Lead Backend C# Engineer - .NET 8/9, AWS (Lambda, SQS), Agentic Workflows (Claude Code) - OUTSIDE at Smart-Sourcer, United Kingdom, 6 Months, £875-£900 per day

Principal C# Backend Engineer - .NET 8/9, AWS (Lambda, SQS), Agentic Workflows (Claude Code), MySQL - OUTSIDE IR35

Reporting to the Director of Engineering, this is a genuinely outstanding contract opportunity for a rockstar Principal C# Engineer to lead the development of a greenfield SaaS product. We're looking for a best of breed', deeply senior, technically hands-on engineer who thrives in complex problem spaces and fast-moving start-up & scale-up environments. You'll need a genuinely Product Centric mindset and approach twinned with experience of AI-Native Engineering and Agentic Workflow.

Skills We're Looking For:

• Senior-Staff-level Back End engineer with deep, current expertise in C# and .NET Core 8/9, capable of architecting and leading the design of distributed REST API microservices at scale.
• Authority in AWS serverless architecture; Lambda-first, with strong working knowledge of API Gateway, SQS, Step Functions, EventBridge and IAM, and a track record of shipping production workloads on this stack.
• Deep data expertise across Aurora RDS MySQL and DynamoDB; schema design, access patterns, indexing, query tuning, single-table vs multi-table trade-offs, and pragmatic thinking around consistency, scaling and cost.
• Hands-on experience with Claude Code and advanced agentic workflows; multi-agent orchestration, context management, custom commands/skills and scaling AI-assisted delivery across a team.
• Proven experience designing event-driven systems with SQS and adjacent AWS messaging; idempotency, retries, ordering, DLQs and operational robustness.
• Strong API design sensibility; versioning, documentation, throttling, backwards compatibility and a genuine obsession with developer experience.
• A strong product brain; comfortable operating without a traditional Product Owner, partnering with BAs, making sensible trade-offs, prioritising ruthlessly and owning the solution through to delivery.
• Excellent communication skills and comfort with ad-hoc client interaction, able to ask the right questions, shape requirements and translate outcomes into shippable work.
• Rigorous engineering standards; Git-based workflows, trunk-based development, CI/CD (ideally GitHub Actions), IaC (AWS CDK or Terraform), comprehensive testing and secure-by-default coding.
• Technical leadership; lifting teams through pairing, mentoring, PR review and example.
• A pragmatic, outcome-oriented mindset; comfortable with ambiguity, biased to shipping, and able to make sensible calls on scope, sequencing and technical debt.

What You'll Own & Deliver:

• Architect, build and ship complex distributed services in C# and .NET Core 8/9, primarily serverless on AWS Lambda, setting the technical bar for the squad and delivering major feature sets end-to-end.
• Design robust data models and persistence patterns across Aurora RDS MySQL and DynamoDB; choosing the right store for the workload, tuning for scale, and modelling for both transactional and high-throughput access patterns.
• Build resilient, event-driven systems using SQS and related AWS messaging primitives; idempotency, retries, DLQs, ordering and clean service boundaries.
• Own each feature's solution end-to-end; partnering with BAs on high-level problems, then driving product thinking, scoping, trade-offs and delivery yourself.
• Leverage Claude Code and advanced agentic workflows; orchestrating sub-agents, managing context, running parallel workstreams and embedding AI-native engineering patterns into everyday delivery.
• Design clean, well-versioned, well-documented APIs that other engineers love to consume; treating developer experience and contract stability as first-class concerns.
• Shape architecture and technical direction with Principal Engineers; making well-reasoned decisions on service boundaries, data design, messaging patterns, consistency guarantees and performance.
• Champion a high-quality engineering culture; test coverage, peer review, CI/CD discipline (GitHub Actions), IaC, secure coding, observability and performance
• Mentor and up-level engineers through pairing, PR review, architectural guidance and practical coaching on AI-assisted development.

£875 - £900 per day. OUTSIDE IR35. 100% remote. 6 months rolling.