diff --git a/src/main/java/com/google/devtools/build/lib/packages/StarlarkSemanticsOptions.java b/src/main/java/com/google/devtools/build/lib/packages/StarlarkSemanticsOptions.java
index 56b64015b25316..cce394667af811 100644
--- a/src/main/java/com/google/devtools/build/lib/packages/StarlarkSemanticsOptions.java
+++ b/src/main/java/com/google/devtools/build/lib/packages/StarlarkSemanticsOptions.java
@@ -140,11 +140,9 @@ public class StarlarkSemanticsOptions extends OptionsBase implements Serializabl
               + "debugging.")
   public boolean experimentalPlatformsApi;
 
-  // TODO(cparsons): Resolve and finalize the transition() API. The transition implementation
-  // function should accept two mandatory parameters, 'settings' and 'attr'.
   @Option(
       name = "experimental_starlark_config_transitions",
-      defaultValue = "false",
+      defaultValue = "true",
       documentationCategory = OptionDocumentationCategory.STARLARK_SEMANTICS,
       effectTags = {OptionEffectTag.LOADING_AND_ANALYSIS},
       metadataTags = {OptionMetadataTag.EXPERIMENTAL},
diff --git a/src/main/java/com/google/devtools/build/lib/syntax/StarlarkSemantics.java b/src/main/java/com/google/devtools/build/lib/syntax/StarlarkSemantics.java
index 52c703af04ff09..8412a5114d9c18 100644
--- a/src/main/java/com/google/devtools/build/lib/syntax/StarlarkSemantics.java
+++ b/src/main/java/com/google/devtools/build/lib/syntax/StarlarkSemantics.java
@@ -225,7 +225,7 @@ public static Builder builderWithDefaults() {
           .experimentalGoogleLegacyApi(false)
           .experimentalJavaCommonCreateProviderEnabledPackages(ImmutableList.of())
           .experimentalPlatformsApi(false)
-          .experimentalStarlarkConfigTransitions(false)
+          .experimentalStarlarkConfigTransitions(true)
           .experimentalStarlarkUnusedInputsList(false)
           .incompatibleBzlDisallowLoadAfterStatement(true)
           .incompatibleDepsetIsNotIterable(false)