What happened

Nippon TmaxSoft first announced the project in Japan on 25 September 2026, in a press release distributed by Kyodo News PR Wire. According to that release, the project began in September 2021 and went live in June 2025, after about 45 months of development. The system is built mainly in COBOL, JCL and assembler, and the release describes it as a run-off system. In insurance, run-off usually means a book of policies that is no longer sold but still has to be serviced.

Sompo Japan chose to rehost: the application code stays largely as it was, and only the platform underneath changes. The release says rehosting was picked over rebuilding or rewriting so that the move could be done faster and with less risk. The trade site IT Leaders, published by Impress, reports that OpenFrame provides COBOL language processors, JCL, databases and transaction monitors on the new platform.

The release gives Sompo Japan's reasons. Mainframe running costs were hard to bring down as the system shrank, and hardware and software maintenance and renewals needed steady investment. Sompo Japan says it has now cut its mainframe maintenance costs and will put the savings into digital services. Neither company disclosed the size of the system, the budget or the savings.

TmaxSoft's chief executive, Lee Hyung-yong, said the Japan unit will be a base for expanding into other Asian markets, according to DigitalToday.

The other route: rewrite with AI agents

On 12 October, AWS published a blog post, written with Cognition, the company behind the Devin coding agent. It describes a workflow in which AWS Transform for mainframe reads COBOL, PL/I and JCL, extracts the business rules with links to the source lines, and writes requirements for each business function. Devin then proposes service boundaries, drafts specifications, turns them into a Jira backlog, writes code and tests, and opens pull requests.

The post puts people at several gates. Business owners confirm the requirements, architects approve the service design, and engineers approve every merge. Rules that nobody can explain are logged as open questions, and the related work waits until a named business owner answers. The post does not report measured results or name a customer.

In the words of AWS and Cognition, AWS Migration and Modernization Blog: "The requirements coming out of AWS Transform are evidence about how the mainframe behaves today"

Why it matters

Rehosting and rewriting solve different problems. Rehosting keeps the business logic and changes the cost base. Rewriting changes the logic's form and needs the business to confirm what the old code actually does. Sompo Japan's project shows that even the lower-risk route took close to four years for one system. Its own statement singles out the assembler code as part of what had to move safely.

What this means for mainframe teams

  • Migrations are long. A 45-month project means years of running the old and new estates side by side. The mainframe still has to meet its batch deadlines every night until the last workload leaves.
  • Know what you have. Code in COBOL, JCL and assembler moves differently. Assembler and undocumented programs are often where the time goes.
  • Moving code is not moving operations. Job order, restart steps, the jobs that may abend and what to do when they do: that knowledge has to move with the code, whichever route you take.
  • Measure before you move. Record run times, SLAs and failure patterns on the current system, so you can tell whether the new platform does the same work as well.
  • Keep the people who know. The AWS workflow stops when a business rule cannot be explained. The staff who can explain it are the ones to keep close during any move.

The bottom line

Sompo Japan picked the slow, careful route and kept its COBOL. AWS and Cognition are betting that AI agents can make the rewrite route practical. Either way, the work that stays on the mainframe during the move still has to run on time, and the people who understand it remain the scarcest part of any plan.

Sources

  • kyodonewsprwire.jp
  • it.impress.co.jp
  • digitaltoday.co.kr
  • finance.biggo.com
  • aws.amazon.com