Machine Learning Engineer

Overview

Rex is looking for machine learning engineers to help train and evaluate AI models on machine learning and LLM engineering tasks. The work includes designing tasks with reference solutions, reviewing AI-generated code and methodology, and writing reference answers that models are measured against. Compensation is USD $75–150 per hour, adjusted by country of residence.

What You'll Do

• Design machine learning and LLM engineering tasks, including data pipelines, training and evaluation code, and experiment design.
• Create reference solutions for the tasks you design.
• Evaluate AI-generated training, evaluation, and data-processing code for correctness and efficiency.
• Review experimental methodology, including data leakage, metric selection, baselines, and reproducibility.
• Write reference answers and rubrics for machine learning questions at a professional level.
• Compare model outputs and provide structured written feedback.
• Document recurring model errors related to ML concepts.
• Follow project guidelines, participate in calibration and review sessions, and incorporate feedback to maintain consistent quality.

Requirements

• Degree in computer science, statistics, or a related field, or equivalent experience.
• At least 3 years of machine learning engineering or applied ML experience.
• Strong Python skills with PyTorch or TensorFlow, and solid grounding in model training, evaluation, and deployment.
• Experience building data pipelines and tracking experiments.
• Fluent written English.
• Ability to work independently, meet deadlines, and remain reliable and detail-oriented in a remote setting.

Preferred Qualifications

• Experience with LLM fine-tuning or evaluation.
• Published work or strong competition results.
• Experience with distributed training or inference optimization.
• Prior AI training or annotation experience.

Legal and Compliance

• All submissions must be lawful, and you must have the right to share the material you provide.
• You must not submit confidential, proprietary, or personal data without a lawful basis.
• Rex may verify identity, credentials, ownership, and licensing, and may reject or remove submissions that do not comply.
• Engagement and payment are subject to verification and to applicable sanctions, export-control, tax, and employment laws.
• The contractor agreement will define ownership and licensing terms for delivered work.