The AS400 isn't the problem. Isolation is.
The IBM AS400, now known as IBM i, is one of the most reliable platforms ever built. Systems that have been running uninterrupted for decades, with uptime that modern cloud architectures can only envy. The DB2 for i database is integrated into the operating system. Security is native. Transactional performance is excellent.
The real problem isn't the AS400 itself, but its isolation. These systems contain enormously valuable data and business logic, but they're often only accessible through 5250 terminals or RPG/COBOL applications that only talk to themselves. In a world where every system must expose APIs, produce events, and integrate with cloud services, the AS400 risks becoming an island.
The good news is that today tools exist to open that island without demolishing it. Anthropic's Model Context Protocol, combined with IBM i's native capabilities, offers a modernization path that doesn't require rewriting anything.
MCP: the universal gateway between Claude and legacy systems
The Model Context Protocol is an open protocol developed by Anthropic that standardizes how AI models connect to external data sources and tools. It works like a universal interface: on one side Claude, on the other any system, including an AS400.
An MCP server is a program that exposes 'tools', functions that Claude can invoke. When Claude needs data or wants to perform an operation, it calls the appropriate tool through the MCP protocol. The server translates the request into the destination system's language and returns the result.
For AS400, this means Claude can query DB2 tables, execute SQL queries, read system metadata, monitor active jobs, and potentially invoke RPG and COBOL programs. All through a standardized and secure interface.
MCP servers for IBM i: a growing ecosystem
The MCP ecosystem for IBM i has developed rapidly in 2025-2026. IBM itself has released an official MCP server in beta, with tools for performance monitoring, security, job management, and database operations. The stated goal is to reach hundreds of native tools by the end of 2026.
In parallel, the community has developed complementary solutions: MCP servers for AI-assisted development, source member management, and AS400 interaction through the 5250 terminal interface. Leading IBM i ISVs are also integrating MCP support into their products.
But the existence of generic tools isn't enough. Every company has a different IBM i environment: specific libraries, custom programs, proprietary data structures, integrations with external systems. The real value lies in the ability to configure and customize the MCP integration for the specific context, connecting Claude not to a generic AS400, but to your AS400, with your business logic.
How the Claude-AS400 integration works
The integration between Claude and an AS400 system via MCP follows a multi-layered architecture. Claude communicates with an MCP server that acts as a bridge: it receives requests from the AI, translates them into operations the IBM i can understand (SQL queries, system commands, object reads) and returns results in a structured format.
The connection to the AS400 can occur through various mechanisms native to the IBM i platform, chosen based on the client's specific environment and required operations. Each tool exposed by the server corresponds to a concrete operation on the system: querying the database, monitoring a process, reading a source file.
Designing this architecture is the crucial step. It's not about installing off-the-shelf software: you need to define which operations to expose, at what granularity, which security controls to apply, and how to handle the IBM i environment's specificities. It's system integration work in the truest sense of the term.
Concrete use cases: what Claude can do with your AS400
Once connected via MCP, Claude becomes an intelligent interface to your AS400 system. The most immediate high-value use cases are manifold.
Conversational business intelligence: users can ask questions in natural language, such as 'What's the revenue by customer for the last 6 months?', and Claude translates the request into SQL queries on DB2, executes the query via MCP, and presents results in an understandable way.
Monitoring and troubleshooting: Claude can monitor active jobs, check queue status, analyze error logs, and suggest corrective actions. An operator can ask 'Why is the billing job stuck?' and get a contextual analysis.
On-demand documentation: Claude can read RPG and COBOL program source members directly from IBM i libraries and produce up-to-date technical documentation in real time.
Development assistance: IBM i developers can use Claude as a copilot for writing SQL queries, CL programs, RPG and COBOL code, with Claude having direct access to the database catalog to suggest correct tables, fields, and relationships.
REST APIs from AS400: the natural complement to MCP
Alongside the MCP approach, there's a complementary strategy that leverages IBM i's native capabilities: exposing existing RPG and COBOL programs as REST APIs, without modifying a single line of source code.
IBM i has native tools that allow making any ILE program callable via HTTP, transforming established business logic into services consumable by modern applications. The most recent platform versions have further enhanced these capabilities.
This approach complements MCP: REST APIs expose transactional functionality, MCP makes it accessible to Claude for intelligent analysis. The result is an AS400 system that maintains all its reliability and business logic, but becomes accessible to both modern microservices and artificial intelligence. The key is designing the right combination of these two strategies for your specific context.
The Strangler Fig strategy: modernize without demolishing
The approach we recommend isn't 'replace the AS400' but 'open the AS400.' It's called the Strangler Fig Pattern, like the strangler fig tree that grows around an existing tree without felling it.
Start by exposing existing functionality as services: REST APIs via IWS for transactional operations, MCP for intelligent access to data and metadata. New development is done in modern languages consuming these services. Over time, functionality is gradually replaced, but the core system continues to operate throughout the transition.
There's no big bang, no risk of operational shutdown, no need for a multi-million budget for a total rewrite project. You proceed module by module, measuring results at every step.
Starting the journey: the Maverick AI approach
Maverick AI specializes in integrating Claude with enterprise systems, including IBM i/AS400 environments. Our approach always starts with a technical assessment of the existing environment, to define the most suitable integration architecture for the client's specific context.
Results are tangible: business users querying AS400 data in natural language, developers writing code assisted by Claude, IT operations with intelligent system monitoring. All without touching the established business logic that already works.
If you have an AS400 and want to understand how Claude can integrate with your system, contact us for more information.