Senior Backend Engineer at Xapien | London

Join our innovative team at reteam as a Backend Engineer! In this role, you will collaborate with cross-functional teams to develop robust backend solutions that power our applications.We are looking for an enthusiastic engineer who is passionate about creating efficient and scalable systems. Your expertise will contribute to enhancing our product offerings and improving user experiences.

Role overview airapps is hiring a Backend Engineer for its London Metropolitan Area team. This role focuses on designing and building scalable server-side applications that support the company’s products and services. What you will do Work closely with colleagues across different functions to develop backend systems Contribute to the architecture and implementation of server-side features Help ensure backend solutions can scale and perform reliably Location This position is based in the London Metropolitan Area.

Join Aircall, a revolutionary unicorn in the AI-powered customer communications sphere, trusted by over 22,000 companies globally to enhance revenue, expedite issue resolution, and empower customer-facing teams. We are transforming the landscape of customer communications by integrating voice, SMS, WhatsApp, and AI into a unified workspace.Our growth is driven by a straightforward principle: to enable teams to work smarter, not harder. Our AI Voice Agent automates routine calls, while AI Assist simplifies post-call tasks, and AI Assist Pro provides real-time insights, allowing individuals to excel in their roles. This synergy results in increased revenue, quicker resolutions, and scalable teams.Headquartered in Paris, with a solid presence in North America anchored in Seattle, Aircall also has teams in vibrant cities such as Madrid, London, Berlin, San Francisco, New York City, Sydney, and Mexico City. Our product is beloved by customers, and we are rapidly scaling, supported by top-tier investors and continuous AI advancements across multiple product lines.At Aircall, you'll become part of a dynamic company. We are ambitious, focused on product development, and execution-oriented, with a clear impact, swift decision-making, and genuine growth opportunities.Our Work Culture at Aircall: We prioritize customer satisfaction, leverage data for decision-making, and are dedicated to delivering significant outcomes. We cherish ownership, continuous improvement, and thoughtful agility. If you thrive in a collaborative, fast-paced environment where trust and impact are essential, you will thrive here.Position Overview:As a Senior Backend Software Engineer, you will take charge of designing, developing, deploying, and maintaining essential features that enhance customer value on our voice platform.You will be expected to advocate for best practices, mentor team members, and contribute to the broader Engineering community as part of your daily responsibilities.Quality, excellence, and agility are at the core of our delivery process, and you will play a pivotal role in elevating these standards.Utilizing a diverse array of backend technologies tailored to specific needs, all hosted on AWS, we create resilient services that deliver added value on top of voice while fully integrating with our customers' critical business tools (CRM, Helpdesk, E-Commerce, etc.).

About Mistral AIAt Mistral AI, we harness the transformative power of artificial intelligence to simplify daily tasks, save precious time, and enhance learning and creativity. Our innovative technology is crafted to seamlessly integrate into the fabric of everyday work life.We are on a mission to democratize AI through high-performance, optimized, and cutting-edge open-source models and solutions. Our robust AI platform is tailored to meet the diverse needs of enterprises, whether on-premises or in the cloud. Our flagship offerings include Le Chat, your AI assistant for both life and work.We pride ourselves on being a dynamic, collaborative team deeply passionate about AI and its potential to reshape society. Our diverse workforce thrives in competitive environments and is dedicated to fostering innovation. With teams distributed across France, the USA, the UK, Germany, and Singapore, we embody creativity, humility, and a strong team spirit.Join us on this exciting journey as we shape the future of AI, making a meaningful impact together. Discover more about our vibrant culture at https://mistral.ai/careers.Role OverviewWe are on the lookout for passionate and talented Software Engineers to join our team. As a Backend Engineer, you will play a pivotal role in developing the core systems that power our key products: AI Studio, Le Chat, and Mistral Code. You will shape how users and developers interact with our AI platform at scale. Your focus will be on building reliable, high-performance backend systems and APIs that support millions of users and developers. Your contributions will directly enhance the user and developer experience, making it more engaging, efficient, and intuitive. We welcome engineers at all levels, from fresh graduates to seasoned professionals who are eager to learn, collaborate, and deliver impactful solutions.Key ResponsibilitiesBased on your expertise, you will engage in crucial components of our technology, including:Backend Development- Design, develop, and maintain scalable and robust backend features and APIs using modern frameworks.- Ensure high performance and reliability across our distributed systems.- Contribute to systems that support authentication, billing, AI tooling, and observability.

About 9fin9fin is a cutting-edge AI platform revolutionizing the global debt markets, which represent the largest asset class exceeding $145 trillion.The landscape of debt markets is extensive, global, and essential, yet it often relies on disjointed data, PDFs, and manual processes. 9fin transforms this outdated infrastructure by providing a unified platform that consolidates proprietary credit data, in-depth analysis, and efficient workflows across international markets.Currently, 9fin empowers over 300 prestigious institutions worldwide, including leading banks, asset managers, private equity firms, law firms, and consulting advisors. The company is experiencing rapid growth, particularly in the US, with exceptional retention rates driven by robust workflow adoption.We are at a pivotal moment. With a validated product-market fit and strong global demand, 9fin is propelling towards becoming the definitive platform for debt markets globally.What You'll Work OnAs a Senior Backend Engineer on our Structured Credit team, you will contribute to the development of our market-leading CLO product and assist in the launch of a new vertical.Our team is dedicated to making a significant impact, leveraging technology to create value for the business. While we have overarching business goals, we enjoy the autonomy to define our team objectives and determine our success metrics. We uphold accountability and proactive behaviors such as ownership.Lead projects within a cross-functional team by defining and designing systems, building proof of concepts, and delivering new service functionalities—including APIs, data processing, and automation—while collaborating with Product and Clients.Engage in backend development and engineering primarily on the services and web applications hosted on the 9fin platform.Play a crucial role within project teams as a senior individual contributor, conducting code reviews, mentoring fellow developers, and participating in early research and experimentation with new technologies to provide insights for new features and products.Continuously enhance the 9fin codebase by seizing opportunities to automate, refactor, and document processes when it has the most significant impact.Work across diverse web platforms involving complex financial data modeling, intricate access control logic, environmental data capture, integration of ML/AI prediction services, and data visualization.

About 9fin9fin is revolutionizing the global debt markets with its cutting-edge AI platform, catering to the world’s largest asset class valued at over $145 trillion.The debt markets are extensive, international, and essential, yet they are often hindered by disjointed data, PDFs, and manual processes. 9fin transforms this outdated framework by providing a unified platform that consolidates proprietary credit data, in-depth analysis, and streamlined workflows across global markets.Currently, 9fin supports over 300 prestigious institutions worldwide, including leading banks, asset managers, private equity firms, law firms, and advisory companies. Our rapid growth is marked by significant expansion in the US and an exceptional retention rate driven by extensive workflow adoption.We are at a pivotal moment in our journey. With a proven product-market fit and substantial global demand, 9fin is on the path to becoming the definitive platform for debt markets globally.What You'll Work OnYou will lead technical projects, defining and designing systems, swiftly creating proof of concepts, and collaborating closely with Product and our clients.Develop code and guide your team in delivering new service functionalities, implementing APIs, managing data routing/processing, and establishing automation mechanisms.Your primary focus will be on backend services and the web applications that support the 9fin platform.Assume a leadership role within project teams, conducting code reviews and mentoring junior developers, while also participating in early research and experimentation with new technologies to inform new features and products.Continuously enhance the 9fin codebase by automating, refactoring, and documenting when possible.Diversity is key: Our web platforms encompass a wide range of areas, including complex financial data modeling, environmental and energy data capture, integration of ML/AI prediction services, and data visualization and automation systems.Collaboration is vital: We form cross-functional teams for every project, incorporating the necessary domain expertise from 9fin in finance, law, and editorial. Your ability to convey complex projects to non-technical audiences will foster productive and efficient team collaboration.Developer Experience: By managing automated processes and enhancing the development environment, you will help improve the overall experience for developers.

About JuniorAt Junior, we are on a mission to revolutionize the investment research landscape with innovative LLM-powered tools designed specifically for private market investors. Our clientele includes some of the world's leading private equity and consulting firms, collectively managing billions in annual investments. As a profitable and bootstrapped enterprise, we have grown our team to 24 talented individuals across our London and NYC offices, and we achieved a remarkable 10x revenue growth in 2025.Discover more about our mission and values here. Role DescriptionAs our first dedicated Backend Engineer focused solely on our internal go-to-market and operations stack, you will play a pivotal role in shaping our technology framework. Your responsibilities will include:Crafting an AI-first tech stack from the ground up, influencing infrastructure decisions and priorities.Rapidly deploying internal tools and receiving immediate feedback from your team members, who will quickly become your strongest advocates!Developing and managing our data warehouse and internal data architecture.Engaging in innovative projects that leverage LLMs, automation, and advanced agent technologies.Cultivating our engineering culture. Sample Set of ProjectsUser Health Reporting + CRM Data Quality: Automate data pipelines to enhance metrics visibility in BI dashboards and ML evaluations, while establishing alert systems for risk signals.User Feedback Integration: Develop a tool that summarizes user feedback calls, prioritizes feature requests, and communicates findings to our Product team.Billing and Invoicing: Implement complex B2B pricing models encompassing usage-based, seat-based, and platform fees, while automating financial reconciliation processes.Data Warehouse Development: Create a data warehouse to integrate product, CRM, and operational data, and generate tailored dashboards for different teams. About YouWe are searching for a backend/data engineer who...

Pelago stands at the forefront of virtual healthcare, specializing in Substance Use Management. Our comprehensive program offers personalized guidance, support, and treatment for individuals aiming to overcome challenges related to tobacco, alcohol, and opioid use. We cater to a diverse spectrum of substance use, from unhealthy habits to active disorders, ensuring that each member receives tailored care that aligns with their health, habits, genetics, and personal objectives. Our array of virtual services encompasses educational resources, cognitive behavioral therapy (CBT), and comprehensive medication-assisted treatment (MAT). Pelago empowers employers and health plans to provide accessible and effective solutions for substance misuse. Having successfully partnered with hundreds of employers and health plans, we have positively impacted over 750,000 lives. After recently securing our Series C funding with over $151 million raised from premier global investors, we invite passionate individuals to join our mission of transforming health outcomes.About Pelago Engineering:Our engineering team is composed of empowered, outcome-focused problem solvers who collaborate closely with product, design, and clinical teams to enhance member outcomes at scale.As AI reshapes the software development landscape, we are proactively refining our development processes to prioritize system design and impactful decision-making over rote implementation.How We Work:Outcome-driven: Engineers tackle substantial problems rather than merely building features. Success is evaluated based on learning, impact, and outcomes—not just speed.AI-native: We leverage AI throughout the software development lifecycle to expedite implementation, testing, and reviews, allowing engineers to concentrate on intent definition, behavior validation, and system resilience design.High autonomy, high accountability: Teams enjoy significant ownership of their domains, with autonomy translating to responsibility for quality, safety, and results.Cross-functional collaboration: Engineers work synergistically with Product, Design, Data, and Clinical teams, sharing responsibilities for discovery, experimentation, and delivery.Quality and safety are paramount: Our work is conducted within a regulated domain that directly impacts members, making reliability, observability, and correctness top priorities.What You’ll Do:Instead of traditional task lists, you will take full ownership of significant problem spaces from discovery through to delivery.

Backend Engineer About OutpostImagine a world where expanding your business globally is as easy as local sales. At Outpost, we are pioneering the AI-driven global trade engine, consolidating all the essential rules to facilitate international sales into a seamless infrastructure. Simply tell us what you’re selling, and we’ll guide you on how to sell it globally.Operating as the Merchant of Record or Tax of Record in over 58 tax jurisdictions, we take on full liability or just the tax layer. From analysis to setup, we absorb the complexities so you can focus on your business.Sell anything, anywhere, without compromise. The RoleWe are looking for a talented Backend Engineer eager to create complex financial infrastructures from the ground up. You will collaborate closely with our engineering leadership to implement payment flows, develop tax calculation engines, and build systems that power international commerce. Your insights will shape product and technical discussions, challenge existing assumptions, and help define our technical direction.Join us in constructing the infrastructure that empowers businesses to sell globally without the typical challenges. You will engage in payment processing, multi-currency ledgers, real-time tax calculations, merchant onboarding, and AI-powered compliance tools. Tackle challenging problems at real scale. What You’ll GetYes, the work can be intense, but you'll be building crucial financial infrastructure that manages hundreds of millions in transaction volume.Your contributions will significantly influence our technical direction, and you'll collaborate with a small team of experienced engineers, helping shape Outpost’s growth. If you're passionate about diving deep into payments, tax, and fintech infrastructure, this is the opportunity for you. What You’ll BuildPayment processing infrastructure capable of handling significant transaction volumesRobust ledger and reconciliation systemsTax calculation engines across multiple jurisdictionsReal-time transaction monitoring and risk management systemsMerchant onboarding and integration frameworksConnections with major e-commerce platformsAI/LLM powered taxation toolsAI/LLM driven fraud and risk management solutions What You’ll Do

Corgi builds insurance solutions for tech startups, using AI to power underwriting and streamline coverage. Backed by $108M in funding and operating as a regulated carrier, the company is expanding across the UK and EU. The platform relies on Django, integrates Stripe for payments, and emphasizes new product development. Role overview This Backend Engineer role is based in London and centers on taking projects from concept to live launch. The team values engineers who build and ship products, not just maintain existing systems. Candidates who have delivered personal projects or launched products with real users will feel at home here. The environment suits those who prefer moving quickly and seeing their work in production without long delays. What matters here Independently developing and launching working products Shipping projects quickly, often within hours or days Comfort working across the stack and tackling new challenges Balancing strong opinions with openness to better solutions Low ego, with motivation driven by results Energy and drive to thrive in a startup setting How the team works Quick decision-making, prioritizing progress over perfection Frequent launches and iterative improvements Products ship and evolve, rather than stalling in review High intensity during launches, with steady momentum at other times Transparency and open decision-making are encouraged Internal competition is seen as a way for everyone to improve This is a hands-on role focused on building. Coasting is not an option. Behaviors that end the role quickly Engaging in office politics, avoiding accountability, or spreading rumors Taking feedback personally instead of using it to improve Choosing complexity when simplicity is possible Missing deadlines after making commitments How to apply Send links to your GitHub, personal website, or live projects Resumes are not accepted Email your application to: sergio@corgi.com If you cannot show delivered work, this role is unlikely to be a fit Location and compensation London-based, with on-site or hybrid options Base salary: £75,000 to £140,000 Equity is available The wide salary range reflects a focus on proven ability to ship, not job titles

Join Spotify as a Backend Engineer specializing in Personalization. In this dynamic role, you will develop and enhance backend systems that deliver personalized experiences to millions of users worldwide. Collaborate with cross-functional teams to design scalable solutions and implement cutting-edge technology that drives user engagement.

Join Herondata as a Principal Backend Engineer and lead the charge in developing robust backend architectures. You will collaborate with cross-functional teams to design, implement, and optimize scalable solutions that support our mission of providing top-tier data services. Your expertise will drive innovation and enhance our platform's performance, ensuring we remain at the forefront of the industry.

Who We AreLightning AI is the innovative force behind PyTorch Lightning, established in 2019. We provide a comprehensive platform designed to streamline the development, training, and deployment of AI systems, effectively bridging the gap between research and production.Our merger with Voltage Park, a neocloud and AI Factory, empowers us to combine developer-centric software solutions with economical, large-scale computing capabilities. We equip teams with essential tools for experimentation, training, and production inference, ensuring built-in security, observability, and control.We cater to solo researchers, startups, and large enterprises alike, operating globally with offices in cities such as New York City, San Francisco, Seattle, and London. Our efforts are supported by notable investors including Coatue, Index Ventures, Bain Capital Ventures, and Firstminute.What We’re Looking ForWe are seeking a skilled Backend Engineer to develop and enhance the Lightning AI platform across various components, from the frontend and CLI to API, billing, security, and integrations. You will take full ownership of key features, driving development from concept to production while collaborating with a talented team of engineers, product managers, and designers. This role offers the chance to create groundbreaking technology that will revolutionize the machine-learning ecosystem!This hybrid position is based in our London office with a requirement of 2 in-office days per week. The salary range for this role is $120,000 - $250,000.

Role Overview hook is hiring a Backend / Fullstack Engineer in London. This role involves building server-side applications and contributing to front-end features that improve how users interact with our products. What You Will Do Develop and maintain backend systems Work on front-end components to support a seamless user experience Participate in the full software development lifecycle, from initial idea through deployment Who We’re Looking For Comfortable working with both backend and frontend technologies Interested in taking projects from concept to launch Ready to collaborate with a team in London

Join Us at IntropicAt Intropic, we're pioneering the future of financial intelligence, merging deep market expertise with cutting-edge AI technology. Established in the financial hub of Canary Wharf, London, our mission is to distill complex data into clarity, precision, and actionable insights. Our culture is driven by values of truth-seeking, speed, and ownership, which shape our approach to building, learning, and collaboration. We prioritize integrity, impact, and a fast-paced environment where curiosity is not just welcomed, but vital. If you are eager for challenges, inspired by innovation, and ready to elevate your intelligence alongside a team of extraordinary minds, Intropic is the place where your ideas can flourish.Who We Are Looking ForAs a thriving fintech start-up with a proven range of products, we are now on a mission to create the next groundbreaking solution. We seek individuals who excel in tackling open-ended challenges across various disciplines. Our engineers engage in more than just standard tasks; your role may involve debugging Python, deploying infrastructure updates, engaging with product early adopters, and strategizing with team leaders. We value individuals over resumes; if this sounds like you, we would be excited to connect!

Transform the Future of Finance.At Light, we are revolutionizing the outdated ERP systems of the factory era with innovative software that feels dynamic and responsive. Our Smart Financial Platform empowers modern, global enterprises with automated accounting, instantaneous reporting, and financial processes that adapt to the pace of business.We're passionate about collaborating with our clients, delivering swiftly, and perfecting our craft. In a short span, Light has evolved from a concept to an essential operational tool for renowned companies such as Lovable, Legora, and Keyshot. Our users don’t just utilize Light—they genuinely enjoy the experience.As a pioneering team, we are establishing a new software category. We are looking for engineers who appreciate the intricacies of debits and credits, designers who prioritize reconciliation states, and operators who view finance as a product. If you are eager to modernize the financial landscape—one workflow at a time—you belong here.Supported by prestigious investors and guided by industry leaders, we are crafting products that define categories, allowing us to innovate boldly and take ownership of our results. Join us in our mission to make Light the global standard for next-generation financial solutions.Your Role as a Backend Engineer:Enhance our core Smart Financial Platform, enabling multinational corporations to streamline their accounting processes through AI and exceptional user experience.Maintain a strong focus on customer requirements while architecting robust and scalable technical solutions.Develop and optimize backend services, APIs, and infrastructure to support our high-performance frontend applications.

About the CompanyAffinidi is a pioneering technology firm focused on reimagining data ownership. We empower both businesses and individuals to take control of their data, providing a holistic approach to managing their digital identity while prioritizing privacy and security.Our innovative technology facilitates decentralized digital identity solutions, ensuring that everyone has the right to own and govern their data. We are dedicated to establishing a trustworthy ecosystem for digital credentials that allows secure data and service exchange across various sectors and borders. About the Role: We are seeking a solution-driven Senior Backend Engineer who possesses substantial expertise in Rust. The ideal candidate will have a track record of delivering robust backend solutions and is eager to contribute to our mission of transforming digital identity.

Join commercetools as a Senior Backend Engineer, where you will play a pivotal role in shaping innovative backend solutions using TypeScript. Collaborate with cross-functional teams to create scalable and resilient microservices that empower our clients to deliver exceptional digital commerce experiences.

About the Role alten is looking for a Backend Software Engineer to join the Space Department in London. This position focuses on building software solutions that support key projects and help move our technology forward.