Principal Engineer, AI Systems

Block is building toward one of the most ambitious technical visions in our history: an AGI-enabled entity that fundamentally transforms how we deliver economic empowerment. We’re assembling a world-class team of AI experts to design and ship autonomous agents and agentic workflows that operate across Square, Cash App, and the broader Block ecosystem. This work is about creating solutions-you’ll be building AI that acts, decides, and completes real tasks for real users from across all of Block’s business functions. As a Principal Engineer, you’ll join as a senior individual contributor with significant technical leadership responsibilities.

You Will

• 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, We may use automated AI tools to evaluate job applications for efficiency and consistency. These tools comply with local regulations, including bias audits, and we handle all personal data in accordance with state and local privacy laws.

• 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, * 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

We’re working to build a more inclusive economy where our customers have equal access to opportunity, and we strive to live by these same values in building our workplace. Block is an equal opportunity employer evaluating all employees and job applicants without regard to identity or any legally protected class. We will consider qualified applicants with arrest or conviction records for employment in accordance with state and local laws and “fair chance” ordinances.

Every benefit we offer is designed with one goal: empowering you to do the best work of your career while building the life you want. Remote work, medical insurance, flexible time off, retirement savings plans, and modern family planning are just some of our offering. Check out our other benefits at Block.