Adding a Preview Version when the Last Version was Stable

When the latest api-version in your TypeSpec spec is a stable version, adding a new preview version is simply adding any new types and operations in the new preview and marking them with the appropriate versioning decoration, as described in TypeSpec Versioning for Azure ResourceManager APIs.

Making Changes to your TypeSpec spec

Add a new version to the Versions enum in your spec for the new preview.
```
enum Versions {
  `2025-10-01`,
 `2026-01-01-preview`,
}
```

Decorate this version with the @previewVersion decorator from the Azure.Core library

enum Versions {
  `2025-10-01`,
 @Azure.Core.previewVersion
  `2026-01-01-preview`,
}

Make changes to the API description based on how the API has changed
- If any types are removed in the new preview (unlikely) mark these with an @removed decorator referencing the new version
```
@removed(Versions.`2026-01-01-preview`)
model Foo  {}
```
- If any types are added, renamed, or otherwise modified in the new version, mark them with the appropriate versioning decorator
```
@added(Versions.`2026-01-01-preview`)
model Foo  {}

@renamedFrom(Versions.`2026-01-01-preview`, "Bar")
model Bar {}
model Baz {}
```
Create a new examples folder for the new version examples\<version> and populate it with examples.

Preparing a PR into the azure-rest-api-specs repo

Navigate to the root directory of the repo in your local fork or clone

C:\repos\azure-rest-api-specs\specifications\myRp > cd \repos\azure-rest-api-specs
C:\repos\azure-rest-api-specs >

Pull the latest version from the repo

C:\repos\azure-rest-api-specs > git fetch upstream main
C:\repos\azure-rest-api-specs > git pull upstream main

Reinstall dependencies
Terminal window
```
C:\repos\azure-rest-api-specs > npm ci
```

Compile your spec

C:\repos\azure-rest-api-specs > cd specification\myRpShortname\resource-manager\Microsoft.MyRP\MyService
C:\repos\azure-rest-api-specs\specification\myRpShortname\resource-manager\Microsoft.MyRP\MyService > npx tsp compile .

Update README.md to include a new entry for the new preview version.