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Legacy Codebase Migration Expert
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About the Role
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
You're a Good Fit If You
- 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.
Role Highlights
Pay & Payout
Independent contractor engagement. Apply via the link below - Mercor handles onboarding and pays weekly via Stripe or Wise.
Common Questions
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