Whereas AT commands are standardized in 3GPP TS 27.005 and 27.007 and all manufacturers need to implement them, there can be differences based on the modem type and vendor.
Based on the modem type - e.g. some power saving commands are only available on newer versions that also have the functionality. Also, parameters can be different because the modem does not support this specific radio type configuration or error code.
Often manufacturers introduce additional proprietary AT commands that either have new functionality or enhance existing AT commands. While these commands can be powerful, considerations for cross-vendor firmware need to be taken.