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Portrait of Rex St. John

Forward Deployed AI Engineer
San Francisco

I build developer platforms and agentic systems.

  • Developer Platforms
  • Forward-Deployed Delivery
  • AI Engineering
  • Agentic Systems
  • Harness Engineering
  • Evaluation & Benchmarking
  • AI Security Engineering
  • Production LLM Apps
  • Technical Writing
  • Sales Engineering
  • Full-Stack Engineering
  • DevOps & CI/CD

Python · PyTorch · TypeScript · React · Next.js · Node · Swift · iOS · Android · Claude API · Anthropic SDK · OpenRouter · OpenAI · Gemini · Grok · Mistral · Llama · MCP · Claude Code · Cursor · Codex · LangGraph · Vercel · DigitalOcean · Latitude · Docker · Kubernetes · Helm · Ansible · Postgres · Prisma · Neon · Inngest · Modal · GitHub Actions · Hetzner · Coolify · Playwright · Solana · sBPF · SVM · Anchor

Sections

Highlights

  • Forward-deployed deliveryScoping and integration inside customer engineering teams, production rollout, runbooks, debugging someone else's stack, onboarding and enablement, executive and stakeholder communication
  • Developer platformAPI design and versioning, SDK development, MCP servers, developer documentation and reference implementations, sample code, self-serve onboarding, sandboxes, CI for developer releases
  • Production LLM applicationsMulti-model routing and fallbacks, cost and latency control, caching, rate limiting and metering, credit systems, prompt-injection defense
  • Agentic systemsAgent orchestration, tool use, multi-model juries and consensus, commit-and-reveal protocols, failure handling, harness engineering
  • Evaluation and measurementLLM-as-judge juries, eval harness design, scoring and calibration, regression suites, reproducibility and provenance, benchmark construction, red teaming
  • AI securityPrompt-injection defense with published benchmarks, untrusted-input normalization, tool-access locks for agent juries, commit-and-reveal voting, security fuzzing, red teaming
  • Languages and frontendPython, PyTorch, TypeScript, React, Next.js, Node.js, Swift, React Native, iOS, Android
  • Infrastructure and DevOpsVercel, GitHub Actions, Hetzner, Coolify, DigitalOcean, Docker, Neon, Postgres and Prisma, Inngest, Modal, Ansible, Helm, Kubernetes, validator operations
  • BlockchainSolana, sBPF, SVM, LiteSVM, Anchor, production validator operations

Recent writings

All writing