diff --git a/codegen/aws/core/src/main/java/software/amazon/smithy/python/aws/codegen/AwsUserAgentIntegration.java b/codegen/aws/core/src/main/java/software/amazon/smithy/python/aws/codegen/AwsUserAgentIntegration.java
index 42329691..df703730 100644
--- a/codegen/aws/core/src/main/java/software/amazon/smithy/python/aws/codegen/AwsUserAgentIntegration.java
+++ b/codegen/aws/core/src/main/java/software/amazon/smithy/python/aws/codegen/AwsUserAgentIntegration.java
@@ -49,6 +49,12 @@ public List<RuntimeClientPlugin> getClientPlugins(GenerationContext context) {
                             "A unique and opaque application ID that is appended to the User-Agent header.")
                     .type(Symbol.builder().name("str").build())
                     .nullable(true)
+                    .useDescriptor(true)
+                    .validator(Symbol.builder()
+                            .name("validate_ua_string")
+                            .namespace("smithy_aws_core.config.validators", ".")
+                            .addDependency(AwsPythonDependency.SMITHY_AWS_CORE)
+                            .build())
                     .build();
 
             final String user_agent_plugin_file = "user_agent";
diff --git a/packages/smithy-aws-core/src/smithy_aws_core/config/validators.py b/packages/smithy-aws-core/src/smithy_aws_core/config/validators.py
index 41b670e0..a2766ecb 100644
--- a/packages/smithy-aws-core/src/smithy_aws_core/config/validators.py
+++ b/packages/smithy-aws-core/src/smithy_aws_core/config/validators.py
@@ -144,3 +144,25 @@ def validate_retry_strategy(
         f"retry_strategy must be RetryStrategy or RetryStrategyOptions, got {type(value).__name__}",
         source,
     )
+
+
+def validate_ua_string(value: Any, source: SourceInfo | None = None) -> str | None:
+    """Validate a User-Agent string component.
+
+    :param value: The UA string value to validate
+    :param source: The source that provided this value
+
+    :returns: The UA string or None if value is None
+
+    :raises ConfigValidationError: If the value is not a string
+    """
+    if value is None:
+        return None
+    if not isinstance(value, str):
+        raise ConfigValidationError(
+            "sdk_ua_app_id",
+            value,
+            f"UA string must be a string, got {type(value).__name__}",
+            source,
+        )
+    return value
diff --git a/packages/smithy-aws-core/tests/unit/config/test_property.py b/packages/smithy-aws-core/tests/unit/config/test_property.py
index 42ea3129..4246d060 100644
--- a/packages/smithy-aws-core/tests/unit/config/test_property.py
+++ b/packages/smithy-aws-core/tests/unit/config/test_property.py
@@ -107,7 +107,6 @@ def _create_config_with_validator(
 
         class ConfigWithValidator:
             region = ConfigProperty("region", validator=validator)
-            retry_strategy = ConfigProperty("retry_strategy", validator=validator)
 
             def __init__(self, resolver: ConfigResolver) -> None:
                 self._resolver = resolver
@@ -153,9 +152,7 @@ class ConfigWithComplexResolver:
             retry_strategy = ConfigProperty(
                 "retry_strategy",
                 resolver_func=mock_resolver,
-                default_value=RetryStrategyOptions(
-                    retry_mode="standard", max_attempts=3
-                ),
+                default_value=RetryStrategyOptions(retry_mode="standard"),
             )
 
             def __init__(self, resolver: ConfigResolver) -> None:
@@ -171,7 +168,7 @@ def __init__(self, resolver: ConfigResolver) -> None:
 
         assert isinstance(result, RetryStrategyOptions)
         assert result.retry_mode == "standard"
-        assert result.max_attempts == 3
+        assert result.max_attempts is None
         assert source_info == SimpleSource("default")
 
     def test_validator_not_called_on_cached_access(self) -> None:
diff --git a/packages/smithy-aws-core/tests/unit/config/test_validators.py b/packages/smithy-aws-core/tests/unit/config/test_validators.py
index 546af536..dbdbb7b6 100644
--- a/packages/smithy-aws-core/tests/unit/config/test_validators.py
+++ b/packages/smithy-aws-core/tests/unit/config/test_validators.py
@@ -8,6 +8,7 @@
     validate_max_attempts,
     validate_region,
     validate_retry_mode,
+    validate_ua_string,
 )
 
 
@@ -49,3 +50,20 @@ def test_invalid_retry_mode_error_message(self) -> None:
             "Invalid value for 'retry_mode': 'random_mode'. retry_mode must be one "
             "of ('standard',), got random_mode" in str(exc_info.value)
         )
+
+
+class TestValidateUaString:
+    def test_allows_string(self) -> None:
+        assert validate_ua_string("abc123") == "abc123"
+
+    def test_none_returns_none(self) -> None:
+        assert validate_ua_string(None) is None
+
+    def test_empty_string_passthrough(self) -> None:
+        assert validate_ua_string("") == ""
+
+    def test_rejects_non_string(self) -> None:
+        with pytest.raises(ConfigValidationError) as exc_info:
+            validate_ua_string(123)
+
+        assert exc_info.value.key == "sdk_ua_app_id"