AI Researcher - Post-Training (f/m/d)

The ideal candidate will have:

• An advanced academic background (Master’s or PhD) in Computer Science, Machine Learning, or a related quantitative field.
• 4+ years industry experience in machine learning, with a solid understanding of modern software engineering practices and tools.
• Fluency with Python including core ML frameworks, experience with Rust or any of SonarQube’s flagship languages (C#, C++, JS/TS, Java) is a plus.
• Expertise in post-training of large language models, including:
• Policy optimization algorithms (e.g. GRPO, PPO)
• Verifier-based RL frameworks (RLVR)
• Supervised fine-tuning (SFT)
• Data-centric AI methods, including synthetic data and curation
• Parameter-efficient fine-tuning (PEFT)
• Preference and Safety Alignment
• Experience of driving research projects, delivering valuable findings and prototypes, and then converting them into products.
• Excellent communication skills in English and a talent for explaining complex scientific topics clearly and concisely.

Additional comments

This role is based in Bochum. We are unable to consider candidates unwilling to be in this location, but we are willing to relocate the right candidate.

In-office culture

We're intentional about this. We believe the best teams are built in the room together. Three anchor days — Mondays, Tuesdays, and Thursdays — create the collaboration rhythm that makes a hub office worth having.

Candidates need to be genuinely based in the location the role is posted — if that's not where you are today, we're happy to support relocation for the right person.

We value diversity, equity, and inclusion

At Sonar, we believe that our diversity is our strength. We are a global company that values and respects different backgrounds, perspectives, and cultures. We are committed to fostering a diverse and inclusive work environment where everyone feels valued and empowered to contribute their best. We are proud to be an equal opportunity employer and welcome all qualified applicants, regardless of race, color, religion, gender, gender identity or expression, sexual orientation, national origin, genetics, disability, age, or veteran status.

If you need any accommodation, please reach out to us at All offers of employment at Sonar are contingent upon the results of a comprehensive background check and reference verification conducted before the start date.

Applications that are submitted through agencies or third party recruiters will not be considered.

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