diff --git a/src/features/clusters/queries/getHarperVersionsQuery.test.ts b/src/features/clusters/queries/getHarperVersionsQuery.test.ts
index fb537ef39..585ba0105 100644
--- a/src/features/clusters/queries/getHarperVersionsQuery.test.ts
+++ b/src/features/clusters/queries/getHarperVersionsQuery.test.ts
@@ -88,9 +88,10 @@ describe('dedupeHarperVersionsByTag', () => {
 });
 
 describe('getHarperVersionsOptions', () => {
-	it('configures the query to hit the HarperVersions cache key without retrying', () => {
-		const options = getHarperVersionsOptions();
-		expect(options.queryKey).toEqual(['HarperVersions']);
+	it('scopes the cache key to the organization (org-first) and does not retry', () => {
+		const options = getHarperVersionsOptions('org_123');
+		// Org-first so it participates in org-scoped `invalidateQueries([organizationId])`.
+		expect(options.queryKey).toEqual(['org_123', 'HarperVersions']);
 		expect(options.staleTime).toBe(60_000);
 		expect(options.retry).toBe(false);
 	});
@@ -108,10 +109,10 @@ describe('getHarperVersionsOptions', () => {
 			} satisfies HarperVersionsResponse,
 		});
 
-		const options = getHarperVersionsOptions();
+		const options = getHarperVersionsOptions('org_1');
 		const result = await (options.queryFn as () => Promise<HarperVersionsResponse>)();
 
-		expect(mockedGet).toHaveBeenCalledWith('/HarperVersions/');
+		expect(mockedGet).toHaveBeenCalledWith('/HarperVersions/', { params: { organizationId: 'org_1' } });
 		expect(result).toEqual({
 			name: 'Harper Versions',
 			description: 'Available Harper versions',
@@ -122,6 +123,25 @@ describe('getHarperVersionsOptions', () => {
 		});
 	});
 
+	it('passes the organizationId through axios params (axios handles encoding)', async () => {
+		mockedGet.mockResolvedValue({
+			data: {
+				name: 'Harper Versions',
+				description: 'Available Harper versions',
+				value: [
+					{ name: 'stable', version: '5.1.21' },
+					{ name: 'deployed on prod-east', version: '5.0.8' },
+				],
+			} satisfies HarperVersionsResponse,
+		});
+
+		const options = getHarperVersionsOptions('org/1');
+		const result = await (options.queryFn as () => Promise<HarperVersionsResponse>)();
+
+		expect(mockedGet).toHaveBeenCalledWith('/HarperVersions/', { params: { organizationId: 'org/1' } });
+		expect(tags(result.value)).toEqual(['5.1.21 stable', '5.0.8 deployed on prod-east']);
+	});
+
 	it('surfaces (rather than swallows) a malformed response with no value array', async () => {
 		// The endpoint's OpenAPI description is broken, so the `as HarperVersionsResponse` cast is not
 		// schema-backed. If it ever returns a body without `value`, the queryFn throws — React Query's
@@ -129,7 +149,7 @@ describe('getHarperVersionsOptions', () => {
 		// fails safely rather than silently rendering an empty picker.
 		mockedGet.mockResolvedValue({ data: { name: 'Harper Versions', description: '' } });
 
-		const options = getHarperVersionsOptions();
+		const options = getHarperVersionsOptions('org_1');
 
 		await expect((options.queryFn as () => Promise<HarperVersionsResponse>)()).rejects.toThrow();
 	});
diff --git a/src/features/clusters/queries/getHarperVersionsQuery.ts b/src/features/clusters/queries/getHarperVersionsQuery.ts
index 7140bbb80..2bf6bbb26 100644
--- a/src/features/clusters/queries/getHarperVersionsQuery.ts
+++ b/src/features/clusters/queries/getHarperVersionsQuery.ts
@@ -45,9 +45,13 @@ export function dedupeHarperVersionsByTag(versions: HarperVersion[]): HarperVers
 	return [...bestByVersion.values()];
 }
 
-async function getHarperVersions() {
+async function getHarperVersions(organizationId: string) {
 	// TODO: OpenAPI from CM is erroring, so this new endpoint isn't described.
-	const { data } = await apiClient.get(`/HarperVersions/` as any);
+	// The list is org-scoped: enterprise orgs also get the versions currently deployed on their
+	// clusters (labeled with the cluster) merged in server-side.
+	const { data } = await apiClient.get(`/HarperVersions/` as any, {
+		params: { organizationId },
+	});
 	const response = data as HarperVersionsResponse;
 	return {
 		...response,
@@ -55,10 +59,13 @@ async function getHarperVersions() {
 	} satisfies HarperVersionsResponse;
 }
 
-export function getHarperVersionsOptions() {
+export function getHarperVersionsOptions(organizationId: string) {
 	return queryOptions({
-		queryKey: ['HarperVersions'],
-		queryFn: getHarperVersions,
+		// Org-first, matching the sibling queries (getPlanTypesQuery, getRegionLocationsQuery, …) so
+		// org-scoped invalidations — `queryClient.invalidateQueries({ queryKey: [organizationId] })`,
+		// used after cluster ops that can change deployed versions — also refresh this list.
+		queryKey: [organizationId, 'HarperVersions'],
+		queryFn: () => getHarperVersions(organizationId),
 		staleTime: 60_000,
 		retry: false,
 	});
diff --git a/src/features/clusters/upsert/index.tsx b/src/features/clusters/upsert/index.tsx
index f9b6ae651..ca30713a3 100644
--- a/src/features/clusters/upsert/index.tsx
+++ b/src/features/clusters/upsert/index.tsx
@@ -73,12 +73,14 @@ export function UpsertCluster() {
 	}));
 	const { data: regionLocationsDedicated } = useQuery(getRegionLocationsOptions({ organizationId }));
 
-	const { data: newHarperVersions } = useQuery(getHarperVersionsOptions());
+	const { data: newHarperVersions } = useQuery(getHarperVersionsOptions(organizationId));
 	const harperVersions = useMemo(() => {
 		if (cluster) {
 			const clusterVersions = cluster.instances?.map(i => i.version).filter(excludeFalsy);
 			if (newHarperVersions && clusterVersions) {
-				const latestClusterVersion = clusterVersions.sort(compareVersions).pop();
+				// Copy before sort — sort mutates in place, and we reuse the full set below.
+				const latestClusterVersion = [...clusterVersions].sort(compareVersions).pop();
+				const clusterVersionSet = new Set(clusterVersions);
 				return {
 					...newHarperVersions,
 					value: [
@@ -87,13 +89,12 @@ export function UpsertCluster() {
 							version: latestClusterVersion,
 						} as const,
 						...(newHarperVersions?.value || []).filter(v => {
-							// Is our version unique from the latest cluster version?
-							return latestClusterVersion !== v.version
-								// Do we have a cluster version?
-								&& (!latestClusterVersion
-									// Or if we do, have we updated to a higher version already?
-									// This can prevent upgrading to, say, "next" v5, and then downgrading to the "latest" v4.
-									|| wasAReleasedBeforeB(latestClusterVersion, v.version));
+							// Drop any version this cluster already runs: the current version is shown once as
+							// "current" above, and the backend also returns it (and any co-tenant instance's
+							// version, mid-upgrade) as a "deployed on <cluster>" entry we don't want to duplicate.
+							return !clusterVersionSet.has(v.version)
+								// Only offer newer releases — no downgrades (e.g. don't drop from "next" v5 to "stable" v4).
+								&& (!latestClusterVersion || wasAReleasedBeforeB(latestClusterVersion, v.version));
 						}),
 					].filter(excludeFalsy),
 				} satisfies HarperVersionsResponse;