Information about what's new in the latest JWST pipeline build, and what was done in previous builds, is provided in this article. It also gives a preview of some updates likely to be coming soon in upcoming builds. The information contained here is generally a high-level summary of changes, with links provided to more extensive external documentation. 

Build lifecycle

JWST pipeline development proceeds according to a quarterly build schedule. Each quarter, the active development version of the JWST Science Calibration Pipeline is frozen, combined with other dependent software (e.g., the JWST Science Data Processing system; SDP) and a particular CRDS reference file context, and tagged to produce a candidate build. This candidate build is then tested extensively prior to becoming an operations build installed by the Data Management System (DMS) at STScI and used to reprocess all previous JWST data as well as newly obtained observations. Once a build is no longer operational, it becomes archived.

There are thus four kinds of builds:

• Development (Dev) build:  Changing daily, uses the Latest CRDS context, not recommended for non-developers.
• Candidate build: Development has finished, currently working on testing and documentation. Uses a fixed CRDS context. Available for experienced users.
• Operations build: Installed at STScI and being used to produce data products available in MAST. Uses a fixed CRDS context. Default recommendation for users.
• Archived build: Outdated operations build that is no longer recommended for general use (may still correspond to some MAST data products until reprocessing is completed).
  

Record of JWST Operations Pipeline builds

Table 1 provides a historical record of JWST operations builds, along with links to the build release notes and tagged software versions. The "CRDS Context" column indicates the fixed context used by default by each pipeline version. Note that many intermediate development tags of the JWST Science Calibration Pipeline (indicated by minor version releases of the jwst package) are never installed in STScI DMS operations, but can be installed by end users. For full information on all jwst releases, see the github software version table.

Table 1. Release notes and associated versions for JWST Operations Pipeline releases

What's new in the latest build?

The latest released JWST Calibration Pipeline is build 12.1. Some highlights are provided here about major relevant changes; please refer to the build 12.1 release notes for additional details.

Please also refer to the calibration notes broken down by instrument mode in the JWST calibration status articles, and the known issues with JWST data articles for instrument-specific information.

Major pipeline updates in build 12.1

• Updated the time-dependent sensitivity corrections for MIRI based on continued analysis of regular monitoring observations.
• Enabled the use of the first readout group by default for very bright MIRI pixels, improving pipeline recovery of fluxes for some sources that saturate in the 3rd group.
• Added automatic source centroiding for MIRI and NIRCam imaging time-series photometry, fixing an issue with extracted fluxes in cases where sources were not well-centered in the expected extraction aperture.
• Added a new option to automatically configure the 1/f correction step (clean_flicker_noise.autoparam=True) for NIRISS and NIRCam imaging. This correction is currently off by default but may be enabled in a future build.
• Major revision to the pipeline logging infrastructure; see ReadTheDocs for further information.

Major reference file updates in build 12.1

Build 12.1 is tied to the CRDS reference file context jwst_1464.pmap. Significant reference file deliveries included in this context include:

• Update to the MIRI MRS, imaging, and coronagraphic photometric calibration based on a reanalysis of standard star observations using the updated time-dependent loss models.  Changes will typically be largest (up to a few percent) for long wavelengths in programs observed during the 2025 calendar year.  Some coronagraphic observations have changed their absolute flux calibration by up to 15% due to a bug in prior calibrations.
• Shifted the MIRI boresight by 0.15 arcsec for consistency with the latest calibration of the fine guidance sensors. The absolute world coordinates reported for all MIRI data will change by 0.15 arcsec (jwst_1428.pmap).
• Improved the NIRCam coronagraphic distortion model (jwst_1417.pmap).
• Updated the NIRSpec IFU flux calibration for high- and medium-resolution gratings (jwst_1427.pmap).
• Updated the NIRSpec MOS pathloss reference files, improving flux calibration accuracy for off-center sources (jwst_1433.pmap).
• Updated bad pixel masks for multiple instruments.

Coming soon

The next JWST pipeline build is build 12.3 (release candidate expected Spring 2026). Build 12.3 will have a longer than usual development cycle, and there will be no build 12.2. The following list indicates some of the areas in which users can expect to see changes and updates in the coming months.

Pipeline development

Ongoing JWST Science Calibration Pipeline development work in build 12.3 includes:

• Support for new NIRCam dispersed Hartmann sensor observations
• Support for new MIRI WFSS observations and continued updates to WFSS contamination modeling.
• Support for new NIRISS SOSS multistripe observations.
• Runtime improvements for NIRISS SOSS
• Improved treatment of persistence flagging
• Improvements to WFSS background subtraction
• Improved MIRI MRS residual fringe correction
• Improvements for IFU resampling artifacts

Reference files

Major reference file updates currently planned for build 12.3 include:

• Updates to the NIRSpec IFU distortion solution.

Reference files

In the early phases of the JWST mission, reference file contexts updated frequently and data within MAST processed with a given build could thus have used different reference files.

As of build 11.1 (December 2024), JWST now uses a fixed CRDS reference file context for each pipeline build (see the CRDS overview and CRDS Migration to Quarterly Calibration Updates).

Ephemeris information

Note that ephemeris information (the 3-dimentional position and velocity as a function of time) for JWST can evolve between the initial processing of a dataset available through MAST and subsequent reprocessing of that data. The Flight Dynamics Facility (FDF) group at Goddard evaluates the ephemeris for JWST's orbit and releases a weekly update that includes the actual ephemeris up to a specific date, and a predicted ephemeris that is used for planning and executing upcoming observations. Both are stored in a database within minutes of the files being delivered by FDF, and the database is accessed by level 1 data processing in the operations pipeline. Subsequent weekly deliveries by FDF will update the predicted ephemeris database values.

To populate the ephemeris headers in the JWST data products, the JWST Data Management System (DMS) uses the definitive ephemeris values, or if they are not yet available, they use the predicted ephemeris values. Most data are initially processed with the predicted ephemeris values, while later reprocessing will use the definitive values. The header keyword EPH_TYPE lists if Definitive or Predicted was used. The ephemeris files (both definitive and predicted) are also ingested into MAST. The ephemeris is used for aberration correction in the WCS parameters in the science headers, so all science types are affected.

References

Bushouse, H., et al. 2023, Zenodo 
JWST Calibration Pipeline