Legacy Codebase Migration Expert
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About the role
Pay: $200/hour
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.