Backend Engineer - API

at xAI · AI Frontier · London, United Kingdom · Engineering

Backend Engineer responsible for building and owning the xAI API that serves models to developers worldwide. This includes end-to-end system ownership for high-throughput, low-latency, and highly available inference, covering model serving infrastructure, request routing, SDK development, rate limiting, observability, and scaling. Requires expertise in Rust or C++, distributed systems, and observability, with preferred experience in LLM inference engines, serving frameworks, and agent orchestration.

What you'd actually do

  1. Build the xAI API that serves our models to developers worldwide
  2. Own the end-to-end system responsible for high-throughput inference, handling billions of tokens per minute with low latency and high availability, including model serving infrastructure, request routing, SDK development, rate limiting, observability, and efficient scaling

Skills

Required

  • Rust
  • C++
  • distributed systems
  • service observability
  • reliability best practices
  • PostgreSQL
  • Clickhouse
  • MongoDB
  • gRPC

Nice to have

  • LLM inference engines
  • serving frameworks
  • SGLang
  • TensorRT
  • vLLM
  • agent SDKs
  • agent orchestration frameworks
  • Docker
  • Kubernetes
  • containerized applications

What the JD emphasized

  • Expert knowledge of either Rust or C++
  • Experience in designing, implementing, and maintaining reliable and horizontally scalable distributed systems
  • Knowledge of service observability and reliability best practices
  • Experience with LLM inference engines and serving frameworks (e.g., SGLang, TensorRT, vLLM)
  • Experience designing or building with agent SDKs and agent orchestration frameworks

Other signals

  • high-throughput inference
  • low latency
  • high availability
  • model serving infrastructure
  • request routing
  • SDK development
  • rate limiting
  • observability
  • efficient scaling
  • LLM inference engines
  • serving frameworks
  • agent SDKs
  • agent orchestration frameworks
Read full job description

ABOUT xAI

xAI’s mission is to create AI systems that can accurately understand the universe and aid humanity in its pursuit of knowledge. Our team is small, highly motivated, and focused on engineering excellence. This organization is for individuals who appreciate challenging themselves and thrive on curiosity. We operate with a flat organizational structure. All employees are expected to be hands-on and to contribute directly to the company’s mission. Leadership is given to those who show initiative and consistently deliver excellence. Work ethic and strong prioritization skills are important. All employees are expected to have strong communication skills. They should be able to concisely and accurately share knowledge with their teammates.

ABOUT THE ROLE:

As an ideal candidate you have a good understanding of how highly scalable and reliable production infrastructure is built. Most of our backend infrastructure is written in Rust. So familiarity with a compiled language such as C++, Rust, or Go is highly beneficial.

RESPONSIBILITIES:

  • Build the xAI API that serves our models to developers worldwide
  • Own the end-to-end system responsible for high-throughput inference, handling billions of tokens per minute with low latency and high availability, including model serving infrastructure, request routing, SDK development, rate limiting, observability, and efficient scaling

BASIC QUALIFICATIONS:

  • Expert knowledge of either Rust or C++
  • Experience in designing, implementing, and maintaining reliable and horizontally scalable distributed systems
  • Knowledge of service observability and reliability best practices
  • Experience in operating commonly used databases such as PostgreSQL, Clickhouse, and MongoDB

PREFERRED SKILLS AND EXPERIENCE:

  • Experience with LLM inference engines and serving frameworks (e.g., SGLang, TensorRT, vLLM)
  • Experience designing or building with agent SDKs and agent orchestration frameworks
  • Experience with Docker, Kubernetes, and containerized applications
  • Expert knowledge of gRPC (unary, response streaming, bi-directional streaming, REST mapping)

_xAI is an equal opportunity employer. For details on data processing, view our _Recruitment Privacy Notice.