diff --git a/backend/internal/service/v1.go b/backend/internal/service/v1.go
index de204f9..ceb1c93 100644
--- a/backend/internal/service/v1.go
+++ b/backend/internal/service/v1.go
@@ -2644,13 +2644,14 @@ func guessRatio(w, h int) string {
 		W int
 		H int
 	}
-	// The 14 ratios actually used across our models. Must stay in sync with the
+	// The 13 ratios actually used across our models. Must stay in sync with the
 	// custom-model picker (CustomModelModal RATIO_OPTS) and the docs 对照表, so a
-	// /v1 `size` maps to exactly one of them.
+	// /v1 `size` maps to exactly one of them. 9:21 is intentionally absent —
+	// no image provider accepts it (Runway 400s on it).
 	candidates := []candidate{
 		{1, 1},
 		{5, 4}, {4, 3}, {3, 2}, {16, 9}, {2, 1}, {21, 9}, {3, 1}, // 横
-		{4, 5}, {3, 4}, {2, 3}, {9, 16}, {9, 21}, {1, 3}, // 竖
+		{4, 5}, {3, 4}, {2, 3}, {9, 16}, {1, 3}, // 竖
 	}
 	best := candidates[0]
 	bestDelta := absFloat(float64(w)/float64(h) - float64(best.W)/float64(best.H))
diff --git a/frontend/src/components/CustomModelModal.vue b/frontend/src/components/CustomModelModal.vue
index ef53498..3f17a0e 100644
--- a/frontend/src/components/CustomModelModal.vue
+++ b/frontend/src/components/CustomModelModal.vue
@@ -6,9 +6,9 @@ import SelectMenu from './SelectMenu.vue'
 
 const emit = defineEmits(['close', 'saved'])
 
-// 14 ratios — the union of what our models actually support; kept in sync with
-// the backend guessRatio() and the docs 对照表.
-const RATIO_OPTS = ['1:1', '5:4', '4:3', '3:2', '16:9', '2:1', '21:9', '3:1', '4:5', '3:4', '2:3', '9:16', '9:21', '1:3']
+// 13 ratios — the union of what our models actually support; kept in sync with
+// the backend guessRatio() and the docs 对照表. 9:21 removed (no image provider accepts it).
+const RATIO_OPTS = ['1:1', '5:4', '4:3', '3:2', '16:9', '2:1', '21:9', '3:1', '4:5', '3:4', '2:3', '9:16', '1:3']
 const IMG_RES = ['1K', '2K', '4K']
 const VID_RES = ['720p', '1080p', '2K', '4K']
 const ALL_RES = ['1K', '2K', '4K', '720p', '1080p']
diff --git a/frontend/src/views/DocsView.vue b/frontend/src/views/DocsView.vue
index ca6126c..70139d5 100644
--- a/frontend/src/views/DocsView.vue
+++ b/frontend/src/views/DocsView.vue
@@ -74,7 +74,6 @@ const sizeTable = [
   { ratio: '3:4 · 竖',   k1: '768x1024',  k2: '1536x2048', k4: '3072x4096' },
   { ratio: '2:3 · 竖',   k1: '800x1200',  k2: '1600x2400', k4: '2400x3600' },
   { ratio: '9:16 · 竖',  k1: '720x1280',  k2: '1152x2048', k4: '2304x4096' },
-  { ratio: '9:21 · 竖超宽', k1: '720x1680', k2: '1080x2520', k4: '2160x5040' },
   { ratio: '1:3 · 竖',   k1: '512x1536',  k2: '768x2304',  k4: '1280x3840' },
 ]