Azure AI search pricing tire its shows grayed or unavailable

Hello @Sundarajj Guruvan

Although East US and East US 2 are supported regions, Microsoft explicitly notes that capacity constraints may apply, especially in high‑demand regions.

Region availability does not guarantee tier availability. A region can support Azure AI Search while still blocking new services on specific SKUs due to capacity limits.

https://learn.microsoft.com/en-us/azure/search/search-region-support

Alternatively you can create service in another region such as Central US, South Central US, West US 2, or West US 3 often have better availability for Basic, S1, and S2 tiers.

https://learn.microsoft.com/azure/search/search-region-support

 AI Search service in the East US 2 region, which you want to update the sku of but unable to through the portal since there currently is a capacity constraint. if you don't want to use a different region
In order to update the sku of your existing search service, may I ask you to try using REST API or ARM template to update your sku? Here are some references on how to create/update your search service with REST API/ARM: 

https://learn.microsoft.com/en-us/azure/search/search-manage-rest#create-or-update-a-service

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