Principal Engineer, AI Systems

Responsibilities

• Ship, architect, build, and own end-to-end delivery of autonomous agents and agentic workflows that deliver real business value for Block, ensuring reliability, safety, and performance at scale
• Design agent orchestration systems including planning, tool use, memory, evaluation, and multi-agent coordination at production scale
• Integrate and optimize frontier LLMs into agent architectures, making decisions on model selection, fine-tuning, prompt engineering, and context retrieval strategies
• Drive deeper model optimization work (fine-tuning, distillation, RLHF) where it unlocks agent capability or efficiency
• Lead detailed technical planning by breaking down ambitious objectives into concrete, sequenced tasks with clear ownership and execution paths
• Provide technical mentorship and guidance to engineers across experience levels, elevating team capabilities through code review, pairing, and knowledge sharing
• Partner closely with technical and non-technical stakeholders to translate business objectives into agent-powered product experiences
• Keep Block at the frontier by continuously evaluating emerging AI capabilities and making pragmatic tradeoffs across model performance, latency, cost, and user experience
• Foster a culture of technical excellence, high-quality delivery, rapid experimentation, and learning within your team and beyond

Requirements

• 15+ years of experience in software engineering or machine learning, with recent professional experience building autonomous agents or agentic workflows in production
• Deep experience building autonomous agents or agentic workflows in production environments—not just prototypes or demos
• Fluency in the core primitives of agentic systems: context management, planning, tool use, memory, evaluation, and multi-step reasoning
• Experience bringing frontier LLM capabilities into production products, with hands-on experience in prompt engineering, retrieval-augmented generation, and model optimization
• A track record of taking AI-powered products from zero to scale in fast-paced, product-driven environments, with the judgment that comes from operating in production
• Strong software engineering fundamentals with the ability to write production-quality code and make sound architectural decisions
• Experience providing technical leadership within teams—you've shaped technical direction, driven execution, and elevated others
• Product-minded engineering approach—you think in terms of user outcomes, not just model metrics
• Excellent collaboration and communication skills, with ability to build alignment across engineering, product, and design
• Comfort navigating extreme ambiguity in a domain that's evolving weekly
• Alignment with Block's mission of economic empowerment and using technology to create access and opportunity

Nice-to-Haves

• Experience at leading AI organizations with a track record of translating research into production agent systems
• Background building or scaling agentic products at startups (including early-stage or pivoting companies)
• Experience with model fine-tuning, distillation, or RLHF to improve agent performance
• Familiarity with agent evaluation, safety, and alignment challenges in production contexts