• Build the foundation for how people work with AI. Your work will span the infrastructure that runs agents and the product experiences that help customers direct, inspect, and use their output.
• Take on engineering problems with depth. Make long-running agents reliable, stream progress into responsive interfaces, deliver the right context securely, and understand what happens across every step of execution.
• Have a direct hand in what we build. Join an early team where you'll shape architecture, make product tradeoffs, and work closely with our co-founders, Yiwen and Aris. You'll see your decisions reach customers and use their feedback to improve the product.

We're backed by Transformation Capital, Twelve Below, Virtue, and the founders of Datavant, Commure, and Paradigm.

SOLSTICE IN TORONTO

We're opening our first engineering office outside New York, in Toronto, and you'll be one of its first engineers. The Toronto team will own a product area end to end, with its own roadmap and on-call. It won't be a queue for work handed over from New York.

• Same time zone as New York, and one of our co-founders will be in Toronto with the team.
• You'll spend your first month in New York working alongside the team in person. We cover travel and accommodation.
• This role will be on-site in Toronto. We'll start remotely for the first few months, with a WeWork stipend for those who prefer it. As the team grows, we'll move into our own Toronto office by the end of the year and work from there five days a week.

We're looking for a Fullstack AI Engineer to build and maintain our agent platform and bring its capabilities into the product. You'll own work across backend services, APIs, agent orchestration, and customer-facing interfaces, with a strong focus on Python and platform engineering.

Python is our primary backend language, and FastAPI powers our APIs. You'll help decide how agents run, recover from failures, access tools and context, and communicate with the application. You'll also build the React and Next.js experiences that give users visibility and control over that work.

You'll partner with product, design, Applied AI, and the broader engineering team to take problems from an initial idea through architecture, implementation, and production. The scope includes both building new capabilities and making the systems behind them easier to operate and extend.

WHAT YOU'LL BE WORKING ON

• Build and maintain the agent platform. Use Python, FastAPI, Restate, and Redis to build the shared systems that power our agents. Shape session management, orchestration, tool access, and context delivery so new AI capabilities can build on a dependable foundation.
• Design APIs that power the product. Build Python and FastAPI services for content creation, document processing, collaboration, and enterprise integrations. Design clear API contracts and PostgreSQL data models that make complex workflows straightforward to build on.
• Solve the hard parts of agent execution. Make long-running workflows recover from failures, handle cancellation and retries, and run in isolated environments. Give agents current documents, assets, and brand context while keeping customer data and permissions properly scoped.
• Bring AI workflows to life in the product. Build with React, Next.js, and TypeScript to show streaming progress and tool activity, support reconnectable sessions, and give users intuitive ways to review, accept, or refine AI output.
• Make the whole system observable. Connect APIs, orchestration, and agent execution through Datadog and OpenTelemetry tracing, structured logs, metrics, and alerts. Build the visibility to explain failures, find bottlenecks, and improve latency, reliability, and cost.
• Make quality measurable. Partner with Applied AI engineers on evaluations and regression checks, using tools such as Braintrust alongside API and integration tests. Turn production traces and customer feedback into better agent behavior and more dependable releases.
• Own the path from idea to production. Work with product and customer teams to choose the right problems, make practical tradeoffs, and ship complete features. Deploy, monitor, and improve what you build as customers use it.

SOME IDEAL TRAITS WE'RE LOOKING FOR

• 5+ years of software engineering experience. You've built and shipped production software, with experience owning backend services or fullstack applications.
• Depth in Python and FastAPI. You've shipped and operated production Python services. You can build well-designed FastAPI APIs and understand asynchronous programming, validation, authentication, and error handling.
• Strong systems fundamentals. You design clear service contracts and data models, work comfortably with PostgreSQL and Redis, and think through concurrency, transactions, idempotency, and failure recovery.
• Experience turning AI into useful software. You've built AI applications or the infrastructure behind them. You can reason about tool calling, context management, agent sessions, and the boundaries between model behavior and application logic.
• The ability to deliver across the stack. You're comfortable working in React, Next.js, and TypeScript and connecting an interface to backend APIs. You care about how the product feels, including usability, accessibility, and performance.
• A habit of making systems understandable. You use traces, logs, and metrics to investigate production issues and build instrumentation that helps the next engineer diagnose them. Testing, security, and maintainability are part of how you ship.
• Ownership and good judgment. You can turn an ambiguous problem into a practical plan, explain the tradeoffs, and follow through. You work closely with others, seek feedback, and care about whether your work solves the customer's problem.

Experience with Restate or Temporal, sandboxed agent execution, streaming systems, or AI evaluation tools is a plus. You don't need experience with every tool in our stack. We value strong fundamentals and the ability to learn quickly. Healthcare or pharma experience is welcome but not required.

• Supplemental health, dental, and vision coverage on top of OHIP
• Equity in an early-stage company, granted on the same schedule as our New York team
• RRSP matching
• Unlimited paid time off
• Your first month in New York, with travel and accommodation covered
• A stipend for professional development

COMPENSATION

The base salary range for this role is CAD $155,000 to $230,000, plus equity. Where you land depends on your experience, seniority, and the scope of responsibility you take on. We pay at the top of the Toronto market, and we grant equity on the same schedule in every office.

This posting is for an existing vacancy. You must be legally entitled to work in Canada. We can't sponsor work permits for this role at this time.