Fullstack Data Scientist - freelancer

Lever, Inc.; Polska; On-site; PLN 210,000 - 380,000; Full time

Job summary

Lever, Inc. is seeking a senior Data Science/AI Engineer in Poland to lead GenAI initiatives from problem framing to production-grade solutions. You will design architectures, build end-to-end applications with RAG pipelines, and collaborate across data, product, and engineering teams.

Strong Python skills and hands-on GenAI framework experience are essential. You will also mentor peers, implement governance and safety controls, and stay updated on evolving GenAI trends, enabling scalable,

Qualifications

• 6+ years of experience in Data Science/AI engineering.
• At least 4+ years of production-ready Python AI-related code development.
• At least 2+ years of production-ready LLM-related code development, preferably RAG-based.
• Strong analytical and problem-solving skills with the ability to optimize AI solutions.
• Solid knowledge of Generative AI including LLMs, chatbots, AI agents, and RAG mechanisms.
• Hands-on experience with GenAI frameworks: LangChain, LlamaIndex, LangGraph, or similar orchestration stacks.
• Hands-on experience designing or operating MCP servers/clients for LLM agents.
• Strong Python skills including production-grade code, packaging, and testing for data/ML services.
• Familiarity with cloud environments (Azure/GCP/AWS) and AI-related managed services.
• CI/CD, testing, and containerized deployments.
• Excellent communication skills in English.

Responsibilities

• Lead discovery and solution design for GenAI use cases, translating business problems into architectures.
• Build end-to-end GenAI applications: data ingestion, retrieval layer, orchestration, API/backend, and UI.
• Design and implement RAG pipelines with vector databases and hybrid search.
• Perform model selection, prompting strategies, and fine-tuning for various models.
• Implement safety, compliance, and governance controls with audit logs and human-in-the-loop where required.
• Collaborate with data engineers, product owners, and full-stack developers on scalable architectures and SLAs.
• Gather technical requirements and estimate planned work.
• Mentor other data scientists/engineers in GenAI best practices; contribute to internal libraries.
• Stay current with GenAI landscape and perform targeted PoCs.

Skills

Python programming

Analytical thinking

Communication in English

Cross-functional collaboration

Problem solving

Tools

LangChain

LlamaIndex

LangGraph

MCP servers/clients

CI/CD tooling

Docker/Kubernetes

Azure/GCP/AWS AI services

GitHub Actions

Job description

Tasks:

• Lead discovery and solution design for GenAI use cases, translating business problems into concrete architectures (LLM decision, RAGs, fine-tuning, agents, guardrails).

• Build end-to-end GenAI applications: data ingestion, retrieval layer, orchestration (e.g. LangChain/LlamaIndex/LangGraph), API/backend, and simple UI where needed.

• Design and implement RAG pipelines with vector databases, hybrid search, rerankers, query transformation, and evaluation frameworks for relevance and robustness.

• Perform model selection, prompting strategies, and fine-tuning (LoRA/QLoRA/SFT) for text, code, and multimodal models, including evaluation and A/B testing.

• Implement safety, compliance, and governance controls (input/output filters, PII handling, audit logs, human-in-the-loop review where required).

• Collaborate with data engineers, product owners, and full-stack developers on scalable architectures, SLAs, and integration with existing enterprise systems.

• Gather technical requirements and estimate planned work.

• Mentor other data scientists/engineers in GenAI patterns, code quality, and best practices; contribute to internal libraries, templates, and reusable components.

• Stay current with GenAI landscape (new open and hosted models, agentic frameworks, evaluation techniques) and perform targeted PoCs to validate them.

What We're Looking For:

• 6+ years of experience in Data Science/AI engineering.

• At least 4+ years of experience in production-ready Python AI-related code development.

• At least 2+ years of experience in production-ready LLM-related code development, preferably based on the Retrieval-Augmented Generation (RAG) concept.

• Strong analytical and problem-solving skills with the ability to optimize AI solutions for diverse applications.

• Strong knowledge and experience in Generative AI, including LLMs, chatbots, AI agents, and RAG mechanisms.

• Deep understanding of LLM evaluators, validators, and guardrails.

• Hands-on experience with one or more GenAI frameworks: LangChain, LlamaIndex, LangGraph, or similar orchestration stacks.

• Hands-on experience designing or operating MCP servers/clients for LLM agents

• Strong Python skills, including production-grade code, packaging, and testing for data/ML services

• Solid understanding of ML/AI concepts: types of algorithms, machine learning frameworks, model efficiency metrics, model lifecycle, AI architectures.

• Proven ability to collaborate effectively across technical and non-technical teams.

• Familiarity with cloud environments such as Azure (preferred), GCP, or AWS, including AI-related managed services.

• Familiarity with CI/CD, testing, and containerized deployments.

• Excellent communication skills in English, with the ability to convey complex technical concepts to various audiences.

What Will Set You Apart:

• Experience in designing and programming ML algorithms and data processing pipelines using Python.

• Good understanding of CI/CD and DevOps concepts, with experience working with selected tools (preferably GitHub Actions, GitLab, or Azure DevOps).

• Experience in productizing ML solutions using technologies like Spark/Databricks or Docker/Kubernetes.

• Experience with agentic AI development frameworks (e.g., BMAD, multi-agent orchestration, spec-driven AI workflows).