Keystone's AI Engineer Bet: Founder Turns Down Acquisition, Open-Sources

Started as an 'AI on-call engineer', automatically triaging tickets, fixing bugs, and handling production incidents; now Proliferate, offering an MIT-licensed, self-hostable company coding agent platform.

Bet an AI engineer could triage tickets, fix bugs, handle incidents, validated with closed-source product, then open-sourced platform as Proliferate.

Completed a $500,000 seed round in September 2025, with investors including M.G. Siegler, Harrison Metal, Partech, Tekton, The HIT Forge, and Y Combinator.

Pablo Hansen completed a master's degree in AI at age 19 and was the first employee at Onyx (YC W24); he founded Keystone in 2025 and was selected for the YC S25 batch; the company's goal was to use AI to automatically triage tickets, fix bugs, and handle incidents, serving as the team's 'on-call AI engineer'.

At Demo Day in September 2025, TechCrunch listed it as one of the 9 companies investors most wanted to back: customers included Lovable, and the founder said it had turned down a seven-figure acquisition offer; that month it completed a $500,000 seed round. The company later renamed to Proliferate and transformed the product from a closed-source bug-fixing tool into an MIT-licensed, self-hostable coding agent platform, focused on 'company-level background agents': each agent has an isolated sandbox, can access internal services, is triggered by any event, and is collaboratively validated in multi-user real-time preview.

Entered from painful scenario: fixing production bugs needs codebase and environment understanding, scalable by AI, time-consuming for humans.

Validated first: had customers like Lovable and acquisition offer before Demo Day.

Refused exit: turned down acquisition, open-sourced platform, upgraded to infrastructure.

Open source lowers trust: MIT license and self-hosting enable enterprise adoption.

Validated narrow bet, then expanded: proved AI fixed bugs with customers and offer, then open-sourced platform for larger battlefield.

As of 2026-09-01: the company operates under the name Proliferate (YC company page status Active, San Francisco, founded in 2025), promoting an MIT-licensed, self-hostable coding agent platform; according to its YC Launch description, the repository has been open-sourced, the team is validating engineering efficiency gains from background agents with a small number of customers, and demo scheduling and self-hosting documentation are open; the YC company page still retains a historical entry for Keystone.