Software Engineer for Legacy Codebase Migration

SaidGig; New York (NY); Remote; USD 227,000 - 324,000; Part time

Job summary

SaidGig is seeking a seasoned software engineer to lead complex migrations and modernisation of large, production-grade legacy systems in high-reliability environments.

The role focuses on end-to-end migration design, evaluation, and validation, including COBOL-to-Java/Python and Java/TypeScript modernization efforts. Remote, hourly engagement with significant ownership expected.

Qualifications

• 5+ years of professional software engineering experience at senior/staff/principal level.
• Deep expertise in legacy codebase migration and modernisation.
• Experience with mature systems with technical debt and complex dependencies.
• Strong knowledge of compatibility, testing, observability, staged rollouts, rollback strategies, and behavioural equivalence.
• Ability to quickly understand unfamiliar codebases and diagnose migration failures.
• Experience modernising core banking, payments, trading, insurance, healthcare, telecom, or other high‑reliability systems.
• For COBOL/mainframe, experience with z/OS, CICS, JCL, DB2, VSAM, and COBOL-to-Java/Python migrations is valuable.

Responsibilities

• Design, implement, review, and evaluate complex codebase migration and modernisation work.
• Analyze legacy code, dependencies, APIs, databases, build systems, and infrastructure to plan migrations.
• Maintain functionality, backward compatibility, data integrity, security, and performance during migrations.
• Create tests and validation approaches to identify regressions and behavioural differences.
• Assess AI-generated migration solutions for correctness and production readiness.

Skills

Legacy migrations

Codebase analysis

Testing & validation

Observability

Rollbacks & releases

High reliability systems

Job description

Role Overview

Help advance frontier AI research by applying hands-on expertise in modernising large, production-grade legacy software systems. This role focuses on complex migrations in mission-critical environments, including financial services, fintech and payments, insurance, healthcare, telecommunications, large technology companies, and similar enterprises.

Key Responsibilities

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


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


• Maintain functionality, backward compatibility, data integrity, security, and performance throughout migrations.


• Create tests and validation approaches that identify regressions and behavioural differences.


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

Qualifications

• At least 5 years of professional software engineering experience, ideally at Senior, Staff, Principal, or equivalent level.


• Deep expertise in legacy codebase migration and modernisation, with personal ownership of or substantial contributions to large-scale production migrations.


• Experience working with mature systems that have 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 quickly understand unfamiliar codebases and diagnose subtle migration failures.


• Experience modernising core banking, payments, trading, insurance, healthcare, telecom, or other high-reliability systems is especially valuable.


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

Relevant Migration Experience

Deep expertise in one or more of the following migration areas is required:

• Language and version upgrades, including Java 8 to 17 or 21, legacy .NET to modern .NET, Python 2 to 3, and PHP 7 to 8.


• Language rewrites, such as COBOL to Java or Python, and JavaScript to TypeScript.


• Framework upgrades or replacements involving Angular, Rails, Django, Spring or Spring Boot, ASP.NET, Next.js, Astro, or similar frameworks.


• Database and ORM migrations, including Oracle or MySQL to PostgreSQL, SQL to NoSQL, Hibernate to jOOQ, Sequelize to Prisma, and raw SQL to an ORM.


• Infrastructure modernisation from VMs or bare metal to containers, Docker, Kubernetes, or cloud-native architectures.


• CI/CD migrations from Jenkins or Travis to GitHub Actions, GitLab CI, or modern deployment pipelines.


• Build and package tooling migrations, including Maven to Gradle, Webpack to Vite, CRA to Next.js, and npm to pnpm.


• API modernisation, including REST to GraphQL, or REST to gRPC, and SOAP or legacy APIs to modern interfaces.


• Authentication migrations from legacy systems to OAuth/OIDC, SAML/SSO, or modern identity and authorisation systems.


• Repository consolidation from polyrepo to monorepo using Bazel, Nx, Turborepo, or similar tooling.


• Migration of unit, integration, browser, and end-to-end testing frameworks.


• Replacement of deprecated or end-of-life libraries, APIs, runtimes, and vendor SDKs.

Work Terms

Remote, hourly engagement.

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

Open-source maintainer experience is not required.

Ongoing work may be available as the research program expands.

Compensation

$200 per hour.