Staff Backend Engineer (B2B - Warsaw)

RTB House

Location: Poland (Remote/Flexible) We are:  RTB House is a global company that provides state-of-the-art marketing technologies for top brands and agencies worldwide. Its proprietary ad-buying engine is the first in the world to be powered entirely by Deep Learning algorithms, enabling advertisers to generate outstanding results and reach their goals at every stage of the funnel.  We are looking for engineers to join our Bidding Platform organization which is the core of the RTB business, processing over 20 million requests per second to participate in real-time auctions and display advertisements to customers from 90+ countries. If you want to work on technically complex and demanding solutions, this is the opportunity for you! Our Staff Engineers are experts who combine deep technical expertise with a strong sense of ownership, and they take on Tech Lead roles in complex, cross-team projects. You will: * Gain deep understanding of our ad technology and become familiar with ad industry standards: OpenRTB, MRAID, VAST etc. * Analyse issues with our end-to-end ad workflows, reproduce problematic cases, and come up with proposals for improvements. * Design technical and operational solutions that improve ad experience and our performance metrics. * Lead implementation of the aforementioned architectural solutions, ensuring its high quality, and evaluating its impact on business performance. * Provide hands-on technical leadership: solving complex system challenges, participating in planning and scoping of projects, and ensuring the implementation of the highest coding standards through participation in code reviews. * Cooperate with stakeholders across the entire organization. Desired experience: * 10+ years of hands-on experience in designing, developing and deploying complex software systems. * 3+ years of tech leadership experience (e.g. tech lead, staff, architect roles) in medium or large organizations. * Excellent understanding of complex, distributed IT systems - from the hardware and networking level, through software, to algorithms. * C1 level in English and Polish. Nice to have: * Experience in the AdTech/Real Time Bidding space. Selected technologies used:  * Java, Python * Aerospike, Memcached * Google Cloud Platform, BigQuery, MinIO * Kafka, Clickhouse * PostgreSQL * Elasticsearch * Kubernetes, Prometheus * Jenkins, Graphite We Offer: * Projects focused on extreme performance and high code quality – clean code and solid code reviews are our standard. * Collaboration within an interdisciplinary, self-sufficient team (including DevOps, database experts, backend developers, product designers, and QA engineers). * Access to modern technologies and the opportunity to apply them in large-scale, high-impact projects. * Cooperation based on B2B contract. * You can cooperate 100 % remotely or choose one of our office spaces in Warsaw or Cracow. You don't need to tick every box to apply. If you are passionate about software engineering, send us your CV, and we'll review it.

Xapien

About Us Every business needs to know who they’re really working with whether it’s suppliers, investors, partners, or third parties. At Xapien, we’re reinventing how organisations do that, combining speed, scale and accuracy with cutting-edge AI. Since 2018, we’ve grown from a deep-tech startup to a global player in AI-driven due diligence and risk intelligence. 2024 was a landmark year as we closed a $10M Series A, earned recognition in the Chartis RiskTech100® and Everest Group’s Leading 50™, and expanded our products, markets and customer base. 2025 was even bigger: With new regulations, rising compliance pressure and growing reputation risks, organisations everywhere are demanding smarter, faster ways to work and they’re turning to us. Customers worldwide from global law firms and private banks to universities and nonprofits rely on Xapien to turn days of manual research into trusted insights, delivered in minutes. Our momentum so far Customers in a diverse range of industries, with particular growth in wealth management, financial services and supply chain onboarding. Demand accelerating beyond our UK headquarters, across multiple continents with new customers in the Middle East, Asia, and Oceania. Why this is an exciting time to join This isn’t just another job role; it’s an opportunity to shape the future of the due diligence industry with a market-leading product trusted by global organisations. Whether you’re in marketing, communications, sales, or finance, you’ll play a critical role in driving growth, building credibility, and defining how we connect our product to a rapidly evolving market. We’re scaling fast with more customers, more releases, and bigger regulatory and market challenges. Expectations are rising, due diligence now means real-time insight, delivered efficiently and with impact. You won’t just be executing campaigns, closing deals, or managing numbers, you’ll be influencing strategy, optimising processes, and helping position a brand that’s setting the new standard for trust and transparency. For people who love learning, innovating, and making an impact that matters now is the moment to be a part of Xapien. The Role We're hiring a Staff Backend Engineer to join our engineering team in a high-impact technical leadership role. You'll work on our most challenging technical problems, own parts of our platform's architecture, and help shape the technical direction of our backend stack. Our tech stack centres on Go microservices, with Temporal workflows and MongoDB running on Kubernetes in GCP. You'll work with modern patterns including event-driven architectures, gRPC and REST APIs, and comprehensive observability with Grafana Cloud. We're an AI-native engineering team. We use Claude Code daily and we're investing heavily in AI-assisted development as a core part of how we build software — not as an experiment, but as a first-class engineering practice. We want engineers who are excited about this and who have ideas about how to push it further: how to decompose work for AI agents, how to maintain quality at higher velocity, and how to help an entire team get dramatically more productive with these tools. You'll take technical ownership of major domains within our platform — whether that's our Investigations pipeline (web scraping, data provider integrations, LLM-powered analysis) or our Core App systems (user journeys, features, and configuration). You'll be a technical authority, establishing patterns that others follow and driving initiatives that span multiple teams. What You'll Do * Own the technical direction and architecture for parts of our platform * Design and build complex backend services and systems that scale * Drive technical decisions that affect multiple teams * Establish patterns, standards, and best practices that others will follow * Shape and evolve our AI-assisted development practices, setting the standards for how the team works effectively with AI tooling * Use AI tooling to multiply your own output and help the wider team do the same, rethinking how engineering work is planned, decomposed, and delegated * Lead complex technical initiatives from design through implementation * Identify and address systemic technical challenges across our backend * Set the standard for high-quality code, whether written by hand or with AI — knowing when to trust, when to intervene, and what good looks like either way * Mentor engineers across the organization, raising the technical bar * Balance technical excellence with pragmatic delivery * Influence technology choices and architectural direction * Collaborate with engineering leadership on technical strategy * Build new systems and features while improving our existing architecture What We're Looking For Essential * 10+ years of professional software engineering experience * Strong backend engineering fundamentals — we use Go, but we're hiring an engineer, not a language specialist. If you're excellent and haven't written Go before, that's fine. * Proven track record of designing and owning large-scale systems * Strong experience with distributed systems, event-driven architectures, or similar complex systems * Deep understanding of databases, particularly MongoDB or similar NoSQL systems * Extensive experience with microservices architecture and inter-service communication * Expert-level understanding of containerization (Docker) and orchestration (Kubernetes) * Experience working with AI coding assistants (Claude Code, Copilot, Cursor, or similar) as a core part of your development workflow, with a perspective on how to get the most value from them * Experience establishing technical standards and patterns across teams * Strong architectural thinking with ability to balance trade-offs * Track record of mentoring and developing other engineers * Ability to drive technical initiatives with minimal guidance * Experience influencing technical direction at an organizational level * Excellent communication skills with ability to articulate complex technical concepts Highly Desirable * Experience with Temporal or similar workflow orchestration systems at scale * Deep knowledge of event streaming platforms like Kafka * Experience with LLMs and AI integration (particularly for Investigations team) * Experience driving AI tooling adoption and practices across an engineering team — establishing shared conventions, measuring impact, and helping engineers level up * Background in SaaS platforms or B2B products at scale * Expert-level knowledge of observability tools (Grafana, Prometheus, etc.) * Deep understanding of authorization patterns, security, and multi-tenancy * Experience with protobuf and gRPC Our Tech Stack * Languages: Go * Databases: MongoDB * Messaging & Orchestration: Temporal, Kafka * APIs: REST, gRPC, protobuf * Infrastructure: Kubernetes, GCP * Observability: Grafana stack * AI/ML: LLMs (OpenAI, Gemini), RAG systems * Development Tools: Claude Code, AI-assisted development workflows What Success Looks Like In your first 6 months, you will have * Owned and driven a significant technical initiative to completion * Established new patterns or improved existing ones across teams * Mentored multiple engineers, visibly raising technical standards * Contributed to architectural decisions * Been recognized as a technical authority in your domain * Made measurable improvements to system reliability, performance, or scalability * Influenced the technical direction of our backend platform * Helped evolve our AI-assisted engineering practices, contributing to how the team gets more value from our tooling Here’s our promise to you: * We are going to work with you - to build a rewarding and fulfilling career with the opportunities, challenges and resources you need to do you your best work. * We succeed together- you will own a meaningful part of the business through our employee shares & equity programme. * Private health insurance to keep you in tip-top condition. * Life Insurance – let's hope nobody ever needs this! * Unlimited holidays – yes, it really is uncapped – take the time you need, when you need it. * Everyone is learning, developing and challenging themselves so we have a £1k professional development fund per year if you want to learn new skills, even new things outside of work. * Most importantly of all, we will work with you, to help you realise your fullest potential, always.

Xapien

About Us Every business needs to know who they’re really working with whether it’s suppliers, investors, partners, or third parties. At Xapien, we’re reinventing how organisations do that, combining speed, scale and accuracy with cutting-edge AI. Since 2018, we’ve grown from a deep-tech startup to a global player in AI-driven due diligence and risk intelligence. 2024 was a landmark year as we closed a $10M Series A, earned recognition in the Chartis RiskTech100® and Everest Group’s Leading 50™, and expanded our products, markets and customer base. 2025 was even bigger: With new regulations, rising compliance pressure and growing reputation risks, organisations everywhere are demanding smarter, faster ways to work and they’re turning to us. Customers worldwide from global law firms and private banks to universities and nonprofits rely on Xapien to turn days of manual research into trusted insights, delivered in minutes. Our momentum so far Customers in a diverse range of industries, with particular growth in wealth management, financial services and supply chain onboarding. Demand accelerating beyond our UK headquarters, across multiple continents with new customers in the Middle East, Asia, and Oceania. Why this is an exciting time to join This isn’t just another job role; it’s an opportunity to shape the future of the due diligence industry with a market-leading product trusted by global organisations. Whether you’re in marketing, communications, sales, or finance, you’ll play a critical role in driving growth, building credibility, and defining how we connect our product to a rapidly evolving market. We’re scaling fast with more customers, more releases, and bigger regulatory and market challenges. Expectations are rising, due diligence now means real-time insight, delivered efficiently and with impact. You won’t just be executing campaigns, closing deals, or managing numbers, you’ll be influencing strategy, optimising processes, and helping position a brand that’s setting the new standard for trust and transparency. For people who love learning, innovating, and making an impact that matters now is the moment to be a part of Xapien. THE ROLE We're hiring a Staff Backend Engineer to join our engineering team in a high-impact technical leadership role. You'll work on our most challenging technical problems, own parts of our platform’s architecture, and help shape the technical direction of our backend stack. Our tech stack center’s on Go microservices, with Temporal workflows, MongoDB and ElasticSearch running on Kubernetes in GCP. You'll work with modern patterns including event-driven architectures, gRPC and REST APIs, and comprehensive observability with Grafana Cloud. You'll take technical ownership of major domains within our platform - whether that's our Investigations pipeline (web scraping, data provider integrations, LLM-powered analysis) or our Core App systems (user journeys, features, and configuration). You'll be a technical authority, establishing patterns that others follow and driving initiatives that span multiple teams. WHAT YOU'LL DO * Own the technical direction and architecture for parts of our platform * Design and build complex backend services and systems that scale * Drive technical decisions that affect multiple teams * Establish patterns, standards, and best practices that others will follow * Lead complex technical initiatives from design through implementation * Identify and address systemic technical challenges across our backend * Write exemplary Go code that sets the standard for quality and design * Mentor engineers across the organization, raising the technical bar * Balance technical excellence with pragmatic delivery * Influence technology choices and architectural direction * Collaborate with engineering leadership on technical strategy * Build new systems and features while improving our existing architecture WHAT WE'RE LOOKING FOR ESSENTIAL * 10+ years of professional software engineering experience * Deep expertise in Go, with mastery of concurrency, performance optimization, and advanced patterns * Proven track record of designing and owning large-scale systems * Strong experience with distributed systems, event-driven architectures, or similar complex systems * Deep understanding of databases, particularly MongoDB or similar NoSQL systems * Extensive experience with microservices architecture and inter-service communication * Expert-level understanding of containerization (Docker) and orchestration (Kubernetes) * Experience establishing technical standards and patterns across teams * Strong architectural thinking with ability to balance trade-offs * Track record of mentoring and developing other engineers * Ability to drive technical initiatives with minimal guidance * Experience influencing technical direction at an organizational level * Excellent communication skills with ability to articulate complex technical concepts HIGHLY DESIRABLE * Experience with Temporal or similar workflow orchestration systems at scale * Deep knowledge of event streaming platforms like Kafka * Experience with LLMs and AI integration (particularly for Investigations team) * Background in SaaS platforms or B2B products at scale * Expert-level knowledge of observability tools (Grafana, Prometheus, etc.) * Deep understanding of authorization patterns, security, and multi-tenancy * Experience with protobuf and gRPC OUR TECH STACK * Languages: Go * Databases: MongoDB * Messaging & Orchestration: Temporal, Kafka * APIs: REST, gRPC, protobuf * Infrastructure: Kubernetes, GCP * Observability: Grafana stack * AI: LLMs (OpenAI, Gemini), RAG systems WHAT SUCCESS LOOKS LIKE In your first 6 months, you will have: * Owned and driven a significant technical initiative to completion * Established new patterns or improved existing ones across teams * Mentored multiple engineers, visibly raising technical standards * Contributed to architectural decisions * Been recognized as a technical authority in your domain * Made measurable improvements to system reliability, performance, or scalability * Influenced the technical direction of our backend platform Here’s our promise to you: * We are going to work with you - to build a rewarding and fulfilling career with the opportunities, challenges and resources you need to do you your best work. * We succeed together- you will own a meaningful part of the business through our employee shares & equity programme. * Private health insurance to keep you in tip-top condition. * Life Insurance – let's hope nobody ever needs this! * Unlimited holidays – yes, it really is uncapped – take the time you need, when you need it. * Everyone is learning, developing and challenging themselves so we have a £1k professional development fund per year if you want to learn new skills, even new things outside of work. * Most importantly of all, we will work with you, to help you realise your fullest potential, always.