Legacy Codebase Migration Expert

Mercor is partnering with a frontier AI research lab to engage experienced software engineers with deep expertise in legacy codebase migration and modernisation. We are looking for engineers who have personally executed complex migrations across large, production-grade systems, particularly in financial services, fintech/payments, insurance, healthcare, telecom, large technology companies, and other mission-critical enterprises. Strong hands-on experience with production migrations is the primary qualification.

What You'll Do

• Design, implement, review, and evaluate complex codebase migration and modernisation tasks.

• Analyse legacy code, dependencies, APIs, databases, build systems, and infrastructure to determine safe migration approaches.

• Preserve functionality, backwards compatibility, data integrity, security, and performance during migrations.

• Develop tests and validation strategies to identify migration regressions and behavioural differences.

• Evaluate AI-generated migration solutions for correctness, completeness, maintainability, and production readiness.

Relevant Migration Experience

Candidates should have deep expertise in one or more of the following:

• Language/version: Java 8 → 17/21, legacy .NET → modern .NET, Python 2 → 3, PHP 7 → 8

• Language rewrites: COBOL → Java/Python, JavaScript → TypeScript

• Frameworks: Angular, Rails, Django, Spring/Spring Boot, ASP.NET, Next.js/Astro, and other major framework upgrades/replacements

• Databases & ORMs: Oracle/MySQL → PostgreSQL, SQL → NoSQL, Hibernate → jOOQ, Sequelize → Prisma, raw SQL → ORM

• Infrastructure: VMs/bare metal → containers, Docker/Kubernetes, cloud-native architectures

• CI/CD: Jenkins/Travis → GitHub Actions, GitLab CI, or modern deployment pipelines

• Build/package tooling: Maven → Gradle, Webpack → Vite, CRA → Next.js, npm → pnpm

• APIs: REST → GraphQL, HTTP/REST → gRPC, SOAP/legacy APIs → modern interfaces

• Authentication: Legacy auth → OAuth/OIDC, SAML/SSO, modern identity and authorisation systems

• Repositories: Polyrepo → monorepo using Bazel, Nx, Turborepo, or similar

• Testing: Migration of unit, integration, browser, and E2E testing frameworks

• Dependencies/SDKs: Replacement of deprecated or EOL libraries, APIs, runtimes, and vendor SDKs

Ideal Background

• 5+ years of professional software engineering experience, ideally Senior, Staff, Principal, or equivalent.

• Personally owned or made substantial technical contributions to large-scale production migrations.

• Experience working with mature systems involving technical debt, complex dependencies, legacy integrations, and significant regression risk.

• Strong knowledge of compatibility, testing, observability, staged rollouts, rollback strategies, and behavioural equivalence.

• Ability to reason deeply about unfamiliar codebases and diagnose subtle migration failures.

• Especially valuable: engineers who have modernised core banking, payments, trading, insurance, healthcare, telecom, or other high-reliability systems.

• For COBOL/mainframe modernisation, experience with technologies such as z/OS, CICS, JCL, DB2, VSAM, batch processing, and COBOL-to-Java/Python migrations is particularly valuable.

Why Join

• Apply your migration expertise to help shape how frontier AI models understand and execute complex software modernisation.

• Work on technically challenging problems modelled after real-world, production-scale legacy systems.

• Contribute expertise developed from large enterprise migrations without needing an open-source maintainer background.

• Opportunity for ongoing work as the research program expands.

We consider all qualified applicants without regard to legally protected characteristics and provide reasonable accommodations upon request.

Contract and Payment Terms

• You will be engaged as an independent contractor.
• This is a fully remote role that can be completed on your own schedule.
• Projects can be extended, shortened, or concluded early depending on needs and performance.
• Your work at Mercor will not involve access to confidential or proprietary information from any employer, client, or institution.
• Payments are weekly on Stripe or Wise based on services rendered.
• Please note: We are unable to support H1-B or STEM OPT candidates at this time.

About Mercor

Mercor partners with leading AI labs and enterprises to train frontier models using human expertise. You will work on projects that focus on training and enhancing AI systems. You will be paid competitively, collaborate with leading researchers, and help shape the next generation of AI systems in your area of expertise.