A list of all relevant changes to build 13.0 of the JWST Operations Pipeline is provided in this article.

Build 13.0 was released as a build candidate in July 2026, and will be installed as an operations build in August 2026. The information provided here focuses mainly on updates to the JWST Science Calibration Pipeline and associated reference files, but includes information relevant to changes in other subsystems that might affect what users see in their data.

Major updates

Data affected by this build

Provided below is a list of science data products in MAST generated by the JWST Science Calibration Pipeline that may be most significantly affected by the updates in build 13.0. The changes listed in the release notes below may affect other modes as well, but many of these will be transparent to the MAST user.

The data and pipeline stages most affected include:

• All pipeline stages for new operational modes (NIRCam superstripe, NIRISS multistripe, MIRI subarrays and FASTGRPAVG)
• Stage 1 processing for some NIRCam subarray observations to improve reference pixel subtraction.
• Stage 3 processing for all imaging mode observations (results reported by the source_catalog step now employ source segmentation to deblend objects).
• Stage 2 and 3 processing for NIRSpec IFU observations (improved astrometric solution and source centroiding during spectral extraction).
• Stage 1 and 2 processing for NIRSpec BOTS and FS observations (enabled 1/f correction by default).

Release notes

Build 13.0 of the JWST Operations Pipeline was released as a candidate build on July 14, 2026 and will be installed as an operations build (13.0) for the Barbara A. Mikulski Archive for Space Telescopes (MAST) on August 25, 2026. The build includes changes to the JWST Science Calibration Pipeline released in version 3.0.0 of the jwst calibration pipeline package via the PyPI repository. This release also includes changes to the JWST Science Data Processing subsystem (SDP) version 2026.2.0 which is the DMS subsystem that creates raw (uncal) products used as input to the calibration pipeline.

Breaking changes

The use of correction_pars within level 2 processing steps barshadow , flat_field , master_background_mos , pathloss  and photom has been removed. They were used to support NIRSpec MSA processing within the Spec2Pipeline but are no longer needed. Any use of them is no longer supported.

The pipeline and single parameters for the cube_build step have been removed. These supported legacy, outdated methods and are no longer available.

The persistence step has undergone a complete rework—pipeline documentation covers the details, but the algorithm now flags pixels with persistence DQ flags for a time period after a saturation event occurs. The step is not enabled by default, but offline reprocessing may benefit from some experimentation.

General changes

Step status keyword values now support FAILED in addition to the default COMPLETE and SKIPPED values. FAILED will be used in cases where step processing is attempted and does not succeed.

The CRDS logger has been added to the stpipe configured loggers list, meaning CRDS log messages will be captured to the logs stored in datamodels.

Pipeline modules

Added S_REGION values to output "cal.fits" files from the Spec2Pipeline for WFSS modes.

Added the adaptive_trace_model step to the Tso3Pipeline.

Step change list

Changes to specific steps in the pipelines are listed below. 

Associations

• Exclude DHS subarrays from the TSO3 association rule.
• Enable creation of pure parallel associations for MIRI WFSS parallel observations.

adaptive_trace_model

• Add support for NIRSpec MOS, FS, and BOTS modes and MIRI LRS slit and slitless modes.
• Add multiprocessing support to adaptive trace model step. Processing time reduced by a factor of 7 for one NIRSpec IFU test case, fitting all 30 slices with 10 cores.
• For oversampled data, interpolate variance arrays as errors for correct weighting then square them afterward, instead of directly interpolating the variances.

ami_analyze / ami_normalize / ami_average

• Add U4COORD and V4COORD to the oifits q4 table.

assign_wcs

• Add chromaticity correction for NIRSpec IFU data by adding support for new "chromcorr" reference file type.
• Unset the S_REGION if the output WCS is not celestial (e.g., NIRSpec lamp exposures).

background

• Fix a bug that included reference pixel values in the SOSS background threshold mask generation.

clean_flicker_noise

• Catch NIRSpec-specific WCS errors and exit the step gracefully. Set the cal_step status to FAILED in this case and others for which processing was attempted but did not complete.

cube_build

• Clean up cube build interface, removing the parameters pipeline and single, which were intended for internal use only. Add a linear_wave parameter, which defines if the output cube has a linear wavelength sampling. The parameter has a default value of True.
• Wrap average RA values to the 0–360 degree range, to fix negative CRVAL1 values in output cubes.
• Fix memory leak by adding missing reference decrements for x_det and y_det.

dq_init 

• Update handling for superstripe exposures to work with a new specialized ramp datamodel (SuperstripeRampModel).

exp_to_source

• Check for an empty string in the slit source_name attribute, to fix an edge case bug in reducing fixed slit regions from NRS_MSASPEC exposures.

extract_1d

• For superstripe exposures, propagate the "int_times_stripe" table to extracted spectra if present.
• Update optimal extraction handling for spectral PSF reference files, to match a new schema that allows multiple apertures in the same reference file.
• Metadata improvements for FITS output for SOSS spectra: stop creating an empty SCI FITS extension containing only header values and stop adding an unnecessary INT_NUM value to EXTRACT1D extensions.

extract_2d

• Fix a bug that caused missing BUNIT header keywords for WFSS MultiSlitModels.

linearity

• Allow inverse linearity coefficients to be provided to the correction algorithm, if they are present in the reference file.

outlier_detection

• Reduce memory usage and improve runtime for rolling median used for tso data. For a MIRI dataset including 2 files each with 40 integrations the memory usage was reduced by a factor of 7 and runtime improved by a factor of 3.

pathloss

• Set the step status to SKIPPED for multi-slit data if no slits were corrected.

persistence

• Refactor the persistence step to implement a flagging window based on prior saturation.
• Improve support for batch processing by separating detector-level information and reusing the persistence array file.

picture_frame

• If MSA metadata files are missing and mask_science_regions is True, set the step to FAILED status and return instead of raising an exception.

pixel_replace

• Add a new algorithm option ("trace_model") to replace pixels from a spectral trace model, running the adaptive_trace_model step first if necessary, and replacing any remaining bad pixels with the mingrad algorithm if needed. Fix a bug in the fit_profile algorithm for IFU data that caused profiles to be fit to data across the whole image rather than just the current slice.

ramp_fitting

• For exposures with uneven readout sampling, set the fitting algorithm to LIKELY. This applies to some multistripe modes with repeated in-frame samples.

refpix

• Added the capability to specify siglimit for the sigma clipping algorithm.
• Propagate a zeroframe array if present for superstripe modes.

resample

• Corrected the "level" and "subtracted" keys in the output resampled model to show correct values for the resampled image.
• Fix a bug where combine_input_sregions would crash if any input image contained a multi-polygon S_REGION.

resample_spec

• Make sure no S_REGION is defined for resampled data that is not sky-like (e.g., NIRSpec lamp exposures).

source_catalog

• Change the default segmentation behavior to be deblend = True.

wfss_contam

• Add optional polynomial fitting of simulated source SEDs.
• Fix off-by-one bug in extraction region of simulated slits as compared with observed slits.
• Update slit metadata in the "contam" and "simul_slits" intermediate products.
• Fix a bug where bad wavelength sampling was causing Order 0 simulations to return all zeros for some filters.
• Process sources brightest first, and update contam estimate after every source, when polynomial fitting is requested.
• Subtract the flat-spectrum simulated contam estimate before the first iteration of polynomial fitting (when requested), making successful fits more likely in that first iteration.
• Remove empty ERR extensions from "_contam" and "_simul_slits" files.

white_light

• Add units to the flux columns in the white light table output.

Other Changes

• Remove usages of the schema-undefined model.meta.wcsinfo for MultiSlitModel types and use wcsinfo from the model's member slits instead.
• Numpy >= 2.0, Astropy >= 6.1.4, and Photutils >= 3.0 are now required.
• Expand stripe utilities to support pure superstripe modes with no reference pixels and stripe modes with repeated in-frame samples.
• Update stripe utilities to process superstripe data taken in non-TSO mode.
• Bumped minimum supported versions for asdf to 5.1, astropy to 7.2, requests to 2.32, scipy to 1.15.3, and synphot to 1.6. 

JWST Science Data Processing subsystem changes

• Implemented a different calculation for measurement time when NGROUPS==1 for all instruments. There are now 3 options: one for NGROUPS==1 when a zeroframe exists (mostly for NIRCam), one for NGROUPS==1 and there is no zeroframe (mostly for the other instruments), and the original calculation for NGROUPS != 1.
• Added two new subarrays for MIRI, the user-facing subarray names for SUBPRISM now include:
  • SUBPRISM -> SLITLESSPRISM
  • SUBPRISM_IP -> SLITLESSPRISM_IP
  • SUBPRISM_IPS -> SLITLESSPRISM_IPS
• Added CAL step keyword S_MIREMI, deleted S_NSCLEN and S_MRSMAT, and added available keyword option “FAILED” to the enum list for every CAL step keyword.
• NIRSpec calibration processing has a new Fore-optics Chromaticity Correction (chromcorr) reference file that is used in the existing assign_wcs step. Keyword R_CHRCOR was added to store the reference file name.