Senior C# Engineer - Agentic Engineering, .NET 9, AWS Lamba & SQS at Smart Sourcer Limited, City of London, £Contract Rate

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