Senior Full Stack Engineer (AI Experiences, Python + React)

Webellian; Warszawa; Hybrid; PLN 260,000 - 340,000; Full time

Benefits offered by this job

Private medical care

Group insurance

Multisport card

English classes

Hybrid work in Warsaw (Mokotów)

Job summary

Webellian is seeking a Senior Full Stack Engineer to craft AI-powered journeys using Python (FastAPI) backend and React/TypeScript frontend. You will own end-to-end implementations, integrate AI and model services, and ensure robust, scalable delivery across interfaces.

You will collaborate with AI specialists and UX designers, contribute to platform patterns, and uphold performance and accessibility standards in delivery. Hybrid work in Warsaw is offered.

Qualifications

• 5+ years professional full-stack development.
• Experience Python backend and React frontend at scale.
• Proficiency in Python 3.12+, FastAPI, async I/O, Pydantic.
• Deep React (TypeScript) knowledge with state management.
• Experience consuming AI/model services, including JSON outputs and streaming.
• Experience with REST APIs, versioning, and BFF-layer responsibilities.
• Kubernetes readiness and liveness probes, scaling.
• CI/CD and GitOps (GitHub Actions, ArgoCD).

Responsibilities

• Build AI-related journeys end to end across backend services and frontend interfaces.
• Integrate AI services into domain workflows and orchestrate multi-step AI calls.
• Surface AI outputs safely in UI with structured summaries and handling of uncertainty.
• Own the API contract between AI integration, backend, and frontend.
• Collaborate on architecture decisions for orchestration and data flows.
• Mentor mid-level engineers and contribute to technical direction.

Skills

Python

FastAPI

React

TypeScript

Async I/O

Pydantic

Kubernetes

CI/CD

Tools

PostgreSQL

Docker

GitHub Actions

React Native

Job description

Senior Full Stack Engineer (AI Experiences, Python + React)

Webellian is a well-established Digital Transformation and IT consulting company committed to creating a positive impact for our clients. We strive to make a meaningful difference in diverse sectors such as insurance, banking, healthcare, retail, and manufacturing. Our passion for cutting-edge and disruptive technologies, as well as our shared values and strong principles, are what motivate us. We are a community of engineers and senior advisors who work with our clients across industries, playing a deep and meaningful role in accelerating and realizing their vision and strategy.

About the position

As a Senior Full Stack Engineer for AI Experiences within Advanced Analytics Team, you will join one of our domain engineering teams to build the product surfaces around AI: the FastAPI services that orchestrate and consume AI, and the React (TypeScript) and React Native interfaces that bring AI-related journeys to life for customers and case handlers. You work across the full stack, from the AI integration layer to the rendered experience, with clear personal ownership of the journeys you ship.

This role builds around AI, not the AI itself. Our AI specialists (AI Engineers, Conversational AI, NLU) own model development, agent behaviour, prompt and NLU design, and evaluation. You own the engineering that turns those AI services into reliable, well-integrated product journeys: consuming the agent and model APIs, orchestrating them into workflows, and surfacing their output cleanly and safely in the UI. The boundary is deliberate so that AI expertise stays with the specialist teams and product delivery stays with you.

You will work in a cross-functional team alongside backend and frontend engineers, UI/UX designers, and AI specialists, on a central engineering platform that provides CI/CD pipelines, deployment tooling, shared backend and frontend frameworks, a shared design system, and AI services you consume via API.

Key responsibilities:

• Build AI-related journeys end to end for your team's domain: FastAPI async services and BFF-layer components that orchestrate AI calls on the backend, and React (TypeScript) web and React Native mobile interfaces that surface AI output on the frontend.
• Integrate the platform's AI and agent services into domain workflows: consume agent and model APIs, orchestrate multi-step and multi-turn AI calls, handle structured outputs and confidence thresholds, and design fallback and human-in-the-loop paths.
• Surface AI output cleanly and safely in the UI: structured summaries, conversational companion experiences, voice flow integrations, streaming responses, and clear handling of uncertain or low-confidence results.
• Own the API contract as the seam between the AI integration layer, the backend, and the frontend: keep it versioned, consumer-driven, and stable across releases.
• Contribute to service and component architecture decisions alongside the team's senior technical lead: orchestration patterns, state management for conversational flows, data fetching, and integration boundaries with core insurance systems.
• Partner with the AI specialist teams on the contract for AI services: give clear product feedback on API shape, latency, output structure, and failure modes, without owning the models, prompts, or evaluation yourself.
• Adopt the central platform's shared Python frameworks, Pydantic models, async patterns, and the shared design system; contribute reusable AI-integration and AI-rendering patterns back to the platform.
• Apply and improve performance and accessibility standards across AI journeys: streaming and latency handling on the backend; code splitting, render performance, and WCAG 2.1 AA compliance for AI-driven interfaces on the frontend.
• Instrument AI journeys for observability against the central stack (Prometheus, Grafana, Application Insights, OpenTelemetry): structured logging, metrics, distributed tracing of multi-step AI calls, and error tracking.
• Work within the central CI/CD pipelines, Helm charts, and ArgoCD-based deployment model; configure Kubernetes-aware service behaviour (probes, graceful shutdown, resource requests, HPA).
• Mentor mid-level engineers through code review, pairing, and design discussion; participate in incident response for AI journeys in your domain and the follow-up improvements.

Required Experience & Skills

5+ years professional experience in full stack development with production ownership of both backend services and frontend applications at scale.

Genuine full-stack depth: able to design, contribute to, and review production code on both the Python backend and the React frontend, not strong on one side and nominal on the other.

Modern Python backend proficiency: Python 3.12+, FastAPI (or equivalent ASGI framework), async I/O at production scale, Pydantic models, and Pythonic API design.

React (TypeScript) depth: component design, hooks, state management (Context, Redux, Zustand, or equivalent), and TypeScript across large codebases.

Experience consuming AI or model services from application code: calling agent, LLM, or ML APIs, handling structured (JSON) outputs, streaming responses, timeouts, retries, and graceful degradation when a call fails or returns low confidence.

Microservice and API architecture: service boundary design, REST API design and versioning, backward compatibility, and BFF-layer responsibilities.

Contract collaboration across the AI-service, backend, and frontend seams: consumer-driven contract testing (Pact or equivalent) and versioning that keeps clients stable across releases.

Kubernetes-aware service design: readiness and liveness probes, graceful shutdown, resource requests and limits, and horizontal pod autoscaling. You do not need to operate the cluster.

CI/CD and GitOps familiarity: GitHub Actions pipelines, containerisation (multi-stage Docker builds), and GitOps deployment with ArgoCD or equivalent.

Testing across the stack: pytest for backend services, Jest and React Testing Library for the frontend, plus integration and contract tests.

Accessibility: WCAG 2.1 AA compliance, semantic HTML, ARIA patterns, and screen reader testing, applied to AI-driven interfaces.

Demonstrated experience mentoring mid-level engineers and contributing to technical direction within a team.

Ways of Working

Comfortable in agile, iterative delivery environments with clear personal ownership of AI journeys and outcomes across the stack.

Collaborative by default: shares work-in-progress, seeks early feedback, and works closely with the AI specialist teams and UX designers on decisions that span the AI-service and product boundaries.

Respects team boundaries: builds the product engineering around AI and leaves model, prompt, NLU, and evaluation ownership with the specialist teams, while giving them sharp, practical feedback on the service contract.

Attention to craft: cares about how AI output is presented, how uncertainty is handled, and how a journey degrades gracefully, not just functional completeness.

Proactive learner: keeps up with the Python, React, and applied-AI ecosystems; comfortable adopting AI-assisted developer tools (e.g. GitHub Copilot, Claude Code) to improve productivity.

Clear written and verbal communication across technical and non-technical stakeholders, including UX designers and AI specialists.

Nice to Have

Experience building AI-driven UX patterns in production: conversational companion UIs, voice interfaces, LLM-powered autocomplete, and structured AI output rendering.

Familiarity with agent or LLM orchestration frameworks as a consumer (LangChain, LlamaIndex, or in-house agent frameworks), without needing to have designed the models or agents yourself.

React Native depth: shared web and mobile delivery, navigation patterns, and platform-specific considerations.

Event-driven systems: Kafka or equivalent message broker at production scale, including consumer group patterns and schema evolution.

Relational database experience: PostgreSQL, async drivers (asyncpg, SQLAlchemy 2.x async), schema design, and migrations (Alembic).

Storybook and design-system contribution at scale.

Insurance or financial services domain knowledge (claims, policy, payments).

Experience in regulated industries (insurance, finance, healthcare) where auditability, data residency, and access control are standard requirements.

What we offer

• Benefits such as private medical care, group insurance, Multisport card
• There are English classes available
• Hybrid work (at least 1 day/2-3 months on-site) in Warsaw (Mokotów)
• Opportunity to work with excellent professionals
• High standards of work and focus on the quality of code
• New technologies in use
• Continuously learning and growth
• International team
• Pinball, PlayStation & much more (on-site)

Join a growing team of dedicated professionals! We love to pass on the knowledge to grow excellence, speak our minds without playing politics, and just enjoy hanging around together. If you share our passions - we want to meet you!