Add 2026-04-01-preview API version to Fleet

[diyellap]

ARM (Control Plane) API Specification Update Pull Request

Tip

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PR review workflow diagram

Please understand this diagram before proceeding. It explains how to get your PR approved & merged.

Purpose of this PR

What's the purpose of this PR? Check the specific option that applies. This is mandatory!

• New resource provider.
• New API version for an existing resource provider. (If API spec is not defined in TypeSpec, the PR should have been created in adherence to OpenAPI specs PR creation guidance).
• Update existing version for a new feature. (This is applicable only when you are revising a private preview API version.)
• Update existing version to fix OpenAPI spec quality issues in S360.
• Convert existing OpenAPI spec to TypeSpec spec (do not combine this with implementing changes for a new API version).
• Other, please clarify:
  • Removes a previous preview API version and introduces a new preview API version with customer requested changes. The previous preview version was 2025-07-01-preview and meets deprecation timeline of < 1 year. Followed this wiki to make required preview changes: https://azure.github.io/typespec-azure/docs/howtos/versioning/arm/02-preview-after-preview/

Due diligence checklist

To merge this PR, you must go through the following checklist and confirm you understood
and followed the instructions by checking all the boxes:

• I confirm this PR is modifying Azure Resource Manager (ARM) related specifications, and not data plane related specifications.
• I have reviewed following Resource Provider guidelines, including
  ARM resource provider contract and
  REST guidelines (estimated time: 4 hours).
  I understand this is required before I can proceed to the diagram Step 2, "ARM API changes review", for this PR.
• A release plan has been created. If not, please create one as it will help guide you through the REST API and SDK creation process.

Additional information

Viewing API changes

For convenient view of the API changes made by this PR, refer to the URLs provided in the table
in the Generated ApiView comment added to this PR. You can use ApiView to show API versions diff.

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Getting help

• First, please carefully read through this PR description, from top to bottom. Please fill out the Purpose of this PR and Due diligence checklist.
• If you don't have permissions to remove or add labels to the PR, request write access per aka.ms/azsdk/access#request-access-to-rest-api-or-sdk-repositories
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• For guidance on SDK breaking change review, refer to https://aka.ms/ci-fix.

[github-actions]

Next Steps to Merge

✅ All automated merging requirements have been met! To get your PR merged, see aka.ms/azsdk/specreview/merge.

Comment generated by summarize-checks workflow run.

[github-actions]

API Change Check

APIView identified API level changes in this PR and created the following API reviews

Language	API Review for Package
Swagger	Microsoft.AzureFleet-AzureFleet
TypeSpec	Microsoft.AzureFleet
Go	sdk/resourcemanager/computefleet/armcomputefleet
Python	azure-mgmt-computefleet
JavaScript	@azure/arm-computefleet
Java	com.azure.resourcemanager:azure-resourcemanager-computefleet

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Comment generated by After APIView workflow run.

[sabanermsft]

Looks good