Senior C# Engineer - Agentic Engineering, .NET 9, AWS Lamba & SQS

Senior C# Engineer - Agentic Engineering, .NET 9, AWS Lamba & SQS

Posted Today by Smart Sourcer Limited

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£800 Per day
Outside
Remote
City of London (EC1)
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.NET Framework Amazon Aurora Amazon DynamoDB Amazon Simple Queue Services Amazon Web Services (AWS) API Design API Gateway Application Programming Interface (API) AWS Identity And Access Management (IAM) AWS Lambda Backwards Compatibility C# (Programming Language) Continuous Integration and Continuous Delivery Github Indexing Infrastructure as Code (IaC) Management Microservices MySQL Query Tuning Secure Coding Software as a Service (SaaS) Software Coding Software Development Workflows

Summary: The Senior C# Engineer role focuses on leading the development of a greenfield SaaS product using .NET 8/9 and AWS technologies. The position requires a hands-on approach to architecting and delivering complex distributed systems while fostering AI-native engineering practices. The ideal candidate will possess strong backend engineering skills and a product-centric mindset, thriving in a dynamic environment. This is a fully remote position with an 11-month rolling contract.

Key Responsibilities:

  • Architecting, building and shipping complex, high-performance distributed services in C#/.NET 8/9 on AWS Lambda.
  • Designing and delivering resilient event-driven systems using SQS and related AWS messaging primitives.
  • Embedding AI-native engineering and agentic workflows into everyday delivery — orchestrating sub-agents, managing context, and running parallel workstreams.
  • Owning features end-to-end: product thinking, scoping, trade-offs, sequencing and delivery.
  • Designing clean, well-versioned, well-documented APIs that other engineers love to consume.
  • Championing a high-quality engineering culture: testing discipline, peer review, CI/CD excellence, observability, performance and secure coding.

Key Skills:

  • Senior/Staff-level backend engineering depth in C# and .NET 8/9.
  • Strong authority in AWS serverless: Lambda-first, with hands-on experience across API Gateway, SQS, Step Functions, EventBridge and IAM.
  • Practical experience with Claude Code (or similar) and advanced agentic workflows.
  • Deep data expertise across Aurora MySQL and DynamoDB.
  • Proven ability to design event-driven systems with SQS.
  • Strong API design sensibility.
  • A product-first mindset.
  • Excellent communication skills and confidence in ad-hoc client interaction.
  • Rigorous engineering standards: Git-based workflows, trunk-based development, CI/CD, IaC, comprehensive testing and secure-by-default coding.
  • Pragmatic, outcome-oriented, comfortable with ambiguity and biased toward shipping.

Salary (Rate): £800/day

City: City of London

Country: United Kingdom

Working Arrangements: remote

IR35 Status: outside IR35

Seniority Level: Senior

Industry: IT

Detailed Description From Employer:

Senior C# Engineer (AI-Native & Agentic Engineering) – .NET 8/9, AWS Lambda/SQS – OUTSIDE IR35

£750–£800/day • 100% Remote • 11-month rolling contract

A rare opportunity to lead the build of a greenfield SaaS product as a deeply senior, hands-on C# engineer. Reporting directly to the Director of Engineering, you’ll operate as the technical spearhead; shaping architecture, driving AI-native engineering patterns, and delivering complex distributed systems at pace.

We’re looking for someone who is product-centric, agentic-minded, and thrives in ambiguity. If you enjoy solving hard problems, owning outcomes end-to-end, and setting the engineering bar for others, this one’s for you.

What You’ll Bring:

  • Senior/Staff-level backend engineering depth in C# and .NET 8/9, with the ability to architect and lead distributed REST microservices at scale.
  • Strong authority in AWS serverless: Lambda-first, with hands-on experience across API Gateway, SQS, Step Functions, EventBridge and IAM.
  • Practical experience with Claude Code (or similar) and advanced agentic workflows — multi-agent orchestration, context management, custom commands/skills, and scaling AI-assisted delivery.
  • Deep data expertise across Aurora MySQL and DynamoDB — schema design, access patterns, indexing, query tuning, and pragmatic trade-offs around consistency, scale and cost.
  • Proven ability to design event-driven systems with SQS: idempotency, retries, ordering, DLQs and operational robustness.
  • Strong API design sensibility: versioning, documentation, throttling, backwards compatibility and a genuine obsession with developer experience.
  • A product-first mindset — comfortable operating without a traditional PO, partnering with BAs, shaping requirements and owning delivery.
  • Excellent communication skills and confidence in ad-hoc client interaction.
  • Rigorous engineering standards: Git-based workflows, trunk-based development, CI/CD (GitHub Actions), IaC (CDK/Terraform), comprehensive testing and secure-by-default coding.
  • Pragmatic, outcome-oriented, comfortable with ambiguity and biased toward shipping.

What You’ll Own:

  • Architecting, building and shipping complex, high-performance distributed services in C#/.NET 8/9 on AWS Lambda.
  • Designing and delivering resilient event-driven systems using SQS and related AWS messaging primitives.
  • Embedding AI-native engineering and agentic workflows into everyday delivery — orchestrating sub-agents, managing context, and running parallel workstreams.
  • Owning features end-to-end: product thinking, scoping, trade-offs, sequencing and delivery.
  • Designing clean, well-versioned, well-documented APIs that other engineers love to consume.
  • Championing a high-quality engineering culture: testing discipline, peer review, CI/CD excellence, observability, performance and secure coding.

Contract Details

£750–£800/day

Outside IR35

100% remote (UK)

11-month rolling contract

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