Senior Data Scientist - Personalization & RL for Global Comms

HelloFresh; Warszawa; On-site; PLN 240,000 - 360,000; Full time

Benefits offered by this job

Global collaboration

Real-world impact

Leadership

End-to-end delivery

Workspace in Warsaw

Job summary

HelloFresh in Warsaw is seeking a Senior Data Scientist within HelloTech to drive AI-enabled communications. You will design, implement, and scale ML models that personalize messages across channels, leveraging contextual bandits and reinforcement learning to optimize user engagement.

You will collaborate with cross‑functional teams to integrate models into high‑throughput systems, iterate on experimentation designs, and ensure robust performance in production across global markets.

Qualifications

• 5+ years of professional experience in data science, ML, or a related quantitative field.
• Proficient in Python and operating in a modern ML stack (e.g. Databricks/Spark, MLflow) in close collaboration with engineers.
• Strong foundation in machine learning for personalization, plus direct experience with reinforcement learning and/or contextual bandits (e.g. Thompson Sampling, epsilon‑greedy, reward design).
• Solid grounding in experimentation and causal inference — designing and analyzing controlled experiments in high‑traffic settings, and reasoning about guardrails, exposure, and bias.
• Hands‑on with classical ML techniques (regression, classification, clustering, recommendation systems) and comfort choosing the right tool for the problem.
• Experience with customer‑behaviour data, segmentation, and production feature pipelines.
• Clear, structured communication and a genuinely collaborative, cross‑functional mindset.

Responsibilities

• Build, own, and iterate on RL and ML models that run in production behind high‑traffic, performance‑critical conversion and communication flows.
• Develop the decisioning logic that determines the best next action for each user across the funnel and the messaging lifecycle.
• Drive the architectural evolution of our contextual‑bandit systems — from online exploration toward offline policy evaluation and deterministic, low‑latency inference.
• Partner with Engineering on system design so models integrate cleanly into the funnel and messaging architecture.
• Own experimentation design for decisioning models: define success metrics and guardrails, and interpret results in high‑noise, high‑traffic environments.
• Keep models safe and effective in production — monitoring performance, input‑data reliability, drift, and latency, and iterating quickly.
• Collaborate with CRM Ops, Marketing Analytics, and platform partners to turn model behaviour into decisions marketers trust.

Skills

Python

ML stack

Reinforcement learning

Contextual bandits

Experimentation

Causal inference

Classical ML

Customer data

Communication

Tools

Databricks/Spark

MLflow

Job description

HelloFresh in Warsaw is seeking a Senior Data Scientist within HelloTech to drive AI-enabled communications. You will design, implement, and scale ML models that personalize messages across channels, leveraging contextual bandits and reinforcement learning to optimize user engagement.

You will collaborate with cross‑functional teams to integrate models into high‑throughput systems, iterate on experimentation designs, and ensure robust performance in production across global markets.