diff --git a/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/cinterop-MetadataDependencyTransformation/p1/build.gradle.kts b/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/cinterop-MetadataDependencyTransformation/p1/build.gradle.kts
index 55c76108179..751c3fb0f6d 100644
--- a/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/cinterop-MetadataDependencyTransformation/p1/build.gradle.kts
+++ b/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/cinterop-MetadataDependencyTransformation/p1/build.gradle.kts
@@ -87,4 +87,8 @@ kotlin {
             header(file("libs/simple.h"))
         }
     }
+
+    sourceSets.all {
+        languageSettings.optIn("kotlinx.cinterop.ExperimentalForeignApi")
+    }
 }
diff --git a/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/cinterop-MetadataDependencyTransformation/p2/build.gradle.kts b/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/cinterop-MetadataDependencyTransformation/p2/build.gradle.kts
index 56e4723f139..cb0aa68a3b9 100644
--- a/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/cinterop-MetadataDependencyTransformation/p2/build.gradle.kts
+++ b/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/cinterop-MetadataDependencyTransformation/p2/build.gradle.kts
@@ -114,4 +114,8 @@ kotlin {
             }
         }
     }
+
+    sourceSets.all {
+        languageSettings.optIn("kotlinx.cinterop.ExperimentalForeignApi")
+    }
 }
diff --git a/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/cinterop-MetadataDependencyTransformation/p3/build.gradle.kts b/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/cinterop-MetadataDependencyTransformation/p3/build.gradle.kts
index 4d93bcac92b..08ec0f85891 100644
--- a/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/cinterop-MetadataDependencyTransformation/p3/build.gradle.kts
+++ b/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/cinterop-MetadataDependencyTransformation/p3/build.gradle.kts
@@ -100,4 +100,8 @@ kotlin {
     sourceSets.commonMain.get().dependencies {
         implementation(project(":p2"))
     }
+
+    sourceSets.all {
+        languageSettings.optIn("kotlinx.cinterop.ExperimentalForeignApi")
+    }
 }
diff --git a/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/common-klib-lib-and-app/build.gradle.kts b/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/common-klib-lib-and-app/build.gradle.kts
index 5a358107ac5..02a8ec4b962 100644
--- a/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/common-klib-lib-and-app/build.gradle.kts
+++ b/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/common-klib-lib-and-app/build.gradle.kts
@@ -78,6 +78,10 @@ kotlin {
 		configure(listOf(mingwX64(), mingwX86())) {
 			compilations["main"].defaultSourceSet.dependsOn(windowsMain)
 		}
+
+		all {
+			languageSettings.optIn("kotlinx.cinterop.ExperimentalForeignApi")
+		}
 	}
 }
 
diff --git a/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/commonize-kt-51517-transitive-cinterop/app/build.gradle.kts b/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/commonize-kt-51517-transitive-cinterop/app/build.gradle.kts
index 8f85695f835..fec7b4fff86 100644
--- a/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/commonize-kt-51517-transitive-cinterop/app/build.gradle.kts
+++ b/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/commonize-kt-51517-transitive-cinterop/app/build.gradle.kts
@@ -47,4 +47,8 @@ kotlin {
             mingwX64Test.dependsOn(this)
         }
     }
+
+    sourceSets.all {
+        languageSettings.optIn("kotlinx.cinterop.ExperimentalForeignApi")
+    }
 }
diff --git a/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/commonize-kt-52050-DIR-supertype/build.gradle.kts b/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/commonize-kt-52050-DIR-supertype/build.gradle.kts
index a3a543c9d8b..33a80458b93 100644
--- a/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/commonize-kt-52050-DIR-supertype/build.gradle.kts
+++ b/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/commonize-kt-52050-DIR-supertype/build.gradle.kts
@@ -21,4 +21,8 @@ kotlin {
     unixMain.dependsOn(commonMain)
     linuxMain.dependsOn(unixMain)
     macosMain.dependsOn(unixMain)
+
+    sourceSets.all {
+        languageSettings.optIn("kotlinx.cinterop.ExperimentalForeignApi")
+    }
 }
diff --git a/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/commonizeCurlInterop/build.gradle.kts b/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/commonizeCurlInterop/build.gradle.kts
index b226c7f394b..75d387eec05 100644
--- a/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/commonizeCurlInterop/build.gradle.kts
+++ b/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/commonizeCurlInterop/build.gradle.kts
@@ -22,6 +22,7 @@ kotlin {
 
     sourceSets.all {
         languageSettings.optIn("kotlin.RequiresOptIn")
+        languageSettings.optIn("kotlinx.cinterop.ExperimentalForeignApi")
     }
 
     targetA.compilations.getByName("main").cinterops.create("curl")
diff --git a/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/commonizeHierarchically/p1/build.gradle.kts b/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/commonizeHierarchically/p1/build.gradle.kts
index f1b196d75e9..02ccfce8b97 100644
--- a/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/commonizeHierarchically/p1/build.gradle.kts
+++ b/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/commonizeHierarchically/p1/build.gradle.kts
@@ -41,6 +41,7 @@ kotlin {
 
     sourceSets.all {
         languageSettings.optIn("kotlin.RequiresOptIn")
+        languageSettings.optIn("kotlinx.cinterop.ExperimentalForeignApi")
     }
 
     targets.withType<KotlinNativeTarget>().forEach { target ->
diff --git a/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/commonizeHierarchicallyMultiModule/p1/build.gradle.kts b/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/commonizeHierarchicallyMultiModule/p1/build.gradle.kts
index 6cef2512b8f..bad0ec371cd 100644
--- a/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/commonizeHierarchicallyMultiModule/p1/build.gradle.kts
+++ b/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/commonizeHierarchicallyMultiModule/p1/build.gradle.kts
@@ -66,9 +66,9 @@ kotlin {
         }
     }
 
-
     sourceSets.all {
         languageSettings.optIn("kotlin.RequiresOptIn")
+        languageSettings.optIn("kotlinx.cinterop.ExperimentalForeignApi")
     }
 
     targets.withType<KotlinNativeTarget>().forEach { target ->
diff --git a/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/commonizeHierarchicallyMultiModule/p2/build.gradle.kts b/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/commonizeHierarchicallyMultiModule/p2/build.gradle.kts
index e356f6f4a04..30f2f2315dc 100644
--- a/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/commonizeHierarchicallyMultiModule/p2/build.gradle.kts
+++ b/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/commonizeHierarchicallyMultiModule/p2/build.gradle.kts
@@ -72,6 +72,7 @@ kotlin {
 
     sourceSets.all {
         languageSettings.optIn("kotlin.RequiresOptIn")
+        languageSettings.optIn("kotlinx.cinterop.ExperimentalForeignApi")
     }
 
     targets.withType<KotlinNativeTarget>().forEach { target ->
diff --git a/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/commonizeHierarchicallyMultiModule/p3/build.gradle.kts b/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/commonizeHierarchicallyMultiModule/p3/build.gradle.kts
index 9a3f0015a3d..bad0ec371cd 100644
--- a/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/commonizeHierarchicallyMultiModule/p3/build.gradle.kts
+++ b/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/commonizeHierarchicallyMultiModule/p3/build.gradle.kts
@@ -68,6 +68,7 @@ kotlin {
 
     sourceSets.all {
         languageSettings.optIn("kotlin.RequiresOptIn")
+        languageSettings.optIn("kotlinx.cinterop.ExperimentalForeignApi")
     }
 
     targets.withType<KotlinNativeTarget>().forEach { target ->
diff --git a/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/commonizeInteropUsingPosixApis/build.gradle.kts b/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/commonizeInteropUsingPosixApis/build.gradle.kts
index 0d92ddea753..f7969fd93e7 100644
--- a/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/commonizeInteropUsingPosixApis/build.gradle.kts
+++ b/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/commonizeInteropUsingPosixApis/build.gradle.kts
@@ -23,6 +23,7 @@ kotlin {
 
     sourceSets.all {
         languageSettings.optIn("kotlin.RequiresOptIn")
+        languageSettings.optIn("kotlinx.cinterop.ExperimentalForeignApi")
     }
 
     targetA.compilations.getByName("main").cinterops.create("withPosix") {
diff --git a/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/commonizeMultipleCInteropsWithTests/build.gradle.kts b/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/commonizeMultipleCInteropsWithTests/build.gradle.kts
index 0ae2f114539..6b676a67d7d 100644
--- a/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/commonizeMultipleCInteropsWithTests/build.gradle.kts
+++ b/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/commonizeMultipleCInteropsWithTests/build.gradle.kts
@@ -140,4 +140,8 @@ kotlin {
             }
         }
     }
+
+    sourceSets.all {
+        languageSettings.optIn("kotlinx.cinterop.ExperimentalForeignApi")
+    }
 }
diff --git a/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/commonizeSQLiteAndCurlInterop/build.gradle.kts b/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/commonizeSQLiteAndCurlInterop/build.gradle.kts
index f88ffa3dcc6..67ad7bfe285 100644
--- a/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/commonizeSQLiteAndCurlInterop/build.gradle.kts
+++ b/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/commonizeSQLiteAndCurlInterop/build.gradle.kts
@@ -22,6 +22,7 @@ kotlin {
 
     sourceSets.all {
         languageSettings.optIn("kotlin.RequiresOptIn")
+        languageSettings.optIn("kotlinx.cinterop.ExperimentalForeignApi")
     }
 
     targetA.compilations.getByName("main").cinterops.create("sqlite")
diff --git a/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/mpp-composite-build/sample4-KT-37051-withCInterop/consumerBuild/consumerA/src/nativeMain/kotlin/ConsumerANative.kt b/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/mpp-composite-build/sample4-KT-37051-withCInterop/consumerBuild/consumerA/src/nativeMain/kotlin/ConsumerANative.kt
index 67236db2c1c..9bd158395d0 100644
--- a/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/mpp-composite-build/sample4-KT-37051-withCInterop/consumerBuild/consumerA/src/nativeMain/kotlin/ConsumerANative.kt
+++ b/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/mpp-composite-build/sample4-KT-37051-withCInterop/consumerBuild/consumerA/src/nativeMain/kotlin/ConsumerANative.kt
@@ -2,6 +2,7 @@
  * Copyright 2010-2023 JetBrains s.r.o. and Kotlin Programming Language contributors.
  * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
  */
+@file:OptIn(kotlinx.cinterop.ExperimentalForeignApi::class)
 
 import kotlinx.cinterop.memScoped
 import platform.posix.fopen
diff --git a/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/mpp-composite-build/sample4-KT-37051-withCInterop/consumerBuild/consumerA/src/src/commonMain/kotlin/ConsumerACommon.kt b/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/mpp-composite-build/sample4-KT-37051-withCInterop/consumerBuild/consumerA/src/src/commonMain/kotlin/ConsumerACommon.kt
deleted file mode 100644
index 800fcda56bf..00000000000
--- a/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/mpp-composite-build/sample4-KT-37051-withCInterop/consumerBuild/consumerA/src/src/commonMain/kotlin/ConsumerACommon.kt
+++ /dev/null
@@ -1,10 +0,0 @@
-/*
- * Copyright 2010-2023 JetBrains s.r.o. and Kotlin Programming Language contributors.
- * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
- */
-
-object ConsumerACommon {
-    init {
-        ProducerACommonX
-    }
-}
\ No newline at end of file
diff --git a/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/mpp-composite-build/sample4-KT-37051-withCInterop/consumerBuild/consumerA/src/src/linuxX64Main/kotlin/ConsumerALinuxX64.kt b/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/mpp-composite-build/sample4-KT-37051-withCInterop/consumerBuild/consumerA/src/src/linuxX64Main/kotlin/ConsumerALinuxX64.kt
deleted file mode 100644
index 68b3ac37a17..00000000000
--- a/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/mpp-composite-build/sample4-KT-37051-withCInterop/consumerBuild/consumerA/src/src/linuxX64Main/kotlin/ConsumerALinuxX64.kt
+++ /dev/null
@@ -1,16 +0,0 @@
-/*
- * Copyright 2010-2023 JetBrains s.r.o. and Kotlin Programming Language contributors.
- * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
- */
-
-import clib.myCFunction
-
-object ConsumerALinuxX64 {
-    init {
-        ProducerACommonX
-        ProducerANative
-        ProducerALinuxX64
-
-        myCFunction()
-    }
-}
\ No newline at end of file
diff --git a/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/mpp-composite-build/sample4-KT-37051-withCInterop/consumerBuild/consumerA/src/src/nativeMain/kotlin/ConsumerANative.kt b/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/mpp-composite-build/sample4-KT-37051-withCInterop/consumerBuild/consumerA/src/src/nativeMain/kotlin/ConsumerANative.kt
deleted file mode 100644
index 67236db2c1c..00000000000
--- a/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/mpp-composite-build/sample4-KT-37051-withCInterop/consumerBuild/consumerA/src/src/nativeMain/kotlin/ConsumerANative.kt
+++ /dev/null
@@ -1,15 +0,0 @@
-/*
- * Copyright 2010-2023 JetBrains s.r.o. and Kotlin Programming Language contributors.
- * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
- */
-
-import kotlinx.cinterop.memScoped
-import platform.posix.fopen
-
-object ConsumerANative {
-    init {
-        memScoped {  }
-        fopen("", "")
-        ProducerANative
-    }
-}
\ No newline at end of file
diff --git a/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/new-mpp-klibs-with-same-name/foo/build.gradle.kts b/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/new-mpp-klibs-with-same-name/foo/build.gradle.kts
index 6833bfa723e..87b533b7608 100644
--- a/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/new-mpp-klibs-with-same-name/foo/build.gradle.kts
+++ b/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/new-mpp-klibs-with-same-name/foo/build.gradle.kts
@@ -20,6 +20,10 @@ kotlin {
     sourceSets["jsMain"].dependencies {
         implementation(kotlin("stdlib-js"))
     }
+
+    sourceSets.all {
+        languageSettings.optIn("kotlinx.cinterop.ExperimentalForeignApi")
+    }
 }
 
 
diff --git a/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/new-mpp-klibs-with-same-name/foo/foo/build.gradle.kts b/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/new-mpp-klibs-with-same-name/foo/foo/build.gradle.kts
index fad615393a2..ad56f150a90 100644
--- a/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/new-mpp-klibs-with-same-name/foo/foo/build.gradle.kts
+++ b/libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/new-mpp-klibs-with-same-name/foo/foo/build.gradle.kts
@@ -19,4 +19,8 @@ kotlin {
     sourceSets["jsMain"].dependencies {
         implementation(kotlin("stdlib-js"))
     }
+
+    sourceSets.all {
+        languageSettings.optIn("kotlinx.cinterop.ExperimentalForeignApi")
+    }
 }