---
title: 'Backend Engineer - API at xAI'
canonical: 'https://feeny.ai/job/backend-engineer-api-xai-london-england-sknwpgcpwva0'
type: 'job'
last_seen: '2026-09-07'
---

# Backend Engineer - API at xAI

- **Company:** xAI
- **Location:** London England, United Kingdom
- **Posted:** 2026-04-24
- **Last confirmed live:** 2026-09-07
- **Apply:** https://job-boards.greenhouse.io/xai/jobs/5120536007

## Job description

SpaceXAI’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 SpaceXAI 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)

## COMPENSATION AND BENEFITS:

£107,000 - £262,000 GBP

Base salary is just one part of our total rewards package at SpaceXAI, which also includes equity, comprehensive healthcare and dental coverage, cash plan, income protection, life insurance, and various other discounts and perks. SpaceXAI is an equal opportunity employer. For details on data processing, view our [Recruitment Privacy Notice](https://x.ai/legal/recruitment-privacy-notice).

## About xAI

## Company Overview
- **One‑liner**: xAI builds artificial intelligence systems to accelerate human scientific discovery and “understand the universe,” with products spanning frontier reasoning models, real‑time voice, and generative media.
- **Entity Type**: Private (last funding round: Series E, January 2026; acquired by SpaceX in February 2026)
- **Headquarters**: Palo Alto, California, USA (additional offices in Seattle, WA; Memphis, TN; London, UK)
- **Founded**: 2023
- **Founders**: Elon Musk

## Core Business
- Primary industry: Artificial Intelligence (AI research, large language models, voice AI, generative media)
- Target customers: B2B (developers via API), B2C (consumers via Grok on 𝕏, SuperGrok subscriptions), Enterprise & Government (xAI for Government)
- Mission: “To understand the universe” – building AI that extends what humanity can know and do.

## Products & Services
- **Grok (base models)** : A conversational AI assistant modeled after *The Hitchhiker’s Guide to the Galaxy*, available on the 𝕏 platform and via API.
- **Grok 4 / Grok 4 Heavy**: The most intelligent reasoning models, featuring native tool use and real‑time search integration (SuperGrok and Premium+ tiers).
- **Grok Voice Agent API / Voice Agent Builder**: Create custom voice agents in under two minutes (no‑code) – includes speech‑to‑text, text‑to‑speech, custom voice cloning, and multilingual support.
- **Grok Imagine API**: State‑of‑the‑art video generation API (quality, cost, latency).
- **Grok‑1.5 / Grok‑2 / Grok‑2 mini**: Earlier model releases with improved reasoning and 128K context length.
- **PromptIDE**: An integrated development environment for prompt engineering and interpretability research.
- **xAI for Government**: A suite of frontier AI products tailored for U.S. government customers.
- **Colossus Supercomputer**: 200,000‑GPU cluster built in 122 days, used for training xAI models; now also leased to Anthropic (Colossus 1 agreement).

All products are delivered as SaaS, API, and model weights (open‑source release of Grok‑1).

## Market Standing
- **Valuation / Funding**: 
  - Series B (May 2024): $6 B 
  - Series C (Dec 2024): $6 B (led by A16Z, BlackRock, Fidelity, Kingdom Holdings, Lightspeed, MGX, Morgan Stanley, OIA, QIA, Sequoia, Valor, Vy Capital, others)
  - Series E (Jan 2026): $20 B
  - Acquisition by SpaceX announced Feb 2, 2026 (terms not disclosed).
- **Key Metric**: Total disclosed funding ~$32 B; annual revenue not publicly available.
- **Notable Investors/Partners**: A16Z, BlackRock, Fidelity, Sequoia Capital, Morgan Stanley, Kingdom Holdings, Lightspeed, MGX, Valor Equity Partners, Vy Capital, Anthropic (Colossus deal), U.S. Department of War (selected Dec 2025).
- **Growth Signals**: 
  - Rapid scaling from founding to 200K‑GPU cluster in 122 days.
  - Over 214 open roles listed on Greenhouse as of mid‑2026.
  - #1 on Big Bench Audio (Grok 4 audio performance).
  - Expanded into voice agents, video generation, and government verticals within 3 years.
  - Acquisition by SpaceX signals deep integration with space‑tech resources.

## Competitive Advantages
- **Compute infrastructure**: Colossus supercomputer – one of the largest GPU clusters in existence, enabling faster training and larger models.
- **Model performance**: Grok 4 claims “most intelligent model in the world” with top benchmarks (Big Bench Audio #1).
- **Vertical integration**: Tight coupling with 𝕏 platform for data, distribution, and real‑time world knowledge.
- **Speed of execution**: “Move quickly and fix things” culture; built Colossus in 122 days.
- **Government contracts**: Early access to public‑sector AI markets (U.S. Department of War).
- **Talent density**: Small, focused team of researchers and engineers; in‑person work accelerates iteration.

## Strategic Focus
- **Continue advancing frontier reasoning** (Grok 4 Heavy, next‑gen models).
- **Expand voice and multimodal APIs** for developers (Voice Agent Builder, Custom Voices Library).
- **Deepen government / defense partnerships** (xAI for Government, Department of War).
- **Scale infrastructure** post‑acquisition via SpaceX resources.
- **Remain “open” where strategic** (open‑source release of Grok‑1 weights).

## Why Work Here
- **Culture**: “Ambitious goals, fast execution” – rejects consensus in favor of first‑principles reasoning. In‑person work prioritized (Palo Alto, Seattle, Memphis, London).
- **Benefits**: 
  - Competitive cash + equity compensation.
  - Comprehensive medical, dental, vision, disability, life insurance.
  - 401(k) plan, fertility benefits, flexible vacation.
  - Visa sponsorship offered.
- **Engineering culture**: No recruiters for assessments – applications reviewed directly by technical team. Interview process: application → screening → technical interviews → offer.
- **Mission‑driven**: Opportunity to work on frontier AI models that aim to “advance humanity.”
- **Perks**: In‑person collaboration, fast‑paced environment, ownership of meaningful projects.

## Sources
1. [x.ai/company](https://x.ai/company)
2. [x.ai/careers](https://x.ai/careers)
3. [job-boards.greenhouse.io/xai](https://job-boards.greenhouse.io/xai)
4. [x.ai/news](https://x.ai/news)
5. [x.ai/careers/open-roles](https://x.ai/careers/open-roles)

## Other roles at xAI

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- [Legal Operations Specialist](https://feeny.ai/job/legal-operations-specialist-xai-palo-alto-yvgq5sxqmheq) — Palo Alto, CA
- [Agency Development Manager](https://feeny.ai/job/agency-development-manager-xai-new-york-6zsw61w04xfw) — New York, NY
- [AI Tutor - Design Specialist](https://feeny.ai/job/ai-tutor-design-specialist-xai-global-gyys8ysv19rj) — Global
- [AI Tutor - Humanities](https://feeny.ai/job/ai-tutor-humanities-xai-global-f8b939y59f97) — Global
- [Network Operations Center Specialist - Memphis](https://feeny.ai/job/network-operations-center-specialist-memphis-xai-southaven-5eaecc9mwq8n) — Southaven, MS / Memphis, TN
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- [Controls Engineer, Supercomputer Infrastructure - Memphis](https://feeny.ai/job/controls-engineer-supercomputer-infrastructure-memphis-xai-southaven-9tds2x1wpwjw) — Southaven, MS / Memphis, TN
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