Senior ML Engineer — Real-Time AdTech Optimization

Sigma Software; Warszawa; On-site; PLN 260,000 - 480,000; Full time

Job summary

Sigma Software is hiring a Senior Machine Learning Engineer in Warsaw to build and optimize production ML models for a live AdTech platform. You will work on censored bid-landscape modeling, real-time win probability, and constrained optimization across large-scale data ecosystems.

You will collaborate with senior engineers and data scientists, contributing to scalable ML platform design and end-to-end model deployment in a fast-moving, data-driven environment.

Qualifications

• 5+ years of experience in ML or DS with production-grade models evaluated against KPIs.
• Strong Python skills with numpy, pandas and scikit-learn.
• Strong SQL skills and handling large-scale datasets.
• Deep experience with XGBoost, LightGBM or CatBoost.
• Knowledge of regularization, calibration methods and categorical features.
• Probability, statistics, confidence intervals and power analysis fundamentals.
• Experience with feature engineering for structured/behavioral data.
• Hands-on with Spark or PySpark; familiar with experimentation and A/B testing.
• Experience with advanced validation, temporal splits and drift analysis.
• Knowledge of SHAP and permutation importance for explainability.
• Upper-Intermediate English or higher.

Responsibilities

• Build and improve censored bid-landscape models to estimate price distributions.
• Develop real-time win probability estimation models responsive to bid dynamics.
• Design hierarchical lift estimation models with confidence-based selection.
• Build conversion propensity models using sparse, delayed, or aggregated labels.
• Develop look-alike audience models using positive-unlabeled learning and embeddings.
• Implement advertiser-level calibration and monitor ranking/calibration quality.
• Design offline evaluation frameworks with IPS, doubly-robust estimators, and reweighting.
• Define exploration and propensity logging for reliable downstream evaluation.
• Develop constrained optimization for campaigns, pricing, and volume targets.
• Collaborate on data diagnostics and evidence-based model recommendations.
• Work with Customer team on post-launch tuning and validation.
• Prepare technical docs and knowledge transfer materials.
• Participate in architecture discussions for scalable ML platform design.

Skills

Python

numpy

pandas

scikit-learn

SQL

XGBoost

LightGBM

CatBoost

calibration methods

probability/ statistics

feature engineering

Spark / PySpark

experimentation frameworks

A/B testing

SHAP / permutation importance

English (Upper-Intermediate)

Tools

Spark

PySpark

Vertex AI

Job description

Sigma Software is hiring a Senior Machine Learning Engineer in Warsaw to build and optimize production ML models for a live AdTech platform. You will work on censored bid-landscape modeling, real-time win probability, and constrained optimization across large-scale data ecosystems.

You will collaborate with senior engineers and data scientists, contributing to scalable ML platform design and end-to-end model deployment in a fast-moving, data-driven environment.