diff --git a/src/vs/vscode.proposed.d.ts b/src/vs/vscode.proposed.d.ts
index bf24ab9b655..a06d8165fab 100644
--- a/src/vs/vscode.proposed.d.ts
+++ b/src/vs/vscode.proposed.d.ts
@@ -1507,9 +1507,9 @@ declare module 'vscode' {
 
 		readonly mime: string;
 		readonly value: unknown;
-		readonly metadata?: Record<string, string | number | boolean | unknown>;
+		readonly metadata?: Record<string, any>;
 
-		constructor(mime: string, value: unknown, metadata?: Record<string, string | number | boolean | unknown>);
+		constructor(mime: string, value: unknown, metadata?: Record<string, any>);
 	}
 
 	// @jrieken
@@ -1517,7 +1517,11 @@ declare module 'vscode' {
 	export class NotebookCellOutput {
 		readonly id: string;
 		readonly outputs: NotebookCellOutputItem[];
-		constructor(outputs: NotebookCellOutputItem[], id?: string);
+		readonly metadata?: Record<string, any>;
+
+		constructor(outputs: NotebookCellOutputItem[], metadata?: Record<string, any>);
+
+		constructor(outputs: NotebookCellOutputItem[], id: string, metadata?: Record<string, any>);
 	}
 
 	//#endregion
diff --git a/src/vs/workbench/api/common/extHostNotebookDocument.ts b/src/vs/workbench/api/common/extHostNotebookDocument.ts
index b20e4c9ed1e..4bd68b65686 100644
--- a/src/vs/workbench/api/common/extHostNotebookDocument.ts
+++ b/src/vs/workbench/api/common/extHostNotebookDocument.ts
@@ -47,7 +47,7 @@ export class ExtHostCell {
 	private _onDidDispose = new Emitter<void>();
 	readonly onDidDispose: Event<void> = this._onDidDispose.event;
 
-	private _outputs: IOutputDto[];
+	private _outputs: extHostTypes.NotebookCellOutput[];
 	private _metadata: extHostTypes.NotebookCellMetadata;
 
 	readonly handle: number;
@@ -64,7 +64,7 @@ export class ExtHostCell {
 		this.handle = _cellData.handle;
 		this.uri = URI.revive(_cellData.uri);
 		this.cellKind = _cellData.cellKind;
-		this._outputs = _cellData.outputs;
+		this._outputs = _cellData.outputs.map(extHostTypeConverters.NotebookCellOutput.to);
 		this._metadata = extHostTypeConverters.NotebookCellMetadata.to(_cellData.metadata ?? {});
 	}
 
@@ -87,7 +87,7 @@ export class ExtHostCell {
 				cellKind: extHostTypeConverters.NotebookCellKind.to(this._cellData.cellKind),
 				document: data.document,
 				get language() { return data!.document.languageId; },
-				get outputs() { return that._outputs.map(extHostTypeConverters.NotebookCellOutput.to); },
+				get outputs() { return that._outputs.slice(0); },
 				set outputs(_value) { throw new Error('Use WorkspaceEdit to update cell outputs.'); },
 				get metadata() { return that._metadata; },
 				set metadata(_value) { throw new Error('Use WorkspaceEdit to update cell metadata.'); },
@@ -97,17 +97,17 @@ export class ExtHostCell {
 	}
 
 	setOutputs(newOutputs: IOutputDto[]): void {
-		this._outputs = newOutputs;
+		this._outputs = newOutputs.map(extHostTypeConverters.NotebookCellOutput.to);
 	}
 
 	setOutputItems(outputId: string, append: boolean, newOutputItems: IOutputItemDto[]) {
-		const output = this._outputs.find(op => op.outputId === outputId);
+		const newItems = newOutputItems.map(extHostTypeConverters.NotebookCellOutputItem.to);
+		const output = this._outputs.find(op => op.id === outputId);
 		if (output) {
-			if (append) {
-				output.outputs = [...output.outputs, ...newOutputItems];
-			} else {
-				output.outputs = newOutputItems;
+			if (!append) {
+				output.outputs.length = 0;
 			}
+			output.outputs.push(...newItems);
 		}
 	}
 
diff --git a/src/vs/workbench/api/common/extHostTypeConverters.ts b/src/vs/workbench/api/common/extHostTypeConverters.ts
index 8b57657a364..039418367df 100644
--- a/src/vs/workbench/api/common/extHostTypeConverters.ts
+++ b/src/vs/workbench/api/common/extHostTypeConverters.ts
@@ -596,7 +596,7 @@ export namespace WorkspaceEdit {
 							editType: notebooks.CellEditType.OutputItems,
 							index: entry.index,
 							outputId: entry.outputId,
-							items: entry.newOutputItems?.map(item => ({ mime: item.mime, value: item.value, metadata: item.metadata })) || [],
+							items: entry.newOutputItems?.map(NotebookCellOutputItem.from) || [],
 							append: entry.append
 						}
 					});
@@ -1476,31 +1476,32 @@ export namespace NotebookCellData {
 	}
 }
 
+export namespace NotebookCellOutputItem {
+	export function from(item: types.NotebookCellOutputItem): notebooks.IOutputItemDto {
+		return {
+			mime: item.mime,
+			value: item.value,
+			metadata: item.metadata
+		};
+	}
+
+	export function to(item: notebooks.IOutputItemDto): types.NotebookCellOutputItem {
+		return new types.NotebookCellOutputItem(item.mime, item.value, item.metadata);
+	}
+}
+
 export namespace NotebookCellOutput {
 	export function from(output: types.NotebookCellOutput): notebooks.IOutputDto {
-
-		const data = Object.create(null);
-		const custom = Object.create(null);
-
-		for (let item of output.outputs) {
-			data[item.mime] = item.value;
-			custom[item.mime] = item.metadata;
-		}
-
 		return {
 			outputId: output.id,
-			outputs: (output.outputs || []).map(op => ({
-				mime: op.mime,
-				value: op.value,
-				metadata: op.metadata
-			})) || [],
-			// metadata: isEmptyObject(custom) ? undefined : { custom }
+			outputs: output.outputs.map(NotebookCellOutputItem.from),
+			metadata: output.metadata
 		};
 	}
 
 	export function to(output: notebooks.IOutputDto): vscode.NotebookCellOutput {
-		const items: types.NotebookCellOutputItem[] = output.outputs.map(op => new types.NotebookCellOutputItem(op.mime, op.value, op.metadata));
-		return new types.NotebookCellOutput(items, output.outputId);
+		const items = output.outputs.map(NotebookCellOutputItem.to);
+		return new types.NotebookCellOutput(items, output.outputId, output.metadata);
 	}
 }
 
diff --git a/src/vs/workbench/api/common/extHostTypes.ts b/src/vs/workbench/api/common/extHostTypes.ts
index c815d8322af..7a2b4b9a1b9 100644
--- a/src/vs/workbench/api/common/extHostTypes.ts
+++ b/src/vs/workbench/api/common/extHostTypes.ts
@@ -703,8 +703,7 @@ export class WorkspaceEdit implements vscode.WorkspaceEdit {
 	}
 
 	private _editNotebookCellOutput(uri: URI, index: number, append: boolean, outputs: vscode.NotebookCellOutput[], metadata: vscode.WorkspaceEditEntryMetadata | undefined): void {
-		let newOutputs: NotebookCellOutput[] = outputs;
-		this._edits.push({ _type: FileEditType.CellOutput, metadata, uri, index, append, newOutputs, newMetadata: undefined });
+		this._edits.push({ _type: FileEditType.CellOutput, metadata, uri, index, append, newOutputs: outputs, newMetadata: undefined });
 	}
 
 	replaceNotebookCellMetadata(uri: URI, index: number, cellMetadata: vscode.NotebookCellMetadata, metadata?: vscode.WorkspaceEditEntryMetadata): void {
@@ -2993,15 +2992,30 @@ export class NotebookCellOutputItem {
 	constructor(
 		readonly mime: string,
 		readonly value: unknown, // JSON'able
-		readonly metadata?: any
+		readonly metadata?: Record<string, any>
 	) { }
 }
 
 export class NotebookCellOutput {
+
+	readonly outputs: NotebookCellOutputItem[];
+	readonly id: string;
+	readonly metadata?: Record<string, any>;
+
 	constructor(
-		readonly outputs: NotebookCellOutputItem[],
-		readonly id: string = generateUuid()
-	) { }
+		outputs: NotebookCellOutputItem[],
+		idOrMetadata?: string | Record<string, any>,
+		metadata?: Record<string, any>
+	) {
+		this.outputs = outputs;
+		if (typeof idOrMetadata === 'string') {
+			this.id = idOrMetadata;
+			this.metadata = metadata;
+		} else {
+			this.id = generateUuid();
+			this.metadata = idOrMetadata ?? metadata;
+		}
+	}
 }
 
 export enum NotebookCellKind {
diff --git a/src/vs/workbench/contrib/notebook/common/model/notebookCellOutputTextModel.ts b/src/vs/workbench/contrib/notebook/common/model/notebookCellOutputTextModel.ts
index 0172d6a1f2d..aa05e729203 100644
--- a/src/vs/workbench/contrib/notebook/common/model/notebookCellOutputTextModel.ts
+++ b/src/vs/workbench/contrib/notebook/common/model/notebookCellOutputTextModel.ts
@@ -16,9 +16,11 @@ export class NotebookCellOutputTextModel extends Disposable implements ICellOutp
 	get outputs() {
 		return this._rawOutput.outputs || [];
 	}
-	// get metadata(): NotebookCellOutputMetadata | undefined {
-	// 	return this._rawOutput.metadata;
-	// }
+
+	get metadata(): Record<string, any> | undefined {
+		return this._rawOutput.metadata;
+	}
+
 	get outputId(): string {
 		return this._rawOutput.outputId;
 	}
@@ -47,10 +49,10 @@ export class NotebookCellOutputTextModel extends Disposable implements ICellOutp
 		this._onDidChangeData.fire();
 	}
 
-	toJSON() {
+	toJSON(): IOutputDto {
 		return {
 			// data: this._data,
-			// metadata: this._rawOutput.metadata,
+			metadata: this._rawOutput.metadata,
 			outputs: this._rawOutput.outputs,
 			outputId: this._rawOutput.outputId
 		};
diff --git a/src/vs/workbench/contrib/notebook/common/notebookCommon.ts b/src/vs/workbench/contrib/notebook/common/notebookCommon.ts
index be7d26f468d..8196d8ac5f2 100644
--- a/src/vs/workbench/contrib/notebook/common/notebookCommon.ts
+++ b/src/vs/workbench/contrib/notebook/common/notebookCommon.ts
@@ -159,13 +159,8 @@ export interface IOutputItemDto {
 
 export interface IOutputDto {
 	outputs: IOutputItemDto[];
-	/**
-	 * { mime_type: value }
-	 */
-	// data: { [key: string]: unknown; }
-
-	// metadata?: NotebookCellOutputMetadata;
 	outputId: string;
+	metadata?: Record<string, unknown>;
 }
 
 export interface ICellOutput {