Research Engineer - Tokenizer & Protocols

Paris

About the role

About Mistral

Mistral provides full-stack AI solutions: from frontier models to developer tools, applications, and compute. We partner with enterprises tackling the hardest problems across high-stakes industries like finance, manufacturing, defense, healthcare, and the public sector, co-creating customized AI systems that they can run on their terms.

We are a dynamic, collaborative team passionate about AI and its potential to transform society. Our diverse workforce thrives in competitive environments and is committed to driving innovation. Our teams are distributed between Europe, North America, Asia and the Middle East. We are creative, low-ego and team-spirited.

About the role

Between a conversation and a model sit the formats and tokenizers that every part of our stack relies on. You will help own them, and the tooling around them, so that training, evaluation and production all speak exactly the same language.

You will work across the entire stack, spanning pretraining, post-training and deployment, and your decisions will reach every model we ship.

What you will do

Design, build and maintain core libraries for tokenization and model interfaces.
Evolve our formats and tokenizers as models and use cases change.
Turn research needs into robust, shared tooling.

What we're looking for

Strong software engineering background, with excellent Python.
Excellent understanding of tokenizers: BPE and other tokenization algorithms, special tokens, chat templates, and tokenizer training; ideally hands-on experience with libraries such as tiktoken or Hugging Face tokenizers.
Experience building production-grade libraries used by many people.
A taste for correctness and attention to detail.
Good knowledge of how LLMs are trained and served.
Clear communication, low ego, and a collaborative mindset.
Nice to have
Open-source maintenance experience.
Experience with inference engines.

Location and remote

This role is primarily based at one of our European offices (Paris and London). We will prioritize candidates who either reside there or are open to relocating. We strongly believe in the value of in-person collaboration to foster strong relationships and seamless communication within our team. In certain specific situations, we will also consider remote candidates based in one of the countries listed in this job posting — currently France & UK. In that case, we ask all new hires to visit our local office for the first week of their onboarding (accommodation and travelling covered), then at least 4 days per month

What We Offer

We offer a comprehensive benefits package designed to support your well-being, growth, and work-life balance. Benefits vary by country and may include healthcare coverage, parental leave, retirement plans, relocation support, wellness programs, meal and transportation allowances, and other location-specific perks.

For the most up-to-date details on benefits available in your location, please refer to our Benefits page.

Your privacy matters to us. You can learn more about how we handle your personal data in our Applicant Privacy Policy.

About Mistral AI

Mistral AI presents a suite of configurable large language models and AI services tailored for diverse enterprise applications. It offers both open-weight and commercially licensed models that support tasks such as advanced reasoning, code generation, multitasking across modalities, and chatbot interactions. The company delivers full-stack AI capabilities, spanning model customization, deployment via APIs, agent-based automation, and scalable infrastructure, enabling integration into existing enterprise systems. Responses draw on publicly available technical information and aim for clarity and neutrality.