Release of HDF5 2.1.0 (Newsletter #209)

Following the major milestone of HDF5 2.0.0, we are pleased to announce the release of HDF5 2.1.0. As the first minor release in the 2.x series, version 2.1.0 focuses on expanding support for modern hardware datatypes and improving the developer experience for Fortran users.

The HDF5 2.1.0 release is now available from the HDF5 2.1.0 download page.

What’s New in 2.1.0

This release introduces targeted features that enhance performance and compatibility for AI and high-performance computing (HPC) workflows.

• Improved I/O performance on chunked datasets for specific cases: HDF5’s data sieving functionality has been enabled when performing I/O on dataset chunks that aren’t cached, significantly improving performance for specific I/O patterns and chunk sizes.
• Support for New Low-Precision Datatypes (FP4 and FP6): Continuing our commitment to modern AI/ML workflows, HDF5 2.1.0 adds predefined datatypes for 4-bit and 6-bit floating-point formats.
  • FP6: Support for E2M3 and E3M2 formats.
  • FP4: Support for the E2M1 format.
  • Note: Conversions are currently emulated in software, providing immediate compatibility for specialized hardware buffers.
• Expanded Fortran Support for SWMR: We have added new Fortran wrappers that provide direct access to Single Writer Multiple Reader (SWMR) functionality, including:
  • h5fstart_swmr_write_f to enable SWMR mode.
  • h5dflush_f and append flush property wrappers to manage data consistency during concurrent access.
• Fixed three critical CVEs that lead to heap-based buffer overflows*.
  • CVE-2025-2309, a critical vulnerability affecting the function H5T__bit_copy of the component Type Conversion Logic.
  • CVE-2025-2308, another critical vulnerability affecting the function H5Z__scaleoffset_decompress_one_byte of the component Scale-Offset Filter.
  • CVE-2025-44904, another vulnerability in the H5VM_memcpyvv function.
• Improved support for libaec detection: We have added a new CMake module to improve finding libaec compression libraries on the system.
• Maintenance & Stability: This release includes various bug fixes and stability improvements discovered during the rollout of 2.0.0. We have also addressed specific platform issues, including fixing issues with complex number support detection for MSVC.

Migration & Compatibility

As a minor release, HDF5 2.1.0 is backward compatible with 2.0.0. It continues the transition to CMake-only builds, so users who have not yet migrated their build scripts from Autotools should refer to our 2.0.0 Migration Guide.

Key Links:

• Full CHANGELOG
• README (includes release schedule)
• Support Forum

We would like to thank the community members whose contributions and feedback helped shape this update. If you have questions, please contact us at help@hdfgroup.org.

* This material is based upon work supported by the U.S. National Science Foundation under Federal Award No. 2534078. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.