Simon Willison’s Weblog

Production code written by Claude should have a higher bar than if it was written by a human. At Anthropic, we have many guardrails in place to make sure this is happening: lots of lint rules, lots of tests, Claude-driven end to end tests, Claude-powered fuzzers running daily, automated code reviews and security reviews, automated code refactoring, and so on. Without these, you can end up with a mess that is hard to maintain down the line.

— Boris Cherny

# 11th September 2026, 5:47 pm / ai, generative-ai, llms, ai-assisted-programming, anthropic, claude, coding-agents, claude-code, agentic-engineering, boris-cherny

More than any of these eval scores, what is most exciting to me is something else: Opus 5 is our least prompt injectable model yet. It is a bit buried in the system card, but across PI evals and red teaming, Opus 5 is very hard to prompt inject successfully.

— Boris Cherny, here's that System Card section, page 73

# 25th July 2026, 12:42 am / ai, prompt-injection, generative-ai, llms, anthropic, claude, boris-cherny

Someone has to prompt the Claudes, talk to customers, coordinate with other teams, decide what to build next. Engineering is changing and great engineers are more important than ever.

— Boris Cherny, Claude Code creator, on why Anthropic are still hiring developers

# 14th February 2026, 11:59 pm / careers, ai, generative-ai, llms, ai-assisted-programming, anthropic, coding-agents, claude-code, boris-cherny

A year ago, Claude struggled to generate bash commands without escaping issues. It worked for seconds or minutes at a time. We saw early signs that it may become broadly useful for coding one day.

Fast forward to today. In the last thirty days, I landed 259 PRs -- 497 commits, 40k lines added, 38k lines removed. Every single line was written by Claude Code + Opus 4.5.

— Boris Cherny, creator of Claude Code

# 27th December 2025, 2:13 pm / ai, generative-ai, llms, ai-assisted-programming, anthropic, claude, coding-agents, claude-code, boris-cherny