastructure — it's essentially the engine room of Anthropic. Lesse said at Grafana Labs' ObservabilityCON event on Tuesday that among her staff, which tallied 200 as of this summer, the era of human-written code is fully over.

"When it comes to our team and how we're actually building and maintaining our systems, all of our code is written by Claude," Lesse said. "Like, literally all of it."

Anthropic's heavy reliance on Claude Code has helped it remain relatively small, as it approaches an initial public offering that could value it at nearly $2 trillion. The company's revenue growth slowed in the third quarter of this year. Maintaining its lofty valuation may depend on selling more companies on the AI-first approach espoused by Lesse and other Anthropic leaders.

Lesse said that people on her teams are still designing systems and verifications, and then offloading the actual coding to Claude. She said that when the company changed the programming language of a major codebase from Python to Rust, workers developed a way to verify the final product.

"But the grunt work of building the pieces and actually monitoring the pieces and actually making sure that we felt good about it, that was agents all the way down," Lesse said.

Lesse said Anthropic already lets agents fix tests autonomously, with no human interaction, and it's thinking about how staff can get comfortable with agents autonomously making changes to the actual codebase, given the improvements in AI models over the last year.

"As engineering leaders, we're like terrified, and we're like, let's be really careful about this, but I think the line is starting to push," Lesse said.

Anthropic has also embraced Claude Code companywide. It released a report last week saying that as AI agents have worked more inside the company, it has hired for a smaller share of junior technical positions. And in May, Anthropic said that Claude then wrote more than 80% of the entire company's production code.

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