Not sure you mean the limit of data size in gzip the app has to download?
I can't find the limit in the document, and I believe that there is no size limit, as explains in the following post.
Anyway, the limit seems to be the number of instruments, and it has some info on the following page.
For the Composite.
60000 instruments before file code and chain expansion;
150000 after file code and chain expansion.
You can find information about other limits for the extraction from the DSS BEST PRACTICES AND LIMITS document.
Assuming I have 30 ContentFieldNames in my request when calling the Composite Request API, does that mean that for an API call, I can request up to 60000 instruments in my IdentifierList, and I should expect a response of the 60000 instrument details?