Darrel Miller and Rachit Kumar Malik announce the largest update ever to OpenAPI.NET, bringing major performance, compatibility, and feature enhancements to help .NET developers keep pace with modern API standards.

OpenAPI.NET v2 & v3 Major Release: The Biggest Update Ever

Authors: Darrel Miller, Rachit Kumar Malik

OpenAPI.NET—the core library underpinning OpenAPI support in the .NET ecosystem—has just received its most important update since launch in 2018. With the simultaneous release of OpenAPI.NET v2 and v3, developers have access to:

Latest OpenAPI Specification support (v3.1.0 in v2, v3.2.0 in v3)
Major performance improvements (up to 50% faster parsing and 35% less memory usage)
Richer model properties, new serialization options, and numerous API surface enhancements

What’s New in OpenAPI.NET v2

Full OpenAPI v3.1 Support: Complete serialization and model compatibility with the latest spec
Performance: Uses System.Text.Json for faster JSON parsing while continuing YAML support. 50% reduction in document processing time, 35% memory savings
Improved API Surface: Native JSON node API use for properties of type “json”
Lazy Reference Resolution: Faster load times for large documents using heavy $ref references
Reduced Dependencies: Reads/writes JSON without extra packages

Upgrade Guide for v2

What’s New in OpenAPI.NET v3

Full OpenAPI v3.2 Support: Serialization and model parity with the latest spec
Enhanced Media Type Support: More robust encoding and schema handling
Hierarchical Tags: Organizational improvements for tags, including kind, summary, and parent relationships
Security Updates: Deprecated flag handling and device authorization flow support
Example Improvements: New properties for example data values and serialization
Extended Parameter Support: More locations and styles for API parameters

Upgrade Guide for v3

Impact on .NET Ecosystem

OpenAPI.NET is foundational for many widely-used .NET tools—including Swashbuckle, Semantic Kernel, NSwag, and direct .NET integrations. The updates make it easier to adopt modern API standards, improve reliability for large-scale systems, and future-proof ASP.NET Core projects (with .NET 10 moving toward native OpenAPI support).

For Developers

Start with v2 upgrade guide, then proceed to v3 guide
Performance, documentation, and reliability are all enhanced for API-centric .NET development
The project is open source and welcomes contributions (see contributing guide)

Key Contributors

This milestone involved numerous community and internal contributors, including: Vincent Biret, Matthieu Costabello, Maggie Kimani, Adrian Obando, Darrel Miller, Irvine Sunday, Martin Costello, Safia Abdalla, Mike Kistler, and Rachit Malik.

Feedback & Getting Involved

Contributions and issues are welcomed via GitHub. Full details, guides, and the full changelog are available on the project’s documentation.

This post appeared first on “Microsoft OpenAPI Blog”. Read the entire article here