Harness Engineer
Confirmed on the employer's own hiring board on Sep 28, 2026. First seen by Alion on Aug 13, 2026. Virio scores B on the Alion truth index.
Harness Engineer
Location: San Francisco (in-person, in-office, full-time ONLY)
Compensation: $150k-$250k base + top of market equity
About Virio
Virio is solving an unsolved problem: how do you write perfect content? The best human strategist researches the space, finds the angle, and knows your goals and constraints - but they're capped by the hours in a day and one human career's worth of expertise. An agent isn't.
Crafting "perfect" content has three components:
1. Research: to identify and collect the best inputs
2. Synthesis: to devise the strategy and execute on it
3. Verification: RL verification of content quality and efficacy
We're backed by operators from LinkedIn, YouTube, HubSpot, Rippling, and Google. The team is almost 100% ex-founders and VCs from Yale, UC Berkeley, Stripe, and more. And we've consecutively added $1M ARR/mo because everyone and their co-founder wants what we're selling.
This problem doesn't have a playbook. We're looking for a Harness Engineer to obsess over AI-for-writing and own that layer end to end: the data feedback loop, evals, and harness design that turn a subjective judgment into something we can measure and improve - so day by day, we can get ever closer to solving content.
What You'll Do
As a Harness Engineer, you'll own the intelligence layer that sits between our AI models and product-the system prompts, tool definitions, context management, and evaluation framework that makes agents actually work in production.
Specifically:
Build and refine the system prompts, tool integrations, and context windows that shape how our models behave across our platform-you'll see how small prompt tweaks cascade into measurable product impact. (Nice to have: background in English, literature, creative writing, or humanities)
Design the evaluation framework (LLM-as-judge evals, deterministic tests, production monitoring) that lets us ship with confidence. You'll define what success looks like and build the metrics to measure it.
Architect the abstraction layer between our product (file systems, artifacts, skills) and the model's capabilities-making complex multi-step workflows feel natural to the model and reliable to users.
Own prompt versioning, experimentation, and iteration. You'll A/B test prompt variations, measure their impact on agent quality, and ship improvements across our production system.
Collaborate with product and engineering to identify signal-where our agents are failing, where users are stuck-and translate that into prompt and architecture improvements.
What Success Looks Like
After 30 days: You understand our agent stack-the system prompts, available tools, context window strategy, and current failure modes. You've shipped your first prompt improvement and measured its impact.
After 90 days: You've designed and implemented our core evaluation framework. Our team uses it as the source of truth for agent quality. You've shipped 2-3 meaningful prompt iterations that improved measurable outputs, and you're comfortable making architecture trade-offs.
After 6 months: You own the harness layer end-to-end. You've architected improvements that reduced hallucination, improved context retention, or increased model reliability. You're driving architectural decisions about how we expose capabilities to the product team. You're writing technical content about how we've solved these problems-attracting the next generation of harness engineers to the company.
Traits That Thrive at Virio
High agency & self-direction - Acts without waiting for requirements or detailed instructions
Small-team intensity comfort - Comfortable working intensely and closely with a small, high-output team
Unorthodox problem solving - Sees non-obvious paths forward and challenges conventional approaches
Quality-driven execution - Detail-oriented with high standards for correctness and quality
Low ego & accountability - Takes full ownership and accountability for outcomes
Benefits
Work directly with the founders
Competitive total compensation aligned to impact and ownership
Meaningful equity upside as part of the founding team
Medical, dental, and vision insurance
401(k) plan
All working meals covered
Relocation support for San Francisco
Company-wide annual off-site
High ownership, high trust, and fast career progression alongside world-class client partners
In-person culture with deep commitment to excellence
This is a full-time, on-site role based in San Francisco. We do not offer hybrid or remote positions.