Member of Technical Staff

Tessl

Tessl is a fast-growing Series A startup based in London, founded by Guy Podjarny. We’ve raised over $100M from world-class investors including Index Ventures, Accel, GV, and Boldstart, and in 2025 we were ranked #2 in Sifted EU’s B2B SaaS Rising 100 and #20 in Sifted's AI 100. At Tessl, we are building the context layer for AI coding agents, and a platform for AI-native software development. As an early member of the team, you’ll help shape how we build, scale and support a company operating at the edge of AI and software development. OVERVIEW OF ROLE Join our engineering team to build real-time AI Native workflows, tooling, and interfaces that will reshape how developers create and maintain software. As a Software Engineer, you’ll be versatile and independent, excited to work with cutting-edge AI tools to build great products. We move quickly, but with purpose - balancing speed with collaboration and thoughtful execution. You’ll collaborate closely with product, design, and the wider Engineering team to bring AI Native development to life in a fast-paced, high-trust environment. WHAT YOU’LL DO No two days will be the same at Tessl! You’ll have a high level of autonomy and be able to make decisions based on what you believe will help you deliver the most success. Here’s an insight into just a few of the things you would be doing: * Design and implement new functionality that you discussed and reviewed with the product team * Spin up a proof of concept to showcase an innovative idea you’ve been thinking about * Rapidly prototype a new language integration for our code generation pipeline, then develop a plan for a scalable implementation. * Pair with a designer to fine-tune interactions in the UI, CLI or existing AI coding agents, making the user experience more intuitive and slick * Integrate a third-party service, e.g. for notifications, so we can focus our own cycles on Tessl’s core capabilities * Collaborate with other teams to plan an architecture that supports collaboration across the platform * Establish an end-to-end testing strategy to increase our confidence when deploying new features to production * Share your technical vision for a new product capability you’ll be leading with the wider engineering team for feedback and alignment WHAT WE’RE LOOKING FOR ESSENTIAL * Proven experience (typically 5+ years or equivalent) as a Software Engineer. You care about code modularity, structure and aesthetics and have firsthand experience in how software is built across teams and environments * Equally comfortable contributing to a mature codebase with strict CI criteria or hacking up a quick prototype to prove/disprove an assumption * Proven experience leveraging the best AI coding tools and agents to accelerate and enhance your own work and efficiency * Comfortable with fast-paced, high-autonomy environments: you’ve ideally thrived in an early-stage startup before * You have demonstrated usage of AI tools in your day-to-day work, and be excited about experimenting, learning, and harnessing the potential of new AI tools and approaches to transform software engineering NICE TO HAVE * Background in AI products or developer tools * Experience in rapid prototyping environments * Programming polyglot experienced in several languages of different paradigms (e.g.: JavaScript/TypeScript, Python, C or C++, Haskell, etc.) * Experience collaborating with AI researchers and bridging between research-focused and engineering-focused teams * Experience building & scaling REST APIs, particularly those conforming to JSON:API * Comfortable working on infrastructure (e.g., setting up CI pipelines, navigating Kubernetes) * If you have a personal or open-source project you’d like to share, we’d love to see it (GitHub links welcome!) SALARY AND BENEFITS Office: Our brand new 10,000 sq. ft office is in the AI hub of Kings Cross, London. We have generous catering and have regular social events such as team lunches, drinks and more. We require all staff to be in our London HQ at least 3 days a week on our anchor days of Monday, Tuesday and Thursday. Salary: We offer a competitive salary based on experience and skills, benchmarked against industry standards. Benefits: 25 days holiday, health insurance, including dental and vision, which extends to partners and dependents, as well as a company-matched pension. We also provide a commuting stipend for those who live outside London, and a cycle to work scheme. APPLICATION PROCESS Here’s an outline of what you can expect during our interview process: 1. Introductory Call 2. Take-Home Exercise 3. On-site Technical Session 4. Culture Conversation 5. Leadership Discussion Throughout the process, if you have any specific requirements or need adjustments, please let us know: we’re happy to accommodate. We care deeply about the warm, inclusive environment we’re building at Tessl and we value diversity – we welcome applications from those typically underrepresented in tech. If you like the sound of this role but are not totally sure whether you’re the right person, do apply anyway! LEARN HOW WE THINK AND WORK * On Tessl, The AI Native Development Startup * Announcing skills on Tessl: the package manager for agent skills * Podcast Episode: The End of Fragmented Agent Context, Guy Podjarny Tessl CEO

Tessl

Tessl is a fast-growing Series A startup based in London, founded by Guy Podjarny. We’ve raised over $100M from world-class investors including Index Ventures, Accel, GV, and Boldstart, and in 2025 we were ranked #2 in Sifted EU’s B2B SaaS Rising 100 and #20 in Sifted's AI 100. At Tessl, we are building the context layer for AI coding agents, and a platform for AI-native software development. As an early member of the team, you’ll help shape how we build, scale and support a company operating at the edge of AI and software development. OVERVIEW OF THE ROLE We're hiring a Research Engineer to join our AI Research (AIR) team. You'll work on the components that make the outer loop real: how agent harnesses orchestrate model behaviour, how we evaluate what's actually working, how pipelines turn production traces into the next round of improvement, and how we diagnose the failure modes that matter to real users. These aren't four separate workstreams — they're parts of one system, and we want people who see them that way. We expect you to sit close to customers — joining calls, watching sessions, reading traces — and to let real workflows shape your research priorities. You'll have meaningful autonomy and the resources to run substantial experiments where the bar for success is shipped impact. You'll report to our AI Research Lead, and collaborate closely with engineering, product, and design. WHAT WE'RE LOOKING FOR We're explicitly building coverage across four skill areas. You don't need to be strong in all of them — but you should bring depth in at least one: * Agent harness and orchestration design — how tools, context, and control flow combine to make a useful agent. * Agentic eval methodology — task and repo-level evals, dataset curation, the craft of measuring what actually matters. * Outer-loop and pipeline thinking — feedback loops, training-data flywheels, bandit-style optimisation, anything that goes beyond a single agent session. * Failure-mode analysis — instrumenting agents, reading traces at volume, surfacing patterns engineering can act on. ESSENTIAL * 4+ years shipping AI/ML products in a startup or applied industry setting, with recent hands-on experience with LLMs and agentic systems. * Demonstrated depth in at least one of the four skill areas above. * Strong product and customer instincts: comfort joining customer calls, watching session recordings, and letting real workflows shape what you work on. * Sharp evaluation judgement: benchmarks where they exist, vibes and quick prototypes where they don't, and the taste to know which is appropriate. * Experience building datasets for evaluation or training, including the pipeline work that goes with it. * Deeply curious about agents and excited about reshaping how software is built. NICE TO HAVE * A Masters or PhD in a relevant computational field. * Direct experience with coding agents or code-generation systems. * Background in RL, bandits, or other outer-loop optimisation frameworks applied to LLMs. * Experience building synthetic data, dataset infrastructure, or internal tooling that other engineers actually used. * A project you can show us (GitHub links welcome) and a thoughtful answer to "Why Tessl?" WHAT YOU'LL DO No two weeks will look the same. A flavour: * Sit in on a customer session, understand how their agents are failing, design an eval that captures it, and drive a fix through to shipped improvement. * Close a piece of the outer loop end to end: production signal in, dataset out, eval scored, harness change shipped, metric moved. * Own a slice of our eval infrastructure: dataset curation, harness configuration, runner, analysis, and the comms back to engineering. * Prototype a new harness or context configuration and measure whether it actually moves the needle on real customer tasks. * Dig through pages of agent traces, build the tooling you need to make sense of them, and brief the team on what you found. * Partner with product and engineering on near-term shipping problems by bringing research rigour. * Pull a recent paper apart, work out what's actually transferable to our platform, and turn it into a concrete experiment. YOU’LL BE SUCCESSFUL IF… In your first 3 months, you might have shipped a new eval suite for a real customer workflow, improved an agent harness based on trace analysis, or built a pipeline that turns production failures into reusable test cases. SALARY AND BENEFITS Competitive salary commensurate with experience. Health insurance extending to partners and dependents, pension contributions, and the rest of what you'd expect. Our office is a couple of minutes from King's Cross — pet friendly, with regular team lunches, drinks, and socials. We're hybrid, with Monday, Tuesday, and Thursday as the primary in-office days. APPLICATION PROCESS * Intro call to understand "Why Tessl?" and to tell you a bit about us. * A call with our AI Research Lead to understand your ways of working and how you use agents. * A 4 hour technical take-home exercise extending our one-shot implementation. * A half-day on-site session including whiteboarding and hands-on activities. * Leadership chats with our Head of People, Head of Engineering and CEO. We care deeply about the warm, inclusive environment we’re building at Tessl and we value diversity – we welcome applications from those typically underrepresented in tech. If you like the sound of this role but are not totally sure whether you’re the right person, do apply anyway! LEARN HOW WE THINK AND WORK * On Tessl, The AI Native Development Startup * Announcing skills on Tessl: the package manager for agent skills * Podcast Episode: The End of Fragmented Agent Context, Guy Podjarny Tessl CEO

xAI

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: The Sandbox service team at SpaceXAI builds and maintains a secure, scalable system that gives our models safe, controlled access to computational environments. This infrastructure powers critical workloads across training and product, enabling models to run code, build software, interact with tools, and even control applications with user interfaces. We provision containers and virtual machines on large-scale clusters, granting models interactive control over these remote environments. Our work spans the full stack: from orchestrating massive jobs and resource scheduling at the cluster level, to fine-tuning filesystem performance on nodes. The Sandbox service enables Grok to safely run and test code in real-time for user queries, and supports reinforcement learning in training, where models interactively explore tools ranging from compilers to productivity apps. BASIC QUALIFICATIONS: * Expert knowledge of Rust, C++ or Go * Familiarity with Python * Deep experience with either Linux or Windows systems (familiarity with both is a strong plus) * Experience with virtualisation and containerisation technologies (e.g., cgroups, KVM, gVisor, QEMU) * Solid knowledge of the networking stack 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.