Senior C# Engineer - AI Native & Agentic Engineering, AWS (Lambda, SQS, SNS) - OUTSIDE IR35 at Smart-Sourcer, United Kingdom, 11 Months, £700-£800 per day

Senior C# Engineer - AI Native & Agentic Engineering, AWS (Lambda, SQS, SNS)

.NET 8/9 AWS Lambda/SQS OUTSIDE IR35 £700-£800/day 100% Remote (UK) 11-month rolling

If you're a deeply senior C# engineer who wants to actually build something new, not maintain legacy, not refactor someone else's mess, this is one of the few roles in the market worth stopping for.

You'll be the technical spearhead for a greenfield SaaS platform, reporting directly to the Director of Engineering and shaping everything from architecture to AI-native delivery patterns. This is high-autonomy, high-impact work for someone who thrives in ambiguity and loves solving hard problems at pace.

Why this role stands out:

• You set the engineering bar, not follow it.
• You get to embed agentic AI workflows into real production systems.
• You own outcomes end-to-end, not just tickets .
• You influence product direction without layers of process or ceremony.

What You'll Bring:

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

What You'll Own:

• Architecting, building and shipping high-performance distributed services in C#/.NET 8/9 on AWS Lambda.
• Designing and delivering resilient event-driven systems using SQS and adjacent 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, sequencing, trade-offs and delivery.
• Designing clean, well-versioned, well-documented APIs that other engineers love to consume.
• Championing a high-quality engineering culture: testing, peer review, CI/CD excellence, observability, performance and secure coding.

Contract Details

• £700-£800/day
• Outside IR35
• 100% remote (UK)
• 11-month rolling contract