Senior Full-Stack Engineer — Flow (AI Agent Platform)

Location: London Victoria Office

Work Pattern: Hybrid (4 days office, 1 day remote)

Team: Flow (Core AI Infrastructure)

About the Role

Flow is our internal AI agent platform. This isn't a basic chatbot bolted onto a help center; it is core agentic infrastructure that reaches across our data warehouse, services, and central systems to execute complex work on behalf of the business. Flow powers both internal and client-facing workflows, delivering true automation and replacing traditional ticketing queues with instant, intelligent actions.

We are looking for a Senior Full-Stack Engineer to help us transition Flow from a fast-moving internal product to durable, productionized platform infrastructure. You will own complex features end-to-end—including agent workflows, reasoning UIs, and cross-system integrations—while raising the engineering bar and shaping the technical direction of a small, autonomous team.

This role sits at the intersection of agentic AI and live operational workflows within a regulated fintech environment. The surface area is the entire company, and your impact will be visible within weeks.

What You'll Do

• Build Action-Oriented Agent Workflows: Design multi-step orchestration, tool use, and retrieval grounded in our data stores using the Strands Agents SDK.

• Architect End-to-End Features: Own development across a React/TypeScript frontend and Python/FastAPI backend, balancing rapid iteration with platform maintainability.

• Own the Reasoning Layer: Extend our Chain-of-Thought UI to ensure explainability. In a regulated environment, showing why an agent made a decision is a core feature, not a nicety.

• Make Agents Measurably Reliable: Build and extend our evaluation harness (Ragas) and observability platform (Langfuse, with session continuity) so we ship changes based on evidence, not vibes.

• Define Evaluation Strategies: Build custom evaluators, datasets, benchmarks, and automated regression suites to catch quality regressions before they hit production.

• Integrate Systems & Clouds: Connect internal APIs, data warehouses, email, and cross-cloud GCP/AWS services with robust error handling and distributed tracing.

• Industrialize Prototypes: Drive the discover → industrialize → productionize lifecycle, turning promising AI prototypes into hardened, daily-deployed services on CD pipelines.

• Mentor & Lead: Uplift mid-level engineers through code reviews, pair programming, and establishing scalable engineering patterns.

• Collaborate Cross-Functionally: Partner with Product, Ops, Trading, and Treasury to identify high-value workflows worth automating (and ruthlessly deprioritize the ones that aren't).

The Tech Stack

Frontend

• React, TypeScript

• Micro-frontend architecture

• Chain-of-Thought / Agent-reasoning UI

• Vite, Vitest

Backend & AI

• Python, FastAPI

• Strands Agents SDK (Agent Orchestration)

• AWS Bedrock

• RAG / Advanced Retrieval

• Ragas (Evaluation), Langfuse (LLM Observability)

Infrastructure

• AWS (ECS Fargate, Lambda, API Gateway, S3) with cross-cloud GCP integration

• Terraform, GitHub Actions

• Docker

• Event-driven integration patterns

What We're Looking For

Must-Haves

• 5+ years of professional software engineering experience.

• Strong Python Backend Expertise: Deep experience with FastAPI (or Django/Flask), asynchronous programming, clean architecture, and writing production-grade code.

• Strong React & TypeScript Skills: Ability to architect non-trivial frontends with sound state management, performance optimization, and comprehensive testing.

• System Design Judgment: A proven track record of designing scalable, maintainable systems and clearly articulating architectural trade-offs.

• API & Integration Skills: Proficiency with REST, streaming (SSE/WebSockets), and the real-world complexities of stitching together messy upstream systems.

• Data Proficiency: Strong SQL/NoSQL skills, query optimization, and data modeling.

• Testing & Ownership Mindset: You treat testing as a core part of the development lifecycle and proactively drive features from ambiguous ideas to production.

• Excellent Communication: Ability to explain technical decisions to both engineers and non-technical stakeholders, alongside a passion for writing useful documentation.

Nice-to-Haves

• Agentic AI Experience: Hands-on experience with agent orchestration (Strands, LangGraph, AutoGen, or similar), RAG, tool use, and context engineering.

• Production LLM Systems: Familiarity with LLM observability (Langfuse), evaluation (Ragas), token/cost management, and reliability patterns.

• AWS Depth: Experience with Lambda, ECS, Bedrock, or equivalent cloud services (cross-cloud exposure is a major plus).

• Event-Driven Architectures: Experience with event streaming and message brokers.

• Regulated Environments: Experience working within fintech, compliance, or similar sectors with strict data-residency and auditability constraints.

• Micro-frontends & IaC: Experience with micro-frontend architecture and Infrastructure as Code (Terraform/CDK).