Software Engineer, Systems - Claude Code

Anthropic•San Francisco, CA

9h•Hybrid

About The Position

Anthropic is seeking a systems-oriented Software Engineer to enhance the performance and reliability of Claude Code and its underlying JavaScript runtime, Bun. This role involves working deeply within the runtime, kernel interfaces, and the agent execution loop to optimize speed, efficiency, and stability. The impact of this work will extend to the Claude Code Agent SDK, Cowork, and other related projects. The position requires a strong focus on low-level systems programming, with an emphasis on optimizing critical code paths for speed and memory usage.

Requirements

Strong background in C and/or C++ and Rust (Zig also welcome)
Deep systems programming experience: syscalls, Linux internals, I/O (kqueue, epoll, io_uring), manual memory management, and performance engineering
Experience working on language runtimes, virtual machines, compilers, or JS engines like JavaScriptCore or SpiderMonkey
5+ years of work experience

Responsibilities

Design, build, and optimize core systems inside Bun and Claude Code—runtime internals, I/O paths, memory management, and the agent execution loop
Drive down memory usage, latency, and startup time across Claude Code and the Bun runtime
Dig into performance problems across the stack: profiling, tracing, and fixing issues anywhere from the kernel interface up through the JS engine to the agent layer
Collaborate with researchers and product engineers to make sure model capabilities translate into a fast, reliable developer experience
Contribute to the Bun runtime and toolkit, which underpins Claude Code, the Agent SDK, Cowork, and other internal Labs products
Stay ahead of advancements in runtimes, compilers, and AI-assisted tooling—experimenting, measuring, and bringing the best ideas into our stack