Zephyr project is provided as source code and build scripts for different target architectures and configurations, and not as a binary image. Updated versions of the Zephyr project are released approximately every three-months.
All Zephyr project source code is maintained in a GitHub repository; you can either download source as a tar.gz file (see the bottom of the GitHub tagged releases page corresponding to each release), or use Git clone and checkout commands, such as:
git clone https://github.com/zephyrproject-rtos/zephyr cd zephyr git checkout tags/v1.13.0
The project’s technical documentation is also tagged to correspond with a specific release and can be found at https://docs.zephyrproject.org/.