The tech preview implementation of the TDigest field directly exposes the merging strategy as a field parameter, corresponding to the four possible values of TDigestState.Type. Upon review however, we think this is too fine grained for the field configuration, and would rather expose something closer to the Percentiles Aggregation's execution hint, (see TDigestExecutionHint) which only has two choices default and high_accuracy, default in this case meaning optimized for performance.