Senior Machine Learning Engineer (m/f/d)

Join our team of machine learning experts to develop and implement cutting-edge models specifically tailored for price optimization. You will work closely with data scientists to deploy low latency services in production with the objective to infer optimal bid price, leveraging theories of opportunity cost. Your work will directly influence pricing strategies for millions of customers.

YOUR ROLE AT SIXT

• You will develop advanced regression prediction models to determine optimal prices under capacity constraints, ensuring architectures capture demand elasticity, capacity limits, and temporal stationarity.
• You will prototype and evaluate novel architectures, including deep MLPs, transformer-based models for tabular/sequence data, CNNs for image inputs, and embedding-rich hybrids—optimized for accuracy, robustness, interpretability, and transfer learning to maximize out-of-sample generalization.
• You will conduct large-scale experimentation and simulation to assess model generalization and analyze behavior across geographies, seasons, and capacity constraints.
• You will design and optimize large-scale model training pipelines, leveraging distributed frameworks (PySpark, Dask, Polars) and multi-GPU/multi-node parallelization for efficient deep learning at scale, ensuring reproducibility, fault tolerance, and cost-efficient scaling on AWS.
• You will build high-performance data engineering pipelines for terabyte-scale datasets using Polars, Dask, or Spark, implementing columnar storage, memory mapping, and data sharding to enable efficient GPU utilization.
• You will implement monitoring and continuous optimization, automating feedback loops, retraining triggers, and hyperparameter tuning (Ray Tune, Optuna), while documenting infrastructure design and mentoring peers on best practices for distributed ML and production-scale architectures.

YOUR SKILLS MATTER

• Deep Learning Modeling: Demonstrated ability to innovate in model design (embeddings, deep MLPs, hybrid architectures) and proven experience with sequence models such as LSTMs, GRUs, and Temporal Convolutional Networks.
• Scalable ML Engineering: Expertise in building and deploying large-scale ML systems handling 50M+ data points or terabyte-scale datasets, leveraging distributed training and GPU acceleration.
• ML Frameworks & Parallelization: Strong proficiency with PyTorch or TensorFlow for large-scale model development and training; skilled in optimizing performance across multi-GPU or distributed environments for datasets exceeding 50M rows.
• Advanced Data Processing: Hands-on experience with PySpark, Dask, and Polars for distributed data preparation and transformation; knowledge of Arrow-based columnar computation and vectorized data pipelines.
• Cloud & HPC: Proficiency with AWS, Kubernetes, and containerized GPU workloads (NVIDIA Docker); experience orchestrating multi-GPU/multi-node clusters for deep learning.
• MLOps & Lifecycle Management: Familiarity with MLflow, Airflow, or Kubeflow for managing large-scale model lifecycles, experiments, and retraining pipelines; strong foundations in deploying and maintaining ML models in production environments and ensuring collaboration between data science and infrastructure teams.

WHAT WE OFFER

• A Global Tech Hub in Lisbon Join a thriving international tech community and work alongside engineers, product experts, and business teams who turn ideas into real impact. Our hubs at Factory Lisboa in Beato and ARTs Lisboa in Parque das Nações are where great tech gets built

• Learning & Knowledge Exchange Level up through regular events with internal and external speakers. We value curiosity, continuous learning, and open exchange – across teams, disciplines, and borders

• Flexible Work Setup Two office days a week, flexible hours, and modern spaces built for both deep focus and team collaboration – work the way that brings out your best

• Time Off & Wellbeing Enjoy 28 vacation days per year, an additional day off on your birthday, one volunteer day annually, and private health insurance that also covers your spouse and children free of charge

• Practical Everyday Benefits Get a yearly Coverflex allowance and a daily meal allowance to make everyday life a little easier

• SIXT Perks Get exclusive rates on all SIXT services, with special discounts extended to your family and friends. Because great perks are even better when you can share them

About us:

We are a globally leading mobility service provider with a revenue of €4.00 billion and around 9,000 employees worldwide. Our mobility platform ONE combines our products SIXT rent (car rental), SIXT share (car sharing), SIXT ride (taxi, ride, and chauffeur services), and SIXT+ (car subscription), giving our customers access to our fleet of 350,000 vehicles, the services of 4,000 cooperation partners, and around 5 million drivers worldwide. Together with our franchise partners, we are present in more than 110 countries at 2,000 rental stations. At SIXT, top-tier customer experience and outstanding customer service are our highest priorities. We believe in true entrepreneurship and long-term stability and align our corporate strategy with foresight. Get started with us and apply now!