diff --git a/src/parser/gjs-gts-parser.js b/src/parser/gjs-gts-parser.js
index ce9702f..b9b662a 100644
--- a/src/parser/gjs-gts-parser.js
+++ b/src/parser/gjs-gts-parser.js
@@ -159,7 +159,7 @@ module.exports = {
 
     let result = null;
     const filePath = options.filePath;
-    if (options.project) {
+    if (options.project || options.projectService) {
       jsCode = replaceExtensions(jsCode);
     }
 
diff --git a/test-projects/configs/flat-ts/eslint.config.mjs b/test-projects/configs/flat-ts/eslint.config.mjs
index a7c9d80..e4bffd9 100644
--- a/test-projects/configs/flat-ts/eslint.config.mjs
+++ b/test-projects/configs/flat-ts/eslint.config.mjs
@@ -21,6 +21,13 @@ import n from 'eslint-plugin-n';
 import globals from 'globals';
 import ts from 'typescript-eslint';
 
+
+import { createRequire } from 'node:module';
+const require = createRequire(import.meta.url);
+const manifestPath = require.resolve('@typescript-eslint/parser/package.json');
+const manifest = require(manifestPath);
+const isV8 = parseInt(manifest.version[0]) >= 8;
+
 const parserOptions = {
   esm: {
     js: {
@@ -29,7 +36,7 @@ const parserOptions = {
     },
     ts: {
       projectService: true,
-      project: true,
+      ...(isV8 ? {} : { project: true }),
       tsconfigRootDir: import.meta.dirname,
     },
   },
diff --git a/test-projects/configs/flat-ts/tsconfig.json b/test-projects/configs/flat-ts/tsconfig.json
index 48ae5f1..f940e9c 100644
--- a/test-projects/configs/flat-ts/tsconfig.json
+++ b/test-projects/configs/flat-ts/tsconfig.json
@@ -1,6 +1,5 @@
 {
   "extends": "@tsconfig/ember/tsconfig.json",
-  "include": ["src/**/*", "unpublished-development-types/**/*"],
   "compilerOptions": {
     "allowJs": true,
     "declarationDir": "declarations",
diff --git a/test-projects/gjs-types/.eslintrc.cjs b/test-projects/gjs-types/.eslintrc.cjs
index 679a698..1e4a766 100644
--- a/test-projects/gjs-types/.eslintrc.cjs
+++ b/test-projects/gjs-types/.eslintrc.cjs
@@ -3,16 +3,24 @@
 const path = require('path');
 
 const parserOptions = {};
-if (process.env.PROJECT_SERVICE) {
+// if (process.env.PROJECT_SERVICE) {
   parserOptions.projectService = {
-    defaultProject: process.env.DEFAULT_PROJECT || 'tsconfig.json',
+    defaultProject: process.env.DEFAULT_PROJECT || process.env.PROJECT || 'tsconfig.json',
     allowDefaultProject: process.env.ALLOW_DEFAULT_PROJECT === 'true' ? ['**/*.js'] : []
   };
-}
+// }
 
 parserOptions.tsconfigRootDir = process.env.TSCONFIG_ROOT_DIR || __dirname;
 parserOptions.project = process.env.PROJECT === undefined ? true : process.env.PROJECT;
 
+const manifestPath = require.resolve('@typescript-eslint/parser/package.json');
+const manifest = require(manifestPath);
+const isV8 = parseInt(manifest.version[0]) >= 8;
+
+if (isV8) {
+  delete parserOptions.project;
+}
+
 module.exports = {
   root: true,
   parserOptions,
diff --git a/test-projects/gts/.eslintrc.cjs b/test-projects/gts/.eslintrc.cjs
index 7b71c38..1226ced 100644
--- a/test-projects/gts/.eslintrc.cjs
+++ b/test-projects/gts/.eslintrc.cjs
@@ -1,9 +1,13 @@
 'use strict';
 
+const manifestPath = require.resolve('@typescript-eslint/parser/package.json');
+const manifest = require(manifestPath);
+const isV8 = parseInt(manifest.version[0]) >= 8;
+
 module.exports = {
   root: true,
   parserOptions: {
-    project: true,
+    ...(isV8 ? {} : { project: true }),
     projectService: true,
     tsconfigRootDir: __dirname
   },