Mojo Libraries Engineer - Senior Staff Engineer

About the role:

At Modular, we're on a mission to make AI accessible to everyone. As a Senior Staff Mojo Libraries Engineer, you'll be a technical leader shaping the future of the Mojo programming language and its Standard Library. Mojo combines performance and expressiveness to unlock the full potential of modern hardware for AI, and you'll be one of the senior voices defining where the language goes next.
In this role, you'll help shape the evolution of the Mojo Standard Library and shepherd proposals that move the Mojo language forward — mentoring engineers across multiple teams, and partnering with compiler, runtime, and kernel leadership to make Mojo the best systems language for AI. Your work will be visible to the open source community, our largest customers, and the broader systems programming world.
LOCATION: Candidates based in the US or Canada are welcome to apply. Our headquarters is in Los Altos, CA, with additional offices in San Francisco and Boston. You're welcome to work from any of our offices or remotely from home.

What you will do:

•  Shape the evolution of the Mojo Standard Library, leading multi-quarter initiatives and helping set the bar for API design, performance, and ergonomics. Help define what "good" looks like for core abstractions that thousands of developers will build on.
• Author and shepherd Mojo language proposals, evaluating tradeoffs against precedent in C++, Rust, Swift, and Python, and building alignment across compiler, library, and product stakeholders to land features that meaningfully improve the developer experience.
• Act as a force multiplier across the engineering organization — mentoring senior engineers, raising the bar in design reviews, and unblocking complex technical problems that span team boundaries.
• Build alignment across compiler, kernel, runtime, and product teams on library architecture, the broader platform roadmap, and customer commitments.
• Own the hardest problems: deep performance work, novel abstractions for emerging hardware, and the kind of foundational design decisions that compound over years.
• Represent Modular externally — engaging the open source community on GitHub, supporting and reviewing high-quality contributions, and participating in technical discussions that shape how the industry thinks about AI infrastructure.
• Stay ahead of the field, tracking Python PEPs, Rust RFCs, C++ proposals, and academic work in systems and compilers, and translating that into concrete improvements to Mojo.

What you bring to the table:

•  10+ years of industry experience building production systems software, with deep expertise in modern systems languages such as C++, Rust, or Swift.
• A track record of technical leadership in environments with strong technical voices — driving multi-team initiatives, building alignment across senior stakeholders, and influencing technical direction through persuasion rather than positional authority.
• Demonstrated experience designing language features, standard library APIs, or core abstractions that have shipped to real users at scale.
• Deep expertise in performance engineering, low-level programming, and memory management, with the judgment to know when low-level control matters and when it doesn't.
• Substantial open source experience — public artifacts (contributions, maintainership, or RFCs to a widely-used systems project) that demonstrate your design judgment and ability to collaborate in the open. A meaningful part of this role involves engaging with the Mojo open source community.
• A collaborative, high-trust working style and strong alignment with Modular's cultural values.

Helpful but not required:

• GPU programming experience — authoring high-performance compute kernels, designing GPU abstractions, or contributing to GPU-focused languages or libraries (CUDA, ROCm, SYCL, Triton, etc.).
• Prior experience contributing to a programming language, compiler, or standard library project (Rust, Swift, C++, Python, LLVM, MLIR, etc.).
• Experience participating in language or library standards bodies (ISO C++, Rust RFCs, Python steering council, etc.) — or comparable experience driving consensus across organizations with competing technical interests.
• Hands-on experience with Mojo, including accepted contributions to the Standard Library.
• Experience working closely with compiler teams on language/library co-design.