Enable Claude Sonnet 4.5 in GovCloud

The error you're encountering is expected behavior for enabling Bedrock models in GovCloud. The process has been updated, and the Model access page approach has been retired in standard AWS regions.

To enable Claude Sonnet 4.5 in your GovCloud account, you need to establish the End User License Agreement (EULA) in your linked standard AWS account using one of these methods:

Method 1: Using the Chat/Playground Feature (Recommended)

1. Sign in to your standard AWS account in either us-east-1 or us-west-2 region
2. Open Amazon Bedrock and navigate to the Chat/Text playground area
3. Select Claude Sonnet 4.5 as your foundation model
4. Write any prompt and click Run to generate a response
5. This invocation will establish the EULA and grant regional entitlement to access the model in GovCloud

Method 2: Using AWS CLI

1. Sign in to your standard AWS account
2. Run aws bedrock list-foundation-models to get all foundation models and copy the Claude Sonnet 4.5 model ID
3. Run aws bedrock list-foundation-model-agreement-offers --model-id <model-ID> and copy the offerToken
4. Run aws bedrock create-foundation-model-agreement --model-id <model-ID> --offer-token <offerToken>

After completing either method, wait a few minutes for the entitlements to propagate from your standard AWS account to GovCloud. Then you should be able to access Claude Sonnet 4.5 in your GovCloud account through US-GOV Cross-Region Inference.
Sources
Updated Process to Enabling Bedrock Models in GovCloud: Chat/Playground Feature or AWS CLI Approach | AWS re:Post
Anthropic’s Claude Sonnet 4.5 is now in Amazon Bedrock in AWS GovCloud (US) - AWS