diff --git a/build/package.json b/build/package.json
index e185594554b..7392e4b602c 100644
--- a/build/package.json
+++ b/build/package.json
@@ -45,7 +45,7 @@
     "minimist": "^1.2.3",
     "request": "^2.85.0",
     "terser": "4.3.8",
-    "typescript": "^4.1.0-dev.20200824",
+    "typescript": "^4.0.1-rc",
     "vsce": "1.48.0",
     "vscode-telemetry-extractor": "^1.6.0",
     "xml2js": "^0.4.17"
diff --git a/build/yarn.lock b/build/yarn.lock
index 01ebd186c4c..d610f9cefa7 100644
--- a/build/yarn.lock
+++ b/build/yarn.lock
@@ -2535,10 +2535,10 @@ typescript@^3.0.1:
   resolved "https://registry.yarnpkg.com/typescript/-/typescript-3.5.3.tgz#c830f657f93f1ea846819e929092f5fe5983e977"
   integrity sha512-ACzBtm/PhXBDId6a6sDJfroT2pOWt/oOnk4/dElG5G33ZL776N3Y6/6bKZJBFpd+b05F3Ct9qDjMeJmRWtE2/g==
 
-typescript@^4.1.0-dev.20200824:
-  version "4.1.0-dev.20200824"
-  resolved "https://registry.yarnpkg.com/typescript/-/typescript-4.1.0-dev.20200824.tgz#34c92d9b6e5124600658c0d4e9b8c125beaf577d"
-  integrity sha512-hTJfocmebnMKoqRw/xs3bL61z87XXtvOUwYtM7zaCX9mAvnfdo1x1bzQlLZAsvdzRIgAHPJQYbqYHKygWkDw6g==
+typescript@^4.0.1-rc:
+  version "4.0.1-rc"
+  resolved "https://registry.yarnpkg.com/typescript/-/typescript-4.0.1-rc.tgz#8adc78223eae56fe71d906a5fa90c3543b07a677"
+  integrity sha512-TCkspT3dSKOykbzS3/WSK7pqU2h1d/lEO6i45Afm5Y3XNAEAo8YXTG3kHOQk/wFq/5uPyO1+X8rb/Q+g7UsxJw==
 
 typical@^4.0.0:
   version "4.0.0"
diff --git a/package.json b/package.json
index 1858ff663b8..a50ce5cc307 100644
--- a/package.json
+++ b/package.json
@@ -164,7 +164,7 @@
     "source-map": "^0.4.4",
     "style-loader": "^1.0.0",
     "ts-loader": "^4.4.2",
-    "typescript": "^4.1.0-dev.20200824",
+    "typescript": "^4.0.1-rc",
     "typescript-formatter": "7.1.0",
     "underscore": "^1.8.2",
     "vinyl": "^2.0.0",
diff --git a/src/vs/platform/workspace/common/workspace.ts b/src/vs/platform/workspace/common/workspace.ts
index c0c34d74f57..0f2e82d0e85 100644
--- a/src/vs/platform/workspace/common/workspace.ts
+++ b/src/vs/platform/workspace/common/workspace.ts
@@ -82,9 +82,9 @@ export interface IWorkspaceFoldersChangeEvent {
 
 export namespace IWorkspace {
 	export function isIWorkspace(thing: unknown): thing is IWorkspace {
-		return !!(thing && typeof thing === 'object'
+		return thing && typeof thing === 'object'
 			&& typeof (thing as IWorkspace).id === 'string'
-			&& Array.isArray((thing as IWorkspace).folders));
+			&& Array.isArray((thing as IWorkspace).folders);
 	}
 }
 
@@ -127,10 +127,10 @@ export interface IWorkspaceFolderData {
 
 export namespace IWorkspaceFolder {
 	export function isIWorkspaceFolder(thing: unknown): thing is IWorkspaceFolder {
-		return !!(thing && typeof thing === 'object'
+		return thing && typeof thing === 'object'
 			&& URI.isUri((thing as IWorkspaceFolder).uri)
 			&& typeof (thing as IWorkspaceFolder).name === 'string'
-			&& typeof (thing as IWorkspaceFolder).toResource === 'function');
+			&& typeof (thing as IWorkspaceFolder).toResource === 'function';
 	}
 }
 
diff --git a/src/vs/workbench/common/editor/editorGroup.ts b/src/vs/workbench/common/editor/editorGroup.ts
index 97c2058102e..57e5432ed19 100644
--- a/src/vs/workbench/common/editor/editorGroup.ts
+++ b/src/vs/workbench/common/editor/editorGroup.ts
@@ -55,7 +55,7 @@ export interface ISerializedEditorGroup {
 export function isSerializedEditorGroup(obj?: unknown): obj is ISerializedEditorGroup {
 	const group = obj as ISerializedEditorGroup;
 
-	return !!(obj && typeof obj === 'object' && Array.isArray(group.editors) && Array.isArray(group.mru));
+	return obj && typeof obj === 'object' && Array.isArray(group.editors) && Array.isArray(group.mru);
 }
 
 export class EditorGroup extends Disposable {
diff --git a/yarn.lock b/yarn.lock
index e813c24b15d..b760c375232 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -9369,10 +9369,10 @@ typescript@^2.6.2:
   resolved "https://registry.yarnpkg.com/typescript/-/typescript-2.6.2.tgz#3c5b6fd7f6de0914269027f03c0946758f7673a4"
   integrity sha1-PFtv1/beCRQmkCfwPAlGdY92c6Q=
 
-typescript@^4.1.0-dev.20200824:
-  version "4.1.0-dev.20200824"
-  resolved "https://registry.yarnpkg.com/typescript/-/typescript-4.1.0-dev.20200824.tgz#34c92d9b6e5124600658c0d4e9b8c125beaf577d"
-  integrity sha512-hTJfocmebnMKoqRw/xs3bL61z87XXtvOUwYtM7zaCX9mAvnfdo1x1bzQlLZAsvdzRIgAHPJQYbqYHKygWkDw6g==
+typescript@^4.0.1-rc:
+  version "4.0.1-rc"
+  resolved "https://registry.yarnpkg.com/typescript/-/typescript-4.0.1-rc.tgz#8adc78223eae56fe71d906a5fa90c3543b07a677"
+  integrity sha512-TCkspT3dSKOykbzS3/WSK7pqU2h1d/lEO6i45Afm5Y3XNAEAo8YXTG3kHOQk/wFq/5uPyO1+X8rb/Q+g7UsxJw==
 
 uc.micro@^1.0.1, uc.micro@^1.0.3:
   version "1.0.3"