As of 2016, the On-the-Fly Reprocessing (OTFR) system for HST data is being replaced with a new system, the HST Online Cache, to facilitate faster access to calibrated HST datasets which will now be stored as static files online. This is being done in a way that is transparent from the perspective of archive users, such that files are still requested using the same interface, just with improved access times. This also means that the old option of having to choose between retrieving "used" or "best" reference files is no longer needed, since each dataset retrieved from the online cache will have been processed and calibrated with the most up-to-date reference files available, and then stored in the online cache.
If new calibrations are subsequently produced and delivered by the HST instrument teams, then all relevant online HST datasets are identified for reprocessing and recalibration. In that case, the affected list of datasets is queued for reprocessing and recalibration. Given the amount of time required to reprocess and recalibrate all data that may be impacted by new reference files, there may be periods of time, after new reference file deliveries, during which retrieval of the affected data may take longer than usual as it goes through full reprocessing and recalibration, in order to ensure that the most up-to-date versions of the calibration files are used. Then, as the reprocessing and recalibration is completed for each dataset, the datasets will be placed into the online cache so that subsequent retrieval of these datasets would be as fast as possible, with the most up-to-date reference files applied.
As of January 2017, all HST data have been reprocessed and recalibrated and are available through the HST Online Cache. Any subsequent reprocessing of data will take place as appropriate, when new reference files or relevant calibration software updates are delivered.