Although Bootstrap 4 is currently in its early alpha stage and has some key features missing, it continues to evolve with each new release. This constant evolution can make maintaining the framework a challenging task.
If you prefer stability, you can still rely on Bootstrap 3, which will receive official support even after the final release of v4:
In the foreseeable future, Bootstrap 3 will be maintained for critical bug fixes and documentation enhancements. The v3 documentation will also remain available after v4’s official launch.
(Source: Bootstrap's official blog)
It's important to remember that utilizing alpha or beta code in production environments is not recommended, even if you are eager to explore the latest advancements.