---
title: 'Sr. Backend Engineer, API at xAI'
canonical: 'https://feeny.ai/job/sr-backend-engineer-api-xai-london-sknwpgcpwva0'
type: 'job'
last_seen: '2026-11-09'
---

# Sr. Backend Engineer, API at xAI

- **Company:** xAI
- **Location:** London, United Kingdom
- **Posted:** 2026-04-24
- **Last confirmed live:** 2026-11-09
- **Apply:** https://job-boards.greenhouse.io/xai/jobs/5120536007

## Job description

SpaceX was founded under the belief that a future where humanity is out exploring the stars is fundamentally more exciting than one where we are not. Today, SpaceX is actively developing the technologies to make this possible, with the ultimate goal of making life multiplanetary and expanding consciousness to the stars.

SpaceXSI is building Super Intelligence to help humanity understand the universe. Our teams are building the full Super Intelligence stack: from our Colossus supercomputers, to Grok models, to our suite of applications, including Grok Bot, Grok Build, Grok Imagine, Grok Voice, and X. We're creating a powerful flywheel where more compute trains better models, better models power more useful products, and what we learn from people using those products shapes what we build next.

## SR. BACKEND ENGINEER, API

We are looking for Backend Engineers to help build and operate highly scalable, reliable production infrastructure. Most of our backend infrastructure is written in Rust. Experience with a compiled language such as Rust,  C++, or Go is highly beneficial.

## RESPONSIBILITIES:

- Build and maintain the unified inference stack as the single surface area for all inference needs across the company
- Own and evolve the platform services that power Chat API, Imagine API, Voice API, Grok Build, and Grok Bot
- Design, build, and maintain Chat API features including batch API, collections API, files API, and related capabilities
- Implement and operate chat moderation and abuse protection systems across the API and [grok.com](http://grok.com)
- Build and maintain the company-wide logging system for all request types, including enforcement of Zero Data Retention (ZDR) policies
- Manage multi-region inference cluster (IC) deployments, data aggregation, data replication, and the distributed authentication system
- Participate in follow-the-sun on-call coverage (UK → Japan → US) to ensure continuous reliability of the inference platform

## BASIC QUALIFICATIONS:

- 5+ years of experience in designing, implementing, and maintaining reliable and horizontally scalable distributed systems
- Experience with Rust or C++

## PREFERRED SKILLS AND EXPERIENCE:

- Experience in operating databases such as PostgreSQL, Clickhouse, and MongoDB
- 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
- 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 SpaceXSI, which also includes equity, comprehensive healthcare and dental coverage, cash plan, income protection, life insurance, and various other discounts and perks. SpaceXSI 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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- [IAM Engineer](https://feeny.ai/job/iam-engineer-xai-austin-hmw1z8pysezr) — Austin, TX / Palo Alto, CA / Washington, DC
- [Sr. Model Engineer, Voice](https://feeny.ai/job/sr-model-engineer-voice-xai-palo-alto-gyr07j2fs6d0) — Palo Alto, CA
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