Japan – Sony Bank and Fujitsu have reported a 30% reduction in the development period for a core banking system after applying generative AI across processes from basic design through integration testing.
The companies began full-scale generative AI use in September 2025, using development assets including design documents, source code, and test assets to support multiple stages of system development. Results measured as of July 2026 showed a 30% shorter development period than conventional methods, along with a 40% reduction in man-hours.
The initiative uses Fujitsu’s Core Banking xBank solution, which is built on a cloud-native architecture and operates on Amazon Web Services (AWS). The environment has enabled the companies to introduce generative AI incrementally across different development processes.
An AI agent centred on Anthropic‘s Claude and Claude Code on Amazon Bedrock is used across the development lifecycle, with human oversight retained for final decisions, approvals and quality assurance. The companies said the approach has moved beyond proof-of-concept trials and has been incorporated into the development process for a core banking system in live operation.
Generative AI is being used across basic design, detailed design, implementation, unit testing and integration testing. Development assets created at earlier stages can be reused in subsequent processes, including generating source code and test cases from design documents.
The companies reported several specific efficiency gains. Impact assessment man-hours during basic design were reduced by up to 90%, while design document creation during detailed design fell by up to 40%. During implementation, the source code generation rate reached 99%, while test execution man-hours during integration testing were reduced by up to 90%.
The initiative also covers applications supporting banking operations, including online transaction processing and batch processing. Fujitsu personnel with expertise in financial operations and system development have been involved in evaluating and improving the AI-supported process as it is expanded.
The cloud-native and microservices-based architecture of Core Banking xBank has also supported the phased deployment. The companies said the AWS environment allows generative AI services to be integrated and tested quickly, while the microservices structure enables individual functions to be evaluated progressively.
The move comes as Japanese financial institutions face lengthy development cycles and high costs when launching new banking services. The companies said the growing maturity of generative AI is creating opportunities to incorporate the technology into live development environments rather than limiting its use to experimental projects.
“Sony Bank considers the advancement of system development capabilities as one of its critical management challenges to respond quickly to changing customer needs and business environments,” said Tatsuya Fukushima, Executive Officer at Sony Bank Incorporated.
“The successful full-scale application of generative AI to the development of our production core banking system is a significant step towards becoming a bank that continuously evolves based on AI. We will continue to promote our evolution into an AI-native bank while ensuring safety and quality through collaboration with Fujitsu, AWS Japan, and Anthropic,” Fukushima continued.
“Fujitsu is promoting the provision of ‘Core Banking xBank’ as a mission-critical foundation that supports the transformation of financial institutions,” said Masaru Yagi, Corporate Executive Officer and EVP at Fujitsu Limited.
“This initiative is an advanced example of the full-scale application of generative AI to the actual development of a core banking system on ‘Core Banking xBank,’ demonstrating a new model for financial system development. We will continue to collaborate with Sony Bank, AWS Japan, and Anthropic to further promote the practical application of AI in the Japanese financial industry,” Yagi continued.
“Applying generative AI across design, build, and testing in the live development of a bank’s core banking system, and achieving a 30% reduction in development time while maintaining the compliance and reliability the industry demands, is a significant milestone for the Japanese financial services. This is exactly the kind of initiative Amazon Bedrock was built to support,” said Yasuhiro Kose, Executive Officer at Amazon Web Services Japan.
“A banking system carries the trust of every customer, so it is essential that organisations use trusted AI that can be applied safely to work of this consequence,” said Hidetoshi Tojo, Executive Officer and Head of Japan at Anthropic Japan G.K..
“Sony Bank and Fujitsu are doing just that by applying Claude across the design, development, and testing of a production core banking system, with human judgment and quality assurance at every stage. We are proud to work alongside Sony Bank, Fujitsu, and AWS Japan on a model Fujitsu will now carry to other banks in Japan,” Tojo continued.
Sony Bank and Fujitsu plan to extend generative AI use across the wider development lifecycle, including requirements definition, as well as into areas such as security, operations and maintenance. They also intend to apply the knowledge and development assets generated through the initiative to peripheral systems.
Sony Bank said it aims to develop into an “AI-native bank” capable of responding more quickly to changing customer needs and business conditions.
Fujitsu plans to apply the development model to other financial institutions using Core Banking xBank. The company also intends to use insights from the initiative in its Uvance for Finance AI Transformation Platform, which is designed to support AI adoption among financial institutions.
