Description
We're looking for a systems-oriented Software Engineer to push the performance and reliability of Claude Code and the JavaScript runtime that powers it. Claude Code is our terminal-first, agentic coding tool, and a huge part of what makes it fast,and what lets us ship quickly,is Bun. This role sits at that intersection: you'll work deep in the runtime, the kernel interfaces it sits on top of, and the agent loop on top of it, making everything faster, leaner, and more reliable.
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
This is low-level work. We're looking for someone who has spent years writing production C, C++, and Rust, who thinks in syscalls and allocators, and who gets excited about shaving microseconds and megabytes off hot paths.
You may be a good fit if you
Have a strong background in C and/or C++ and Rust (Zig also welcome)
Have deep systems programming experience: syscalls, Linux internals, I/O (kqueue, epoll, io_uring), manual memory management, and performance engineering
Have worked on language runtimes, virtual machines, compilers, or JS engines like JavaScriptCore or SpiderMonkey
Have 5+ years of work experience
The annual compensation range for this role is $320,000-$485,000 USD.