diff --git a/src/vs/vscode.proposed.d.ts b/src/vs/vscode.proposed.d.ts
index 07d093275ef..e956e67ffc7 100644
--- a/src/vs/vscode.proposed.d.ts
+++ b/src/vs/vscode.proposed.d.ts
@@ -1081,10 +1081,8 @@ declare module 'vscode' {
 		readonly cellKind: CellKind;
 		readonly document: TextDocument;
 		readonly language: string;
-		/** @deprecated use WorkspaceEdit.replaceCellOutput */
-		outputs: CellOutput[];
-		/** @deprecated use WorkspaceEdit.replaceCellMetadata */
-		metadata: NotebookCellMetadata;
+		readonly outputs: CellOutput[];
+		readonly metadata: NotebookCellMetadata;
 	}
 
 	export interface NotebookDocumentMetadata {
diff --git a/src/vs/workbench/api/browser/mainThreadNotebook.ts b/src/vs/workbench/api/browser/mainThreadNotebook.ts
index 1a2b21cf966..8da7fd54186 100644
--- a/src/vs/workbench/api/browser/mainThreadNotebook.ts
+++ b/src/vs/workbench/api/browser/mainThreadNotebook.ts
@@ -569,29 +569,6 @@ export class MainThreadNotebooks extends Disposable implements MainThreadNoteboo
 		textModel?.updateLanguages(languages);
 	}
 
-	async $spliceNotebookCellOutputs(viewType: string, resource: UriComponents, cellHandle: number, splices: NotebookCellOutputsSplice[]): Promise<void> {
-		this.logService.debug('MainThreadNotebooks#spliceNotebookCellOutputs', resource.path, cellHandle);
-		const textModel = this._notebookService.getNotebookTextModel(URI.from(resource));
-
-		if (!textModel) {
-			return;
-		}
-
-		const cell = textModel.cells.find(cell => cell.handle === cellHandle);
-
-		if (!cell) {
-			return;
-		}
-
-		textModel.applyEdits(textModel.versionId, [
-			{
-				editType: CellEditType.OutputsSplice,
-				index: textModel.cells.indexOf(cell),
-				splices
-			}
-		], true, undefined, () => undefined, undefined);
-	}
-
 	async $postMessage(editorId: string, forRendererId: string | undefined, value: any): Promise<boolean> {
 		const editor = this._notebookService.getNotebookEditor(editorId) as INotebookEditor | undefined;
 		if (editor?.isNotebookEditor) {
diff --git a/src/vs/workbench/api/common/extHost.protocol.ts b/src/vs/workbench/api/common/extHost.protocol.ts
index a3b6da5c89b..c9fd1ee383c 100644
--- a/src/vs/workbench/api/common/extHost.protocol.ts
+++ b/src/vs/workbench/api/common/extHost.protocol.ts
@@ -789,7 +789,6 @@ export interface MainThreadNotebookShape extends IDisposable {
 	$onNotebookKernelChange(handle: number, uri: UriComponents | undefined): void;
 	$tryApplyEdits(viewType: string, resource: UriComponents, modelVersionId: number, edits: ICellEditOperation[]): Promise<boolean>;
 	$updateNotebookLanguages(viewType: string, resource: UriComponents, languages: string[]): Promise<void>;
-	$spliceNotebookCellOutputs(viewType: string, resource: UriComponents, cellHandle: number, splices: NotebookCellOutputsSplice[]): Promise<void>;
 	$postMessage(editorId: string, forRendererId: string | undefined, value: any): Promise<boolean>;
 	$setStatusBarEntry(id: number, statusBarEntry: INotebookCellStatusBarEntryDto): Promise<void>;
 	$tryOpenDocument(uriComponents: UriComponents, viewType?: string): Promise<URI>;
diff --git a/src/vs/workbench/api/common/extHostNotebookDocument.ts b/src/vs/workbench/api/common/extHostNotebookDocument.ts
index 463590a32e7..f107d17ef31 100644
--- a/src/vs/workbench/api/common/extHostNotebookDocument.ts
+++ b/src/vs/workbench/api/common/extHostNotebookDocument.ts
@@ -72,7 +72,7 @@ export class ExtHostCell extends Disposable {
 	private _onDidChangeOutputs = new Emitter<ISplice<IOutputDtoWithId>[]>();
 	readonly onDidChangeOutputs: Event<ISplice<IOutputDtoWithId>[]> = this._onDidChangeOutputs.event;
 
-	private _outputs: any[];
+	private _outputs: any[]; // it's `IOutputDtop[]`
 	private _outputMapping = new WeakMap<vscode.CellOutput, string | undefined /* output ID */>();
 
 	private _metadata: vscode.NotebookCellMetadata;
@@ -124,12 +124,9 @@ export class ExtHostCell extends Disposable {
 				document: data.document,
 				get language() { return data!.document.languageId; },
 				get outputs() { return that._outputs; },
-				set outputs(value) { that._updateOutputs(value); },
+				set outputs(value) { throw new Error('Use WorkspaceEdit to update cell outputs.'); },
 				get metadata() { return that._metadata; },
-				set metadata(value) {
-					that.setMetadata(value);
-					that._updateMetadata();
-				},
+				set metadata(value) { throw new Error('Use WorkspaceEdit to update cell metadata.'); },
 			});
 		}
 		return this._cell;
@@ -140,33 +137,13 @@ export class ExtHostCell extends Disposable {
 		this._onDidDispose.fire();
 	}
 
-	setOutputs(newOutputs: vscode.CellOutput[]): void {
+	setOutputs(newOutputs: IOutputDtoWithId[]): void {
 		this._outputs = newOutputs;
-	}
-
-	private _updateOutputs(newOutputs: vscode.CellOutput[]) {
-		const rawDiffs = diff<vscode.CellOutput>(this._outputs || [], newOutputs || [], (a) => {
-			return this._outputMapping.has(a);
-		});
-
-		const transformedDiffs: ISplice<IOutputDtoWithId>[] = rawDiffs.map(diff => {
-			for (let i = diff.start; i < diff.start + diff.deleteCount; i++) {
-				this._outputMapping.delete(this._outputs[i]);
-			}
-
-			return {
-				deleteCount: diff.deleteCount,
-				start: diff.start,
-				toInsert: diff.toInsert.map((output): IOutputDtoWithId => {
-					const uuid = UUID.generateUuid();
-					this._outputMapping.set(output, uuid);
-					return { ...output, outputId: uuid };
-				})
-			};
-		});
-
-		this._outputs = newOutputs;
-		this._onDidChangeOutputs.fire(transformedDiffs);
+		this._outputMapping = new WeakMap<vscode.CellOutput, string | undefined /* output ID */>();
+		for (const output of this._outputs) {
+			this._outputMapping.set(output, output.outputId);
+			delete output.outputId;
+		}
 	}
 
 	setMetadata(newMetadata: vscode.NotebookCellMetadata): void {
@@ -390,12 +367,6 @@ export class ExtHostNotebookDocument extends Disposable {
 					this._cellDisposableMapping.set(extCell.handle, store);
 				}
 
-				const store = this._cellDisposableMapping.get(extCell.handle)!;
-
-				store.add(extCell.onDidChangeOutputs((diffs) => {
-					this.eventuallyUpdateCellOutputs(extCell, diffs);
-				}));
-
 				return extCell;
 			});
 
@@ -464,23 +435,6 @@ export class ExtHostNotebookDocument extends Disposable {
 		this._emitter.emitCellMetadataChange(event);
 	}
 
-	async eventuallyUpdateCellOutputs(cell: ExtHostCell, diffs: ISplice<IOutputDtoWithId>[]) {
-		const outputDtos: NotebookCellOutputsSplice[] = diffs.map(diff => {
-			const outputs = diff.toInsert;
-			return [diff.start, diff.deleteCount, outputs];
-		});
-
-		if (!outputDtos.length) {
-			return;
-		}
-
-		await this._proxy.$spliceNotebookCellOutputs(this._viewType, this.uri, cell.handle, outputDtos);
-		this._emitter.emitCellOutputsChange({
-			document: this.notebookDocument,
-			cells: [cell.cell]
-		});
-	}
-
 	getCell(cellHandle: number): ExtHostCell | undefined {
 		return this._cells.find(cell => cell.handle === cellHandle);
 	}