diff --git a/extensions/configuration-editing/src/settingsDocumentHelper.ts b/extensions/configuration-editing/src/settingsDocumentHelper.ts
index a21ec18e310..76c5e3d34e3 100644
--- a/extensions/configuration-editing/src/settingsDocumentHelper.ts
+++ b/extensions/configuration-editing/src/settingsDocumentHelper.ts
@@ -60,15 +60,6 @@ export class SettingsDocument {
 			return provideInstalledExtensionProposals(alreadyConfigured, `: [\n\t"ui"\n]`, range, true);
 		}
 
-		// extensions.supportUntrustedWorkspaces
-		if (location.path[0] === 'extensions.supportUntrustedWorkspaces' && location.path.length === 2 && location.isAtPropertyKey) {
-			let alreadyConfigured: string[] = [];
-			try {
-				alreadyConfigured = Object.keys(parse(this.document.getText())['extensions.supportUntrustedWorkspaces']);
-			} catch (e) {/* ignore error */ }
-			return provideWorkspaceTrustExtensionProposals(alreadyConfigured, range);
-		}
-
 		return this.provideLanguageOverridesCompletionItems(location, position);
 	}
 
diff --git a/src/vs/workbench/contrib/extensions/browser/extensionSupportCompletionProvider.ts b/src/vs/workbench/contrib/extensions/browser/extensionSupportCompletionProvider.ts
new file mode 100644
index 00000000000..e124dd0be11
--- /dev/null
+++ b/src/vs/workbench/contrib/extensions/browser/extensionSupportCompletionProvider.ts
@@ -0,0 +1,61 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+import { localize } from 'vs/nls';
+import { CancellationToken } from 'vs/base/common/cancellation';
+import { getLocation, parse } from 'vs/base/common/json';
+import { Disposable } from 'vs/base/common/lifecycle';
+import { Position } from 'vs/editor/common/core/position';
+import { ITextModel } from 'vs/editor/common/model';
+import { CompletionContext, CompletionList, CompletionProviderRegistry, CompletionItemKind, CompletionItem } from 'vs/editor/common/modes';
+import { IExtensionManagementService } from 'vs/platform/extensionManagement/common/extensionManagement';
+import { IWorkbenchContribution } from 'vs/workbench/common/contributions';
+import { Range } from 'vs/editor/common/core/range';
+
+
+export class ExtensionSupportCompletionProvider extends Disposable implements IWorkbenchContribution {
+	constructor(
+		@IExtensionManagementService extensionManagementService: IExtensionManagementService,
+	) {
+		super();
+
+		this._register(CompletionProviderRegistry.register({ language: 'jsonc', pattern: '**/settings.json' }, {
+			provideCompletionItems: async (model: ITextModel, position: Position, _context: CompletionContext, token: CancellationToken): Promise<CompletionList> => {
+				const suggestions: CompletionItem[] = [];
+
+				const getWordRangeAtPosition = (model: ITextModel, position: Position): Range | null => {
+					const wordAtPosition = model.getWordAtPosition(position);
+					return wordAtPosition ? new Range(position.lineNumber, wordAtPosition.startColumn, position.lineNumber, wordAtPosition.endColumn) : null;
+				};
+
+				const location = getLocation(model.getValue(), model.getOffsetAt(position));
+				const range = getWordRangeAtPosition(model, position) ?? Range.fromPositions(position, position);
+
+				// extensions.supportUntrustedWorkspaces
+				if (location.path[0] === 'extensions.supportUntrustedWorkspaces' && location.path.length === 2 && location.isAtPropertyKey) {
+					let alreadyConfigured: string[] = [];
+					try {
+						alreadyConfigured = Object.keys(parse(model.getValue())['extensions.supportUntrustedWorkspaces']);
+					} catch (e) {/* ignore error */ }
+
+					const installedExtensions = (await extensionManagementService.getInstalled()).filter(e => e.manifest.main);
+					const proposedExtensions = installedExtensions.filter(e => alreadyConfigured.indexOf(e.identifier.id) === -1);
+
+					if (proposedExtensions.length) {
+						suggestions.push(...proposedExtensions.map(e => {
+							const text = `"${e.identifier.id}": {\n\t"supported": true,\n\t"version": "${e.manifest.version}"\n},`;
+							return { label: e.identifier.id, kind: CompletionItemKind.Value, insertText: text, filterText: text, range };
+						}));
+					} else {
+						const text = '"vscode.csharp": {\n\t"supported": true,\n\t"version": "0.0.0"\n},';
+						suggestions.push({ label: localize('exampleExtension', "Example"), kind: CompletionItemKind.Value, insertText: text, filterText: text, range });
+					}
+				}
+
+				return { suggestions };
+			}
+		}));
+	}
+}
diff --git a/src/vs/workbench/contrib/extensions/browser/extensions.contribution.ts b/src/vs/workbench/contrib/extensions/browser/extensions.contribution.ts
index 7b258529436..3ceca350c6b 100644
--- a/src/vs/workbench/contrib/extensions/browser/extensions.contribution.ts
+++ b/src/vs/workbench/contrib/extensions/browser/extensions.contribution.ts
@@ -72,6 +72,7 @@ import { Query } from 'vs/workbench/contrib/extensions/common/extensionQuery';
 import { Promises } from 'vs/base/common/async';
 import { EditorExtensions } from 'vs/workbench/common/editor';
 import { WORKSPACE_TRUST_EXTENSION_SUPPORT } from 'vs/workbench/services/workspaces/common/workspaceTrust';
+import { ExtensionSupportCompletionProvider } from 'vs/workbench/contrib/extensions/browser/extensionSupportCompletionProvider';
 
 // Singletons
 registerSingleton(IExtensionsWorkbenchService, ExtensionsWorkbenchService);
@@ -1325,6 +1326,7 @@ workbenchRegistry.registerWorkbenchContribution(ExtensionsViewletViewsContributi
 workbenchRegistry.registerWorkbenchContribution(ExtensionActivationProgress, LifecyclePhase.Eventually);
 workbenchRegistry.registerWorkbenchContribution(ExtensionDependencyChecker, LifecyclePhase.Eventually);
 workbenchRegistry.registerWorkbenchContribution(ExtensionEnablementByWorkspaceTrustRequirement, LifecyclePhase.Restored);
+workbenchRegistry.registerWorkbenchContribution(ExtensionSupportCompletionProvider, LifecyclePhase.Restored);
 
 // Running Extensions
 const actionRegistry = Registry.as<IWorkbenchActionRegistry>(WorkbenchActionExtensions.WorkbenchActions);