Principal AI Engineer

About Apollo.io

Apollo.io is the leading go-to-market solution for revenue teams, trusted by over 500,000 companies and millions of users globally, from rapidly growing startups to some of the world's largest enterprises. Founded in 2015, the company is one of the fastest growing companies in SaaS, raising approximately $250 million to date and valued at $1.6 billion. Apollo.io provides sales and marketing teams with easy access to verified contact data for over 210 million B2B contacts and 35 million companies worldwide, along with tools to engage and convert these contacts in one unified platform. By helping revenue professionals find the most accurate contact information and automating the outreach process, Apollo.io turns prospects into customers. Apollo raised a series D in 2023 and is backed by top-tier investors, including Sequoia Capital, Bain Capital Ventures, and more, and counts the former President and COO of Hubspot, JD Sherman, among its board members.

Apollo.io is the leading go-to-market solution for revenue teams, trusted by over 500,000 companies and millions of users globally, from rapidly growing startups to some of the world's largest enterprises. Our platform helps sales and marketing teams prospect smarter, automate workflows, and close more deals, all within a unified, AI-native platform. Backed by world-class investors including Sequoia and Bain Capital, and recently valued at $1.6B following our Series D, Apollo is one of the fastest-growing SaaS companies in the world.

Why This Role Matters

We are entering a new phase of AI-native growth and are looking for a Principal AI Engineer to lead the design and deployment of cutting-edge agentic systems, AI assistants, and LLM-powered features. This role is pivotal to Apollo’s AI roadmap, owning the architecture and productionization of intelligent systems that power the workflows of thousands of GTM teams globally. You’ll be a technical thought leader on the AI Engineering team and work alongside product, backend, and platform leaders to drive forward Apollo’s competitive edge in applied AI.

What You'll Own & Deliver

End-to-End Agentic Systems

• Autonomous AI Agents: Architect and lead the development of multi-agent systems capable of long-horizon planning, reasoning, and API orchestration.
• Workflow Automation: Build reusable agentic components that integrate deeply into sales and marketing processes.
• LLM Platformization: Own and evolve our in-house platform for scalable, low-latency, and cost-efficient LLM and agent deployments.

AI Assistants and Search

• Conversational AI & UI: Lead design of interfaces powered by natural language understanding and retrieval-augmented generation (RAG).
• Semantic & Personalized Search: Build embedding-based, intent-aware search and personalization systems tuned to business user needs.
• Email Intelligence: Drive innovation in personalized outreach generation using context-aware generation pipelines.

Production-Grade Applied AI

• Latency & Cost Optimization: Tune inference pipelines, caching layers, and model selection logic for high-scale, cost-aware performance.
• Evaluation at Scale: Define and drive robust offline and online testing methodologies (A/B, sandboxing, human evals) across agents and LLM flows.
• Feedback Loops: Architect human-in-the-loop systems and telemetry to improve accuracy, UX, and explainability over time.

What We’re Looking For

Technical & Production Depth

• 10+ years of software engineering experience, with at least 3 years in applied LLM or agentic AI systems (2023–present).
• Proven success in deploying LLM-powered products used by real users at scale, not just prototypes or internal tools.
• Deep backend & systems engineering expertise with Python, distributed systems, and scalable APIs.
• Familiarity with LangChain, LlamaIndex, or similar orchestration frameworks.
• Experience with RAG pipelines, vector DBs, embedding models, and semantic search tuning.
• Experience managing perfor