Note: Upgrading the driver version to include CDRIVER-5925 requires a potentially involved libbson upgrade (SERVER-97106). To avoid waiting on this, we should cherry pick the changes made as part of CDRIVER-5925 within our vendored version of the driver (see Kevin's comment).

Setting the batch size of the watch to 0 will allow the server to return immediately and avoid having the operation run on the cluster even if the client crashes or abandons the cursor. 

mongocxx::options::change_stream options;
options.batch_size(0); // Send batchSize:0 to aggregate to have aggregate return immediately.
mongocxx::change_stream stream = collection.watch(options);