diff --git a/codegen-lite-maven-plugin/src/main/java/software/amazon/awssdk/codegen/lite/maven/plugin/DefaultsModeGenerationMojo.java b/codegen-lite-maven-plugin/src/main/java/software/amazon/awssdk/codegen/lite/maven/plugin/DefaultsModeGenerationMojo.java
new file mode 100644
index 000000000000..0f3217b4cd1f
--- /dev/null
+++ b/codegen-lite-maven-plugin/src/main/java/software/amazon/awssdk/codegen/lite/maven/plugin/DefaultsModeGenerationMojo.java
@@ -0,0 +1,65 @@
+/*
+ * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License").
+ * You may not use this file except in compliance with the License.
+ * A copy of the License is located at
+ *
+ *  http://aws.amazon.com/apache2.0
+ *
+ * or in the "license" file accompanying this file. This file is distributed
+ * on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
+ * express or implied. See the License for the specific language governing
+ * permissions and limitations under the License.
+ */
+
+package software.amazon.awssdk.codegen.lite.maven.plugin;
+
+import java.io.File;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import org.apache.maven.plugin.AbstractMojo;
+import org.apache.maven.plugins.annotations.Mojo;
+import org.apache.maven.plugins.annotations.Parameter;
+import org.apache.maven.project.MavenProject;
+import software.amazon.awssdk.codegen.lite.CodeGenerator;
+import software.amazon.awssdk.codegen.lite.defaultsmode.DefaultConfiguration;
+import software.amazon.awssdk.codegen.lite.defaultsmode.DefaultsLoader;
+import software.amazon.awssdk.codegen.lite.defaultsmode.DefaultsModeGenerator;
+
+/**
+ * The Maven mojo to generate defaults mode related classes.
+ */
+@Mojo(name = "generate-defaults-mode")
+public class DefaultsModeGenerationMojo extends AbstractMojo {
+
+    private static final String DEFAULTS_MODE_BASE = "software.amazon.awssdk.defaultsmode";
+
+    @Parameter(property = "outputDirectory", defaultValue = "${project.build.directory}")
+    private String outputDirectory;
+
+    @Parameter(defaultValue = "${project}", readonly = true)
+    private MavenProject project;
+
+    @Parameter(property = "defaultConfigurationFile", defaultValue =
+        "${basedir}/src/main/resources/software/amazon/awssdk/internal/defaults/sdk-default-configuration.json")
+    private File defaultConfigurationFile;
+
+    public void execute() {
+        Path baseSourcesDirectory = Paths.get(outputDirectory).resolve("generated-sources").resolve("sdk");
+        Path testsDirectory = Paths.get(outputDirectory).resolve("generated-test-sources").resolve("sdk-tests");
+
+        DefaultConfiguration configuration = DefaultsLoader.load(defaultConfigurationFile);
+
+        generateDefaultsModeClass(baseSourcesDirectory, configuration);
+
+        project.addCompileSourceRoot(baseSourcesDirectory.toFile().getAbsolutePath());
+        project.addTestCompileSourceRoot(testsDirectory.toFile().getAbsolutePath());
+    }
+
+    public void generateDefaultsModeClass(Path baseSourcesDirectory, DefaultConfiguration configuration) {
+        Path sourcesDirectory = baseSourcesDirectory.resolve(DEFAULTS_MODE_BASE.replace(".", "/"));
+        new CodeGenerator(sourcesDirectory.toString(), new DefaultsModeGenerator(DEFAULTS_MODE_BASE, configuration)).generate();
+    }
+
+}
diff --git a/codegen-lite/pom.xml b/codegen-lite/pom.xml
index 32682a7f93e8..f3cddc67b4fa 100644
--- a/codegen-lite/pom.xml
+++ b/codegen-lite/pom.xml
@@ -57,6 +57,11 @@
             <artifactId>utils</artifactId>
             <version>${awsjavasdk.version}</version>
         </dependency>
+        <dependency>
+            <groupId>software.amazon.awssdk</groupId>
+            <artifactId>json-utils</artifactId>
+            <version>${awsjavasdk.version}</version>
+        </dependency>
         <dependency>
             <groupId>com.squareup</groupId>
             <artifactId>javapoet</artifactId>
diff --git a/codegen-lite/src/main/java/software/amazon/awssdk/codegen/lite/defaultsmode/DefaultConfiguration.java b/codegen-lite/src/main/java/software/amazon/awssdk/codegen/lite/defaultsmode/DefaultConfiguration.java
new file mode 100644
index 000000000000..c18a68996c72
--- /dev/null
+++ b/codegen-lite/src/main/java/software/amazon/awssdk/codegen/lite/defaultsmode/DefaultConfiguration.java
@@ -0,0 +1,65 @@
+/*
+ * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License").
+ * You may not use this file except in compliance with the License.
+ * A copy of the License is located at
+ *
+ *  http://aws.amazon.com/apache2.0
+ *
+ * or in the "license" file accompanying this file. This file is distributed
+ * on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
+ * express or implied. See the License for the specific language governing
+ * permissions and limitations under the License.
+ */
+
+package software.amazon.awssdk.codegen.lite.defaultsmode;
+
+import java.util.Map;
+
+/**
+ * Container for default configuration
+ */
+public class DefaultConfiguration {
+    /**
+     * The transformed configuration values for each mode
+     */
+    private Map<String, Map<String, String>> modeDefaults;
+
+    /**
+     * The documentation for each mode
+     */
+    private Map<String, String> modesDocumentation;
+
+    /*
+     * The documentation for each configuration option
+     */
+    private Map<String, String> configurationDocumentation;
+
+    public Map<String, Map<String, String>> modeDefaults() {
+        return modeDefaults;
+    }
+
+    public DefaultConfiguration modeDefaults(Map<String, Map<String, String>> modeDefaults) {
+        this.modeDefaults = modeDefaults;
+        return this;
+    }
+
+    public Map<String, String> modesDocumentation() {
+        return modesDocumentation;
+    }
+
+    public DefaultConfiguration modesDocumentation(Map<String, String> documentation) {
+        this.modesDocumentation = documentation;
+        return this;
+    }
+
+    public Map<String, String> configurationDocumentation() {
+        return configurationDocumentation;
+    }
+
+    public DefaultConfiguration configurationDocumentation(Map<String, String> configurationDocumentation) {
+        this.configurationDocumentation = configurationDocumentation;
+        return this;
+    }
+}
diff --git a/codegen-lite/src/main/java/software/amazon/awssdk/codegen/lite/defaultsmode/DefaultsLoader.java b/codegen-lite/src/main/java/software/amazon/awssdk/codegen/lite/defaultsmode/DefaultsLoader.java
new file mode 100644
index 000000000000..05d938c65a13
--- /dev/null
+++ b/codegen-lite/src/main/java/software/amazon/awssdk/codegen/lite/defaultsmode/DefaultsLoader.java
@@ -0,0 +1,206 @@
+/*
+ * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License").
+ * You may not use this file except in compliance with the License.
+ * A copy of the License is located at
+ *
+ *  http://aws.amazon.com/apache2.0
+ *
+ * or in the "license" file accompanying this file. This file is distributed
+ * on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
+ * express or implied. See the License for the specific language governing
+ * permissions and limitations under the License.
+ */
+
+package software.amazon.awssdk.codegen.lite.defaultsmode;
+
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.IOException;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import software.amazon.awssdk.annotations.SdkInternalApi;
+import software.amazon.awssdk.protocols.jsoncore.JsonNode;
+import software.amazon.awssdk.protocols.jsoncore.JsonNodeParser;
+import software.amazon.awssdk.protocols.jsoncore.JsonNodeVisitor;
+import software.amazon.awssdk.utils.Logger;
+
+/**
+ * Loads sdk-default-configuration.json into memory. It filters out unsupported configuration options from the file
+ */
+@SdkInternalApi
+public final class DefaultsLoader {
+    private static final Logger log = Logger.loggerFor(DefaultsLoader.class);
+
+    private static final Set<String> UNSUPPORTED_OPTIONS = new HashSet<>();
+
+    static {
+        UNSUPPORTED_OPTIONS.add("stsRegionalEndpoints");
+        UNSUPPORTED_OPTIONS.add("tlsNegotiationTimeoutInMillis");
+    }
+
+    private DefaultsLoader() {
+    }
+
+    public static DefaultConfiguration load(File path) {
+        return loadDefaultsFromFile(path);
+    }
+
+    private static DefaultConfiguration loadDefaultsFromFile(File path) {
+        DefaultConfiguration defaultsResolution = new DefaultConfiguration();
+        Map<String, Map<String, String>> resolvedDefaults = new HashMap<>();
+
+        try (FileInputStream fileInputStream = new FileInputStream(path)) {
+            JsonNodeParser jsonNodeParser = JsonNodeParser.builder().build();
+
+            Map<String, JsonNode> sdkDefaultConfiguration = jsonNodeParser.parse(fileInputStream)
+                                                                          .asObject();
+
+            Map<String, JsonNode> base = sdkDefaultConfiguration.get("base").asObject();
+            Map<String, JsonNode> modes = sdkDefaultConfiguration.get("modes").asObject();
+
+            modes.forEach((mode, modifiers) -> applyModificationToOneMode(resolvedDefaults, base, mode, modifiers));
+
+            Map<String, JsonNode> documentation = sdkDefaultConfiguration.get("documentation").asObject();
+            Map<String, JsonNode> modesDocumentation = documentation.get("modes").asObject();
+            Map<String, JsonNode> configDocumentation = documentation.get("configuration").asObject();
+
+            defaultsResolution.modesDocumentation(
+                modesDocumentation.entrySet()
+                                  .stream()
+                                  .collect(HashMap::new, (m, e) -> m.put(e.getKey(), e.getValue().asString()), Map::putAll));
+            defaultsResolution.configurationDocumentation(
+                configDocumentation.entrySet()
+                                   .stream()
+                                   .filter(e -> !UNSUPPORTED_OPTIONS.contains(e.getKey()))
+                                   .collect(HashMap::new, (m, e) -> m.put(e.getKey(), e.getValue().asString()), Map::putAll));
+
+        } catch (IOException e) {
+            throw new RuntimeException(e);
+        }
+
+        defaultsResolution.modeDefaults(resolvedDefaults);
+
+        return defaultsResolution;
+    }
+
+    private static void applyModificationToOneConfigurationOption(Map<String, String> resolvedDefaultsForCurrentMode,
+                                                                  String option,
+                                                                  JsonNode modifier) {
+        String resolvedValue;
+        String baseValue = resolvedDefaultsForCurrentMode.get(option);
+
+        if (UNSUPPORTED_OPTIONS.contains(option)) {
+            return;
+        }
+
+        Map<String, JsonNode> modifierMap = modifier.asObject();
+
+        if (modifierMap.size() != 1) {
+            throw new IllegalStateException("More than one modifier exists for option " + option);
+        }
+
+        String modifierString = modifierMap.keySet().iterator().next();
+
+        switch (modifierString) {
+            case "override":
+                resolvedValue = modifierMap.get("override").visit(new StringJsonNodeVisitor());
+                break;
+            case "multiply":
+                resolvedValue = processMultiply(baseValue, modifierMap);
+                break;
+            case "add":
+                resolvedValue = processAdd(baseValue, modifierMap);
+                break;
+            default:
+                throw new UnsupportedOperationException("Unsupported modifier: " + modifierString);
+        }
+
+        resolvedDefaultsForCurrentMode.put(option, resolvedValue);
+    }
+
+    private static void applyModificationToOneMode(Map<String, Map<String, String>> resolvedDefaults,
+                                                   Map<String, JsonNode> base,
+                                                   String mode,
+                                                   JsonNode modifiers) {
+
+        log.info(() -> "Apply modification for mode: " + mode);
+        Map<String, String> resolvedDefaultsForCurrentMode =
+            base.entrySet().stream().filter(e -> !UNSUPPORTED_OPTIONS.contains(e.getKey()))
+                .collect(HashMap::new, (m, e) -> m.put(e.getKey(),
+                                                       e.getValue().visit(new StringJsonNodeVisitor())), Map::putAll);
+
+
+        // Iterate the configuration options and apply modification.
+        modifiers.asObject().forEach((option, modifier) -> applyModificationToOneConfigurationOption(
+            resolvedDefaultsForCurrentMode, option, modifier));
+
+        resolvedDefaults.put(mode, resolvedDefaultsForCurrentMode);
+    }
+
+    private static String processAdd(String baseValue, Map<String, JsonNode> modifierMap) {
+        String resolvedValue;
+        String add = modifierMap.get("add").asNumber();
+        int parsedAdd = Integer.parseInt(add);
+        int number = Math.addExact(Integer.parseInt(baseValue), parsedAdd);
+        resolvedValue = String.valueOf(number);
+        return resolvedValue;
+    }
+
+    private static String processMultiply(String baseValue, Map<String, JsonNode> modifierMap) {
+        String resolvedValue;
+        String multiply = modifierMap.get("multiply").asNumber();
+        double parsedValue = Double.parseDouble(multiply);
+
+        double resolvedNumber = Integer.parseInt(baseValue) * parsedValue;
+        int castValue = (int) resolvedNumber;
+
+        if (castValue != resolvedNumber) {
+            throw new IllegalStateException("The transformed value must be be a float number: " + castValue);
+        }
+
+        resolvedValue = String.valueOf(castValue);
+        return resolvedValue;
+    }
+
+    private static final class StringJsonNodeVisitor implements JsonNodeVisitor<String> {
+        @Override
+        public String visitNull() {
+            throw new IllegalStateException("Invalid type encountered");
+        }
+
+        @Override
+        public String visitBoolean(boolean b) {
+            throw new IllegalStateException("Invalid type (boolean) encountered " + b);
+        }
+
+        @Override
+        public String visitNumber(String s) {
+            return s;
+        }
+
+        @Override
+        public String visitString(String s) {
+            return s;
+        }
+
+        @Override
+        public String visitArray(List<JsonNode> list) {
+            throw new IllegalStateException("Invalid type (list) encountered: " + list);
+        }
+
+        @Override
+        public String visitObject(Map<String, JsonNode> map) {
+            throw new IllegalStateException("Invalid type (map) encountered: " + map);
+        }
+
+        @Override
+        public String visitEmbeddedObject(Object o) {
+            throw new IllegalStateException("Invalid type (embedded) encountered: " + o);
+        }
+    }
+}
diff --git a/codegen-lite/src/main/java/software/amazon/awssdk/codegen/lite/defaultsmode/DefaultsModeGenerator.java b/codegen-lite/src/main/java/software/amazon/awssdk/codegen/lite/defaultsmode/DefaultsModeGenerator.java
new file mode 100644
index 000000000000..0a318e1f69c9
--- /dev/null
+++ b/codegen-lite/src/main/java/software/amazon/awssdk/codegen/lite/defaultsmode/DefaultsModeGenerator.java
@@ -0,0 +1,189 @@
+/*
+ * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License").
+ * You may not use this file except in compliance with the License.
+ * A copy of the License is located at
+ *
+ *  http://aws.amazon.com/apache2.0
+ *
+ * or in the "license" file accompanying this file. This file is distributed
+ * on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
+ * express or implied. See the License for the specific language governing
+ * permissions and limitations under the License.
+ */
+
+package software.amazon.awssdk.codegen.lite.defaultsmode;
+
+import static javax.lang.model.element.Modifier.FINAL;
+import static javax.lang.model.element.Modifier.PRIVATE;
+import static javax.lang.model.element.Modifier.PUBLIC;
+import static javax.lang.model.element.Modifier.STATIC;
+
+import com.squareup.javapoet.AnnotationSpec;
+import com.squareup.javapoet.ClassName;
+import com.squareup.javapoet.CodeBlock;
+import com.squareup.javapoet.FieldSpec;
+import com.squareup.javapoet.MethodSpec;
+import com.squareup.javapoet.ParameterizedTypeName;
+import com.squareup.javapoet.TypeSpec;
+import java.util.Locale;
+import java.util.Map;
+import javax.lang.model.element.Modifier;
+import software.amazon.awssdk.annotations.Generated;
+import software.amazon.awssdk.annotations.SdkPublicApi;
+import software.amazon.awssdk.codegen.lite.PoetClass;
+import software.amazon.awssdk.utils.Validate;
+import software.amazon.awssdk.utils.internal.EnumUtils;
+
+/**
+ * Generates DefaultsMode enum
+ */
+public class DefaultsModeGenerator implements PoetClass {
+
+    private static final String VALUE = "value";
+    private static final String VALUE_MAP = "VALUE_MAP";
+
+    private final String basePackage;
+    private final DefaultConfiguration configuration;
+
+    public DefaultsModeGenerator(String basePackage, DefaultConfiguration configuration) {
+        this.basePackage = basePackage;
+        this.configuration = configuration;
+    }
+
+    @Override
+    public TypeSpec poetClass() {
+        TypeSpec.Builder builder = TypeSpec.enumBuilder(className())
+                                           .addField(valueMapField())
+                                           .addField(String.class, VALUE, Modifier.PRIVATE, Modifier.FINAL)
+                                           .addModifiers(PUBLIC)
+                                           .addJavadoc(documentation())
+                                           .addAnnotation(SdkPublicApi.class)
+                                           .addAnnotation(AnnotationSpec.builder(Generated.class)
+                                                                        .addMember(VALUE,
+                                                                                   "$S",
+                                                                                   "software.amazon.awssdk:codegen")
+                                                                        .build())
+                                           .addMethod(fromValueSpec())
+                                           .addMethod(toStringBuilder().addStatement("return $T.valueOf($N)", String.class,
+                                                                                     VALUE).build())
+                                           .addMethod(createConstructor());
+
+        builder.addEnumConstant("LEGACY", enumValueTypeSpec("legacy", javaDocForMode("legacy")));
+
+        configuration.modeDefaults().keySet().forEach(k -> {
+            String enumKey = sanitizeEnum(k);
+            builder.addEnumConstant(enumKey, enumValueTypeSpec(k, javaDocForMode(k)));
+        });
+
+        builder.addEnumConstant("AUTO", enumValueTypeSpec("auto", javaDocForMode("auto")));
+
+        return builder.build();
+    }
+
+    @Override
+    public ClassName className() {
+        return ClassName.get(basePackage, "DefaultsMode");
+    }
+
+    private TypeSpec enumValueTypeSpec(String value, String documentation) {
+        return TypeSpec.anonymousClassBuilder("$S", value)
+                       .addJavadoc(documentation)
+                       .build();
+    }
+
+    private FieldSpec valueMapField() {
+        ParameterizedTypeName mapType = ParameterizedTypeName.get(ClassName.get(Map.class),
+                                                                  ClassName.get(String.class),
+                                                                  className());
+        return FieldSpec.builder(mapType, VALUE_MAP)
+                        .addModifiers(PRIVATE, STATIC, FINAL)
+                        .initializer("$1T.uniqueIndex($2T.class, $2T::toString)", EnumUtils.class, className())
+                        .build();
+    }
+
+    private String sanitizeEnum(String str) {
+        return str.replace('-', '_').toUpperCase(Locale.US);
+    }
+
+    private String javaDocForMode(String mode) {
+        return configuration.modesDocumentation().getOrDefault(mode, "");
+    }
+
+    private CodeBlock documentation() {
+        CodeBlock.Builder builder = CodeBlock.builder()
+                                             .add("A defaults mode determines how certain default configuration options are "
+                                                  + "resolved in "
+                                                  + "the SDK. "
+                                                  + "Based on the provided "
+                                                  + "mode, the SDK will vend sensible default values tailored to the mode for "
+                                                  + "the following settings:")
+                                             .add(System.lineSeparator());
+
+        builder.add("<ul>");
+        configuration.configurationDocumentation().forEach((k, v) -> {
+            builder.add("<li>" + k + ": " + v + "</li>");
+        });
+        builder.add("</ul>").add(System.lineSeparator());
+
+        builder.add("<p>All options above can be configured by users, and the overridden value will take precedence.")
+               .add("<p><b>Note:</b> for any mode other than {@link #LEGACY}, the vended default values might change "
+                    + "as best practices may evolve. As a result, it is encouraged to perform testing when upgrading the SDK if"
+                    + " you are using a mode other than {@link #LEGACY}")
+               .add(System.lineSeparator());
+
+        return builder.add("<p>While the {@link #LEGACY} defaults mode is specific to Java, other modes are "
+                           + "standardized across "
+                           + "all of the AWS SDKs</p>")
+                      .add(System.lineSeparator())
+                      .add("<p>The defaults mode can be configured:")
+                      .add(System.lineSeparator())
+                      .add("<ol>")
+                      .add("<li>Directly on a client via {@code ClientOverrideConfiguration.Builder#defaultsMode"
+                           + "(DefaultsMode)}.</li>")
+                      .add(System.lineSeparator())
+                      .add("<li>On a configuration profile via the \"defaults_mode\" profile file property.</li>")
+                      .add(System.lineSeparator())
+                      .add("<li>Globally via the \"aws.defaultsMode\" system property.</li>")
+                      .add("<li>Globally via the \"AWS_DEFAULTS_MODE\" environment variable.</li>")
+                      .add("</ol>")
+                      .build();
+    }
+
+
+    private MethodSpec fromValueSpec() {
+        return MethodSpec.methodBuilder("fromValue")
+                         .returns(className())
+                         .addModifiers(Modifier.PUBLIC, Modifier.STATIC)
+                         .addJavadoc("Use this in place of valueOf to convert the raw string returned by the service into the " +
+                                     "enum value.\n\n" +
+                                     "@param $N real value\n" +
+                                     "@return $T corresponding to the value\n", VALUE, className())
+                         .addParameter(String.class, VALUE)
+                         .addStatement("$T.paramNotNull(value, $S)", Validate.class, VALUE)
+                         .beginControlFlow("if (!VALUE_MAP.containsKey(value))")
+                         .addStatement("throw new IllegalArgumentException($S + value)", "The provided value is not a"
+                                                                                         + " valid "
+                                                                                         + "defaults mode ")
+                         .endControlFlow()
+                         .addStatement("return $N.get($N)", VALUE_MAP, VALUE)
+                         .build();
+    }
+
+    private MethodSpec createConstructor() {
+        return MethodSpec.constructorBuilder()
+                         .addModifiers(Modifier.PRIVATE)
+                         .addParameter(String.class, VALUE)
+                         .addStatement("this.$1N = $1N", VALUE)
+                         .build();
+    }
+
+    private static MethodSpec.Builder toStringBuilder() {
+        return MethodSpec.methodBuilder("toString")
+                         .returns(String.class)
+                         .addModifiers(Modifier.PUBLIC)
+                         .addAnnotation(Override.class);
+    }
+
+}
diff --git a/codegen-lite/src/test/java/software/amazon/awssdk/codegen/lite/defaultsmode/DefaultsModeGenerationTest.java b/codegen-lite/src/test/java/software/amazon/awssdk/codegen/lite/defaultsmode/DefaultsModeGenerationTest.java
new file mode 100644
index 000000000000..5a753db0af1d
--- /dev/null
+++ b/codegen-lite/src/test/java/software/amazon/awssdk/codegen/lite/defaultsmode/DefaultsModeGenerationTest.java
@@ -0,0 +1,45 @@
+/*
+ * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License").
+ * You may not use this file except in compliance with the License.
+ * A copy of the License is located at
+ *
+ *  http://aws.amazon.com/apache2.0
+ *
+ * or in the "license" file accompanying this file. This file is distributed
+ * on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
+ * express or implied. See the License for the specific language governing
+ * permissions and limitations under the License.
+ */
+package software.amazon.awssdk.codegen.lite.defaultsmode;
+
+import static org.hamcrest.MatcherAssert.assertThat;
+import static software.amazon.awssdk.codegen.lite.PoetMatchers.generatesTo;
+
+import java.io.File;
+import java.nio.file.Paths;
+import org.junit.Before;
+import org.junit.Test;
+
+public class DefaultsModeGenerationTest {
+
+    private static final String DEFAULT_CONFIGURATION = "/software/amazon/awssdk/codegen/lite/test-sdk-default-configuration.json";
+    private static final String DEFAULTS_MODE_BASE = "software.amazon.awssdk.defaultsmode";
+
+    private File file;
+    private DefaultConfiguration defaultConfiguration;
+
+    @Before
+    public void before() throws Exception {
+        this.file = Paths.get(getClass().getResource(DEFAULT_CONFIGURATION).toURI()).toFile();
+        this.defaultConfiguration = DefaultsLoader.load(file);
+    }
+
+    @Test
+    public void defaultsModeEnum() {
+        DefaultsModeGenerator generator = new DefaultsModeGenerator(DEFAULTS_MODE_BASE, defaultConfiguration);
+        assertThat(generator, generatesTo("defaults-mode.java"));
+    }
+
+}
diff --git a/codegen-lite/src/test/resources/software/amazon/awssdk/codegen/lite/defaultsmode/defaults-mode.java b/codegen-lite/src/test/resources/software/amazon/awssdk/codegen/lite/defaultsmode/defaults-mode.java
new file mode 100644
index 000000000000..0d78d3a2fd2f
--- /dev/null
+++ b/codegen-lite/src/test/resources/software/amazon/awssdk/codegen/lite/defaultsmode/defaults-mode.java
@@ -0,0 +1,95 @@
+package software.amazon.awssdk.defaultsmode;
+
+import java.util.Map;
+import software.amazon.awssdk.annotations.Generated;
+import software.amazon.awssdk.annotations.SdkPublicApi;
+import software.amazon.awssdk.utils.Validate;
+import software.amazon.awssdk.utils.internal.EnumUtils;
+
+/**
+ * A defaults mode determines how certain default configuration options are resolved in the SDK. Based on the provided
+ * mode, the SDK will vend sensible default values tailored to the mode for the following settings:
+ * <ul>
+ * <li>retryMode: PLACEHOLDER</li>
+ * <li>s3UsEast1RegionalEndpoints: PLACEHOLDER</li>
+ * <li>connectTimeoutInMillis: PLACEHOLDER</li>
+ * </ul>
+ * <p>
+ * All options above can be configured by users, and the overridden value will take precedence.
+ * <p>
+ * <b>Note:</b> for any mode other than {@link #LEGACY}, the vended default values might change as best practices may
+ * evolve. As a result, it is encouraged to perform testing when upgrading the SDK if you are using a mode other than
+ * {@link #LEGACY}
+ * <p>
+ * While the {@link #LEGACY} defaults mode is specific to Java, other modes are standardized across all of the AWS SDKs
+ * </p>
+ * <p>
+ * The defaults mode can be configured:
+ * <ol>
+ * <li>Directly on a client via {@code ClientOverrideConfiguration.Builder#defaultsMode(DefaultsMode)}.</li>
+ * <li>On a configuration profile via the "defaults_mode" profile file property.</li>
+ * <li>Globally via the "aws.defaultsMode" system property.</li>
+ * <li>Globally via the "AWS_DEFAULTS_MODE" environment variable.</li>
+ * </ol>
+ */
+@SdkPublicApi
+@Generated("software.amazon.awssdk:codegen")
+public enum DefaultsMode {
+    /**
+     * PLACEHOLDER
+     */
+    LEGACY("legacy"),
+
+    /**
+     * PLACEHOLDER
+     */
+    STANDARD("standard"),
+
+    /**
+     * PLACEHOLDER
+     */
+    MOBILE("mobile"),
+
+    /**
+     * PLACEHOLDER
+     */
+    CROSS_REGION("cross-region"),
+
+    /**
+     * PLACEHOLDER
+     */
+    IN_REGION("in-region"),
+
+    /**
+     * PLACEHOLDER
+     */
+    AUTO("auto");
+
+    private static final Map<String, DefaultsMode> VALUE_MAP = EnumUtils.uniqueIndex(DefaultsMode.class, DefaultsMode::toString);
+
+    private final String value;
+
+    private DefaultsMode(String value) {
+        this.value = value;
+    }
+
+    /**
+     * Use this in place of valueOf to convert the raw string returned by the service into the enum value.
+     *
+     * @param value
+     *        real value
+     * @return DefaultsMode corresponding to the value
+     */
+    public static DefaultsMode fromValue(String value) {
+        Validate.paramNotNull(value, "value");
+        if (!VALUE_MAP.containsKey(value)) {
+            throw new IllegalArgumentException("The provided value is not a valid defaults mode " + value);
+        }
+        return VALUE_MAP.get(value);
+    }
+
+    @Override
+    public String toString() {
+        return String.valueOf(value);
+    }
+}
diff --git a/codegen-lite/src/test/resources/software/amazon/awssdk/codegen/lite/test-sdk-default-configuration.json b/codegen-lite/src/test/resources/software/amazon/awssdk/codegen/lite/test-sdk-default-configuration.json
new file mode 100644
index 000000000000..5c9f0fab48b7
--- /dev/null
+++ b/codegen-lite/src/test/resources/software/amazon/awssdk/codegen/lite/test-sdk-default-configuration.json
@@ -0,0 +1,64 @@
+{
+  "version": 1,
+  "base": {
+    "retryMode": "standard",
+    "stsRegionalEndpoints": "regional",
+    "s3UsEast1RegionalEndpoints": "regional",
+    "connectTimeoutInMillis": 1000,
+    "tlsNegotiationTimeoutInMillis": 1000
+  },
+  "modes": {
+    "standard": {
+      "connectTimeoutInMillis": {
+        "multiply":2
+      },
+      "tlsNegotiationTimeoutInMillis": {
+        "multiply":2
+      }
+    },
+    "in-region": {
+      "connectTimeoutInMillis": {
+        "multiply": 1
+      },
+      "tlsNegotiationTimeoutInMillis": {
+        "multiply": 1
+      }
+    },
+    "cross-region": {
+      "connectTimeoutInMillis": {
+        "multiply": 2.8
+      },
+      "tlsNegotiationTimeoutInMillis": {
+        "multiply": 2.8
+      }
+    },
+    "mobile": {
+      "connectTimeoutInMillis": {
+        "override": 10000
+      },
+      "tlsNegotiationTimeoutInMillis": {
+        "add": 10000
+      },
+      "retryMode": {
+        "override": "adaptive"
+      }
+    }
+  },
+  "documentation": {
+    "modes": {
+      "standard": "PLACEHOLDER",
+      "in-region": "PLACEHOLDER",
+      "cross-region": "PLACEHOLDER",
+      "mobile": "PLACEHOLDER",
+      "auto": "PLACEHOLDER",
+      "legacy": "PLACEHOLDER"
+    },
+    "configuration": {
+      "retryMode": "PLACEHOLDER",
+      "stsRegionalEndpoints": "PLACEHOLDER",
+      "s3UsEast1RegionalEndpoints": "PLACEHOLDER",
+      "connectTimeoutInMillis": "PLACEHOLDER",
+      "tlsNegotiationTimeoutInMillis": "PLACEHOLDER"
+    }
+  }
+}
\ No newline at end of file
diff --git a/core/profiles/src/main/java/software/amazon/awssdk/profiles/ProfileProperty.java b/core/profiles/src/main/java/software/amazon/awssdk/profiles/ProfileProperty.java
index 88b0328871b9..6faf0cad42f2 100644
--- a/core/profiles/src/main/java/software/amazon/awssdk/profiles/ProfileProperty.java
+++ b/core/profiles/src/main/java/software/amazon/awssdk/profiles/ProfileProperty.java
@@ -99,6 +99,13 @@ public final class ProfileProperty {
      */
     public static final String RETRY_MODE = "retry_mode";
 
+    /**
+     * The "defaults mode" to be used for clients created using the currently-configured profile. Defaults mode determins how SDK
+     * default configuration should be resolved. See the {@code DefaultsMode} class JavaDoc for more
+     * information.
+     */
+    public static final String DEFAULTS_MODE = "defaults_mode";
+
     /**
      * Aws region where the SSO directory for the given 'sso_start_url' is hosted. This is independent of the general 'region'.
      */
diff --git a/core/sdk-core/pom.xml b/core/sdk-core/pom.xml
index 3f59dc6a2e1a..204b49d4213d 100644
--- a/core/sdk-core/pom.xml
+++ b/core/sdk-core/pom.xml
@@ -238,6 +238,19 @@
                     </archive>
                 </configuration>
             </plugin>
+            <plugin>
+                <groupId>software.amazon.awssdk</groupId>
+                <artifactId>codegen-lite-maven-plugin</artifactId>
+                <version>${awsjavasdk.version}</version>
+                <executions>
+                    <execution>
+                        <phase>generate-sources</phase>
+                        <goals>
+                            <goal>generate-defaults-mode</goal>
+                        </goals>
+                    </execution>
+                </executions>
+            </plugin>
         </plugins>
 
         <pluginManagement>
diff --git a/core/sdk-core/src/main/java/software/amazon/awssdk/core/SdkSystemSetting.java b/core/sdk-core/src/main/java/software/amazon/awssdk/core/SdkSystemSetting.java
index 8fe7845d2f71..be9ba3629161 100644
--- a/core/sdk-core/src/main/java/software/amazon/awssdk/core/SdkSystemSetting.java
+++ b/core/sdk-core/src/main/java/software/amazon/awssdk/core/SdkSystemSetting.java
@@ -19,6 +19,7 @@
 import software.amazon.awssdk.core.client.config.ClientOverrideConfiguration;
 import software.amazon.awssdk.core.retry.RetryMode;
 import software.amazon.awssdk.core.retry.RetryPolicy;
+import software.amazon.awssdk.defaultsmode.DefaultsMode;
 import software.amazon.awssdk.utils.SystemSetting;
 
 /**
@@ -168,6 +169,12 @@ public enum SdkSystemSetting implements SystemSetting {
      */
     AWS_MAX_ATTEMPTS("aws.maxAttempts", null),
 
+    /**
+     * Which {@link DefaultsMode} to use, case insensitive
+     * @see DefaultsMode
+     */
+    AWS_DEFAULTS_MODE("aws.defaultsMode", null),
+
     ;
 
     private final String systemProperty;
diff --git a/core/sdk-core/src/main/java/software/amazon/awssdk/core/client/config/ClientOverrideConfiguration.java b/core/sdk-core/src/main/java/software/amazon/awssdk/core/client/config/ClientOverrideConfiguration.java
index 81b99d999667..4a57d3885456 100644
--- a/core/sdk-core/src/main/java/software/amazon/awssdk/core/client/config/ClientOverrideConfiguration.java
+++ b/core/sdk-core/src/main/java/software/amazon/awssdk/core/client/config/ClientOverrideConfiguration.java
@@ -31,6 +31,7 @@
 import software.amazon.awssdk.core.retry.RetryMode;
 import software.amazon.awssdk.core.retry.RetryPolicy;
 import software.amazon.awssdk.core.sync.ResponseTransformer;
+import software.amazon.awssdk.defaultsmode.DefaultsMode;
 import software.amazon.awssdk.metrics.MetricPublisher;
 import software.amazon.awssdk.profiles.ProfileFile;
 import software.amazon.awssdk.profiles.ProfileFileSystemSetting;
@@ -60,6 +61,7 @@ public final class ClientOverrideConfiguration
     private final String defaultProfileName;
     private final List<MetricPublisher> metricPublishers;
     private final ExecutionAttributes executionAttributes;
+    private final DefaultsMode defaultsMode;
 
     /**
      * Initialize this configuration. Private to require use of {@link #builder()}.
@@ -75,6 +77,7 @@ private ClientOverrideConfiguration(Builder builder) {
         this.defaultProfileName = builder.defaultProfileName();
         this.metricPublishers = Collections.unmodifiableList(new ArrayList<>(builder.metricPublishers()));
         this.executionAttributes = ExecutionAttributes.unmodifiableExecutionAttributes(builder.executionAttributes());
+        this.defaultsMode = builder.defaultsMode();
     }
 
     @Override
@@ -201,6 +204,15 @@ public List<MetricPublisher> metricPublishers() {
         return metricPublishers;
     }
 
+    /**
+     * The optional defaults mode that should be used to determine the default configuration
+     * @return the optional defaults mode
+     * @see Builder#defaultsMode(DefaultsMode)
+     */
+    public Optional<DefaultsMode> defaultsMode() {
+        return Optional.of(defaultsMode);
+    }
+
     /**
      *  Returns the additional execution attributes to be added for this client.
      *
@@ -469,6 +481,16 @@ default Builder retryPolicy(RetryMode retryMode) {
         <T> Builder putExecutionAttribute(ExecutionAttribute<T> attribute, T value);
 
         ExecutionAttributes executionAttributes();
+
+        /**
+         * Sets the defaults mode that will be used to determine the default configuration
+         * @param defaultsMode the defaultsMode to use
+         * @return This object for method chaining.
+         * @see DefaultsMode
+         */
+        <T> Builder defaultsMode(DefaultsMode defaultsMode);
+
+        DefaultsMode defaultsMode();
     }
 
     /**
@@ -485,6 +507,7 @@ private static final class DefaultClientOverrideConfigurationBuilder implements
         private String defaultProfileName;
         private List<MetricPublisher> metricPublishers = new ArrayList<>();
         private ExecutionAttributes.Builder executionAttributesBuilder = ExecutionAttributes.builder();
+        private DefaultsMode defaultsMode;
 
         @Override
         public Builder headers(Map<String, List<String>> headers) {
@@ -667,6 +690,21 @@ public ExecutionAttributes executionAttributes() {
             return executionAttributesBuilder.build();
         }
 
+        @Override
+        public Builder defaultsMode(DefaultsMode mode) {
+            this.defaultsMode = mode;
+            return this;
+        }
+
+        @Override
+        public DefaultsMode defaultsMode() {
+            return defaultsMode;
+        }
+
+        public void setDefaultsMode(DefaultsMode mode) {
+            defaultsMode(mode);
+        }
+
         @Override
         public ClientOverrideConfiguration build() {
             return new ClientOverrideConfiguration(this);
diff --git a/core/sdk-core/src/main/java/software/amazon/awssdk/core/internal/defaultsmode/DefaultsModeResolver.java b/core/sdk-core/src/main/java/software/amazon/awssdk/core/internal/defaultsmode/DefaultsModeResolver.java
new file mode 100644
index 000000000000..f0a71f5df37d
--- /dev/null
+++ b/core/sdk-core/src/main/java/software/amazon/awssdk/core/internal/defaultsmode/DefaultsModeResolver.java
@@ -0,0 +1,99 @@
+/*
+ * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License").
+ * You may not use this file except in compliance with the License.
+ * A copy of the License is located at
+ *
+ *  http://aws.amazon.com/apache2.0
+ *
+ * or in the "license" file accompanying this file. This file is distributed
+ * on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
+ * express or implied. See the License for the specific language governing
+ * permissions and limitations under the License.
+ */
+
+package software.amazon.awssdk.core.internal.defaultsmode;
+
+import java.util.Locale;
+import java.util.Optional;
+import java.util.function.Supplier;
+import software.amazon.awssdk.annotations.SdkInternalApi;
+import software.amazon.awssdk.core.SdkSystemSetting;
+import software.amazon.awssdk.core.retry.RetryMode;
+import software.amazon.awssdk.defaultsmode.DefaultsMode;
+import software.amazon.awssdk.profiles.ProfileFile;
+import software.amazon.awssdk.profiles.ProfileFileSystemSetting;
+import software.amazon.awssdk.profiles.ProfileProperty;
+import software.amazon.awssdk.utils.OptionalUtils;
+
+/**
+ * Allows customizing the variables used during determination of a {@link DefaultsMode}. Created via {@link #create()}.
+ */
+@SdkInternalApi
+public final class DefaultsModeResolver {
+
+    private static final DefaultsMode SDK_DEFAULT_DEFAULTS_MODE = DefaultsMode.LEGACY;
+    private Supplier<ProfileFile> profileFile;
+    private String profileName;
+    private DefaultsMode mode;
+
+    private DefaultsModeResolver() {
+    }
+
+    public static DefaultsModeResolver create() {
+        return new DefaultsModeResolver();
+    }
+
+    /**
+     * Configure the profile file that should be used when determining the {@link RetryMode}. The supplier is only consulted
+     * if a higher-priority determinant (e.g. environment variables) does not find the setting.
+     */
+    public DefaultsModeResolver profileFile(Supplier<ProfileFile> profileFile) {
+        this.profileFile = profileFile;
+        return this;
+    }
+
+    /**
+     * Configure the profile file name should be used when determining the {@link RetryMode}.
+     */
+    public DefaultsModeResolver profileName(String profileName) {
+        this.profileName = profileName;
+        return this;
+    }
+
+    /**
+     * Configure the {@link DefaultsMode} that should be used if the mode is not specified anywhere else.
+     */
+    public DefaultsModeResolver defaultMode(DefaultsMode mode) {
+        this.mode = mode;
+        return this;
+    }
+
+    /**
+     * Resolve which defaults mode should be used, based on the configured values.
+     */
+    public DefaultsMode resolve() {
+        return OptionalUtils.firstPresent(DefaultsModeResolver.fromSystemSettings(), () -> fromProfileFile(profileFile,
+                                                                                                           profileName))
+                            .orElseGet(this::fromDefaultMode);
+    }
+
+    private static Optional<DefaultsMode> fromSystemSettings() {
+        return SdkSystemSetting.AWS_DEFAULTS_MODE.getStringValue()
+                                                 .map(value -> DefaultsMode.fromValue(value.toLowerCase(Locale.US)));
+    }
+
+    private static Optional<DefaultsMode> fromProfileFile(Supplier<ProfileFile> profileFile, String profileName) {
+        profileFile = profileFile != null ? profileFile : ProfileFile::defaultProfileFile;
+        profileName = profileName != null ? profileName : ProfileFileSystemSetting.AWS_PROFILE.getStringValueOrThrow();
+        return profileFile.get()
+                          .profile(profileName)
+                          .flatMap(p -> p.property(ProfileProperty.DEFAULTS_MODE))
+                          .map(value -> DefaultsMode.fromValue(value.toLowerCase(Locale.US)));
+    }
+
+    private DefaultsMode fromDefaultMode() {
+        return mode != null ? mode : SDK_DEFAULT_DEFAULTS_MODE;
+    }
+}
diff --git a/core/sdk-core/src/main/resources/software/amazon/awssdk/internal/defaults/sdk-default-configuration.json b/core/sdk-core/src/main/resources/software/amazon/awssdk/internal/defaults/sdk-default-configuration.json
new file mode 100644
index 000000000000..e99d2b038098
--- /dev/null
+++ b/core/sdk-core/src/main/resources/software/amazon/awssdk/internal/defaults/sdk-default-configuration.json
@@ -0,0 +1,53 @@
+{
+  "version": 1,
+  "base": {
+    "retryMode": "standard",
+    "stsRegionalEndpoints": "regional",
+    "s3UsEast1RegionalEndpoints": "regional",
+    "connectTimeoutInMillis": 1100,
+    "tlsNegotiationTimeoutInMillis": 1100
+  },
+  "modes": {
+    "standard": {
+      "connectTimeoutInMillis": {
+        "override": 3100
+      },
+      "tlsNegotiationTimeoutInMillis": {
+        "override": 3100
+      }
+    },
+    "in-region": {
+      "connectTimeoutInMillis": {
+        "multiply": 1
+      },
+      "tlsNegotiationTimeoutInMillis": {
+        "multiply": 1
+      }
+    },
+    "cross-region": {
+      "connectTimeoutInMillis": {
+        "override": 3100
+      },
+      "tlsNegotiationTimeoutInMillis": {
+        "override": 3100
+      }
+    }
+  },
+  "documentation": {
+      "modes": {
+        "standard": "PLACEHOLDER",
+        "in-region": "PLACEHOLDER",
+        "cross-region": "PLACEHOLDER",
+        "mobile": "PLACEHOLDER",
+        "auto": "PLACEHOLDER",
+        "legacy": "PLACEHOLDER"
+      },
+      "configuration": {
+        "retryMode": "PLACEHOLDER",
+        "stsRegionalEndpoints": "PLACEHOLDER",
+        "s3UsEast1RegionalEndpoints": "PLACEHOLDER",
+        "connectTimeoutInMillis": "PLACEHOLDER",
+        "tlsNegotiationTimeoutInMillis": "PLACEHOLDER"
+      }
+  }
+}
\ No newline at end of file
diff --git a/core/sdk-core/src/test/java/software/amazon/awssdk/core/internal/defaultsmode/DefaultsModeTest.java b/core/sdk-core/src/test/java/software/amazon/awssdk/core/internal/defaultsmode/DefaultsModeTest.java
new file mode 100644
index 000000000000..60e1538c83f9
--- /dev/null
+++ b/core/sdk-core/src/test/java/software/amazon/awssdk/core/internal/defaultsmode/DefaultsModeTest.java
@@ -0,0 +1,135 @@
+/*
+ * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License").
+ * You may not use this file except in compliance with the License.
+ * A copy of the License is located at
+ *
+ *  http://aws.amazon.com/apache2.0
+ *
+ * or in the "license" file accompanying this file. This file is distributed
+ * on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
+ * express or implied. See the License for the specific language governing
+ * permissions and limitations under the License.
+ */
+
+package software.amazon.awssdk.core.internal.defaultsmode;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+
+import java.nio.file.Files;
+import java.nio.file.Paths;
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.concurrent.Callable;
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.Parameterized;
+import software.amazon.awssdk.core.SdkSystemSetting;
+import software.amazon.awssdk.defaultsmode.DefaultsMode;
+import software.amazon.awssdk.profiles.ProfileFileSystemSetting;
+import software.amazon.awssdk.testutils.EnvironmentVariableHelper;
+import software.amazon.awssdk.utils.Validate;
+
+@RunWith(Parameterized.class)
+public class DefaultsModeTest {
+    private static final EnvironmentVariableHelper ENVIRONMENT_VARIABLE_HELPER = new EnvironmentVariableHelper();
+
+    @Parameterized.Parameter
+    public TestData testData;
+
+    @Parameterized.Parameters
+    public static Collection<Object> data() {
+        return Arrays.asList(new Object[] {
+            // Test defaults
+            new TestData(null, null, null, null, DefaultsMode.LEGACY),
+            new TestData(null, null, "PropertyNotSet", null, DefaultsMode.LEGACY),
+
+            // Test resolution
+            new TestData("legacy", null, null, null, DefaultsMode.LEGACY),
+            new TestData("standard", null, null, null, DefaultsMode.STANDARD),
+            new TestData("auto", null, null, null, DefaultsMode.AUTO),
+            new TestData("lEgAcY", null, null, null, DefaultsMode.LEGACY),
+            new TestData("sTanDaRd", null, null, null, DefaultsMode.STANDARD),
+            new TestData("AUtO", null, null, null, DefaultsMode.AUTO),
+
+            // Test precedence
+            new TestData("standard", "legacy", "PropertySetToLegacy", DefaultsMode.LEGACY, DefaultsMode.STANDARD),
+            new TestData("standard", null, null, DefaultsMode.LEGACY, DefaultsMode.STANDARD),
+            new TestData(null, "standard", "PropertySetToLegacy", DefaultsMode.LEGACY, DefaultsMode.STANDARD),
+            new TestData(null, "standard", null, DefaultsMode.LEGACY, DefaultsMode.STANDARD),
+            new TestData(null, null, "PropertySetToStandard", DefaultsMode.LEGACY, DefaultsMode.STANDARD),
+            new TestData(null, null, "PropertySetToAuto", DefaultsMode.LEGACY, DefaultsMode.AUTO),
+            new TestData(null, null, null, DefaultsMode.STANDARD, DefaultsMode.STANDARD),
+
+            // Test invalid values
+            new TestData("wrongValue", null, null, null, IllegalArgumentException.class),
+            new TestData(null, "wrongValue", null, null, IllegalArgumentException.class),
+            new TestData(null, null, "PropertySetToUnsupportedValue", null, IllegalArgumentException.class),
+
+            // Test capitalization standardization
+            new TestData("sTaNdArD", null, null, null, DefaultsMode.STANDARD),
+            new TestData(null, "sTaNdArD", null, null, DefaultsMode.STANDARD),
+            new TestData(null, null, "PropertyMixedCase", null, DefaultsMode.STANDARD),
+            });
+    }
+
+    @Before
+    @After
+    public void methodSetup() {
+        ENVIRONMENT_VARIABLE_HELPER.reset();
+        System.clearProperty(SdkSystemSetting.AWS_DEFAULTS_MODE.property());
+        System.clearProperty(ProfileFileSystemSetting.AWS_PROFILE.property());
+        System.clearProperty(ProfileFileSystemSetting.AWS_CONFIG_FILE.property());
+    }
+
+    @Test
+    public void differentCombinationOfConfigs_shouldResolveCorrectly() throws Exception {
+        if (testData.envVarValue != null) {
+            ENVIRONMENT_VARIABLE_HELPER.set(SdkSystemSetting.AWS_DEFAULTS_MODE.environmentVariable(), testData.envVarValue);
+        }
+
+        if (testData.systemProperty != null) {
+            System.setProperty(SdkSystemSetting.AWS_DEFAULTS_MODE.property(), testData.systemProperty);
+        }
+
+        if (testData.configFile != null) {
+            String diskLocationForFile = diskLocationForConfig(testData.configFile);
+            Validate.isTrue(Files.isReadable(Paths.get(diskLocationForFile)), diskLocationForFile + " is not readable.");
+            System.setProperty(ProfileFileSystemSetting.AWS_PROFILE.property(), "default");
+            System.setProperty(ProfileFileSystemSetting.AWS_CONFIG_FILE.property(), diskLocationForFile);
+        }
+
+        Callable<DefaultsMode> result = DefaultsModeResolver.create().defaultMode(testData.defaultMode)::resolve;
+        if (testData.expected instanceof Class<?>) {
+            Class<?> expectedClassType = (Class<?>) testData.expected;
+            assertThatThrownBy(result::call).isInstanceOf(expectedClassType);
+        } else {
+            assertThat(result.call()).isEqualTo(testData.expected);
+        }
+    }
+
+    private String diskLocationForConfig(String configFileName) {
+        return getClass().getResource(configFileName).getFile();
+    }
+
+
+    private static class TestData {
+        private final String envVarValue;
+        private final String systemProperty;
+        private final String configFile;
+        private final DefaultsMode defaultMode;
+        private final Object expected;
+
+        TestData(String systemProperty, String envVarValue, String configFile, DefaultsMode defaultMode, Object expected) {
+            this.envVarValue = envVarValue;
+            this.systemProperty = systemProperty;
+            this.configFile = configFile;
+            this.defaultMode = defaultMode;
+            this.expected = expected;
+        }
+    }
+}
\ No newline at end of file
diff --git a/core/sdk-core/src/test/resources/software/amazon/awssdk/core/internal/defaultsmode/PropertyMixedCase b/core/sdk-core/src/test/resources/software/amazon/awssdk/core/internal/defaultsmode/PropertyMixedCase
new file mode 100644
index 000000000000..b400595208f4
--- /dev/null
+++ b/core/sdk-core/src/test/resources/software/amazon/awssdk/core/internal/defaultsmode/PropertyMixedCase
@@ -0,0 +1,2 @@
+[default]
+defaults_mode = sTanDard
\ No newline at end of file
diff --git a/core/sdk-core/src/test/resources/software/amazon/awssdk/core/internal/defaultsmode/PropertyNotSet b/core/sdk-core/src/test/resources/software/amazon/awssdk/core/internal/defaultsmode/PropertyNotSet
new file mode 100644
index 000000000000..399487f9b5e5
--- /dev/null
+++ b/core/sdk-core/src/test/resources/software/amazon/awssdk/core/internal/defaultsmode/PropertyNotSet
@@ -0,0 +1 @@
+[default]
\ No newline at end of file
diff --git a/core/sdk-core/src/test/resources/software/amazon/awssdk/core/internal/defaultsmode/PropertySetToAuto b/core/sdk-core/src/test/resources/software/amazon/awssdk/core/internal/defaultsmode/PropertySetToAuto
new file mode 100644
index 000000000000..353d1deb69e6
--- /dev/null
+++ b/core/sdk-core/src/test/resources/software/amazon/awssdk/core/internal/defaultsmode/PropertySetToAuto
@@ -0,0 +1,2 @@
+[default]
+defaults_mode = auto
\ No newline at end of file
diff --git a/core/sdk-core/src/test/resources/software/amazon/awssdk/core/internal/defaultsmode/PropertySetToLegacy b/core/sdk-core/src/test/resources/software/amazon/awssdk/core/internal/defaultsmode/PropertySetToLegacy
new file mode 100644
index 000000000000..db8ae0695416
--- /dev/null
+++ b/core/sdk-core/src/test/resources/software/amazon/awssdk/core/internal/defaultsmode/PropertySetToLegacy
@@ -0,0 +1,2 @@
+[default]
+defaults_mode = legacy
\ No newline at end of file
diff --git a/core/sdk-core/src/test/resources/software/amazon/awssdk/core/internal/defaultsmode/PropertySetToStandard b/core/sdk-core/src/test/resources/software/amazon/awssdk/core/internal/defaultsmode/PropertySetToStandard
new file mode 100644
index 000000000000..fe9ff9fce00e
--- /dev/null
+++ b/core/sdk-core/src/test/resources/software/amazon/awssdk/core/internal/defaultsmode/PropertySetToStandard
@@ -0,0 +1,2 @@
+[default]
+defaults_mode = standard
\ No newline at end of file
diff --git a/core/sdk-core/src/test/resources/software/amazon/awssdk/core/internal/defaultsmode/PropertySetToUnsupportedValue b/core/sdk-core/src/test/resources/software/amazon/awssdk/core/internal/defaultsmode/PropertySetToUnsupportedValue
new file mode 100644
index 000000000000..7f88da4108ab
--- /dev/null
+++ b/core/sdk-core/src/test/resources/software/amazon/awssdk/core/internal/defaultsmode/PropertySetToUnsupportedValue
@@ -0,0 +1,2 @@
+[default]
+defaults_mode = unsupported-value
\ No newline at end of file