Principal Product Engineer - AI CheckoutThe RolePrincipal Product Engineer, AI Checkout is the most senior individual-contributor engineering seat on the team. You will design, build, and own Phoenix's checkout and post-purchase system which is the surface millions of merchant customers pass through and reinvent it for an agent-native future. This is a hands-on, principal-level IC role: no direct reports, maximum leverage. You set the technical bar for how Phoenix builds AI-native commerce software and you ship the hardest parts yourself.
We want a hardcore engineer with real depth across both backend and frontend, whose center of gravity is systems thinking and who is a genuine AI power user, not a tourist. You code with agents daily, you understand how LLM and memory systems work, and you have shipped agentic features to production. You raise the ceiling of everyone around you through the code and design you put on the table, not through delegation.
You'll Own- The AI-native checkout. Architect and build a modular, high-conversion checkout and post-purchase system, one that AI agents can read, extend, and operate on behalf of merchants.
- The full stack, end to end. From the React / Next.js front end through TypeScript / Node services, payment tokenization, and order capture. You own the whole vertical slice.
- The systems underneath. High-performance rendering (SSR, streaming, hydration), gRPC / gRPC-web service boundaries, CDN and edge caching, and the data models behind them.
- Agentic product capabilities. LLM-driven flows, tool calling, schema-constrained generation, and the structured context and memory that agents use to run merchant checkouts safely.
- Payments integration. Work with the payments team so checkout logic is seamless across processors (Stripe, Spreedly, TSYS) while staying inside PCI-compliant front-end constraints (tokenized / hosted fields).
- Conversion and experimentation. Real-time analytics hooks, A/B testing, dynamic upsells and post-purchase offers, and relentless funnel optimization.
- Mission-critical reliability. SLOs, telemetry, on-call, and incident response for checkouts that cannot go down.
- The engineering bar. Clean, well-tested, documented code; ADRs / RFCs; and an operationalized agentic SDLC (Claude Code, Vercel AI SDK) that raises the whole team's velocity and quality.
What We're Looking ForRequired- 10+ years building and shipping web platforms, with staff/principal-level impact as a hands-on individual contributor.
- True full-stack depth. Deep backend (TypeScript / Node Express, Fastify, or Nest) and production-grade frontend (React / Next.js, or Angular). Systems thinking is your center of gravity.
- Strong systems design. High-performance rendering (SSR / streaming / hydration), CDN-backed and edge caching, gRPC / gRPC-web service design, and solid API design (auth, pagination, versioning, rate limits, secure middleware).
- Right-tool data modeling. Relational (Postgres / MySQL) for integrity and transactions, document stores where denormalization fits, and Redis for hot paths. You choose the right model rather than defaulting to one.
- Genuine AI power user. You code with AI every day, Claude Code or an equivalent agentic coding setup, a dialed-in IDE and environment, and real leverage. You are not someone we have to convince to adopt agents; you already operate that way.
- You understand how LLM systems work. Context windows, memory systems, tool calling, schema-constrained generation, RAG, and eval loops. You can reason about them, not just call an API.
- Shipped agentic AI to production. Hands-on LLM/agent product experience with the Vercel AI SDK or similar, real features in front of real users.
- Testing depth. Unit (Jest), integration, and E2E (Playwright).
- Operability. SLO / SLA thinking, telemetry, on-call, and incident response.
- Excellent written communication. ADRs / RFCs, and a track record of raising the engineering bar for everyone around you.
Preferred Experience- DTC commerce, checkout, or ecommerce tooling experience
- Payments or fintech infrastructure background (Stripe, Spreedly, TSYS) and PCI-compliant front-end patterns (tokenized / hosted fields)
- Page-builder / drag-and-drop builder infrastructure (Puck, Builder.io, Webflow, or similar)
- Kotlin
- GCP (Cloud Run / GKE, Cloud CDN / Load Balancing, Pub/Sub)
- Advanced caching patterns (edge workers, cache tags / keys, surrogate keys)
- Liquid templating or Shopify ecosystem experience
Hard No- Old-school engineer who defaults to a prior domain over AI and treats agents as a passing fad.
- AI-fluent "prompt jockey" with shallow CS and systems fundamentals who can't hold a real systems-design conversation.
- Backend-only or frontend-only; can't operate across the full stack.
- Framework tourist who has never built and maintained real, production-grade UI/UX for a product company to industry best practices.
- Comfort-seekers who prioritize a 40-50-hour work week and pace themselves accordingly.
Traits We Value- High ownership. You own outcomes, not activities, and you ship the hardest parts yourself.
- Systems thinker. You reason about the whole system, not just the file in front of you.
- Builder mentality. Hands-on, high-throughput, and obsessed with shipping.
- AI-native by default. You reach for agents to move faster and raise quality, and you keep your setup sharp.
- Product judgment. You can articulate what makes a great checkout experience versus a mediocre one.
- Calm under pressure. Commerce and payments do not wait for ideal conditions.
- Bar-raiser. A players want to work near you because of the standard you set and the problems you bring.
$225,000 - $275,000 a year
