Legacy System Migration Cost and Timeline Reduced by Approximately 60% — Proven in Core System with Hundreds of Thousands of Lines of Code

DEN-NO Solutions Inc. (Headquarters: Shibuya-ku, Tokyo; CEO: Masaki Ueno; hereinafter "DEN-NO") has successfully reduced both cost and timeline to approximately one-third (about 60% reduction) compared to conventional methods, while maintaining quality, in a core system migration project involving hundreds of thousands of lines of code conducted jointly with With One Co., Ltd. (Headquarters: Chuo-ku, Tokyo; listed on TOKYO PRO Market), using DEN-NO’s proprietary AI agent in collaboration with human engineers.

This case demonstrates that legacy system migration, which traditionally required significant time and expense, can now be executed within realistic cost and schedule constraints through the use of AI.

## Cost and Timeline of Core System Migration Reduced by Approximately 60%

### Why Many Companies Are Unable to Proceed with Migration

Modernizing legacy systems is an urgent priority for many enterprises. However, in practice, numerous companies continue to postpone migration despite requesting estimates from development vendors, as the quoted costs and timelines often far exceed acceptable limits.

The root cause lies in the conventional migration approach, which relies heavily on manual labor for all phases including code analysis, coding, and testing. As long as human labor is the foundation, there are inherent limits to reducing cost and time. DEN-NO addresses this structural challenge through a hybrid approach combining its proprietary AI agent with human collaboration. The effectiveness of this approach has now been demonstrated in an actual migration project.

### Project Overview

This project involved migrating a core system built on a legacy framework that has reached end-of-support to a modern programming language and framework.

- Target System: Core service management system (Scale: Hundreds of thousands of lines)
- Migration Scope: FuelPHP → Latest PHP + Laravel 12
- Implementation Structure: Joint execution by DEN-NO and With One Co., Ltd.
- Background: Urgent need to address security and BCP risks due to end-of-support for the language and framework. Previous consultations with multiple vendors failed to align on cost and timeline, resulting in delayed action.

### Results

Compared to estimates based on conventional methods, the following results were achieved:

- Cost: Approximately one-third (over 60% reduction)
- Timeline: Approximately one-third (same as above)
- Quality: The migrated system is operating stably in production, achieving quality equivalent to conventional migration methods.

(*Reduction effects may vary depending on the target system and requirements.)

### Two Key Mechanisms Enabling Significant Effort Reduction

The reduction is made possible not by generic AI tools or fully automated AI processes, but by combining a "proprietary AI agent dedicated to migration" with "human-led quality assurance."

On the technical side, DEN-NO’s in-house developed AI agent, specialized for migration workflows, automatically performs tasks from legacy code analysis and transformation to testing, drastically reducing manual labor.

On the quality side, all AI-generated outputs are reviewed by human engineers. Critical processes requiring business knowledge—such as acceptance testing and go/no-go decisions for production migration—are handled by experienced technical experts.

Speed and cost are compressed by AI, while quality is ensured by humans—this clear division of roles enables both cost reduction and quality preservation.

### Consultation Services

DEN-NO welcomes inquiries from companies struggling to initiate legacy system migration due to high cost and timeline estimates. We accept consultations regardless of the target system’s language or scale (migration feasibility assessed via free diagnosis).

#### Overview of Free Diagnosis

- Required Submission: System overview and partial source code (*after NDA execution)
- Deliverable: Diagnostic report summarizing current risks and migration feasibility
- Cost: Free (*Clients may decide whether to proceed with paid migration based on diagnosis results.)

This methodology is offered as a service under the name "DENNO AI Migration."

- Service Details: https://denno-sol.com/service/migration/
- Inquiries and Free Diagnosis Applications: https://denno-sol.com/contact/

Migration using this method is primarily conducted in collaboration with partner companies, including SIers. We welcome inquiries from SIers, development firms, and consulting companies interested in partnership via the contact link above.

### Company Overview: DEN-NO Solutions Inc.

Born as a startup from the University of Tokyo, DEN-NO Solutions is pioneering new value creation through AI, including the automation of system migration.

- Address: 609 Miyamasuza Building, 2-19-15 Shibuya, Shibuya-ku, Tokyo 150-0002
- Business: AI-powered system migration, AI solution development
- Website: https://denno-sol.com
- Email: info@denno-sol.com (*Media inquiries welcome)

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