Founding Harness Engineer - AI Agents (US only)
About The Position
We're hiring for our partner company, an early-stage startup building an AI coworker: an agent that lives inside a team's everyday tools and actually gets work done. They need a senior Founding Harness Engineer to build the layer that makes it behave. How it pulls in context, when it speaks up, which tool it reaches for, when it stops and asks permission, and how it finishes a long task without falling over halfway. You'll join a seasoned founder and a founding team who spent years building technology in the services world. They watched clients ask for agents long before anyone could deliver them, so they know where the real demand is. The role starts as a contract, with a path to full-time once it's clearly working for both sides. It is remote-friendly anywhere in the US, and hours that overlap with Pacific time will make the founder very happy. If you've shipped tool-using agents to real users and want to build the next one from day one, read on.
Requirements
- You’ve shipped tool-using LLM agents to real users in production. Demos and prompt wrappers don’t count
- Good instincts for agent initiative, and the test results to back them up
- Hands-on experience building eval and regression suites for LLM behavior
- You understand safe tool execution, prompt injection, and multi-tenant data risk
- Solid backend skills in Python or TypeScript (async jobs, retries, state)
- You take a fuzzy problem from prototype to production and can explain the tradeoffs along the way
- Excellent written and verbal communication; you can explain a tradeoff to a founder or a user without a whiteboard
Nice To Haves
- MCP, or integrations with tools like Slack, Gmail, Notion, or Linear
- Eval and tracing tools such as Braintrust, Langfuse, or LangSmith
- You’ve been an early engineer at a startup before and still liked it
- A founding seat. You own the agent harness and shape how the product behaves
Responsibilities
- Build the agent runtime: context, tool choice, approval waits, and knowing when to act, ask, or stay quiet
- Write and keep tuning the system prompts. Proactive is great. Spamming the team channel is not
- Own the eval and regression harness. Prompt changes are code, so they get tested like code
- Make long-running work survive interruptions, retries, and the occasional flaky API
- Put the guardrails in: approval gates for risky actions and strict separation between customers' data
- Work directly with the founder and early users, and turn what you hear into shipped behavior
Benefits
- Competitive compensation + equity
- A direct line to the founder and early users, with no layers in between
- Remote anywhere in the US, ideally keeping hours that overlap with Pacific time
- The tools and models you need to do the job properly
- A small, experienced team that trusts you to run your own work
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What This Job Offers
Job Type
Full-time
Career Level
Senior
Education Level
No Education Listed
