Q: How often is the online edition of CMOS updated? 

A. Your question is frequently asked and is answered on the Manual’s FAQ page:

The editorial guidelines presented in the 17th edition of The Chicago Manual of Style will remain consistent throughout the life of the edition and in all formats in which the Manual is published. In other words, no changes in styles or rules will be made to the current edition, either in print or online.

Moreover, the content of the Manual online is intended to be identical to the content of the printed book. Occasionally, however, a typographical correction or other minor clarification is needed. Such errors will be corrected online as soon as they are discovered and will also be corrected in subsequent impressions of the printed book.