Senior/Staff Software Engineer (Full-Stack Engineer)

About the Role

We’re looking for a Senior/Staff Full Stack Engineer to architect and build the foundational systems that define how users interact with Actively’s AI Agents through web interface as well as real-time workflows enabled via Chat.

For most of Actively's history, our intelligence has run quietly in the background, wired into Salesforce, Outreach, and the tools your customers already use. We're now building the product itself: the surface where users actually see what agents are doing, give direction, and collaborate in real time.

This is a foundational role. You'll own the core product experiences that define how Actively feels, from Python/FastAPI backends and workflows to the React/TypeScript interfaces that bring them to life. You'll establish the design patterns, platform architecture, and technical standards that every future surface is built on top of. You'll prototype new agent interactions, run experiments, and work directly with customers to make complex AI behavior feel natural and trustworthy.

For more on how we think about human-agent collaboration, see our blog post.

What You’ll Do

• Own end-to-end features. Design, build, and ship customer-facing experiences across the stack, from Python/FastAPI services and background workers to polished React/TypeScript UIs.
• Define Actively’s product platform. Architect the frameworks, patterns, and shared product components that make every product surface fast, consistent, and cohesive.
• Design and prototype intelligent AI interactions. Collaborate with agent SDKs and internal frameworks to build new user experiences for configuring, debugging, and collaborating with agents including conversational interfaces, feedback loops, and workflow builders.
• Build for real usage at scale. Operate across the full stack to ensure high performance, reliability, and seamless data flow, working across SQL/NoSQL stores, caching layers, and task execution pipelines, and contributing to backend systems where needed to deliver a cohesive end-to-end experience.
• Customer-driven iteration. Work directly with customers and alongside other teams to translate real feedback and behavior into simple, easy-to-use experiences, experimenting and refining quickly based on what customers actually need.

Who You Are

• A seasoned, product-minded engineer. You have 5+ years of experience building and shipping high-impact, customer-facing products end-to-end — from backend APIs to refined UI experiences. 
• Product-minded and design-curious. You care about usability, polish, and the emotional feel of software as much as the systems behind it.
• Frontend-strong, backend-capable. You have deep experience with React, TypeScript, and modern web frameworks, and you’re comfortable working in Python/FastAPI backends to craft seamless full-stack flows. 
• A systems thinker. You recognize the patterns behind good architecture and design frameworks that help others move faster without sacrificing quality. You think in terms of type safety, API contracts, and shared platform primitives.
• Iterative by nature. You thrive in fast feedback loops; building, learning, and refining quickly based on real-world use and customer insight.
• Grounded and self-directed. You thrive in environments where the path isn't fully defined — making architectural and product calls without waiting for direction, owning outcomes end-to-end, and bringing structure to ambiguity. You've operated in a mode where you decided what to build, how to build it, and why it mattered.
• A builder in the AI space. You've shipped real AI-powered products and not just prototypes and know how to turn LLM capabilities into fast, trustworthy, user-facing experiences. You stay current on the ecosystem because you're building with it, not just watching it.

Nice to Haves

• Track record of building 0→1 products in fast-moving, resource-constrained environments. 
• Experience as an early or founding engineer, where you owned architecture, product calls, and shipping and not just execution
• Deep experience building agentic UI systems, such as chat interfaces, agent inboxes, or task orchestration UIs.