diff --git a/packages/aws-credentials-http/.changes/next-release/aws-credentials-http-bugfix-bd4ef625870a44faa848494a7489ad19.json b/packages/aws-credentials-http/.changes/next-release/aws-credentials-http-bugfix-bd4ef625870a44faa848494a7489ad19.json
new file mode 100644
index 0000000..b786adc
--- /dev/null
+++ b/packages/aws-credentials-http/.changes/next-release/aws-credentials-http-bugfix-bd4ef625870a44faa848494a7489ad19.json
@@ -0,0 +1,4 @@
+{
+  "type": "bugfix",
+  "description": "Normalize empty container credential URI query strings to `None`."
+}
diff --git a/packages/aws-credentials-http/src/aws_credentials_http/resolvers.py b/packages/aws-credentials-http/src/aws_credentials_http/resolvers.py
index 1e6a781..0dd3f8a 100644
--- a/packages/aws-credentials-http/src/aws_credentials_http/resolvers.py
+++ b/packages/aws-credentials-http/src/aws_credentials_http/resolvers.py
@@ -95,7 +95,7 @@ async def _resolve_uri_from_env(self) -> URI:
                 host=parsed.hostname or "",
                 port=parsed.port,
                 path=parsed.path,
-                query=parsed.query,
+                query=parsed.query or None,
             )
         else:
             raise SmithyIdentityError(
diff --git a/packages/aws-credentials-sts/.changes/next-release/aws-credentials-sts-dependency-f1c7b755958249a394c8fad72970ff83.json b/packages/aws-credentials-sts/.changes/next-release/aws-credentials-sts-dependency-f1c7b755958249a394c8fad72970ff83.json
new file mode 100644
index 0000000..a220e70
--- /dev/null
+++ b/packages/aws-credentials-sts/.changes/next-release/aws-credentials-sts-dependency-f1c7b755958249a394c8fad72970ff83.json
@@ -0,0 +1,4 @@
+{
+  "type": "dependency",
+  "description": "Update STS credential resolution to use the new async client configuration API."
+}
diff --git a/packages/aws-credentials-sts/src/aws_credentials_sts/resolvers.py b/packages/aws-credentials-sts/src/aws_credentials_sts/resolvers.py
index 7aefe00..8e5725b 100644
--- a/packages/aws-credentials-sts/src/aws_credentials_sts/resolvers.py
+++ b/packages/aws-credentials-sts/src/aws_credentials_sts/resolvers.py
@@ -126,16 +126,18 @@ async def get_identity(
 
     async def _assume_role(self) -> AWSCredentialsIdentity:
         from aws_sdk_sts.client import AsyncSTSClient
-        from aws_sdk_sts.config import Config
+        from aws_sdk_sts.config import AsyncSTSConfig
         from aws_sdk_sts.models import AssumeRoleInput
 
         if self._client is None:
+            overrides: dict[str, object] = {
+                "aws_credentials_identity_resolver": self._source_resolver,
+                "region": self._region,
+            }
+            if self._http_client is not None:
+                overrides["transport"] = self._http_client
             self._client = AsyncSTSClient(
-                config=Config(
-                    aws_credentials_identity_resolver=self._source_resolver,
-                    region=self._region,
-                    transport=self._http_client,
-                )
+                config=await AsyncSTSConfig.resolve(**overrides)
             )
 
         response = await self._client.assume_role(