Senior Backend Software Engineer - Application Development

xai seeks a Backend Engineer in London, UK to focus on API development. This role involves designing and building APIs that form the backbone of the company’s products and services. Key responsibilities Design and implement APIs to support xai’s solutions Collaborate with frontend developers and product managers to ensure seamless feature integration Optimize API performance and maintain reliability This position offers the chance to work closely with both technical and product teams, shaping the way xai’s services communicate and perform.

At Flowdesk, we are on a mission to establish a global financial institution for digital assets, meticulously crafted to foster market integrity and enhance efficiency.In a swiftly evolving market landscape, we employ a disciplined, first-principles methodology in all our operations. This approach is woven into our core services, including institutional liquidity provision, trading solutions, OTC execution, and extensive treasury management services. By adhering to these principles, we navigate the complexities of the financial world, constructing robust and scalable systems across our diverse business lines.We invite individuals who share our passion for systematic approaches to join us in revolutionizing the financial markets infrastructure to be more transparent and efficient.Our APIs serve as the gateway for external trading interactions, and we are excited to announce an opening for a Senior Software Engineer – API Trading. In this role, you will design, develop, and scale our public trading APIs to a competitive standard. You will take ownership of the API surface that clients integrate with (REST, WebSocket, FIX), ensuring it is clear, well-documented, and collaborates closely with trading, product, and security teams to deliver a best-in-class experience.This is a hands-on, senior individual contributor role that emphasizes technical ownership and cross-team collaboration.Your mission will involve:Designing and building competitive trading APIsArchitecting and implementing public trading APIs (REST, WebSocket, and FIX) using Rust.Ensuring low-latency and high-throughput access to trading workflows including orders, balances, positions, and executions.Owning the API lifecycle from start to finishDefining and maintaining OpenAPI specifications and related interface contracts.Keeping APIs consistent, versioned, and simple for external client integration.Creating clear, accurate, and engaging API documentation that developers will find valuable.Building secure and robust authentication flowsDesigning and implementing authentication and authorization for public trading APIs.Applying best practices for key management, signatures, rate limiting, replay protection, and preventing abuse.Collaborating across trading, product, and engineering teamsWorking closely with stakeholders to understand trading needs and constraints.Translating trading and product requirements into clean API designs and dependable backend workflows.Partnering with frontend and tooling teams (TypeScript) to ensure seamless integration.Raising the bar on reliability and qualityEnsuring APIs are observable, thoroughly tested, and resilient under peak loads.Contributing to the development of standards, patterns, and tools for API development across the team.Mentoring team members and participating in code reviews.

JavaScript/API EngineerAre you passionate about revolutionizing capitalism and supporting noble causes? Do you enjoy crafting innovative products that can significantly impact people's lives?At Percent, we aspire to build a world where doing good is effortless. Our inaugural mission is to channel 1% of global retail spending towards charitable initiatives.With our third round of funding secured to turn this vision into reality, we are searching for an exceptional JavaScript/API Engineer to join our enthusiastic team. You will play a pivotal role in developing an array of remarkable features for our key stakeholders, including some of the largest charitable organizations globally.We offer:A supportive and enjoyable team environmentA strong focus on people and collaborationA substantial and impactful projectA modern office located in central LondonDelicious company lunches every TuesdayAn opportunity to address global challenges while maintaining a positive mindsetA creative and unconventional work cultureYou should possess:A passion for contributing to a better worldA willingness to take shared ownership of a significant projectStrong proficiency in Object-Oriented JavaScript and Node.jsExperience with various database technologiesCapability to handle high-volume API calls and scale solutions globallyUnderstanding of networking protocolsFamiliarity with numerous AWS servicesKnowledge of network configurationsExperience with monitoring systems, continuous integration, and testingA creative and unconventional approachAdditionally, while not mandatory, it would be beneficial to have knowledge of:Serverless architectures (AWS Lambda)HTTP/2Containerization technologiesVideo streaming solutionsInfrastructure as codeA fondness for tea breaksWe provide:Competitive compensation for the right candidate along with excellent equity optionsAn opportunity to become a partner in our missionA prime location in Soho/PiccadillyA highly comfortable workspaceFresh fruit every day (or biscuits for those with a sweet tooth)A fully stocked luxury coffee and tea machine available at all times

Senior PHP Backend Developer - £500 per day (12+ Months, Remote Work Available, Outside IR35)We are seeking an experienced PHP Developer to join our team, working on an innovative Greenfield backend REST API project tailored for the transport sector. Collaborating closely with a Senior API Engineer, you will be part of a smaller, established, and friendly agency dedicated to delivering a significant project for a prominent client in the transport industry.Work Location:Options available in London, Bristol, or Cornwall, with full flexibility for remote work.

Join a Pioneering CompanyAt Palantir, we develop cutting-edge software that revolutionizes data-driven decision-making and operations. Our platforms empower partners to create life-saving medications, foresee supply chain challenges, locate missing individuals, and much more by connecting the right data with the right people.Role OverviewAs a Backend Software Engineer at Palantir, you will engineer scalable software that reshapes how organizations leverage data. You will actively participate throughout the product lifecycle—from ideation and design to prototyping and delivering production-ready solutions. Collaborating closely with both technical and non-technical team members, you’ll identify customers' challenges and create products that effectively address them. We promote cross-team interactions to foster the sharing of skills, context, and experiences, enabling you to gain insights into various technologies and product facets. Our engineers operate independently, making impactful decisions within a supportive community that encourages growth and development into strong technical contributors and engineering leaders.Your daily responsibilities will be dynamic, adapting to user needs and technical hurdles. One day, you might partner with other engineers to design a groundbreaking system that facilitates a new workflow; the next day, you could focus on optimizing performance for low-latency operational results.Our Product Development teams consist of small, agile groups of Software Engineers, each dedicated to specific product facets. These teams collaborate to build cross-functional capabilities, enhance user workflows, and consistently improve our software’s efficiency and reliability.We are seeking engineers who are enthusiastic about tackling real-world challenges and empowering both developers and end-users to maximize their potential. If you are driven to create reliable, high-performance, and scalable systems and to design robust APIs and primitives, this role presents a unique opportunity to significantly impact our products and the communities that utilize them.Unique Opportunity: Frontline ProgramFoundry Software Engineers may be selected for the Frontline Program, a distinct opportunity to engage directly with customers. In this short-term assignment, you will work alongside users to gain invaluable insights into product application and the challenges they encounter. Unlike standard engineering roles, Frontline involves tackling complex, ambiguous problems, empowering you to deliver impactful solutions across critical industries and institutions.

Your ContributionThe Senior Software Engineer III (Backend) plays a pivotal role in tackling intricate tasks and is instrumental in advancing the objectives of their team. This role includes leading small projects or components while crafting robust feature sets that adhere to high architectural quality standards.Key ResponsibilitiesAdvanced Software Development: Actively participate in the design and implementation of sophisticated software solutions, ensuring optimal functionality, scalability, testability, and reliability. Assist with system design and grooming processes.Code Quality and Optimization: Enhance and maintain code quality through thorough review practices, optimization strategies, and adherence to industry best practices.Innovative Problem Solving: Tackle complex technical challenges with creative solutions.Collaboration and Communication: Collaborate effectively within the engineering team and across various departments, working alongside other engineers, product managers, and stakeholders.Continuous Learning and Adaptation: Stay current with emerging technology trends and continuously enhance skills and knowledge.Technical Documentation: Produce and maintain comprehensive technical documentation for clarity and accessibility.

Join Our Team!At Plum, we are revolutionizing how people save and invest. Our mission is to empower individuals to grow their wealth for life, whether they are saving for their first home or enjoying retirement. Since our inception in 2016, over 2 million users across 10 European countries have saved more than £2 billion with our innovative automation and AI technology. We've been recognized with awards from esteemed organizations like Deloitte and Finder, reflecting our commitment to excellence.We are a passionate team of over 200 Plumsters working collaboratively across Europe, and we are eager to welcome more talented individuals to help us achieve our vision.Your RoleAs a Senior Backend Engineer at Plum, you will play a crucial role in shaping our technology and product offerings. We seek engineers who are not only technically adept but also understand the importance of delivering outstanding products to our customers.

At Spotify, we are on a mission to revolutionize the way creators and listeners engage with long-form storytelling through our Audiobooks initiative. Our objective is to create a seamless ecosystem for audiobook content, facilitating smooth transfers from publishers to listeners. This includes building the robust systems necessary for content ingestion, processing, and efficient delivery across our rapidly expanding global catalog. We are seeking a talented Senior Backend Engineer to join a dynamic and impactful team within the Audiobooks Pipeline sector. This team's primary responsibility is to design and scale systems that handle the ingestion, processing, and transformation of audiobook and eBook content, metadata, and royalties, ensuring that listeners receive the right content with utmost efficiency and quality. While this role encompasses full-stack responsibilities, the emphasis will be on backend and data-centric development. We are looking for an individual who thrives in uncertain environments, is passionate about learning, and is excited to tackle complex challenges across the tech stack.

Join xAI as a Backend Engineer, where you will play a vital role in building robust production systems that support grok.com and our API. We are looking for a highly motivated individual with expertise in scalable infrastructure and a passion for problem-solving. Your experience with Rust or C++, along with your ability to design and maintain distributed systems, will be crucial as you contribute directly to our mission of advancing AI technologies. Strong communication skills and a commitment to excellence are essential in our collaborative environment.

Join Duffel as a Backend Software Engineer and play a pivotal role in shaping the future of travel technology. We are seeking passionate individuals who thrive on solving complex challenges and are excited about creating scalable and efficient backend systems.

Join the dynamic team at Sony Interactive Entertainment Global as a Senior Software Engineer specializing in Rendering API. In this pivotal role, you will be responsible for developing and optimizing rendering technologies that enhance the gaming experience for millions of users worldwide. You will collaborate closely with cross-functional teams to bring innovative solutions to life, ensuring top-notch performance and visual fidelity in our gaming products.

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.).

TL;DRDeducta is a rapidly expanding startup catering to some of the globe's most prestigious enterprises. With strong funding, we are committed to addressing today's most significant business challenges.We are seeking a Senior Backend Engineer who will play a pivotal role in the design, development, and upkeep of our core systems.In this role, your key responsibilities will include:Creating and sustaining high-performance, low-latency APIs for enterprise-level data processing systems.Delivering exceptional code promptly. Location: London, UK. Our office is situated near London Bridge, and we prioritize in-person collaboration. Compensation: The total compensation for this position begins at £150,000. Visa Sponsorship: We are willing to sponsor a visa for the ideal candidate to join our team. What is Deducta?Deducta is a leading data intelligence platform for global corporations. We provide unparalleled clarity into mission-critical data for some of the world's largest and most intricate organizations, starting with spend data.We are at the forefront of significant business transformations. Our partners leverage Deducta to achieve impactful results at remarkable speeds.‍What is the Role?We process vast datasets containing essential enterprise information from diverse sources and formats, structuring it effectively. Our system utilizes cutting-edge LLMs to tackle this challenge with unmatched precision and at previously unimaginable scales.As a Senior Backend Engineer, you will be responsible for designing, developing, and maintaining the foundational architecture of our platform as it expands.Your contributions will include:Designing, constructing, and maintaining data ingestion and processing engines capable of supporting mission-critical operations for the largest firms globally.Developing and sustaining ultra-fast, high-volume, and well-documented APIs to facilitate these systems.Driving business growth through a blend of creativity and experimentation to enhance our product, alongside proactive problem-solving for our clients.Working closely with both technical and non-technical team members to comprehend our customers' challenges and create solutions that address them.Success in this role means:Leading development initiatives from concept to production.Consistently driving enhancements and new features. Who will be the right fit?We are in search of a technically outstanding engineer who excels in a role that offers autonomy and ownership.You might be a great fit if you possess…Strong experience in object-oriented programming within cloud environments (e.g. AWS, GCP, or Azure), with .NET experience considered a plus.Familiarity with SOLID principles, domain-driven design, and Clean Architecture methodologies.A passion for...

Role overview Wise seeks an Engineering Lead to focus on API experience in London. The role involves leading a team that designs and builds API solutions for customers at scale. This position centers on both technical leadership and team guidance. What you will do Guide and support engineers as they develop Wise’s API products Encourage new ideas and drive technical improvements within the team Oversee the creation and maintenance of scalable, reliable APIs Work to ensure Wise APIs align with customer needs and meet industry standards Location This position is based in London.

About UsAt Heidi, we are pioneering an AI Care Partner that assists healthcare professionals at every stage, from documentation to patient care delivery. Our mission is to enhance healthcare capacity while maintaining a deeply human touch. In just 18 months, we have reclaimed over 18 million hours for clinicians and facilitated more than 73 million patient visits. Currently, Heidi powers over two million patient interactions weekly across 116 countries in more than 110 languages.Founded by healthcare professionals, Heidi unites clinicians, engineers, designers, scientists, creatives, and mathematicians, all dedicated to enhancing the human connection central to healthcare. With nearly $100 million in funding, we are expanding our reach in the USA, UK, Canada, and Europe, collaborating with major health systems, including the NHS and Beth Israel Lahey Health, among others.We are agile in our approach, focused on what works, and poised to shape the future of healthcare. Are you ready to take on this challenge?Your RoleAs a Senior Backend Engineer, you will be instrumental in executing backend features, leveraging your deep technical understanding to meet user requirements. You will thrive in a hyper-growth startup environment, with substantial experience in building SaaS products.With a solid grasp of the challenges engineers face, you will prioritize key features and capabilities through effective design principles. Your ability to bridge technical specifics with business needs will enable you to transform high-level concepts into practical solutions.Embracing challenging scenarios, you will appreciate the dynamics of a flexible, flat-structured work environment and quickly navigate the complexities of developing AI healthcare products on an international scale. We believe that exceptional talent can emerge from diverse backgrounds; if you have a proven history of delivering technically demanding products and features, we want to hear from you.

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 Spotify as a Senior Backend Engineer - Subscriptions and play a pivotal role in enhancing our subscription services.In this position, you will collaborate with cross-functional teams to design and implement scalable backend systems, ensuring seamless integration and exceptional user experiences.

Join us in revolutionizing travel!Travel is more than just a journey; it connects us with loved ones, opens up new adventures, and creates unforgettable experiences. Yet, the frustrations of travel can often overshadow the excitement. Over 4 billion airline passengers depend on outdated technology that fails to meet the expectations of today's connected traveler.At Duffel, we are on a transformative mission to modernize the travel infrastructure. We aim to simplify complex systems and develop innovative tools that ensure a seamless travel experience for everyone.As part of the Y Combinator S18 cohort, we are proudly backed by notable investors including Benchmark, Blossom, Index Ventures, and Kima Ventures, who have played a pivotal role in the growth of some of the world’s leading companies.Position OverviewIf you are passionate about customer success and excel at solving intricate technical challenges, this is the perfect opportunity for you. Duffel is seeking a Customer Success Engineer (CSE) to deliver expert technical support to our key clients. In this role, you'll assist customers by answering their inquiries and recommending effective ways to leverage our APIs to create outstanding travel experiences. Furthermore, you will work closely with various teams across Duffel, including Product, Engineering, Finance, and Travel Operations, to guarantee an exceptional customer journey with our products and services.

As a Senior Backend Developer specializing in Ruby on Rails, you will play a pivotal role in architecting, developing, and validating server-side logic for web applications. Your expertise will be essential in crafting efficient, reusable, and robust Ruby code, while optimizing systems for peak performance and scalability. You will work collaboratively within cross-functional teams, integrating front-end components into our applications. Your responsibilities will also include conducting code reviews, mentoring junior developers, and converting business requirements into effective technical solutions.The ideal candidate will possess a Bachelor's or Master's degree in a related discipline, along with a minimum of eight years of hands-on experience in Ruby on Rails development. You should be well-versed in various software testing methodologies, demonstrate strong analytical skills, and have excellent proficiency in English.