Senior Software Engineer, Runtime

Every day, tens of millions of people come to Roblox to explore, create, play, learn, and connect with friends in 3D immersive digital experiences– all created by our global community of developers and creators. At Roblox, we’re building the tools and platform that empower our community to bring any experience that they can imagine to life. Our vision is to reimagine the way people come together, from anywhere in the world, and on any device. We’re on a mission to connect a billion people with optimism and civility, and looking for amazing talent to help us get there. A career at Roblox means you’ll be working to shape the future of human interaction, solving unique technical challenges at scale, and helping to create safer, more civil shared experiences for everyone. The Game Engine team at Roblox works on the systems that power the experiences at the heart of the metaverse. Our code is the technical foundation in our client, editor, and our simulation servers. The Game Engine team is broadly split into departments — Audio-Video-Communication, Avatar, Core AI, Digital Matter, Productivity, and Systems. This position is for the Systems Runtime pod. The Runtime pod builds and maintains the foundational C++ components that power the entire Roblox engine and Studio stack. We own the runtime layer — the performance, efficiency, and usability of the core primitives that every other engineering team relies on. Think of Runtime as the “standard library” and execution engine for Roblox's C++ world. Our ownership centers on three pillars: • Concurrency System — our task scheduler and fiber runtime power how work is parallelized across CPU cores, letting teams scale features across platforms while keeping code understandable and debuggable. • Memory System — we own the engine's memory allocator stack, tracking pipelines, and observability tooling to make memory behavior predictable and prevent leaks and fragmentation. • Profiling and Observability — we build and evolve the MicroProfiler and telemetry pipelines to help engineers diagnose real-world regressions and keep the client fast at global scale. This role centers on our Concurrency system. You will own the scheduler and fiber runtime that the rest of the engine is built on, research and implement the performance work needed for 3K-player servers and genre expansion initiatives, and act as the point of contact other engine teams come to with concurrency asks. You will debug real production failures across PC, Mac, mobile, and console, and build deep intuition for how compilers, CPU architectures, and operating systems interact. A single well-designed primitive or optimization here makes hundreds of internal engineers more productive and millions of player sessions smoother. You Will : • Take ownership of part of the engine's Concurrency system — the task scheduler, fiber runtime, and async APIs that every other engine team builds on. • Research and implement performance improvements that unblock platform initiatives – unlocking higher fidelity and richer experiences. • Serve as a point of contact for concurrency across the org: design reviews, hard parallelism bugs, and asks from other engine teams. • Improve the ergonomics, testability, and debuggability of concurrent code across PC, Mac, mobile, and console. You Have: • Strong modern C++ (C++17 or newer) in a large, complex production codebase • Deep multithreading/concurrency experience — schedulers, thread pools, lock-free programming, atomics, memory models • Comfort profiling and reasoning about performance at the OS/CPU level Nice to Have: • Game engine or real-time systems experience • Fiber/coroutine runtimes, work-stealing or job-system schedulers • Cross-platform low-level development (Android, iOS, cons