Mainframe migration and mainframe modernization are related but different problems. Understanding which one you actually have changes which companies are the right fit.
Migration is primarily about where the workload runs — moving from z/OS to cloud, from on-premises mainframe to hybrid infrastructure, from one platform to another. The application logic may or may not change significantly in the process. The primary risk is operational: keeping production running during the transition.
Modernization is primarily about how the application works — updating the architecture, the language, the development practices, the operational model. The workload may stay on the same infrastructure during modernization or move to new infrastructure as part of it. The primary risk is fidelity: ensuring the modernized system does what the original did.
Most real programs involve both. You’re moving the workload and changing how the application works simultaneously — which is where the complexity compounds and where the companies that handle both well become significantly more valuable than those that specialize in one.
Before building a vendor shortlist, Recode is a platform for finding and comparing companies in software modernization, application migration, and legacy transformation — useful before you start narrowing.
1. Corsac Technologies
Website: corsactech.com
Location: United States
Founded: 2007
Team size: 50-249
Core stack: Hybrid cloud (AWS/Azure/GCP), DevOps/DevSecOps, CI/CD pipelines, app & data modernization, security/compliance practices, rehosting/replatforming/refactoring patterns, mainframe integration patterns
Corsac Technologies uses an AI-driven software modernization approach to accelerate mainframe migration and modernization simultaneously — handling the application analysis, dependency extraction, business logic documentation, and risk reduction that both workstreams require. What makes their approach particularly relevant for combined migration-and-modernization programs is the analysis phase: their AI framework produces system visibility before any architectural or infrastructure decisions get locked in.
Their RAG architecture treats the mainframe codebase as a searchable dataset rather than a system to be manually decoded. The Multi-Agent Swarm maps migration dependencies and modernization complexity simultaneously — identifying which components can migrate cleanly, which require modernization before migration, and which carry hidden dependencies that would surface as production incidents if migration proceeded without understanding them first. The dependency graph and complexity heatmap that result inform both the migration architecture and the modernization roadmap.
Canary deployments handle the migration cutover with automated rollback built in. Dual-environment parallel operation keeps legacy mainframe running until the migration is validated. SOC 2 Type II, HIPAA, PCI DSS, GDPR certifications cover the regulated industries where both migration and modernization require compliance sign-off.
Key differentiator: AI-driven analysis that informs both migration architecture and modernization roadmap simultaneously — the foundation that prevents mid-program scope discoveries
2. Reliqsy
Website: reliqsy.com
Location: United States
Founded: 2014
Core stack: RAG, Multi-Agent Swarm, AI-powered code analysis, dependency mapping, technical debt auditing, behavioral validation, dual-write synchronization, automated rollback, canary deployments
Reliqsy combines AI with the practical expertise of modernization and migration specialists — using an AI-powered approach to analyze legacy mainframe code, extract business logic, and accelerate both refactoring and migration processes. The dual challenge of migration and modernization is where Reliqsy’s governance model is most relevant — because both processes carry distinct risks that need to be managed simultaneously rather than sequentially.
For migration specifically: dual-write keeps mainframe and target environment databases synchronized throughout, automated rollback fires at concrete thresholds if migration degrades performance, and SRE oversight maintains manual override capability during traffic shifting. For modernization specifically: behavioral validation confirms the modernized code replicates original mainframe behavior, Pull Request review gates every AI-generated change before production, and the modernization roadmap requires engineer sign-off before code generation starts. Both processes get governed through the same Migration Health Dashboard giving stakeholders unified visibility.
Key differentiator: Unified governance across migration and modernization simultaneously — risk controls for both workstreams in one framework
3. IBM
Website: ibm.com
Location: 170+ countries
Founded: 1911
Team size: 300,000+
Core stack: IBM Z / z/OS, Red Hat OpenShift, IBM Wazi, watsonx Code Assistant for Z, IBM Z & Cloud Modernization Stack, Ansible, hybrid cloud integration
IBM’s strength in combined mainframe migration and modernization is the coexistence model — their IBM Z & Cloud Modernization Stack enables mainframe workloads to run alongside cloud-native applications rather than requiring full migration as a precondition for modernization benefits. Organizations can expose mainframe capabilities via APIs to modern applications, modernize incrementally while keeping z/OS running core workloads, and migrate specific workloads to cloud when the modernization makes that feasible rather than as a prerequisite.
Key differentiator: Mainframe-and-cloud coexistence model — migration and modernization as parallel tracks rather than sequential phases
4. Kyndryl
Website: kyndryl.com
Location: 66 countries
Founded: 2021
Team size: 80,000
Core stack: Kyndryl Bridge (AIOps), IBM Z integration, AWS/Azure/GCP hybrid delivery, AI & GenAI modernization support, automation
Kyndryl’s multi-path approach to mainframe migration and modernization — supporting rehosting, replatforming, refactoring, and full off-mainframe moves — means the path gets determined by actual analysis rather than a preset methodology. Their Kyndryl Bridge AIOps platform gives organizations operational visibility during the parallel-run phase when legacy mainframe and modern environments run simultaneously — which is the period where operational risk is highest in any combined migration-modernization program.
Key differentiator: Multi-path migration and modernization with AIOps visibility during parallel operation — operational intelligence when both environments are running simultaneously
5. Accenture
Website: accenture.com
Location: Global
Founded: 1989
Team size: 1,000-9,999
Core stack: Hybrid cloud (AWS/Azure), API integration, DevOps/CI/CD, portfolio rationalization, rehosting/replatforming/refactoring patterns
For combined mainframe migration and modernization programs, Accenture’s portfolio rationalization work addresses the sequencing question that most organizations get wrong: which workloads should migrate first, which should modernize before migrating, and which should be retired rather than either migrated or modernized. Getting that sequencing wrong creates migration programs that move technical debt to new infrastructure rather than eliminating it.
Key differentiator: Migration and modernization sequencing through portfolio rationalization — determines the right order before execution budget gets committed
6. Luxoft
Website: luxoft.com
Location: 29 countries
Founded: 2000
Team size: 12,900
Hourly rate: $50-$99/hr
Core stack: COBOL, Assembler, IMS, JCL, tool-assisted modernization, CI/CD enablement, automated testing
Luxoft’s direct mainframe language expertise — COBOL, Assembler, IMS, JCL — is particularly valuable in combined migration-modernization programs where the application behavior needs to be understood precisely before either the migration architecture or the modernization approach gets defined. Automated testing validates behavioral parity at each stage of both the migration and the modernization, giving organizations evidence that what arrived at the new environment does what the original mainframe did.
Key differentiator: Direct mainframe language depth informing both migration architecture and modernization approach — behavioral testing across both workstreams
7. HCL Tech
Website: hcltech.com
Location: India (global)
Team size: 200,000+
Core stack: Hybrid mainframe + cloud modernization, AI-driven code analysis, proprietary accelerators, rehost/replatform/refactor frameworks, IBM Z ecosystem alignment
HCLTech’s business capability-led approach applies to combined migration-modernization programs in a useful way — grouping related mainframe applications by business function and determining the right migration-modernization combination for each group rather than applying a single approach across the portfolio. Some business capabilities warrant full modernization before migration. Others can migrate first and modernize on the new platform. HCLTech’s framework supports both.
Key differentiator: Business capability-led sequencing for mixed migration-modernization portfolios — different approaches for different application groups
8. CGI
Website: cgi.com
Location: Montreal, Canada (global)
Founded: 1976
Team size: 94,000
Core stack: CGI M8 automated modernization environment, Unix/Linux migration targets, tool-assisted refactoring/replatforming, portfolio migration frameworks
CGI’s M8 automated environment handles mainframe-to-Unix/Linux migrations at portfolio scale — which is the migration path that most commonly accompanies mainframe modernization for organizations moving off z/OS entirely. Their documented cost reduction outcomes and portfolio migration frameworks reduce the timeline and financial risk of large combined programs. Fifty years of mainframe delivery experience means edge cases get handled by people who’ve seen them before.
Key differentiator: Portfolio-scale mainframe-to-Unix/Linux migration with M8 automated tooling and documented cost outcomes
9. Astadia
Website: astadia.com
Location: United States
Founded: 2002
Team size: 350
Core stack: Astadia FastTrack methodology, automation suite, GenAI support, automated testing, cloud-ready replatform/refactor routes, AWS partnership
Astadia’s combined migration-modernization approach is specifically built for organizations committed to cloud as the target — their FastTrack methodology and GenAI-assisted code conversion handle the mainframe application transformation required to make migration to cloud architectures viable. The AWS partnership gives them direct leverage on AWS-target programs. For organizations that have decided on cloud as the destination for both their migration and their modernization, their specialist focus on that combination is directly relevant.
Key differentiator: Combined mainframe migration and cloud modernization with GenAI-assisted conversion — specialist focus on the cloud-target combined program
10. Wipro
Website: wipro.com
Location: India (global)
Founded: 1945
Team size: 250,000+
Core stack: AI-driven code analysis, automation accelerators, rehost/replatform/refactor + hybrid integration, DevOps + CI/CD enablement, governance frameworks
Wipro’s combined mainframe migration and modernization services embed CI/CD from the start of both workstreams — so the result of the combined program isn’t just a migrated and modernized mainframe, it’s a system that’s easier to change and operate on the new platform than the mainframe was on the old one. For organizations in banking, telecom, and retail where the combined program needs to satisfy regulatory governance throughout, their compliance frameworks address that requirement continuously rather than at final validation.
Key differentiator: CI/CD and compliance governance embedded throughout combined migration-modernization delivery
How to Choose Mainframe Migration and Modernization Companies
Clarify whether you need migration, modernization, or both
Before evaluating any company, be specific about which problem you’re solving. Migration without modernization moves your mainframe workload to new infrastructure but doesn’t change how the applications work — useful for cost and operational reasons, but it brings the technical debt with it. Modernization without migration may keep the workload on the same infrastructure while changing how applications are built and maintained. Most programs involve both, and the companies that handle the combined program well are different from those that specialize in one. Defining what you actually need changes which evaluation criteria matter most.
Evaluate the analysis phase methodology specifically
Combined migration-modernization programs fail when the analysis phase is wrong — when the scope of the migration is underestimated because the mainframe dependencies weren’t fully mapped, or when the modernization approach is chosen before the application complexity is understood. Ask how companies conduct the analysis phase for combined programs: how they map migration dependencies, how they assess modernization complexity, and how they use that analysis to sequence the combined program rather than just estimating timeline.
Ask about parallel operation capability
The highest-risk phase of any combined migration-modernization program is when both legacy mainframe and modern environments run simultaneously. How long that phase lasts, how both environments are monitored, what triggers cutover, and what triggers rollback — these are operational questions that reveal whether a company has run real combined programs or is proposing an approach that sounds reasonable on paper.
Check cutover risk controls for the combined program
Migration cutover and modernization validation are distinct risk events that need distinct controls. Ask specifically how companies manage each: what the data synchronization approach is during migration cutover, what the behavioral validation approach is during modernization, and how both sets of controls interact when migration and modernization happen simultaneously.
Look for companies that sequence migration and modernization intelligently
Some mainframe applications should modernize before migrating. Others can migrate first and modernize on the new platform. Others should be retired rather than either migrated or modernized. Companies that apply a single approach to all workloads regardless of these differences don’t produce programs that reflect actual complexity. Ask specifically how companies make sequencing decisions for mixed migration-modernization portfolios. For a broader comparison of mainframe migration and modernization companies, Recode lets you search and compare vendors across software modernization, application migration, and legacy transformation.
