diff --git a/src/ui/src/assets/custom-agent-deprecation-banner-bg.png b/src/ui/src/assets/custom-agent-deprecation-banner-bg.png
new file mode 100644
index 000000000..e366587fa
Binary files /dev/null and b/src/ui/src/assets/custom-agent-deprecation-banner-bg.png differ
diff --git a/src/ui/src/builder/BuilderApp.vue b/src/ui/src/builder/BuilderApp.vue
index 9cefa8e43..3da4b1fbb 100644
--- a/src/ui/src/builder/BuilderApp.vue
+++ b/src/ui/src/builder/BuilderApp.vue
@@ -1,5 +1,13 @@
 <template>
 	<div class="BuilderApp" tabindex="-1" :style="WDS_CSS_PROPERTIES">
+		<BuilderDeprecationBanner
+			v-if="showDeprecationBanner"
+			class="deprecationBanner"
+			:is-organization-admin="isOrganizationAdmin"
+			:is-post-cutoff="isPostCutoff"
+			:show-dismiss="!isPostCutoff && !dismissed"
+			@dismiss="onDismissBanner"
+		/>
 		<div
 			class="mainGrid"
 			:class="{ openPanels: ssbm.openPanels.value.size > 0 }"
@@ -76,6 +84,16 @@
 					<BuilderPanelSwitcher class="panelSwitcher" />
 				</template>
 			</ShareResizeVertical>
+			<div
+				v-if="showDeprecationBanner"
+				aria-hidden="true"
+				class="deprecationDimmer"
+			/>
+			<div
+				v-if="showDeprecationBanner"
+				aria-hidden="true"
+				class="deprecationBlocker"
+			/>
 		</div>
 
 		<!-- INSTANCE TRACKERS -->
@@ -176,6 +194,10 @@ import { defineAsyncComponentWithLoader } from "@/utils/defineAsyncComponentWith
 import BuilderAppSocketTimeoutModal from "./BuilderAppSocketTimeoutModal.vue";
 import { useSocketTimeout } from "./useSocketTimeout";
 import BlueprintsNavigationStack from "@/components/blueprints/BlueprintsNavigationStack.vue";
+import BuilderDeprecationBanner from "./BuilderDeprecationBanner.vue";
+
+const DEPRECATION_BANNER_DISMISSED_KEY =
+	"customAgentDeprecationBannerDismissed";
 
 provide(injectionKeys.isAutogenModalShown, ref(false));
 
@@ -204,6 +226,29 @@ const ssbm = inject(injectionKeys.builderManager);
 const notesManager = inject(injectionKeys.notesManager);
 const collaborationManager = inject(injectionKeys.collaborationManager);
 
+// Deprecation banner
+const dismissed = ref(
+	localStorage.getItem(DEPRECATION_BANNER_DISMISSED_KEY) === "true",
+);
+const isPreCutoffFlagEnabled = computed(() =>
+	wf.featureFlags.value.includes("beforeDeprecationCutoffAbv2"),
+);
+const isPostCutoff = computed(() =>
+	wf.featureFlags.value.includes("afterDeprecationCutoffAbv2"),
+);
+const isOrganizationAdmin = computed(() => wf.isOrganizationAdmin.value);
+const showDeprecationBanner = computed(
+	() =>
+		wf.isWriterCloudApp.value &&
+		(isPostCutoff.value ||
+			(isPreCutoffFlagEnabled.value && !dismissed.value)),
+);
+
+function onDismissBanner() {
+	localStorage.setItem(DEPRECATION_BANNER_DISMISSED_KEY, "true");
+	dismissed.value = true;
+}
+
 const tracking = useWriterTracking(wf);
 const toasts = useToasts();
 
@@ -533,6 +578,8 @@ onUnmounted(() => {
 	position: relative;
 	overflow: hidden;
 	background: var(--builderBackgroundColor);
+	display: flex;
+	flex-direction: column;
 }
 
 .BuilderApp__noteTracker__note {
@@ -541,14 +588,42 @@ onUnmounted(() => {
 	pointer-events: auto;
 }
 
+.deprecationBanner {
+	flex-shrink: 0;
+	z-index: 10;
+}
+
 .mainGrid {
+	position: relative;
 	width: 100vw;
-	height: 100vh;
+	flex: 1;
+	min-height: 0;
 	grid-template-columns: auto 1fr;
 	grid-template-rows: var(--builderTopBarHeight) minmax(0, 1fr);
 	display: grid;
 }
 
+.deprecationDimmer {
+	pointer-events: none;
+	position: absolute;
+	inset: 0;
+	z-index: 6;
+	background-color: #e4e7ed;
+	opacity: 0.65;
+}
+
+.deprecationBlocker {
+	pointer-events: all;
+	cursor: not-allowed;
+	position: absolute;
+	top: var(--builderTopBarHeight);
+	left: 0;
+	right: 0;
+	bottom: 0;
+	z-index: 6;
+	background: transparent;
+}
+
 .builderHeader {
 	grid-column: 1 / 3;
 	grid-row: 1;
diff --git a/src/ui/src/builder/BuilderDeprecationBanner.vue b/src/ui/src/builder/BuilderDeprecationBanner.vue
new file mode 100644
index 000000000..9e08982de
--- /dev/null
+++ b/src/ui/src/builder/BuilderDeprecationBanner.vue
@@ -0,0 +1,291 @@
+<template>
+	<section
+		aria-label="Custom agent deprecation notice"
+		class="BuilderDeprecationBanner"
+	>
+		<img
+			:src="bannerBg"
+			alt=""
+			aria-hidden="true"
+			class="BuilderDeprecationBanner__background"
+		/>
+		<div aria-hidden="true" class="BuilderDeprecationBanner__overlay" />
+		<div class="BuilderDeprecationBanner__content">
+			<div class="BuilderDeprecationBanner__copy">
+				<p class="BuilderDeprecationBanner__title">{{ title }}</p>
+				<p class="BuilderDeprecationBanner__body">
+					{{ body }}
+					<a
+						:href="LEARN_MORE_URL"
+						target="_blank"
+						rel="noopener noreferrer"
+						class="BuilderDeprecationBanner__learnMore"
+						:aria-label="`Learn more (opens in new tab)`"
+						>Learn more</a
+					>
+				</p>
+			</div>
+			<div class="BuilderDeprecationBanner__actions">
+				<WdsButton
+					v-if="showMigrateButton"
+					variant="neutral"
+					size="small"
+					class="BuilderDeprecationBanner__cta"
+					@click="onMigrateClick"
+				>
+					<svg
+						xmlns="http://www.w3.org/2000/svg"
+						width="16"
+						height="16"
+						viewBox="0 0 24 24"
+						fill="none"
+						stroke="currentColor"
+						stroke-width="2"
+						stroke-linecap="round"
+						stroke-linejoin="round"
+						aria-hidden="true"
+						style="flex-shrink: 0"
+					>
+						<path
+							d="M22 19a2 2 0 0 1-2 2H4a2 2 0 0 1-2-2V5a2 2 0 0 1 2-2h5l2 3h9a2 2 0 0 1 2 2z"
+						/>
+						<line x1="12" y1="11" x2="12" y2="17" />
+						<line x1="9" y1="14" x2="15" y2="14" />
+					</svg>
+					{{ migrateLabel }}
+				</WdsButton>
+				<WdsButton
+					v-else-if="showPlaybookButton"
+					variant="neutral"
+					size="small"
+					class="BuilderDeprecationBanner__cta"
+					@click="onPlaybookClick"
+				>
+					{{ CREATE_PLAYBOOK_LABEL }}
+					<svg
+						xmlns="http://www.w3.org/2000/svg"
+						width="16"
+						height="16"
+						viewBox="0 0 24 24"
+						fill="none"
+						stroke="currentColor"
+						stroke-width="2"
+						stroke-linecap="round"
+						stroke-linejoin="round"
+						aria-hidden="true"
+						style="flex-shrink: 0"
+					>
+						<line x1="7" y1="17" x2="17" y2="7" />
+						<polyline points="7 7 17 7 17 17" />
+					</svg>
+				</WdsButton>
+				<WdsButton
+					v-if="!isPostCutoff && showDismiss"
+					variant="secondary"
+					size="smallIcon"
+					aria-label="Dismiss deprecation notice"
+					class="BuilderDeprecationBanner__dismiss"
+					@click="$emit('dismiss')"
+				>
+					<svg
+						xmlns="http://www.w3.org/2000/svg"
+						width="16"
+						height="16"
+						viewBox="0 0 24 24"
+						fill="none"
+						stroke="currentColor"
+						stroke-width="2"
+						stroke-linecap="round"
+						stroke-linejoin="round"
+						aria-hidden="true"
+					>
+						<line x1="18" y1="6" x2="6" y2="18" />
+						<line x1="6" y1="6" x2="18" y2="18" />
+					</svg>
+				</WdsButton>
+			</div>
+		</div>
+	</section>
+</template>
+
+<script setup lang="ts">
+import { computed, inject } from "vue";
+import WdsButton from "@/wds/WdsButton.vue";
+import injectionKeys from "@/injectionKeys";
+import bannerBg from "@/assets/custom-agent-deprecation-banner-bg.png";
+
+const LEARN_MORE_URL =
+	"https://docs.google.com/document/d/1Zi1zNMVesciYSqL5Qv5oBskIiBysY5vghocyA0LdBYc/edit";
+const CREATE_PLAYBOOK_LABEL = "Create a playbook";
+const MIGRATE_AGENT_LABEL = "Migrate agent";
+const MIGRATE_AGENTS_LABEL = "Migrate agents";
+
+const DEPRECATION_CUTOFF_DATE = new Date("2026-09-10T00:00:00");
+
+function getDaysUntilCutoff(): number {
+	const msPerDay = 1000 * 60 * 60 * 24;
+	const diff = DEPRECATION_CUTOFF_DATE.getTime() - Date.now();
+	return Math.max(0, Math.ceil(diff / msPerDay));
+}
+
+function formatDaysTitle(daysRemaining: number): string {
+	const dayLabel = daysRemaining === 1 ? "day" : "days";
+	return `In ${daysRemaining} ${dayLabel} this Agent Builder is going away`;
+}
+
+const props = defineProps<{
+	isOrganizationAdmin: boolean;
+	isPostCutoff: boolean;
+	daysRemaining?: number;
+	showDismiss?: boolean;
+}>();
+
+defineEmits<{
+	dismiss: [];
+}>();
+
+const wf = inject(injectionKeys.core);
+
+const daysRemaining = computed(
+	() => props.daysRemaining ?? getDaysUntilCutoff(),
+);
+
+const title = computed(() => {
+	if (props.isPostCutoff) {
+		return "This agent builder is no longer supported";
+	}
+	return formatDaysTitle(daysRemaining.value);
+});
+
+const body = computed(() => {
+	if (props.isPostCutoff) {
+		return props.isOrganizationAdmin
+			? "Migrate your team's agents to the new Agent Builder now."
+			: "Create a Playbook instead.";
+	}
+	return props.isOrganizationAdmin
+		? "This legacy agent editor will no longer be available - migrate your agent to the new Agent Builder now."
+		: "This legacy agent editor will no longer be available - create a Playbook instead.";
+});
+
+const migrateLabel = computed(() =>
+	props.isPostCutoff ? MIGRATE_AGENTS_LABEL : MIGRATE_AGENT_LABEL,
+);
+
+const showMigrateButton = computed(() => props.isOrganizationAdmin);
+const showPlaybookButton = computed(() => !props.isOrganizationAdmin);
+
+const playbooksUrl = computed(() => {
+	if (!wf) return "#";
+	const orgId = wf.writerOrgId.value;
+	if (!orgId) return "#";
+	return `/organization/${orgId}/team/default/ai-studio/agent-flow`;
+});
+
+function onMigrateClick() {
+	if (!wf) return;
+	const orgId = wf.writerOrgId.value;
+	if (!orgId) return;
+	window.location.href = `/organization/${orgId}/team/default/ai-studio/agents`;
+}
+
+function onPlaybookClick() {
+	window.open(playbooksUrl.value, "_blank", "noopener,noreferrer");
+}
+</script>
+
+<style scoped>
+.BuilderDeprecationBanner {
+	position: relative;
+	isolation: isolate;
+	flex-shrink: 0;
+	height: 80px;
+	width: 100%;
+	overflow: hidden;
+}
+
+.BuilderDeprecationBanner__background {
+	position: absolute;
+	inset: 0;
+	width: 100%;
+	height: 100%;
+	object-fit: cover;
+	object-position: center;
+}
+
+.BuilderDeprecationBanner__overlay {
+	pointer-events: none;
+	position: absolute;
+	inset: 0;
+	background: linear-gradient(
+		to bottom,
+		rgb(0 0 0 / 80%),
+		rgb(0 0 0 / 40%),
+		transparent
+	);
+}
+
+.BuilderDeprecationBanner__content {
+	position: relative;
+	display: flex;
+	height: 80px;
+	align-items: center;
+	justify-content: space-between;
+	gap: 16px;
+	padding: 14px 24px 14px 40px;
+}
+
+.BuilderDeprecationBanner__copy {
+	min-width: 0;
+	max-width: 720px;
+	color: white;
+}
+
+.BuilderDeprecationBanner__title {
+	margin: 0;
+	font-size: 18px;
+	font-weight: 500;
+	line-height: 1.35;
+}
+
+.BuilderDeprecationBanner__body {
+	margin: 0;
+	font-size: 12px;
+	line-height: 1.5;
+}
+
+.BuilderDeprecationBanner__learnMore {
+	color: inherit;
+	text-decoration: underline;
+	text-underline-offset: 2px;
+	white-space: nowrap;
+}
+
+.BuilderDeprecationBanner__actions {
+	display: flex;
+	flex-shrink: 0;
+	align-items: center;
+	gap: 8px;
+}
+
+.BuilderDeprecationBanner__cta {
+	border-color: white !important;
+	background-color: white !important;
+	color: black !important;
+	gap: 6px !important;
+}
+
+.BuilderDeprecationBanner__cta:hover {
+	background-color: rgb(255 255 255 / 90%) !important;
+}
+
+.BuilderDeprecationBanner__dismiss {
+	color: white !important;
+	background-color: transparent !important;
+	border-color: transparent !important;
+}
+
+.BuilderDeprecationBanner__dismiss:hover {
+	background-color: rgb(255 255 255 / 10%) !important;
+}
+</style>
diff --git a/src/ui/src/core/index.ts b/src/ui/src/core/index.ts
index 630803241..38f8a4a9e 100644
--- a/src/ui/src/core/index.ts
+++ b/src/ui/src/core/index.ts
@@ -70,6 +70,7 @@ export function generateCore() {
 				organizationId: string;
 				apiKey?: string;
 				baseUrl?: string;
+				isOrganizationAdmin?: boolean;
 		  }
 		| undefined
 	>();
@@ -140,6 +141,9 @@ export function generateCore() {
 	const writerBaseUrl = computed(
 		() => writerApplication.value?.baseUrl ?? "https://api.writer.com",
 	);
+	const isOrganizationAdmin = computed(
+		() => writerApplication.value?.isOrganizationAdmin ?? false,
+	);
 	const isWriterCloudApp = computed(() =>
 		Boolean(writerAppId.value || writerOrgId.value),
 	);
@@ -1171,6 +1175,7 @@ export function generateCore() {
 		writerAppId,
 		writerApiKey,
 		writerBaseUrl,
+		isOrganizationAdmin,
 		...navigationStack,
 		getFirstBlueprint,
 		getFirstPage,
diff --git a/src/writer/app_runner.py b/src/writer/app_runner.py
index dde662f7c..9d717ab9e 100644
--- a/src/writer/app_runner.py
+++ b/src/writer/app_runner.py
@@ -189,11 +189,14 @@ def _handle_session_init(
         writer_app_id = headers.get("x-agent-id") or os.getenv("WRITER_APP_ID")
         writer_org_id = headers.get("x-organization-id") or os.getenv("WRITER_ORG_ID")
         writer_base_url = os.getenv("WRITER_BASE_URL", "https://api.writer.com")
+        is_org_admin_header = headers.get("x-is-org-admin", "").lower()
+        is_org_admin = is_org_admin_header == "true"
         if writer_app_id is not None and writer_org_id is not None:
             writer_application = WriterApplicationInformation(
                 id=writer_app_id,
                 organizationId=writer_org_id,
-                baseUrl=writer_base_url
+                baseUrl=writer_base_url,
+                isOrganizationAdmin=is_org_admin,
             )
             if writer.Config.mode == "edit":
                 writer_application.apiKey = os.getenv("WRITER_API_KEY")
diff --git a/src/writer/ss_types.py b/src/writer/ss_types.py
index 43b122710..517cacb00 100644
--- a/src/writer/ss_types.py
+++ b/src/writer/ss_types.py
@@ -73,6 +73,7 @@ class WriterApplicationInformation(BaseModel):
     organizationId: str
     baseUrl: Optional[str] = None
     apiKey: Optional[str] = None
+    isOrganizationAdmin: Optional[bool] = False
 
 
 class AutogenRequestBody(BaseModel):