14 Best Legacy System Modernization Companies in LA, USA (2026)

Gilzor works on legacy products where older architecture has started limiting feature development, integrations, performance, or maintainability. Its modernization work can involve restructuring tightly coupled applications, decomposing systems into more manageable modules, introducing APIs, improving performance, and rebuilding selected components rather than automatically replacing an entire platform.

The company also has experience taking over existing production codebases and supporting long-running products. One published modernization project involved rebuilding the legacy Android application of an established real estate marketplace while preserving the workflows and backend relationships already supporting the product.

Net Solutions handles application modernization through assessment, architecture changes, migration, integration work, and progressive replacement of legacy components. Its approach does not assume that every old application needs a complete rebuild. Depending on the condition of the software, projects can involve rehosting, refactoring, rearchitecting, rebuilding, or replacing selected areas.

The company maintains a Los Angeles office on Wilshire Boulevard. Its published modernization work includes projects where existing services remained operational while new architecture was introduced in stages, which is relevant for organizations whose systems cannot simply be switched off during migration.

TechAhead combines product engineering with cloud and legacy modernization. The company works on aging applications by upgrading technology stacks, refactoring architecture, improving integrations, redesigning cloud infrastructure, and moving workloads away from outdated on-premises environments. Its modernization services also cover microservices transformation, cloud-native architecture, data migration, and application modernization planning.

Its US headquarters is in Agoura Hills in the Los Angeles metropolitan area. This makes TechAhead particularly relevant to Southern California organizations that want local access alongside engineering capabilities spanning applications, cloud infrastructure, AI, DevSecOps, and long-term managed development.

Simform provides application modernization across assessment, migration, rearchitecture, and interface redesign. Its engineers can analyze existing application infrastructure before deciding whether workloads should be rehosted, refactored, replatformed, or moved toward a more substantial architectural change. Database migration, code updates, deployment, testing, and documentation can be handled within the modernization engagement.

The company has a dedicated Los Angeles service presence and references modernization work involving subscription and billing platforms, ERP integrations, complex data migration, and broader digital infrastructure programs. That combination is relevant when modernization affects both application architecture and connected business systems. 

Slalom works on legacy modernization through application assessment, cloud migration, code analysis, refactoring, and staged replacement of outdated systems. Its AWS practice specifically covers modernization of legacy platforms into AWS-native architectures, including work involving COBOL, microservices, agent-assisted code analysis, and phased migration intended to limit disruption. 

The consultancy has a Los Angeles office and serves industries including entertainment, finance, healthcare, retail, technology, and higher education in the local market. Published modernization work also demonstrates experience mapping large legacy codebases and moving mainframe workloads into modern cloud environments.

EPAM's modernization practice covers applications, platforms, data, infrastructure, and legacy migration. Its legacy application work includes portfolio assessment, disposition planning, data migration, automated testing, managed services, and code transformation, including transitions from older mainframe technologies toward modern languages and cloud environments. 

The company maintains a Los Angeles office on Wilshire Boulevard. Its delivery model is particularly relevant to organizations with broad application estates where modernization extends beyond a single application and requires coordinated work across engineering, infrastructure, data, testing, and ongoing operations. 

Thoughtworks focuses directly on legacy modernization, including application, product, data platform, and mainframe transformation. Its work increasingly combines established incremental modernization techniques with AI-assisted analysis, helping engineering teams understand poorly documented systems, reproduce existing behavior, and move important functionality toward cloud-native platforms without treating the project as a single large cutover.

Thoughtworks lists Los Angeles as one of its US community hubs. The company's published projects include modernization of decades-old mainframe systems and legacy supply chain applications where understanding existing business logic is a central part of the migration process.

Accenture approaches legacy modernization as part of broader application and cloud transformation. Its services cover application estate assessment, architecture planning, application decomposition, cloud migration, mainframe transformation, integration, data migration, and phased modernization strategies designed around business continuity.

The company has a Los Angeles-area office in Culver City and has worked on large modernization initiatives connected to the region. One example involved moving Los Angeles County systems toward AWS while replacing selected legacy components with cloud-native services and maintaining the broader transition roadmap.

Deloitte provides application and legacy modernization services ranging from assessment and portfolio rationalization to code transformation, cloud migration, rearchitecture, and deployment. Its innoWake technology supports automated analysis and refactoring of legacy applications, including scenarios where older code and data need to be migrated to modern languages and platforms.

For organizations with mainframe or long-lived enterprise applications, Deloitte can also support phased modernization instead of requiring a single replacement event. The company has a substantial Los Angeles office in downtown LA, providing a local presence for broader consulting and technology programs.

Globant brings legacy modernization into larger digital engineering and integration programs. Its current modernization work includes legacy system assessment, API migration, integration-layer redesign, code migration, and decomposition of monolithic logic. The company's work with MuleSoft also illustrates an approach in which modernization begins by understanding existing dependencies before APIs and integration flows are rebuilt.

Globant has a Los Angeles-area office inside the Intuit Dome in Inglewood. That office supports its regional presence while the wider organization works across software engineering, digital platforms, AI, cloud, and transformation projects.

Sidebench is a Los Angeles software and product development company with particular experience in healthcare technology. Its work includes modernizing legacy systems, addressing interoperability problems, designing digital products, and connecting new applications with existing organizational infrastructure. This makes it relevant where modernization is closely tied to user-facing applications and workflow redesign rather than infrastructure migration alone.

The company has also worked with organizations in the Los Angeles public sector and maintains local contact operations. Its mix of strategy, UX, development, and systems integration can suit organizations that need to reconsider how an older platform functions for both staff and end users.

Frenchy Digital is a Los Angeles-based development agency that works on modernization, migration, application engineering, and ongoing software support. Its 2026 legacy modernization material covers system inventory, dependency analysis, characterization testing, code review, staged migration, and the use of AI agents to assist engineers with understanding older codebases.

The company also handles application and website migrations where integrations, infrastructure, security, deployment pipelines, and existing content or data have to move together. Its local office is on South Bentley Avenue, giving organizations in Los Angeles access to a locally headquartered development provider.

QServices explicitly offers legacy system modernization to Los Angeles businesses, although its engineering organization is remote rather than based in the city. Its work includes migration from older .NET and VB.NET environments, React front ends, Azure architecture, API development, data migration, and strangler-pattern replacement where individual modules move to a modern platform in stages.

The company describes Los Angeles engagements around media, healthcare, real estate, and logistics. Its delivery model includes Pacific Time overlap and optional on-site visits for major project milestones, making it an option for businesses comfortable working with a distributed engineering partner.

Metastability focuses on legacy rescue and modernization for systems that cannot tolerate a disruptive replacement. Its approach uses phased migration, with new components introduced alongside the existing application and production traffic shifted gradually after the replacement has been validated. Architecture mapping, risk analysis, documentation, monitoring, and post-launch maintenance can be included in the engagement.

The company identifies itself as a Los Angeles engineering partner and publishes a modernization case involving an aging VoIP platform where the old system remained operational during the transition. This narrower focus can appeal to mid-market businesses dealing with one difficult, business-critical application.