Cherny: Anthropic Can No Longer Demonstrate Prompt Injection on Opus 5
Boris Cherny · Boris Cherny: We Cut 80% of Claude Code’s Prompt · Y Combinator · Jul 27, 2026 · at 2:46
Boris Cherny, Head of Claude Code at Anthropic, explains Anthropic's mechanistic interpretability-based defenses against prompt injection.
0:00 / 0:35exact quote · 35.7s
▶ Watch the full episode on YouTube → 720p mp4 · rendered on demand · StarZero watermark
“So essentially, if you combine a well-aligned model, so this is, like, essentially three years of research into alignment, With a prompt injection classifier, which we run for all traffic, and what this is doing is it's based on Chrysola's mechanistic interpretability work, where it's literally, we're looking at neurons in the model's brain that light up when prompt injection happens. So the model won't even tell you, but we can actually see those neurons, and we can figure out and diagnose that it's happening, and then you combine that with the auto mode classifier, and with these three layers, We just cannot demonstrate prompt injection anymore.”
quote is from the automated transcript, cleaned for reading: filler sounds and stutters are removed, nothing is rephrased. names can be misheard (the analysis reads context, assessments check outside sources). how →
More from Boris Cherny
Cherny: Bun codebase was rewritten to Rust in 11 days using Claude
“And he had the model rewrite it from Zig to Rust. It was one prompt. It was a dynamic workflow, and a dynamic workflows are a feature in quad code that essentially let you orchestrate, you know, dozens, 100,000 of agents to do work productively. And it ran for…”
Cherny: Claude routines do the maintenance work of hundreds of engineers
“And so now we have every day, maybe 20 or 30 of these routines. It's running across all of our code bases and It's not totally there yet, but we're on the path to fully automating the maintenance of our apps by doing this. And this is, again, hundreds of agent…”
Claude Code increased Anthropic engineer productivity by 150 percent
“And since Quad Code came out, productivity per engineer at Anthropic has grown a 150%.”
Cherny uninstalled his IDE and lands 20 AI-written PRs daily
“For me personally, it's been a hundred percent for like since Opus 4.5. I just, I uninstalled my IDE. I don't edit a single line of code by hand. It's just a hundred percent quad code in Opus. And you know, I land, you know, like 20 pairs a day, every day.”
Claude generates between 70 and 90 percent of Anthropic's codebase
“If you look at Anthropic overall, it ranges between, like, 70 to 90% you know, depending on the team. For a lot of teams, it's also, like, a hundred percent. For a lot of people, it's a hundred percent.”
Cherny predicts AI will generally solve coding for everyone
“So continuing to trace the exponential, I think what will happen is coding will be generally solved for everyone. And I think today coding is practically solved, you know, for me, and I think it'll be the case for everyone you know, regardless of domain.”