diff --git a/website/playground/webgpu/src/config/models.js b/website/playground/webgpu/src/config/models.js
index 5bb93ddf311..4b37df63a81 100644
--- a/website/playground/webgpu/src/config/models.js
+++ b/website/playground/webgpu/src/config/models.js
@@ -23,6 +23,8 @@ export const MODELS = [
     tagline: 'Larger · Built with Llama',
     approxBytes: 744e6,
     approxBytesIsEstimate: false,
+    // fp32 KV cache the program allocates for its full context.
+    kvCacheBytes: 587202560,
     arch: { layers: 16, dModel: 2048, ffn: 8192, heads: 32, kvHeads: 8, vocab: 128256 },
     assets: {
       "baseUrl": "https://huggingface.co/executorch-community/Llama-3.2-1B-Instruct-ExecuTorch-WebGPU/resolve/f2b116fc0b746ec8ba8adb93258b9e8b439cefa7/", // @lint-ignore (base URL, files resolve under it)
@@ -74,6 +76,8 @@ export const MODELS = [
     tagline: 'Fastest · 100+ languages',
     approxBytes: 416e6,
     approxBytesIsEstimate: false,
+    // fp32 KV cache the program allocates for its full context.
+    kvCacheBytes: 2055208960,
     arch: { layers: 28, dModel: 1024, ffn: 3072, heads: 16, kvHeads: 8, vocab: 151936 },
     assets: {
       "baseUrl": "https://huggingface.co/executorch-community/Qwen3-0.6B-ExecuTorch-WebGPU/resolve/65fa8ec0b8996b4a0157cdb89ea766b000b1134a/", // @lint-ignore (base URL, files resolve under it)
@@ -124,6 +128,8 @@ export const MODELS = [
     tagline: 'Larger · by Google DeepMind',
     approxBytes: 675e6,
     approxBytesIsEstimate: false,
+    // fp32 KV cache the program allocates for its full context.
+    kvCacheBytes: 477102080,
     arch: { layers: 26, dModel: 1152, ffn: 6912, heads: 4, kvHeads: 1, vocab: 262144 },
     assets: {
       "baseUrl": "https://huggingface.co/executorch-community/Gemma-3-1B-IT-ExecuTorch-WebGPU/resolve/91864e518e371b57a6433c180490ce5ab31639ec/", // @lint-ignore (base URL, files resolve under it)
diff --git a/website/playground/webgpu/src/ui/demo-chat.js b/website/playground/webgpu/src/ui/demo-chat.js
index 8f14e44e8fb..ea3a174e193 100644
--- a/website/playground/webgpu/src/ui/demo-chat.js
+++ b/website/playground/webgpu/src/ui/demo-chat.js
@@ -14,6 +14,7 @@ import { icon } from './icons.js';
 import { onDeviceNote } from './on-device.js';
 import { metricTile } from './metric.js';
 import { attachVoiceInput } from './voice-input.js';
+import { confirmModelMemory } from './memory-guard.js';
 
 const SUGGESTED_PROMPTS = [
   'Explain WebGPU to a 10-year-old',
@@ -168,6 +169,7 @@ export function mountChat(root, demo) {
   async function load() {
     if (gpuState.get().status !== 'ready' || state.phase === 'loading' || !state.source || state.source.kind === 'unavailable') return;
     const model = state.model;
+    if (!(await confirmModelMemory(model)) || model !== state.model) return;
     const controller = new AbortController();
     Object.assign(state, { phase: 'loading', loadError: null, loadAbort: controller, load: { stage: 'runtime', fractions: {}, bytes: null } });
     renderAll();
diff --git a/website/playground/webgpu/src/ui/demo-effects.js b/website/playground/webgpu/src/ui/demo-effects.js
index 7893bbc7a1d..4d8f1ec42d8 100644
--- a/website/playground/webgpu/src/ui/demo-effects.js
+++ b/website/playground/webgpu/src/ui/demo-effects.js
@@ -14,6 +14,7 @@ import { appIcon } from './app-icons.js';
 import { hfBadge } from './hf-badge.js';
 import { icon } from './icons.js';
 import { onDeviceNote } from './on-device.js';
+import { confirmModelMemory } from './memory-guard.js';
 
 const NORM = { mean: [0.5, 0.5, 0.5], std: [0.5, 0.5, 0.5] };
 const LOAD_STAGES = [
@@ -112,6 +113,7 @@ export function mountEffects(root, demo) {
 
   async function load() {
     if (gpuState.get().status !== 'ready' || state.phase === 'loading') return;
+    if (!(await confirmModelMemory(model))) return;
     const controller = new AbortController();
     Object.assign(state, { phase: 'loading', loadError: null, loadAbort: controller, load: { stage: 'runtime', fractions: {}, detail: '' } });
     renderAll();
diff --git a/website/playground/webgpu/src/ui/demo-segment.js b/website/playground/webgpu/src/ui/demo-segment.js
index a63bd0bea5e..441d8823e56 100644
--- a/website/playground/webgpu/src/ui/demo-segment.js
+++ b/website/playground/webgpu/src/ui/demo-segment.js
@@ -11,6 +11,7 @@ import { appIcon } from './app-icons.js';
 import { hfBadge } from './hf-badge.js';
 import { icon } from './icons.js';
 import { onDeviceNote } from './on-device.js';
+import { confirmModelMemory } from './memory-guard.js';
 
 const COLORS = ['#3b82f6', '#f97316', '#10b981', '#e11d48', '#8b5cf6', '#eab308', '#06b6d4', '#ec4899'];
 const MAX_WORKING_SIDE = 2048;
@@ -125,6 +126,7 @@ export function mountSegment(root, demo) {
 
   async function load() {
     if (state.phase === 'loading' || gpuState.get().status !== 'ready') return;
+    if (!(await confirmModelMemory(model))) return;
     const controller = new AbortController();
     loadAbort = controller;
     Object.assign(state, { phase: 'loading', loadError: null, load: { stage: 'runtime', done: new Set(), loaded: 0, total: 0, fromCache: false } });
diff --git a/website/playground/webgpu/src/ui/demo-stt.js b/website/playground/webgpu/src/ui/demo-stt.js
index 6241b9aa547..9780e44e075 100644
--- a/website/playground/webgpu/src/ui/demo-stt.js
+++ b/website/playground/webgpu/src/ui/demo-stt.js
@@ -15,6 +15,7 @@ import { appIcon } from './app-icons.js';
 import { hfBadge } from './hf-badge.js';
 import { icon } from './icons.js';
 import { onDeviceNote } from './on-device.js';
+import { confirmModelMemory } from './memory-guard.js';
 
 const MAX_REC_SECONDS = 300;
 const MIN_CLIP_SECONDS = 0.4;
@@ -221,6 +222,7 @@ export function mountStt(root, demo) {
 
   async function load() {
     if (state.phase === 'loading') return;
+    if (!(await confirmModelMemory(model))) return;
     loadAbort = new AbortController();
     Object.assign(state, { phase: 'loading', loadError: null, load: { stage: 'runtime', fractions: {}, loaded: 0, total: 0, detail: '' } });
     renderStage();
diff --git a/website/playground/webgpu/src/ui/demo-vision.js b/website/playground/webgpu/src/ui/demo-vision.js
index faee2e7b9b8..dfdef0c493b 100644
--- a/website/playground/webgpu/src/ui/demo-vision.js
+++ b/website/playground/webgpu/src/ui/demo-vision.js
@@ -16,6 +16,7 @@ import { appIcon } from './app-icons.js';
 import { hfBadge } from './hf-badge.js';
 import { icon } from './icons.js';
 import { onDeviceNote } from './on-device.js';
+import { confirmModelMemory } from './memory-guard.js';
 
 const TASKS = { depth: createDepthTask, detect: createDetectTask, bgremove: createMattingTask, superres: createSuperresTask };
 const COPY = {
@@ -137,6 +138,7 @@ export function mountVision(root, demo) {
 
   async function load() {
     if (gpuState.get().status !== 'ready' || state.phase === 'loading') return;
+    if (!(await confirmModelMemory(model))) return;
     const controller = new AbortController();
     Object.assign(state, { phase: 'loading', loadError: null, loadAbort: controller, load: { stage: 'runtime', fractions: {}, detail: '' } });
     renderAll();
diff --git a/website/playground/webgpu/src/ui/demo-vlm.js b/website/playground/webgpu/src/ui/demo-vlm.js
index 2560488fa0a..107bd8f7829 100644
--- a/website/playground/webgpu/src/ui/demo-vlm.js
+++ b/website/playground/webgpu/src/ui/demo-vlm.js
@@ -11,6 +11,7 @@ import { appIcon } from './app-icons.js';
 import { hfBadge } from './hf-badge.js';
 import { icon } from './icons.js';
 import { onDeviceNote } from './on-device.js';
+import { confirmModelMemory } from './memory-guard.js';
 
 const QUICK = ['Describe this image', 'What text can you read?', 'How many people are there?', 'What’s unusual here?'];
 const MAX_NEW_TOKENS = 192;
@@ -213,6 +214,7 @@ export function mountVlm(root, demo) {
 
   async function load() {
     if (state.phase === 'loading' || !state.source || state.source.kind === 'unavailable') return;
+    if (!(await confirmModelMemory(model))) return;
     const controller = new AbortController();
     Object.assign(state, { phase: 'loading', loadError: null, loadAbort: controller, load: { stage: 'runtime', fractions: {}, detail: '' } });
     loaderEls = null;
diff --git a/website/playground/webgpu/src/ui/memory-guard.js b/website/playground/webgpu/src/ui/memory-guard.js
new file mode 100644
index 00000000000..0a8dd71c9b2
--- /dev/null
+++ b/website/playground/webgpu/src/ui/memory-guard.js
@@ -0,0 +1,73 @@
+// Asks before loading a model that likely needs more memory than a phone or
+// tablet gives one browser tab. iOS Safari closes the tab outright (no error the
+// page can catch), so the check has to happen before the download starts.
+import { h } from '../lib/dom.js';
+import { formatBytes } from '../lib/format.js';
+import { icon } from './icons.js';
+
+// Above this estimate, phones and tablets are warned. The chat models
+// (estimated 1.8-2.9 GB) close the tab on iPhones; the vision models stay
+// under 0.3 GB.
+export const MOBILE_PEAK_LIMIT = 400e6;
+
+const accepted = new Set();
+
+export function isMobileDevice(nav = globalThis.navigator) {
+  if (!nav) return false;
+  const ua = nav.userAgent ?? '';
+  if (/iPhone|iPad|iPod|Android/i.test(ua)) return true;
+  // iPadOS Safari reports a desktop Mac user agent.
+  return /Macintosh/.test(ua) && (nav.maxTouchPoints ?? 0) > 1;
+}
+
+// Rough peak while loading: the downloaded bytes, the runtime's copy of the
+// program, and GPU buffers for the weights plus any preallocated KV cache.
+export function estimatePeakBytes(model) {
+  return 2 * (model.approxBytes ?? 0) + (model.kvCacheBytes ?? 0);
+}
+
+export function needsMemoryWarning(model, nav = globalThis.navigator) {
+  const lowMemory = typeof nav?.deviceMemory === 'number' && nav.deviceMemory <= 4;
+  return (isMobileDevice(nav) || lowMemory) && estimatePeakBytes(model) > MOBILE_PEAK_LIMIT;
+}
+
+// Resolves true to go ahead. Asks once per model per page load.
+export function confirmModelMemory(model) {
+  if (accepted.has(model.id) || !needsMemoryWarning(model) || typeof HTMLDialogElement === 'undefined') {
+    return Promise.resolve(true);
+  }
+  return new Promise((resolve) => {
+    const finish = (ok) => {
+      if (ok) accepted.add(model.id);
+      dialog.close();
+      dialog.remove();
+      resolve(ok);
+    };
+    const cancel = h('button', { class: 'btn btn--ghost', type: 'button', onclick: () => finish(false) }, 'Cancel');
+    const dialog = h(
+      'dialog',
+      { class: 'memory-guard', 'aria-labelledby': 'memory-guard-title' },
+      h('div', { class: 'memory-guard__icon', 'aria-hidden': 'true' }, icon('alert', 22)),
+      h('h2', { class: 'memory-guard__title', id: 'memory-guard-title' }, 'This model may be too big for this device'),
+      h(
+        'p',
+        { class: 'memory-guard__body' },
+        `${model.name} needs about ${formatBytes(estimatePeakBytes(model))} of memory while it loads. `,
+        'Phones and tablets often close the tab when a page uses that much. It works best on a laptop or desktop.',
+      ),
+      h(
+        'div',
+        { class: 'memory-guard__actions' },
+        cancel,
+        h('button', { class: 'btn btn--primary', type: 'button', onclick: () => finish(true) }, 'Load anyway'),
+      ),
+    );
+    dialog.addEventListener('cancel', (e) => {
+      e.preventDefault();
+      finish(false);
+    });
+    document.body.append(dialog);
+    dialog.showModal();
+    cancel.focus();
+  });
+}
diff --git a/website/playground/webgpu/styles/app.css b/website/playground/webgpu/styles/app.css
index 3d6c8749caa..bff5b78dc53 100644
--- a/website/playground/webgpu/styles/app.css
+++ b/website/playground/webgpu/styles/app.css
@@ -1389,3 +1389,11 @@ p { margin: 0; }
 .model-row--stored { border-color: color-mix(in srgb, var(--live) 45%, var(--border)); box-shadow: inset 4px 0 0 var(--live), var(--shadow-sm); }
 .model-row--stored .model-row__name { font-weight: 700; }
 .model-row:not(.model-row--stored) .model-row__name { color: var(--text-2); font-weight: 600; }
+
+/* Memory warning before loading a large model on a phone or tablet */
+.memory-guard { max-width: min(420px, calc(100vw - 32px)); padding: 24px; border: 1px solid var(--border); border-radius: var(--radius); background: var(--surface); color: var(--text); box-shadow: var(--shadow-md); }
+.memory-guard::backdrop { background: rgba(15, 23, 42, 0.45); }
+.memory-guard__icon { display: inline-flex; color: var(--accent); margin-bottom: 8px; }
+.memory-guard__title { margin: 0 0 8px; font-size: 18px; font-weight: 700; }
+.memory-guard__body { margin: 0 0 20px; line-height: 1.5; color: var(--text-2); }
+.memory-guard__actions { display: flex; justify-content: flex-end; gap: 10px; flex-wrap: wrap; }
diff --git a/website/playground/webgpu/tests/memory-guard.test.mjs b/website/playground/webgpu/tests/memory-guard.test.mjs
new file mode 100644
index 00000000000..57665f02213
--- /dev/null
+++ b/website/playground/webgpu/tests/memory-guard.test.mjs
@@ -0,0 +1,36 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+import { getModel } from '../src/config/models.js';
+import { estimatePeakBytes, isMobileDevice, needsMemoryWarning } from '../src/ui/memory-guard.js';
+
+const IPHONE = { userAgent: 'Mozilla/5.0 (iPhone; CPU iPhone OS 26_0 like Mac OS X) AppleWebKit/605.1.15 Version/26.0 Mobile/15E148 Safari/604.1', maxTouchPoints: 5 };
+const IPAD = { userAgent: 'Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/605.1.15 Version/26.0 Safari/605.1.15', maxTouchPoints: 5 };
+const MAC = { userAgent: 'Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/605.1.15 Version/26.0 Safari/605.1.15', maxTouchPoints: 0 };
+const ANDROID = { userAgent: 'Mozilla/5.0 (Linux; Android 15; Pixel 9) AppleWebKit/537.36 Chrome/141.0 Mobile Safari/537.36', deviceMemory: 8 };
+const LAPTOP_4GB = { userAgent: 'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 Chrome/141.0 Safari/537.36', deviceMemory: 4 };
+const LAPTOP_8GB = { ...LAPTOP_4GB, deviceMemory: 8 };
+
+test('phones and tablets are detected, including iPadOS with a desktop user agent', () => {
+  assert.equal(isMobileDevice(IPHONE), true);
+  assert.equal(isMobileDevice(IPAD), true);
+  assert.equal(isMobileDevice(ANDROID), true);
+  assert.equal(isMobileDevice(MAC), false);
+  assert.equal(isMobileDevice(LAPTOP_8GB), false);
+});
+
+test('chat models count their KV cache in the estimate', () => {
+  const qwen = getModel('qwen3-0.6b');
+  assert.equal(estimatePeakBytes(qwen), 2 * qwen.approxBytes + 28 * 2 * 8 * 128 * 8960 * 4);
+});
+
+test('chat and speech models warn on phones; small vision models do not; desktops never', () => {
+  for (const id of ['qwen3-0.6b', 'gemma-3-1b-it', 'whisper-base']) {
+    assert.equal(needsMemoryWarning(getModel(id), IPHONE), true, id);
+    assert.equal(needsMemoryWarning(getModel(id), MAC), false, id);
+    assert.equal(needsMemoryWarning(getModel(id), LAPTOP_8GB), false, id);
+  }
+  for (const id of ['depth-anything-v2-small', 'modnet', 'real-esrgan', 'dfine-small', 'sam2-hiera-tiny']) {
+    assert.equal(needsMemoryWarning(getModel(id), IPHONE), false, id);
+  }
+  assert.equal(needsMemoryWarning(getModel('qwen3-0.6b'), LAPTOP_4GB), true);
+});