diff --git a/src/vs/vscode.proposed.d.ts b/src/vs/vscode.proposed.d.ts
index 0c534c0dbe6..03a9b1c0f74 100644
--- a/src/vs/vscode.proposed.d.ts
+++ b/src/vs/vscode.proposed.d.ts
@@ -1667,10 +1667,11 @@ declare module 'vscode' {
 		languages: string[];
 		displayOrder?: GlobPattern[];
 		metadata: NotebookDocumentMetadata;
-
 	}
 
 	export interface NotebookConcatTextDocument {
+		isClosed: boolean;
+		dispose(): void;
 		onDidChange: Event<void>;
 		version: number;
 		getText(): string;
@@ -1750,6 +1751,13 @@ declare module 'vscode' {
 		export let activeNotebookDocument: NotebookDocument | undefined;
 
 		// export const onDidChangeNotebookDocument: Event<NotebookDocumentChangeEvent>;
+
+		/**
+		 *
+		 * @param notebook
+		 * @param selector
+		 */
+		export function createConcatTextDocument(notebook: NotebookDocument, selector?: DocumentSelector): NotebookConcatTextDocument;
 	}
 
 	//#endregion
diff --git a/src/vs/workbench/api/common/extHost.api.impl.ts b/src/vs/workbench/api/common/extHost.api.impl.ts
index 37cfd826110..bb7efbed94d 100644
--- a/src/vs/workbench/api/common/extHost.api.impl.ts
+++ b/src/vs/workbench/api/common/extHost.api.impl.ts
@@ -73,6 +73,7 @@ import { IExtHostTunnelService } from 'vs/workbench/api/common/extHostTunnelServ
 import { IExtHostApiDeprecationService } from 'vs/workbench/api/common/extHostApiDeprecationService';
 import { ExtHostAuthentication } from 'vs/workbench/api/common/extHostAuthentication';
 import { ExtHostTimeline } from 'vs/workbench/api/common/extHostTimeline';
+import { ExtHostNotebookConcatDocument } from 'vs/workbench/api/common/extHostNotebookConcatDocument';
 
 export interface IExtensionApiFactory {
 	(extension: IExtensionDescription, registry: ExtensionDescriptionRegistry, configProvider: ExtHostConfigProvider): typeof vscode;
@@ -910,6 +911,10 @@ export function createApiFactoryAndRegisterActors(accessor: ServicesAccessor): I
 			},
 			get activeNotebookDocument(): vscode.NotebookDocument | undefined {
 				return extHostNotebook.activeNotebookDocument;
+			},
+			createConcatTextDocument(notebook, selector) {
+				checkProposedApiEnabled(extension);
+				return new ExtHostNotebookConcatDocument(extHostNotebook, extHostDocuments, notebook, selector);
 			}
 		};
 
diff --git a/src/vs/workbench/api/common/extHostNotebookConcatDocument.ts b/src/vs/workbench/api/common/extHostNotebookConcatDocument.ts
index 60e87eca726..887ac671ccf 100644
--- a/src/vs/workbench/api/common/extHostNotebookConcatDocument.ts
+++ b/src/vs/workbench/api/common/extHostNotebookConcatDocument.ts
@@ -6,7 +6,7 @@
 import * as types from 'vs/workbench/api/common/extHostTypes';
 import * as vscode from 'vscode';
 import { Event, Emitter } from 'vs/base/common/event';
-import { ExtHostNotebookDocument, ExtHostNotebookController, ExtHostCell } from 'vs/workbench/api/common/extHostNotebook';
+import { ExtHostNotebookController, ExtHostCell } from 'vs/workbench/api/common/extHostNotebook';
 import { ExtHostDocuments } from 'vs/workbench/api/common/extHostDocuments';
 import { PrefixSumComputer } from 'vs/editor/common/viewModel/prefixSumComputer';
 import { DisposableStore } from 'vs/base/common/lifecycle';
@@ -17,6 +17,7 @@ import { isEqual } from 'vs/base/common/resources';
 export class ExtHostNotebookConcatDocument implements vscode.NotebookConcatTextDocument {
 
 	private _disposables = new DisposableStore();
+	private _isClosed = false;
 
 	private _cells!: ExtHostCell[];
 	private _cellLengths!: PrefixSumComputer;
@@ -29,7 +30,7 @@ export class ExtHostNotebookConcatDocument implements vscode.NotebookConcatTextD
 	constructor(
 		extHostNotebooks: ExtHostNotebookController,
 		extHostDocuments: ExtHostDocuments,
-		private readonly _notebook: ExtHostNotebookDocument,
+		private readonly _notebook: vscode.NotebookDocument,
 		private readonly _selector: vscode.DocumentSelector | undefined,
 	) {
 		this._init();
@@ -54,6 +55,11 @@ export class ExtHostNotebookConcatDocument implements vscode.NotebookConcatTextD
 
 	dispose(): void {
 		this._disposables.dispose();
+		this._isClosed = true;
+	}
+
+	get isClosed() {
+		return this._isClosed;
 	}
 
 	private _init() {
@@ -62,7 +68,7 @@ export class ExtHostNotebookConcatDocument implements vscode.NotebookConcatTextD
 		const cellLineCounts: number[] = [];
 		for (let cell of this._notebook.cells) {
 			if (cell.cellKind === CellKind.Code && (!this._selector || score(this._selector, cell.uri, cell.language, true))) {
-				this._cells.push(cell);
+				this._cells.push(<ExtHostCell>cell);
 				cellLengths.push(cell.document.getText().length + 1);
 				cellLineCounts.push(cell.document.lineCount);
 			}