Open Source Maintainer / Core Contributor – Software Engineer

1\. Overview

Join a leading AI lab's cutting-edge GenAI team and help build foundational AI models from the ground up. We're seeking talented open-source maintainers and core contributors with deep, hands-on ownership of a mature, widely used open-source codebase to bring real-world engineering and code review judgment and elevate the quality of our AI training data. This is a full-time commitment of 40 hours per week.

This is a W-2 employment position with Cincinnatus LLC, with the opportunity to be placed at a leading AI Lab as part of their extended workforce.

2\. Key Responsibilities

• Guide research and engineering teams to close knowledge gaps and improve AI model performance in software engineering, code review, and open-source maintenance topics.
• Design challenging, realistic engineering tasks grounded in the open-source codebase the expert knows best, such as the features, refactors and bug fixes a maintainer would assign, and write accurate, well-structured reference solutions.
• Evaluate AI-written code, tests and grading rubrics against the repository's architecture, conventions and quality bar, and provide clear, written technical feedback.
• Build, run and test the project locally, including with Docker, to confirm that tasks, solutions and tests behave as intended.
• Write precise rationales that explain what a strong solution looks like and where AI-generated changes fall short.
• Collaborate with other subject matter experts to ensure consistency and accuracy in training data.

3\. Core Qualifications

• Maintainer (named in MAINTAINERS or CODEOWNERS, or 10+ PR reviews in the last 12 months) or core contributor (3+ substantive merged PRs in the last 12 months) of a widely used open-source project.
• The repository is 2+ years old, has real users and an active code review culture, and is primarily human-written.
• Years of sustained open-source contributions, with a public history that can be verified against the candidate's own GitHub account.
• Senior-level code review judgment, including the ability to critically assess AI-written code, tests and edge cases.
• Hands-on ability to build and run the project and its test suite locally, including with Docker.
• Ability to engage reliably for 40 hours/week during weekdays on an exclusive basis: no other full-time role and no other AI training or evaluation projects, including other Mercor projects, during the engagement.
• Authorized to work in the United States on a W-2 basis.
• Able to complete any necessary background checks and confidentiality agreements before starting, and to work on a company-provided device to protect the security of information.
• Writes all rationales and feedback personally, in their own words.
• Strong written communication skills and the ability to explain complex technical decisions clearly.

About Cincinnatus LLC

Cincinnatus LLC is an enterprise staffing company that partners with leading technology companies to source and employ highly skilled professionals for contingent and contract-based opportunities. Cincinnatus serves as the employer of record for these engagements, providing W-2 employment, payroll, benefits, and compliance, while placing employees directly within client teams to work on high-impact initiatives.

Equal Employment Opportunity

Cincinnatus is proud to be an Equal Employment Opportunity employer. We do not discriminate based upon race, religion, color, national origin, sex (including pregnancy, childbirth, reproductive health decisions, or related medical conditions), sexual orientation, gender identity, gender expression, age, status as a protected veteran, status as an individual with a disability, genetic information, political views or activity, or any other legally protected characteristic.

Where you can work

This role is 100% remote, for applicants located in United States.