OS/400
OS/400 is the original name of the operating system IBM now calls IBM i. It shipped with the AS/400 on August 26, 1988, became i5/OS in 2004 and IBM i in 2008, so the RPG, COBOL and Db2 for i objects that today's AI tools read sit on one unbroken operating system line.
What OS/400 is
OS/400 is the first name of the operating system that runs AS/400 and IBM i machines. IBM shipped it on August 26, 1988. It was built from an earlier IBM operating system called CPF, which ran the System/38, and it could also run older System/36 work. Its database was part of the operating system from the start, not a separate product you bought. That database got the name DB2/400 in 1994 and is called Db2 for i today.
How the name changed over time
One operating system, three names
- Aug 26, 1988OS/400 ships with the AS/400.
- Dec 22, 1995Release V3R6 ships. It is the first OS/400 release that runs on PowerPC chips.
- Jun 11, 2004Release V5R3 ships as i5/OS. IBM describes it as a different name for the same operating system.
- Apr 2008IBM renames i5/OS to IBM i and folds System i into IBM Power Systems. Release 6.1 had shipped that March.
- Apr 18, 2025IBM i 7.6 ships, the newest release in the same line.
Release dates from IBM's own IBM i release life cycle page.
Can you still run OS/400 today?
Not with IBM support behind it. Every release that carried the OS/400 name is past its end of support date. The machine may still boot and still run the business, but IBM has stopped fixing it.
When IBM support ended, by release
| Release | Name it shipped under | IBM support ended |
|---|---|---|
| V5R2 | OS/400 | April 30, 2007 |
| V5R3 | i5/OS | April 30, 2009 |
| V5R4 | i5/OS, later IBM i 5.4 | September 30, 2013 |
| 6.1 | IBM i | September 30, 2015 |
| 7.4 | IBM i | September 30, 2026 |
| 7.5 | IBM i | Not yet announced |
| 7.6 | IBM i | Not yet announced |
IBM says the change in service level for 7.5 and 7.6 will be announced with at least 12 months of notice.
After September 30, 2026, IBM i 7.4 joins the unsupported list. That leaves 7.5, shipped May 10, 2022, and 7.6, shipped April 18, 2025.
Why OS/400 still matters for AI work
Because the old code did not have to be rewritten. OS/400 programs are not compiled straight down to the chip. They are compiled to a middle layer called the Technology Independent Machine Interface, or TIMI. Think of TIMI as a recipe written so any kitchen can cook it. When IBM swapped the original 48-bit chips for PowerPC in 1995, the operating system threw away the old machine instructions and translated the recipe again for the new chip. Programs kept running without being recompiled.
So the RPG and COBOL programs and Db2 for i tables an AI tool reads on a modern IBM Power server can be the very same objects a shop compiled under OS/400 decades ago. The business rules an AI assistant is asked to explain are often older than the hardware they sit on.
TIMI kept programs running across the chip change. It does not upgrade them. An AI tool still has to read whatever the original programmer wrote, and IBM does not publish a minimum IBM i release for watsonx Code Assistant for i or the IBM i MCP Server.
Related Terms
IBM i
IBM's operating system for Power servers running traditional AS/400-lineage business applications, with Db2 for i built directly into the OS.
AS/400
IBM's original 1988 midrange business computer platform; the term is still used informally to refer to IBM i systems and shops even though IBM has rebranded the hardware and OS multiple times since.
Db2 for i
The relational database management system built into every IBM i operating system, tightly integrated with IBM i rather than a separately installed database product.
RPG
Report Program Generator, the primary business application programming language on IBM i and its AS/400 predecessors, still running the majority of production logic in most IBM i shops.
COBOL
A long-established business programming language still running production logic on IBM i and other legacy enterprise platforms alongside RPG.
watsonx Code Assistant for i
IBM's November 2025 preview announcement of an AI code assistant purpose-built for RPG on IBM i. The preview track was superseded by IBM Bob, which reached general availability in March 2026.
IBM i MCP Server
An open-source, IBM-published server implementing the Model Context Protocol (MCP), letting AI agents and LLMs query Db2 for i data and take defined actions on IBM i using natural language. In beta since October 2025.
Profound AI
Profound AI connects AI models to your IBM i system. Built by Profound Logic, it lets hosted and on-premises large language models work with Db2 for i tables, RPG and COBOL programs, service programs and web services, and it has supported the Model Context Protocol since June 2025.