Changes to default STS endpoint resolution

[yenfryherrerafeliz]

Discussed in #3158

^{Originally posted by yenfryherrerafeliz July 31, 2025}
In AWS SDK for PHP v3.351.12, we updated the default AWS STS endpoints resolution from legacy (global endpoint) to regional. This aligns with AWS best practices and brings AWS SDK for PHP in line with other AWS SDKs that already default to regional endpoints.
Regional endpoints eliminate cross-regional calls and reduce inter-region dependencies, improving both performance and reliability for your applications. This change may affect your application's behavior after updating, particularly if your code relies on the previous global endpoint behavior.
If you encounter problems, you can revert to the legacy behavior using either:

• Set sts_regional_endpoints = legacy in your shared AWS config file
• Set the AWS_STS_REGIONAL_ENDPOINTS=legacy environment variable

For more information about transitioning to regional service endpoints, please refer to the AWS STS announcement and the blog post.