Software Engineer, Systems - Claude Code

Anthropic•San Francisco, CA

2d•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 deep work within the runtime, kernel interfaces, and the agent execution loop to optimize speed, efficiency, and stability. The engineer's contributions will also impact the Claude Code Agent SDK, Cowork, and other related projects. The position requires a strong background in low-level programming, focusing on production C, C++, and Rust, with an emphasis on syscalls, allocators, and micro-optimization.

Requirements

Strong background in C, C++, and/or Rust (Zig is also acceptable).
Deep systems programming experience, including 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 (e.g., JavaScriptCore, SpiderMonkey).
5+ years of work experience.

Responsibilities

Design, build, and optimize core systems within Bun and Claude Code, including runtime internals, I/O paths, memory management, and the agent execution loop.
Reduce memory usage, latency, and startup time across Claude Code and the Bun runtime.
Investigate and resolve performance issues across the entire stack, from kernel interfaces to the JS engine and agent layer, using profiling and tracing techniques.
Collaborate with researchers and product engineers to ensure model capabilities translate into a fast and reliable developer experience.
Contribute to the Bun runtime and toolkit, which supports Claude Code, the Agent SDK, Cowork, and other internal Labs products.
Stay current with advancements in runtimes, compilers, and AI-assisted tooling, experimenting with and integrating new ideas into the stack.