Stairway unveils step 5 preview model, enters top three of global open-source AI rankings

On September 20, 2026, Stairway announced the release of its flagship model, Step 5 Preview, designed for AI programming, software engineering, and professional tasks such as finance. The model will be fully open-sourced on October 15, 2026. It features a sparse MoE architecture with 600B total parameters and 27B active parameters, supporting a 1 million token context window. It scored 44 on the Artificial Analysis Intelligence Index (AA), placing it among the top three open-source models globally. Its single-task cost is 1/8 that of Anthropic’s Claude Opus 5. The Step 5 Preview model was tested on StepCodeBench, covering 553 code repositories, 9 task types, 20 application domains, and 33 programming languages. It can handle bug fixes, feature development, code refactoring, and environment configuration. It also autonomously transforms an ESP32-S3 board into a Vibe Coding keyboard with Bluetooth and voice input, capable of running for over three hours. In benchmark tests, Step 5 Preview performed well in complex software engineering, professional work, and financial tasks, ranking second to GPT-6 Astra or Claude Opus 5 in evaluations like ALE-CLI, FrontierFinance, and DRACO.