Senior AI Engineer

About lemlist:

lemlist is a global B2B SaaS business with $43M ARR, fully bootstrapped, profitable, and growing fast.

We're a team of 140 people, remote-friendly, shipping one of the most loved Sales Engagement Platforms worldwide.

Our mission: help any business grow.

Our vision: build the most advanced AI-powered Sales Engagement experience on the market.

Role — Senior AI Engineer (Hands-On)

We are looking for an Senior AI Engineer to design, build and scale the future AI architecture of lemlist.

Your mission:

This role will provide opportunities to work with cutting-edge technologies and deliver impactful AI solutions.

Expand the existing foundation supporting our AI uses-cases to strengthen its scalability and operability.

We want to move from simple prompt calls to AI systems able to chain actions, reason on user data, and automate complex workflows.

You won't be "just integrating LLMs".

You will define how AI works inside lemlist.

This is a 0 → 1 role with massive impact.

What you will doAI Architecture (your #1 responsibility):

• Design and implement our agentic architecture (LangGraph, Mastra, custom JS framework…)

• Define context management, memory, data flow, and action orchestration

• Build safe, deterministic, observable multi-step agents

AI Variables / Agentic AI Loops:

• Build AI variables capable of autonomous action loops, e.g.:

  "For each lead in this list, enrich X, apply Y rules, trigger Z actions"

AI Copilot:

• Deliver our Copilot v1:

  Semi-agentic at first,

  with the possibility to extend to autonomous workflows if feasible.

AI Engineering:

• Build evaluation pipelines (llm eval, regression tests, drift detection)

• Implement 360 monitoring of all output (latency, cost, quality, hallucinations)

• Conduct error analysis and improve models to address bias, fairness, and explainability.

• Document technical processes and results, ensuring knowledge sharing within teams.

• Optimize for performance, reliability, and cost

Collaboration & Enablement

• Work closely with our :

  • Data Scientist

  • Devs

  • PM / CPO

• Mentor the team on AI engineering best practices

• Own the technical decisions for AI

Key Results — 6 months

• A stable agentic architecture in production

• Multi-step autonomous workflows

• AI Copilot v1 delivering real value inside the product

• Set-up an AI global monitoring and evaluation

• Developed a clear AI engineering culture within lemlist

What you bring

• Strong software engineering background (Node, Typescript, Python)

• Real experience building industrialised AI features in production

• Solid knowledge of:

  • Agentic systems

  • Context / state machine logic

  • Retrieval-Augmented Generation architecture

  • LLM evaluation and monitoring

• Ability to own technical direction end-to-end

• Leadership and communication skills

• Strong problem-solving and critical-thinking skills.

• Passion for building "real" AI systems used by thousands of users

• Passion for continuous learning and staying updated with the latest AI trends.

Nice to have

• Experience with LangChain / LangGraph / custom agent frameworks

• Experience with LLM evaluation frameworks (ex: Trulens, DeepEval, Opik…)

• Experience in SaaS

• Experience mentoring engineers

• Open source contribution

• Ability to explain complex AI concepts to non-technical stakeholders.

Good to know / benefits:

• Fully remote

• Alan Blue healthcare

• Swile, Navigo

• 48GB Macbook Pro + office budget

• Annual team retreat

• Profit sharing: when lemlist wins, everyone wins

Recruitment Process

• Interview with Lucas (TAM)

• Interview with Mickael (CTO)

• Technical interview with Mickael, Eliott (Data Lead), Ahmed (Data Scientist)

• Final interview with Charles (CEO)

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