Senior Software Engineer (Python & AI/LLM)

Company Description

Sellence is building cutting-edge sales CRM engines designed to deliver personalized customer experiences for B2C brands. We aim to significantly increase conversion rates and return on ad spend (ROAS) through intelligent automation. We are moving fast, solving complex problems in agentic AI, and looking for a technical leader to help shape our future.

We are hiring a full-time Senior Software Engineer with deep expertise in Python and LLM application development to join our Tel Aviv-based team (hybrid with remote flexibility).

In this role, you will take ownership of the backend architecture and the AI engine that powers our agentic B2C sales CRM.

You will not just build features; you will make high-level architectural decisions, ensure system scalability, and define best practices for our LLM integrations. You will play a pivotal role in translating complex product requirements into robust, high-performance systems while mentoring other engineers and driving technical excellence.

• System Architecture & Backend Ownership: Architect, build, and maintain high-throughput backend services and APIs using FastAPI. Ensure systems are designed for high availability, low latency, and ease of scaling.
• Advanced AI Agent Orchestration: Lead the design and engineering of complex, stateful agentic workflows. Optimize prompt chains, function-calling logic, and memory management to create human-like sales conversations.
• RAG Strategy & Implementation: Define and implement advanced Retrieval-Augmented Generation (RAG) strategies. Optimize vector search performance using PostgresML/Weaviate to ensure context retrieval is both accurate and cost-effective.
• LLMOps & Evaluation Frameworks: Establish rigorous evaluation pipelines (LLM-as-a-judge, unit testing for prompts) to monitor model performance. Drive the strategy for continuous improvement of response quality and reliability.
• Database Architecture: Own the database schema design and data modeling layers. Write highly optimized SQL queries and manage migrations to support complex analytics and real-time AI decision-making.
• Technical Leadership & Mentorship: Champion software engineering best practices (code reviews, CI/CD, documentation). Mentor junior team members and collaborate with Product and Data Science teams to drive the technical roadmap.

• 5+ years of professional software engineering experience with mastery of Python.
• Deep expertise in building production-grade backend services with FastAPI (or similar asynchronous frameworks) in a Linux environment.
• Expert-level SQL skills with significant experience designing schemas for relational databases (PostgreSQL preferred) and optimizing complex queries.
• Proven track record building applications on top of LLM APIs (OpenAI, Anthropic, Gemini). You understand the nuances of context windows, token optimization, and temperature settings.
• Strong experience designing RAG architectures and working with vector databases (e.g., Weaviate, PostgresML, Pinecone) in a production setting.
• Solid understanding of asynchronous programming (Asyncio), concurrency, and distributed system design patterns.
• Bachelor’s degree in Computer Science, Engineering, or a related field (MSc is a plus).
• Background in CRM, or Sales Automation platforms - advantages (Bonus Points)