• 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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• A sign instructing San Francisco gym-goers not to vibe code between sets went viral.
• The sign was an "AI-generated fake," according to the gym.
• Amid tech's vibe-coding obsession and fitness boom, it's no surprise the image has gotten heat.

Don't hog the leg press while prompting Claude.

A screen with the logo of Fitness SF, a Bay Area chain of gyms, went viral among techies on X and Instagram on Monday. The image instructed gym-goers to refrain from writing code or prompting AI during their workouts. "Be present. Lift harder. Ship later," the image reads.

Troy Macfarland, Fitness SF's director of marketing, said, however, that the image was an "AI-generated fake." The gym does have etiquette signs that mention phone usage and being courteous, he wrote, but none mention vibe coding.

"This person altered our actual images displayed on the screen," Macfarland wrote. "I will give an 'A' for creativity to him."

It's not clear whether the image was generated with AI, Photoshop, or some other tool. Ian Brash, whose post with the image got almost 7,000 likes, did not respond to a request for comment.

In San Francisco's AI mania, it's no surprise a sign like that blew up on X. Techies weighed in, cracking their own jokes about how tied they were to their coding agents.

One X user told Fitness SF to give their copywriter a raise. A Cognition engineer said that vibe coding between sets was encouraged at his company's gym.

"Vibe coding at the gym?" one X user wrote. "You're worried about the wrong weights."

One reaction image often appears in the comment sections of posts like this one. It shows a muscled man, holding a giant nuclear bomb in his hands, jumping into the city of San Francisco. One VC posted it with the message: "Even I have limits."

Claude Code and cardio

The sign tapped into two of the buzziest subcultures in tech.

First, there's AI coding. Ever since the launch of Claude Code and OpenAI's Codex, engineers have been tied to their phones (or walking around with half-open laptops) to continue building. Some techies told Business Insider that their love of vibe coding created distance between them and their girlfriends.

Then there's the gym. Tech bros are getting fit, pumping themselves full of peptides and getting shredded at early-morning Equinox sessions. A developer at the gym used to be an anomaly; now, it's the norm.

Some techies seemed skeptical from the start. One X user quoted the post, writing that there was "no way this is real."

Another user responded that they didn't know about that specific sign, but they did know about the underlying issue. "This is a real problem at the Equinox in San Francisco," they wrote.