The API CK-4 oils will substitute the current API CJ-4 Engine oils and will be compatible with the majority of the applications whereupon the engine producers recommend currently CJ-4. The new CK-4 oils will provide a series of improvement over the CJ-4, including improved shear stability, oxidation resistance and aeration control.
Source: http://www.api.org/news-policy-and-issues/news/2016/11/18/new-api-certified-diesel-engine-oils-are