diff --git a/CHANGELOG.md b/CHANGELOG.md
index 67c6cab5ec..8832eb9a53 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,6 +9,7 @@
 ### Fixed
 
 - Fixed crash when using 3rd party loggers that don't implement `setLevel`. (#8631)
+- Fixed "Slow operations are prohibited on EDT" by migrating `FlutterProjectOpenProcessor` to Kotlin and using `openProjectAsync`. (#8629)
 
 ## 88.1.0
 
diff --git a/build.gradle.kts b/build.gradle.kts
index f17d9de79b..2c70a28158 100644
--- a/build.gradle.kts
+++ b/build.gradle.kts
@@ -141,6 +141,12 @@ sourceSets {
         "third_party/vmServiceDrivers"
       )
     )
+    kotlin.srcDirs(
+      listOf(
+        "src",
+        "third_party/vmServiceDrivers"
+      )
+    )
     // Add kotlin.srcDirs if we start using Kotlin in the main plugin.
     resources.srcDirs(
       listOf(
diff --git a/src/io/flutter/editor/FlutterStudioProjectOpenProcessor.java b/src/io/flutter/editor/FlutterStudioProjectOpenProcessor.java
deleted file mode 100644
index a6681b5a21..0000000000
--- a/src/io/flutter/editor/FlutterStudioProjectOpenProcessor.java
+++ /dev/null
@@ -1,57 +0,0 @@
-/*
- * Copyright 2018 The Chromium Authors. All rights reserved.
- * Use of this source code is governed by a BSD-style license that can be
- * found in the LICENSE file.
- */
-package io.flutter.editor;
-
-import com.intellij.openapi.module.Module;
-import com.intellij.openapi.project.Project;
-import com.intellij.openapi.vfs.VirtualFile;
-import com.intellij.projectImport.ProjectOpenProcessor;
-import com.intellij.ui.EditorNotifications;
-import io.flutter.FlutterUtils;
-import io.flutter.project.FlutterProjectOpenProcessor;
-import io.flutter.pub.PubRoot;
-import io.flutter.utils.FlutterModuleUtils;
-import org.jetbrains.annotations.NotNull;
-import org.jetbrains.annotations.Nullable;
-
-public class FlutterStudioProjectOpenProcessor extends FlutterProjectOpenProcessor {
-  @Override
-  public @NotNull String getName() {
-    return "Flutter Studio";
-  }
-
-  @Override
-  public boolean canOpenProject(@Nullable VirtualFile file) {
-    if (file == null) return false;
-    final PubRoot root = PubRoot.forDirectory(file);
-    return root != null && root.declaresFlutter();
-  }
-
-  @Nullable
-  @Override
-  public Project doOpenProject(@NotNull VirtualFile virtualFile, @Nullable Project projectToClose, boolean forceOpenInNewFrame) {
-    final ProjectOpenProcessor importProvider = getDelegateImportProvider(virtualFile);
-    if (importProvider == null) return null;
-
-    importProvider.doOpenProject(virtualFile, projectToClose, forceOpenInNewFrame);
-    // A callback may have caused the project to be reloaded. Find the new Project object.
-    Project project = FlutterUtils.findProject(virtualFile.getPath());
-    if (project == null || project.isDisposed()) {
-      return project;
-    }
-    for (Module module : FlutterModuleUtils.getModules(project)) {
-      if (FlutterModuleUtils.declaresFlutter(module) && !FlutterModuleUtils.isFlutterModule(module)) {
-        FlutterModuleUtils.setFlutterModuleType(module);
-        FlutterModuleUtils.enableDartSDK(module);
-      }
-    }
-    project.save();
-    EditorNotifications.getInstance(project).updateAllNotifications();
-
-    //FlutterProjectCreator.disableUserConfig(project);
-    return project;
-  }
-}
diff --git a/src/io/flutter/editor/FlutterStudioProjectOpenProcessor.kt b/src/io/flutter/editor/FlutterStudioProjectOpenProcessor.kt
new file mode 100644
index 0000000000..fae83178f5
--- /dev/null
+++ b/src/io/flutter/editor/FlutterStudioProjectOpenProcessor.kt
@@ -0,0 +1,81 @@
+/*
+ * Copyright 2025 The Chromium Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+package io.flutter.editor
+
+import com.intellij.openapi.application.writeAction
+import com.intellij.openapi.project.Project
+import com.intellij.openapi.vfs.VirtualFile
+import com.intellij.projectImport.ProjectOpenProcessor
+import com.intellij.ui.EditorNotifications
+import io.flutter.FlutterUtils
+import io.flutter.project.FlutterProjectOpenProcessor
+import io.flutter.pub.PubRoot
+import io.flutter.utils.FlutterModuleUtils
+
+/**
+ * Originally `FlutterStudioProjectOpenProcessor.java`.
+ *
+ * This processor is specific to Android Studio (or when the Flutter Studio plugin is active).
+ * It extends `FlutterProjectOpenProcessor` to provide specialized handling for Android Studio,
+ * particularly ensuring that the project is correctly re-detected if the opening process causes a reload.
+ *
+ * Converted to Kotlin to support `openProjectAsync`.
+ */
+class FlutterStudioProjectOpenProcessor : FlutterProjectOpenProcessor() {
+  override val name: String
+    get() = "Flutter Studio"
+
+  override fun canOpenProject(file: VirtualFile): Boolean {
+    val root = PubRoot.forDirectory(file)
+    return root != null && root.declaresFlutter()
+  }
+
+  /**
+   * Replaces the deprecated `doOpenProject`.
+   *
+   * Performs the same logic as the original Java implementation but using `suspend` and `writeAction`.
+   *
+   * Key differences from the base class:
+   * - Explicitly looks up the project again using `FlutterUtils.findProject` after opening, as the project instance might have changed
+   *   (e.g. if the platform closed and reopened it during import).
+   * - Ensures Dart SDK is enabled and notifications are updated.
+   */
+  override suspend fun openProjectAsync(
+    virtualFile: VirtualFile,
+    projectToClose: Project?,
+    forceOpenInNewFrame: Boolean,
+  ): Project? {
+    val importProvider = getDelegateImportProvider(virtualFile) ?: return null
+    val project = importProvider.openProjectAsync(virtualFile, projectToClose, forceOpenInNewFrame)
+    
+    // A callback may have caused the project to be reloaded. Find the new Project object.
+    val newProject = FlutterUtils.findProject(virtualFile.path)
+    if (newProject == null || newProject.isDisposed) {
+      return newProject
+    }
+
+    writeAction {
+      for (module in FlutterModuleUtils.getModules(newProject)) {
+        if (FlutterModuleUtils.declaresFlutter(module) && !FlutterModuleUtils.isFlutterModule(module)) {
+          FlutterModuleUtils.setFlutterModuleType(module)
+          FlutterModuleUtils.enableDartSDK(module)
+        }
+      }
+      newProject.save()
+      EditorNotifications.getInstance(newProject).updateAllNotifications()
+    }
+    
+    return newProject
+  }
+
+  override fun doOpenProject(
+    virtualFile: VirtualFile,
+    projectToClose: Project?,
+    forceOpenInNewFrame: Boolean,
+  ): Project? {
+    return null
+  }
+}
diff --git a/src/io/flutter/project/FlutterProjectOpenProcessor.java b/src/io/flutter/project/FlutterProjectOpenProcessor.java
deleted file mode 100644
index 69427c9a98..0000000000
--- a/src/io/flutter/project/FlutterProjectOpenProcessor.java
+++ /dev/null
@@ -1,97 +0,0 @@
-/*
- * Copyright 2017 The Chromium Authors. All rights reserved.
- * Use of this source code is governed by a BSD-style license that can be
- * found in the LICENSE file.
- */
-package io.flutter.project;
-
-import com.intellij.openapi.application.ApplicationInfo;
-import com.intellij.openapi.module.Module;
-import com.intellij.openapi.project.Project;
-import com.intellij.openapi.vfs.VirtualFile;
-import com.intellij.projectImport.ProjectOpenProcessor;
-import icons.FlutterIcons;
-import io.flutter.FlutterBundle;
-import io.flutter.FlutterUtils;
-import io.flutter.ProjectOpenActivity;
-import io.flutter.pub.PubRoot;
-import io.flutter.utils.FlutterModuleUtils;
-import org.jetbrains.annotations.NotNull;
-import org.jetbrains.annotations.Nullable;
-
-import javax.swing.*;
-import java.util.Objects;
-
-public class FlutterProjectOpenProcessor extends ProjectOpenProcessor {
-
-  @Override
-  public @NotNull String getName() {
-    return FlutterBundle.message("flutter.module.name");
-  }
-
-  @Override
-  public Icon getIcon() {
-    return FlutterIcons.Flutter;
-  }
-
-  @Override
-  public boolean canOpenProject(@Nullable VirtualFile file) {
-    if (file == null) return false;
-    final ApplicationInfo info = ApplicationInfo.getInstance();
-    if (FlutterUtils.isAndroidStudio()) {
-      return false;
-    }
-    final PubRoot root = PubRoot.forDirectory(file);
-    return root != null && root.declaresFlutter();
-  }
-
-  /**
-   * Runs when a project is opened by selecting the project directly, possibly for import.
-   * <p>
-   * Doesn't run when a project is opened via recent projects menu (and so on). Actions that
-   * should run every time a project is opened should be in
-   * {@link ProjectOpenActivity} or {@link io.flutter.FlutterInitializer}.
-   */
-  @Nullable
-  @Override
-  public Project doOpenProject(@NotNull VirtualFile file, @Nullable Project projectToClose, boolean forceOpenInNewFrame) {
-    // Delegate opening to the platform open processor.
-    final ProjectOpenProcessor importProvider = getDelegateImportProvider(file);
-    if (importProvider == null) return null;
-
-    final Project project = importProvider.doOpenProject(file, projectToClose, forceOpenInNewFrame);
-    if (project == null || project.isDisposed()) return project;
-
-    // Convert any modules that use Flutter but don't have IntelliJ Flutter metadata.
-    convertToFlutterProject(project);
-
-    // Project gets reloaded; should this be: FlutterUtils.findProject(file.getPath());
-    return project;
-  }
-
-  @Nullable
-  protected ProjectOpenProcessor getDelegateImportProvider(@NotNull VirtualFile file) {
-    //noinspection DataFlowIssue
-    return EXTENSION_POINT_NAME.getExtensionList().stream().filter(
-      processor -> processor.canOpenProject(file) && !Objects.equals(processor.getName(), getName())
-    ).findFirst().orElse(null);
-  }
-
-  /**
-   * Sets up a project that doesn't have any Flutter modules.
-   * <p>
-   * (It probably wasn't created with "flutter create" and probably didn't have any IntelliJ configuration before.)
-   */
-  private static void convertToFlutterProject(@NotNull Project project) {
-    for (Module module : FlutterModuleUtils.getModules(project)) {
-      if (FlutterModuleUtils.declaresFlutter(module) && !FlutterModuleUtils.isFlutterModule(module)) {
-        FlutterModuleUtils.setFlutterModuleAndReload(module, project);
-      }
-    }
-  }
-
-  @Override
-  public boolean isStrongProjectInfoHolder() {
-    return true;
-  }
-}
diff --git a/src/io/flutter/project/FlutterProjectOpenProcessor.kt b/src/io/flutter/project/FlutterProjectOpenProcessor.kt
new file mode 100644
index 0000000000..dab85dac64
--- /dev/null
+++ b/src/io/flutter/project/FlutterProjectOpenProcessor.kt
@@ -0,0 +1,116 @@
+/*
+ * Copyright 2025 The Chromium Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+package io.flutter.project
+
+import com.intellij.openapi.application.ApplicationInfo
+import com.intellij.openapi.application.writeAction
+import com.intellij.openapi.module.Module
+import com.intellij.openapi.project.Project
+import com.intellij.openapi.vfs.VirtualFile
+import com.intellij.projectImport.ProjectOpenProcessor
+import icons.FlutterIcons
+import io.flutter.FlutterBundle
+import io.flutter.FlutterUtils
+import io.flutter.pub.PubRoot
+import io.flutter.utils.FlutterModuleUtils
+import java.util.Objects
+import javax.swing.Icon
+
+/**
+ * Originally `FlutterProjectOpenProcessor.java`.
+ *
+ * This processor handles opening Flutter projects when they are selected directly (e.g. via "Open" in the IDE).
+ * It delegates the actual opening to the platform's default processor (e.g. Gradle or Maven processor if applicable,
+ * or the generic project opener) and then ensures that any modules in the project are correctly configured as Flutter modules.
+ *
+ * Converted to Kotlin to support `openProjectAsync` which is a suspend function.
+ */
+open class FlutterProjectOpenProcessor : ProjectOpenProcessor() {
+  override val name: String
+    get() = FlutterBundle.message("flutter.module.name")
+
+  override fun getIcon(file: VirtualFile): Icon? {
+    return FlutterIcons.Flutter
+  }
+
+  override fun canOpenProject(file: VirtualFile): Boolean {
+    val info = ApplicationInfo.getInstance()
+    if (FlutterUtils.isAndroidStudio()) {
+      return false
+    }
+    val root = PubRoot.forDirectory(file)
+    return root != null && root.declaresFlutter()
+  }
+
+  /**
+   * Replaces the deprecated `doOpenProject`.
+   *
+   * This method is `suspend` and must be used instead of `doOpenProject` to avoid `IllegalStateException` in newer IDE versions.
+   *
+   * It performs the following steps:
+   * 1. Finds a delegate processor (e.g. Gradle) to open the project.
+   * 2. Opens the project asynchronously.
+   * 3. Once opened, checks if the project contains Flutter modules that are not yet configured as such (e.g. missing module type).
+   * 4. Configures these modules as Flutter modules within a write action.
+   */
+  override suspend fun openProjectAsync(
+    virtualFile: VirtualFile,
+    projectToClose: Project?,
+    forceOpenInNewFrame: Boolean,
+  ): Project? {
+    // Delegate opening to the platform open processor.
+    val importProvider = getDelegateImportProvider(virtualFile) ?: return null
+    val project = importProvider.openProjectAsync(virtualFile, projectToClose, forceOpenInNewFrame)
+    if (project == null || project.isDisposed) return project
+
+    // Convert any modules that use Flutter but don't have IntelliJ Flutter metadata.
+    writeAction {
+      convertToFlutterProject(project)
+    }
+
+    return project
+  }
+
+  /**
+   * Deprecated method, kept to satisfy the compiler/interface.
+   *
+   * We return `null` to indicate that this processor does not support the synchronous opening method
+   * and that `openProjectAsync` should be used instead.
+   */
+  override fun doOpenProject(
+    virtualFile: VirtualFile,
+    projectToClose: Project?,
+    forceOpenInNewFrame: Boolean,
+  ): Project? {
+    return null
+  }
+
+  protected open fun getDelegateImportProvider(file: VirtualFile): ProjectOpenProcessor? {
+    return EXTENSION_POINT_NAME.extensionList.stream().filter { processor: ProjectOpenProcessor ->
+      processor.canOpenProject(file) && !Objects.equals(
+        processor.name,
+        name
+      )
+    }.findFirst().orElse(null)
+  }
+
+
+  companion object {
+    /**
+     * Sets up a project that doesn't have any Flutter modules.
+     *
+     *
+     * (It probably wasn't created with "flutter create" and probably didn't have any IntelliJ configuration before.)
+     */
+    private fun convertToFlutterProject(project: Project) {
+      for (module in FlutterModuleUtils.getModules(project)) {
+        if (FlutterModuleUtils.declaresFlutter(module) && !FlutterModuleUtils.isFlutterModule(module)) {
+          FlutterModuleUtils.setFlutterModuleAndReload(module, project)
+        }
+      }
+    }
+  }
+}