A mostly-dormant format for years, STEP-XML is finding new use as AI and enterprise-based processes grow in influence across manufacturing
STEP-XML is a distinctive STEP data format aimed at supporting assembly data for complete model-based product definition. Known officially as ISO 10303 Part 28, the standard was originally published in 2007 but thus far has not been widely used. It has mainly been used by third-party plug-in modules to write out assembly data for long term data archiving. As of 2025, there are now some major CAD programs that directly write the STEP-XML format but most CAD users are likely not familiar with it. However, its distinct properties make it valuable to Large Language Model (LLM) AI and Model-Based Enterprise (MBE) processes, whose growth trajectory suggests the format may rise in prominence in coming years.
Differences Between STEP and STEP-XML
Most CAD users are familiar with STEP as the most common standards-based format to exchange model data between CAD/CAM software. (The effective exchange of data between product design, manufacturing, and inspection systems is referred to as "the digital thread.") The original STEP model file, known officially as ISO 10303 Part 21, was introduced in 1994 and has grown through several different application protocols (AP203 & AP214), leading up to the current unified AP242 standard published in 2014.
The part 28 STEP-XML files (which use the extension STPX) and original part 21 STEP files (which use the extension STP) complement each other similarly to how SolidWorks SLDASM and SLDPRT files complement each other (or Autodesk Inventor IAM and IPT files). Assembly file formats usually don't support part geometry definitions and STEP-XML follows that pattern. Proprietary CAD assembly formats traditionally only supported linking to the part formats from the same application, but the flexibility to link non-native files has been growing. STEP-XML assembly files have the full flexibility to link to CAD models in any format. Typically a STEP-XML assembly links to parts or sub-assemblies defined in standards-based formats like STEP-XML, STEP (AP242) or JT (ISO 14306) in order to maintain broad interoperability with CAD/CAM software of today and tomorrow.
The XML Standard: Readable by People and Machines
Users of manufacturing or engineering software may have heard of XML before. It is an open standard nearly as old as STEP and used widely by business application developers as a markup language and file format to exchange data. XML provides a text format readable by both humans and machines. The popularity and readability of XML is an attribute that has led to strong support by LLM AI, many models of which have been trained on structured data formats like XML.
In contrast, Part 21 STEP data is written using a specialized language called EXPRESS which generally requires special software libraries to interpret, such as the Kubotek Kosmos 3D Framework SDK.
XML Usage in CAD/CAM & Manufacturing
XML is also excellent for capturing hierarchical relationships in mechanical assemblies, so it has been used as the basis of a few significant CAD/CAM formats (these formats share the benefits of XML but are not directly compatible with STEP-XML).
- 3DXML: CAD users may be familiar with the proprietary 3DXML file format used by CATIA V6 and SolidWorks from Dassault Systemes
- PLMXML: Siemens Digital Industries Software has created a format called PLMXML for which they offer an open set of XSD definitions that document structure, content, and data types
- QIF: The QIF standard file format used in inspection and metrology, published as ISO 23952 in 2020, also uses the XML language
The QIF format has also inherited several of the important benefits found in STEP-XML but not found in the original STEP AP203 and AP214 application protocols. These modern standard CAD formats — QIF, STEP AP242, and STEP-XML — all provide support for assembly-level PMI and Unique Universal IDs (UUID). These features are critical to model-based processes for unambiguous product definition without reliance on generating derivative drawings, and for traceability of the digital thread.
CAD Software with STEP-XML Integration
Kubotek Kosmos is committed to STEP-XML and with the August 2025 release 7.1 of View and Convert programs has begun the rollout of multi-threaded read support for STEP-XML across all of our products. It is possible that many CAD/CAM users won’t see STEP-XML files anytime soon because they don’t need to receive the entire assembly structure for the work they do. Given the other advantages of STEP-XML, we aim to help them be ready when they do.
Working with Standards Committees
The STEP CAD file standards continue to evolve to meet manufacturing industry needs for data exchange of precise product definitions. Through partnership with the PDES/LOTAR organizations, Kubotek Kosmos actively participates in specification and testing work on the STEP standard. Kubotek Kosmos CTO/COO Ram Eswaran currently serves on the board of PDES, Inc., an international consortium helping public and private sectors effectively implement digital manufacturing standards.
