Fujitsu Limited and RIKEN have developed a 256-qubit superconducting quantum computer, which will be integrated into their hybrid quantum computing platform starting in Q1 2025. The computer builds on the 64-qubit version, launched with the Japanese Ministry of Education, Culture, Sports, Science and Technology’s support in October 2023. The 256-qubit superconducting quantum computer will enable users to tackle complex challenges like analyzing larger molecules and implementing error correction algorithms. The platform will also enable seamless collaboration between quantum and classical computers, enabling efficient execution of hybrid quantum-classical algorithms. The computer overcomes technical challenges, including appropriate cooling within the dilution refrigerator. Scalable 3D connection structure: Enables efficient scaling of qubit count without requiring complex redesigns by arranging 4-qubit unit cells in a 3D configuration; The 256-qubit machine utilizes the same unit cell design established in its 64-qubit predecessor, effectively demonstrating the scalability of this architectural approach. Quadrupled implementation density within dilution refrigerator: Quadrupled implementation density achieved within the dilution refrigerator, allowing the 256-qubit machine to operate within the same cooling unit as the 64-qubit system; Highly optimized design that carefully balances heat generation from control circuits with the cooling capacity of the refrigerator, while maintaining the necessary ultra-high vacuum and extremely low temperatures