Hardware Lab Kit API Updates and New Unreferenced File Check in February Refresh
What’s Changing? The refreshed Windows Hardware Lab Kit (HLK) available starting February 2026 for Windows 11, version 25H2, Windows Server 2025, and Windows 11, version 24H2 will introduce a new check during HLK packaging. If the attached driver package includes one or more files that were not referenced by an .inf, the following warning will display at the end of packaging: This will not affect package generation. Even if the warning appears, an .hlkx will still be created regardless. It is highly recommended to validate that all files are referenced before testing. To do so, attach the driver package, create an .hlkx package (test results not necessary), and observe whether the warning appears. This validation can be performed any time after target selection. The PackageWriter class in the Microsoft.Windows.Kits.Hardware.ObjectModel.Submission namespace will include the following updates: The AddDriver and AddReplacementDriver methods will include a new check for files in the driver package that were not referenced by an .inf file. This information will be available through the warningMessages output arg. There will also be new AddDriver and AddReplacementDriver overloads that expose the unreferenced file information through new output arguments in addition to warningMessages. See Creating a Package for code samples accessing data on unreferenced files using the updated API. See Microsoft Learn for more details. Actions Required To address an unreferenced file, first navigate to the log path to see which attached files were not referenced. If creating an original submission package... Option 1 (recommended): Remove the driver package from the project. Remove the unreferenced files from the driver package, then re-attach. Option 2 (recommended): Remove the driver package and modify the .inf to reference all the files. Re-test the driver and attach the modified driver package. Option 3: Keep the driver package attached, even with the unreferenced files. If submitting to HDC, please see this documentation for any policy updates regarding submissions with unreferenced files. If creating a DUA package... Option 1 (recommended): Replace the attached driver package with a new one. Before re-attaching, remove any unreferenced files from the driver package. Option 2: Create a new original submission. Modify the .inf to reference all the attached files. Re-test the driver and attach the modified driver package. Option 3: Keep the driver package attached, even with the unreferenced files. If submitting to HDC, please see this documentation for any policy updates regarding submission with unreferenced files. Tips The new unreferenced file check supports most compressed files. If a file is compressed and its extension ends in “_”, the new warning will not appear so long as the decompressed version of the file is properly referenced by the .inf. If a .cab is included as a source location in the .inf’s [SourceDisksNames] section, HLK will examine the .cab’s contents during the unreferenced file check. If a .cab is referenced as a driver file in the .inf, it will be treated as such during the unreferenced file check, and the .cab’s contents will not be examined. What is not supported: Attaching compressed .cat files. Attaching double-compressed files (e.g. A user compresses a file individually, and then packs the already-compressed file into a cab. Or a user compresses files into a .cab, and then compresses the .cab a second time so it now ends with an underscore). Troubleshooting Issue: “Failed to analyze driver package for unreferenced files” This means that the HLK was not able to successfully finish the unreferenced file check. It does not indicate whether the attached files were referenced or not. Confirm there are no files missing from the attached driver package (i.e. the .inf referenced a file, but the file wasn’t attached). Issue: A file is being identified as unreferenced, but the .inf includes the file. It could be that the file is included in the .inf, but the .inf section that it’s in is not referenced properly. Run infverif to identify any unreferenced sections. Also, check whether the file should (or should not) be placed under a subdirectory. The relative path of each driver file in the attached package must exactly mirror what is specified in the .inf file. Issue: An .inf is being identified as an unreferenced file. Confirm that the .inf is placed at the top root of the driver package (not in a subdirectory). Issue: How do I check whether a file is signed? Please see How to validate the Microsoft signature - Windows drivers | Microsoft Learn Related Links Add driver and supplemental content to your package | Microsoft Learn PackageWriter.AddDriver Method | Microsoft Learn PackageWriter.AddReplacementDriver Method | Microsoft Learn Creating a Package | Microsoft Learn For additional questions/assistance, please reach out to Microsoft support team by creating a support ticket here - Windows HLK Support
