# Senior Member of Technical Staff, Harness Engineering

**Company:** [Harper](https://hotfix.jobs/companies/harper)
**Location:** San Francisco, CA
**Role:** ML Engineering
**Salary:** $187k – $264k/yr
**Experience:** 3+ years
**Skills:** LLMs, Agent Frameworks, Prompt Engineering, API Design, Sandbox, Isolation, Open-Source, Foundation Models
**Posted:** 2026-06-01

> As a Senior Member of Technical Staff, Harness Engineering, you will build the core substrate for Harper's AI agents, focusing on agent loop primitives, execution environment infrastructure, and tool layer ownership. You will work with frontier coding agents and internal agents, shipping primitives that agent teams depend on.

## Job Description

## What You'll Do
* Build agent loop primitives - Prompt construction, tool routing, retry/timeout/budget logic, multi-agent orchestration
* Ship execution-environment infra - Sandbox lifecycle, isolation, blast-radius limits, filesystem + network policy for agents
* Own the tool layer for assigned domains - Schema, auth, rate-limit, observability per tool. Tools other engineers consume.
* Wire model-provider routing - Provider fallback chains, eval-driven model selection, cost/latency tradeoffs
* Ship harness SDK improvements - Whatever makes pod engineers faster
* Eat your own dog food - You write code with our harness daily and feel every rough edge

## You Might Be a Fit If…
* You've shipped production agentic systems (not demos - real users, real traffic)
* You've worked with at least one major agent framework
* You can describe a tool-design or sandbox decision you'd defend in three years
* You write code with AI daily and manage 3+ parallel sessions
* You're 3–6 years into your career

## Requirements
* 3–6 years software engineering experience
* Production agent / LLM systems experience - agent loops, tool integration, prompt engineering at scale
* Strong written communication - API contracts, integration guides, internal docs
* Based in San Francisco or willing to relocate

## Nice to Have
* Sandbox/isolation infrastructure experience
* Open-source contributions to agent frameworks
* Foundation-model partner or early-access experience

## Compensation
* OTE: $187,000–$264,000 cash compensation (base salary + target performance bonus)
* Equity: competitive equity, so you share in the company you are helping build
* Location: San Francisco, in-office

## Benefits
* Health, dental, and vision insurance
* Commuter benefits
* Team meals and snacks

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