In addition to bug fixes and foundation work for larger features, this preview includes updates to ensure that converters and comparers are handled by type mapping and to support using converters with value generators.  

Here’s a summary of what’s new in this preview release:

• HTTP/2 performance improvements
• Typed results for minimal APIs
• OpenAPI improvements for minimal APIs
• Return multiple results types from minimal APIs
• Route groups
• Client results in SignalR
• gRPC JSON transcoding
• Project template option to use Program.Main method instead of top-level statements
• Rate limiting middleware 

The fourth preview of .NET 7 includes enhancements to observability in the .NET implementation of OpenTelemetry, the addition of properties to track microseconds and nanoseconds in date and time structures, new metrics for caching extensions, performance-boosting “on stack replacement,” APIs to work with .tar archives, and additional features as part of an ongoing effort to improve the performance of and add features to regular expressions in .NET 7.  

ASP.NET Core 7 has built-in dark mode for error pages 

What’s Coming for Blazor in .NET 7?  

ts main advantages affect:

• Startup time
• Memory usage
• Access to restricted platforms (where no just-in time (JIT) compilation is allowed)
• Smaller size on disk 

Here’s a summary of what’s new in this preview release:

• Support for route handler filters in minimal APIs
• Improved unit testability for minimal route handlers
• Bind using TryParse in MVC and API controllers
• New Results.Stream() overloads
• Improved HTTP/2 performance when using many streams on a connection
• New ServerReady event for measuring startup time
• Developer exception page dark mode 

Several improvements to the update pipeline are now part of Preview 3, including:

• Improve SQL Server insertion logic (also make RETURNING the default INSERT strategy for retrieving db-generated values for other providers).
• Use RETURNING/OUTPUT clause for UPDATE/DELETE
• Refactor ReaderModificationCommandBatch
• Reimplement MaxBatchSize as a pre-check  

start experimenting with new features like:

• Native AOT
• Default GC regions
• ASP.NET Core startup time improvements 

Vectorize IndexOf for OrdinalIgnoreCase