Founding Software Engineer; Accel​/Index

About Day One Partners

Day One Partners is a search firm that partners with venture capital firms to help build high-growth startups. We lead confidential searches for leadership and critical roles across a range of company stages, industries, and functions

We’re partnering with a 2x Founder and Thiel fellow who just raised a significant seed round from Accel and Index to recruit2 additional founding engineers with strong product instincts and an obsessive attention to detail.

Teams everywhere are experimenting with AI agents plugged into tools like Slack and email — but those platforms weren’t designed for true human–AI collaboration
.

We’re rebuilding workplace communication from the ground up so humans and agents can actually work together — seamlessly, intuitively, and productively.

If that excites you, keep reading.

You’ll thrive here if you:

• Love the messy beauty of early stage building and want those late nights with a small team you’ll remember years later.
• Crave the dopamine of shipping product that reaches hundreds of thousands of users — not slow-moving enterprise deployments.
• Want to do the best work of your life alongside people who push you to be better — and help build that team, too.

• You don’t love LLMs or use them daily. (If you’re not there yet, aim to be!)
• You don’t value craft or can’t point to software that genuinely inspires you.

• Architect and ship core messaging infrastructure that feels instant, reliable, and magical.
• Focus on the invisible but critical layers — from retrieval and evaluations to performance optimization.
• Prototype new interaction patterns for how humans and AI agents work together.
• Build an API and developer platform that outside builders genuinely love using.
• Experiment with tool calling and retrieval systems to find what works in practice.
• Raise the bar for engineering craft
  , contribute to recruiting, and help define a world-class culture.
• Use our product daily, give direct feedback, and help turn insights into tangible improvements.

• 3+ years of professional software engineering experience, with at least 1 year in a senior IC role.
• Proven experience building or scaling AI-powered applications
  .
• Ability to move fast without compromising quality.
• Strong product sense and attention to the small details that make great software exceptional.