Senior Data Scientist

Senior Data Scientist

Location: Poland — remote (occasional meetings with team - max. once per quarter)
Experience: Senior
Language: Polish – native, English – min. B2Join neXa as a Senior Data Scientist and work on advanced ML models powering advertising, ranking, and recommendation systems in a large-scale, data-intensive environment.
This is a hands-on ML modeling role focused on designing, training, improving, and productionizing machine learning models. We are looking for someone with strong Deep Learning and Neural Networks experience who can independently take ownership of modeling problems end-to-end.
Important: Hands-on experience with Neural Networks and Deep Learning is mandatory. Experience limited to LLMs, GenAI, MLOps, AI Engineering, or prompt engineering is not sufficient for this role.
What you'll do
• Design, train, refine, and evaluate ML scoring models, including models related to CTR, CVR, and RoAS.
• Develop model strategies combining user, product, and placement signals.
• Design solutions suitable for high-throughput and low-latency production environments.
• Work closely with Engineering and Business teams to translate business goals into measurable modeling outcomes and technical roadmaps.
• Take ownership of the full model development lifecycle — from problem framing and feature engineering to evaluation and production handoff.
• Ensure high standards of quality and production readiness across Data Science workstreams.
• Provide technical guidance and mentor other Data Scientists.
• Work with large-scale datasets and independently make technical decisions within your area of responsibility.
Requirements
• Extensive hands-on experience designing, training, and improving Deep Learning models for production use cases.
• Strong practical experience with Neural Networks.
• Proficiency with PyTorch or TensorFlow.
• Strong Python skills, including writing production-level, testable, and documented code.
• Advanced SQL skills and experience working with large-scale data.
• Practical knowledge of Pandas and NumPy.
• Experience with public cloud infrastructure, preferably GCP.
• Experience with ML-oriented cloud services such as Vertex AI and Vertex Pipelines.
• Understanding of CI/CD practices.
• Experience leading model development end-to-end, from problem definition and feature design through evaluation and production deployment.
• Ability to mentor other Data Scientists and contribute to improving modeling standards.
• Relevant academic background or extensive professional experience in a STEM field.
• Strong independence, ownership, and decision-making skills.
• Professional working proficiency in English and native-level Polish.
Nice to have
• Experience developing ML models for low-latency online applications.
• Background in advertising, marketing, ranking, recommendation systems, or personalization.
• Experience with CTR/CVR modeling or predicting business events such as clicks and conversions.
• Knowledge of traditional ML techniques, including Gradient Boosted Trees.
• Experience in technical leadership, mentoring, or coordinating model development across a broader team.
• Experience using AI-assisted coding tools to improve engineering productivity and code quality.
• Experience with Docker.
Technologies
Python, PyTorch, TensorFlow, SQL, BigQuery, GCP, Vertex AI, Vertex Pipelines, Docker, Deep Learning, Neural Networks, Experiment Design, Low-Latency Model Development
Why join?
• Work on large-scale ML problems with real business impact.
• Build and improve production-grade models rather than working solely on exploratory analysis.
• Collaborate closely with experienced Engineering, Data Science, and Business teams.
• Have significant ownership over modeling decisions and technical solutions.
• Work on challenging problems involving advertising, ranking, and recommendation systems.
• Long-term collaboration in remote friendly environment.