diff --git a/extensions/copilot/package.json b/extensions/copilot/package.json
index dbce0cbc6a0..9885cdf356f 100644
--- a/extensions/copilot/package.json
+++ b/extensions/copilot/package.json
@@ -78,7 +78,7 @@
     }
   ],
   "activationEvents": [
-    "onStartupFinished",
+    "onCopilotEnabled",
     "onLanguageModelChat:copilot",
     "onUri",
     "onFileSystem:ccreq",
diff --git a/src/vs/workbench/contrib/positronAssistant/browser/aiExtensionActivation.ts b/src/vs/workbench/contrib/positronAssistant/browser/aiExtensionActivation.ts
new file mode 100644
index 00000000000..efeacde4dbc
--- /dev/null
+++ b/src/vs/workbench/contrib/positronAssistant/browser/aiExtensionActivation.ts
@@ -0,0 +1,75 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (C) 2026 Posit Software, PBC. All rights reserved.
+ *  Licensed under the Elastic License 2.0. See LICENSE.txt for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+import { Disposable } from '../../../../base/common/lifecycle.js';
+import { IConfigurationService } from '../../../../platform/configuration/common/configuration.js';
+import { IWorkbenchContribution } from '../../../common/contributions.js';
+import { IExtensionService } from '../../../services/extensions/common/extensions.js';
+import { ChatConfiguration } from '../../chat/common/constants.js';
+import { AI_ENABLED_KEY } from '../common/positronAIConfiguration.js';
+
+/**
+ * Custom activation event fired while Positron's AI features are enabled, i.e.
+ * while `ai.enabled` (the main AI switch) is `true`.
+ *
+ * Heavyweight AI extensions (e.g. the bundled `positron-assistant`) declare this
+ * as an activation event instead of `onStartupFinished`, so they stay unloaded
+ * (and off the memory budget) when AI is turned off, and activate eagerly when
+ * it's on.
+ */
+export const AI_ENABLED_ACTIVATION_EVENT = 'onAiEnabled';
+
+/**
+ * Custom activation event fired while chat/Copilot is enabled, i.e. while
+ * `chat.disableAIFeatures` is not `true`.
+ *
+ * The bundled Copilot extension declares this instead of `onStartupFinished`.
+ * `positron-assistant` declares it too: it registers the default chat
+ * participants the Copilot chat UI depends on, but is not a declared extension
+ * dependency of Copilot, so it must listen for this event to come up alongside
+ * it.
+ */
+export const COPILOT_ACTIVATION_EVENT = 'onCopilotEnabled';
+
+/**
+ * Fires the custom AI activation events while their backing settings are on,
+ * both at startup and when the user changes either setting at runtime:
+ *
+ * - {@link AI_ENABLED_ACTIVATION_EVENT} while `ai.enabled` is `true`.
+ * - {@link COPILOT_ACTIVATION_EVENT} while `chat.disableAIFeatures` is not `true`.
+ *
+ * VS Code cannot unload an already-activated extension without a reload, so
+ * turning a setting off at runtime does not deactivate anything here; the AI
+ * extensions' individual features are each gated on their own preconditions and
+ * go quiet on their own. See `.claude/rules/ai-gating.md`.
+ */
+export class AiExtensionActivationContribution extends Disposable implements IWorkbenchContribution {
+	constructor(
+		@IConfigurationService private readonly _configurationService: IConfigurationService,
+		@IExtensionService private readonly _extensionService: IExtensionService,
+	) {
+		super();
+
+		this._update();
+		this._register(this._configurationService.onDidChangeConfiguration(e => {
+			if (e.affectsConfiguration(AI_ENABLED_KEY) || e.affectsConfiguration(ChatConfiguration.AIDisabled)) {
+				this._update();
+			}
+		}));
+	}
+
+	private _update(): void {
+		// `ai.enabled` defaults to `true`; activate only when it reads exactly
+		// `true` (an unset value already reads through as the `true` default).
+		if (this._configurationService.getValue<boolean>(AI_ENABLED_KEY) === true) {
+			this._extensionService.activateByEvent(AI_ENABLED_ACTIVATION_EVENT);
+		}
+		// `chat.disableAIFeatures` is inverted: `true` means AI is off. Activate
+		// for every other value (including the unset default).
+		if (this._configurationService.getValue<boolean>(ChatConfiguration.AIDisabled) !== true) {
+			this._extensionService.activateByEvent(COPILOT_ACTIVATION_EVENT);
+		}
+	}
+}
diff --git a/src/vs/workbench/contrib/positronAssistant/browser/positronAssistant.contribution.ts b/src/vs/workbench/contrib/positronAssistant/browser/positronAssistant.contribution.ts
index cde1683e0ea..f8adbf3f644 100644
--- a/src/vs/workbench/contrib/positronAssistant/browser/positronAssistant.contribution.ts
+++ b/src/vs/workbench/contrib/positronAssistant/browser/positronAssistant.contribution.ts
@@ -24,6 +24,7 @@ import { CodeAttributionSource, IConsoleCodeAttribution } from '../../../service
 import { EditorContextKeys } from '../../../../editor/common/editorContextKeys.js';
 import { NextEditSuggestionsStatusBarEntry } from './nextEditSuggestionsStatusBar.js';
 import { CommitMessageMenuContribution, registerCommitMessageGeneration } from './commitMessageAction.js';
+import { AiExtensionActivationContribution } from './aiExtensionActivation.js';
 import { PositronAssistantToolsContribution } from './tools/positronAssistantTools.js';
 
 // Register the `ai.enabled` main switch for Positron's AI features.
@@ -122,4 +123,12 @@ class PositronAssistantContribution extends Disposable implements IWorkbenchCont
 Registry.as<IWorkbenchContributionsRegistry>(WorkbenchExtensions.Workbench).registerWorkbenchContribution(PositronAssistantContribution, LifecyclePhase.Restored);
 Registry.as<IWorkbenchContributionsRegistry>(WorkbenchExtensions.Workbench).registerWorkbenchContribution(NextEditSuggestionsStatusBarEntry, LifecyclePhase.Restored);
 Registry.as<IWorkbenchContributionsRegistry>(WorkbenchExtensions.Workbench).registerWorkbenchContribution(CommitMessageMenuContribution, LifecyclePhase.Restored);
+
+// Fire the custom AI activation events (`onAiEnabled`, `onCopilotEnabled`) so
+// the bundled AI extensions activate lazily while their backing settings are
+// on. Registered at `Eventually` to preserve the deferred timing those
+// extensions had under `onStartupFinished`.
+Registry.as<IWorkbenchContributionsRegistry>(WorkbenchExtensions.Workbench).registerWorkbenchContribution(AiExtensionActivationContribution, LifecyclePhase.Eventually);
+
 Registry.as<IWorkbenchContributionsRegistry>(WorkbenchExtensions.Workbench).registerWorkbenchContribution(PositronAssistantToolsContribution, LifecyclePhase.Restored);
+