diff --git a/studio/setup.ps1 b/studio/setup.ps1
index c6932121c9..8e15976e8c 100644
--- a/studio/setup.ps1
+++ b/studio/setup.ps1
@@ -1129,6 +1129,25 @@ if ($script:StudioVtOk -and -not $env:NO_COLOR) {
     Write-Host "  $Rule" -ForegroundColor DarkGray
 }
 
+# WebView2 caches keyed by the app bundle id hold copies of the previous
+# frontend and can keep serving it after an update (old styles linger).
+# Cache-only paths: Local Storage, IndexedDB, cookies, settings, models,
+# and the studio database are untouched.
+if ($env:LOCALAPPDATA) {
+    $wvDefault = Join-Path $env:LOCALAPPDATA "ai.unsloth.studio\EBWebView\Default"
+    $wvCleared = $false
+    foreach ($wvSub in @("Cache", "Code Cache", "GPUCache", "Service Worker")) {
+        $wvPath = Join-Path $wvDefault $wvSub
+        if (Test-Path -LiteralPath $wvPath) {
+            try {
+                Remove-Item -LiteralPath $wvPath -Recurse -Force -ErrorAction Stop
+                $wvCleared = $true
+            } catch { }
+        }
+    }
+    if ($wvCleared) { substep "cleared stale WebView caches (ai.unsloth.studio); settings and data kept" }
+}
+
 # Back up User PATH under HKCU\Software\Unsloth before any modifications.
 try {
     $envKey = [Microsoft.Win32.Registry]::CurrentUser.OpenSubKey('Environment', $false)
diff --git a/studio/setup.sh b/studio/setup.sh
index 3c97f77065..13d654cdd6 100755
--- a/studio/setup.sh
+++ b/studio/setup.sh
@@ -475,6 +475,50 @@ rm -rf "$REPO_ROOT/unsloth_compiled_cache"
 rm -rf "$SCRIPT_DIR/backend/unsloth_compiled_cache"
 rm -rf "$SCRIPT_DIR/tmp/unsloth_compiled_cache"
 
+# WebView caches keyed by the app bundle id hold copies of the previous
+# frontend and can keep serving it after an update (old styles linger).
+# Cache-only paths: LocalStorage, IndexedDB, cookies, settings, models,
+# and the studio database are untouched.
+_clear_webview_caches() {
+    _wvc_bid="ai.unsloth.studio"
+    _wvc_paths=()
+    case "$(uname -s 2>/dev/null)" in
+        Darwin)
+            _wvc_paths=(
+                "$HOME/Library/Caches/$_wvc_bid"
+                "$HOME/Library/WebKit/$_wvc_bid/WebsiteData/CacheStorage"
+                "$HOME/Library/WebKit/$_wvc_bid/WebsiteData/ServiceWorkers"
+                "$HOME/Library/WebKit/$_wvc_bid/WebsiteData/DiskCache"
+            )
+            ;;
+        Linux)
+            # wry keys the WebKitGTK base-cache dir to the app DATA dir (same
+            # as base-data), so cache subdirs also live under
+            # ~/.local/share/<bid>. Clear only the cache-typed subdirs there;
+            # sibling localstorage/, indexeddb/, and cookies stay.
+            _wvc_data="${XDG_DATA_HOME:-$HOME/.local/share}/$_wvc_bid"
+            _wvc_paths=(
+                "${XDG_CACHE_HOME:-$HOME/.cache}/$_wvc_bid"
+                "$_wvc_data/WebKitCache"
+                "$_wvc_data/CacheStorage"
+                "$_wvc_data/serviceworkers"
+                "$_wvc_data/ServiceWorkers"
+            )
+            ;;
+        *) return 0 ;;
+    esac
+    _wvc_cleared=false
+    for _wvc_p in "${_wvc_paths[@]}"; do
+        [ -e "$_wvc_p" ] || continue
+        rm -rf "$_wvc_p" 2>/dev/null && _wvc_cleared=true || true
+    done
+    if [ "$_wvc_cleared" = true ]; then
+        substep "cleared stale WebView caches ($_wvc_bid); settings and data kept"
+    fi
+    return 0
+}
+_clear_webview_caches
+
 # ── Detect Colab ──
 IS_COLAB=false
 keynames=$'\n'$(printenv | cut -d= -f1)
diff --git a/studio/src-tauri/src/main.rs b/studio/src-tauri/src/main.rs
index 405b390177..e422124f0c 100644
--- a/studio/src-tauri/src/main.rs
+++ b/studio/src-tauri/src/main.rs
@@ -161,6 +161,64 @@ fn setup_tray(app: &tauri::App) -> Result<(), Box<dyn std::error::Error>> {
     Ok(())
 }
 
+// Clear WebView caches before the webview initializes. An in-app update runs
+// setup.sh/setup.ps1 while the old WebView still holds these files (its clear
+// silently fails), so without this a relaunch can serve the previous frontend
+// from cache. Cache-only paths; LocalStorage, IndexedDB, cookies, and app
+// data are kept. Mirrors setup.sh _clear_webview_caches / setup.ps1.
+fn clear_webview_caches(bundle_id: &str) {
+    use std::path::PathBuf;
+    let mut paths: Vec<PathBuf> = Vec::new();
+    #[cfg(target_os = "windows")]
+    if let Ok(local) = std::env::var("LOCALAPPDATA") {
+        if !local.is_empty() {
+            let profile = PathBuf::from(local)
+                .join(bundle_id)
+                .join("EBWebView")
+                .join("Default");
+            for sub in ["Cache", "Code Cache", "GPUCache", "Service Worker"] {
+                paths.push(profile.join(sub));
+            }
+        }
+    }
+    #[cfg(target_os = "macos")]
+    if let Ok(home) = std::env::var("HOME") {
+        if !home.is_empty() {
+            let home = PathBuf::from(home);
+            paths.push(home.join("Library/Caches").join(bundle_id));
+            let data = home.join("Library/WebKit").join(bundle_id).join("WebsiteData");
+            for sub in ["CacheStorage", "ServiceWorkers", "DiskCache"] {
+                paths.push(data.join(sub));
+            }
+        }
+    }
+    #[cfg(target_os = "linux")]
+    if let Ok(home) = std::env::var("HOME") {
+        if !home.is_empty() {
+            let home = PathBuf::from(home);
+            let cache = std::env::var("XDG_CACHE_HOME")
+                .ok()
+                .filter(|v| !v.is_empty())
+                .map(PathBuf::from)
+                .unwrap_or_else(|| home.join(".cache"));
+            paths.push(cache.join(bundle_id));
+            // wry keys the WebKitGTK base-cache dir to the app data dir.
+            let data = std::env::var("XDG_DATA_HOME")
+                .ok()
+                .filter(|v| !v.is_empty())
+                .map(PathBuf::from)
+                .unwrap_or_else(|| home.join(".local/share"))
+                .join(bundle_id);
+            for sub in ["WebKitCache", "CacheStorage", "serviceworkers", "ServiceWorkers"] {
+                paths.push(data.join(sub));
+            }
+        }
+    }
+    for p in paths {
+        let _ = fs::remove_dir_all(&p);
+    }
+}
+
 fn main() {
     // Fix PATH for GUI apps (macOS .app bundles, Linux AppImage, Windows)
     // GUI apps don't inherit shell dotfile PATH — this spawns the user's
@@ -171,6 +229,11 @@ fn main() {
     info!("Unsloth Studio desktop app starting");
     windows_job::initialize();
 
+    // Must run before the Builder: the config-defined window (and its
+    // WebView, which locks these files) exists by the time setup hooks run.
+    let context = tauri::generate_context!();
+    clear_webview_caches(&context.config().identifier);
+
     tauri::Builder::default()
         .plugin(tauri_plugin_single_instance::init(|app, _args, _cwd| {
             if let Some(window) = app.get_webview_window("main") {
@@ -247,7 +310,7 @@ fn main() {
                 api.prevent_close();
             }
         })
-        .build(tauri::generate_context!())
+        .build(context)
         .expect("error while building tauri application")
         .run(|app, event| {
             if let tauri::RunEvent::Exit = event {
diff --git a/tests/run_all.sh b/tests/run_all.sh
index eaa726f73c..147aaf1645 100755
--- a/tests/run_all.sh
+++ b/tests/run_all.sh
@@ -14,6 +14,8 @@ sh "$TESTS_DIR/sh/test_nvcc_meets_llama_minimum.sh"
 sh "$TESTS_DIR/sh/test_resolve_cuda_archs.sh"
 sh "$TESTS_DIR/sh/test_strixhalo_wsl_reroute.sh"
 sh "$TESTS_DIR/sh/test_uninstall_shared_icon.sh"
+# bash, not sh: the extracted setup.sh function uses bash arrays (dash chokes).
+bash "$TESTS_DIR/sh/test_setup_webview_cache_clear.sh"
 sh "$TESTS_DIR/sh/test_torch_flavor.sh"
 sh "$TESTS_DIR/sh/test_redact_install_output.sh"
 sh "$TESTS_DIR/sh/test_install_uv_override_space.sh"
diff --git a/tests/sh/test_setup_webview_cache_clear.sh b/tests/sh/test_setup_webview_cache_clear.sh
new file mode 100755
index 0000000000..19a3ee0064
--- /dev/null
+++ b/tests/sh/test_setup_webview_cache_clear.sh
@@ -0,0 +1,103 @@
+#!/bin/bash
+# SPDX-License-Identifier: AGPL-3.0-only
+# Copyright 2026-present the Unsloth AI Inc. team. All rights reserved. See /studio/LICENSE.AGPL-3.0
+# Unit tests for _clear_webview_caches() from studio/setup.sh.
+#
+# The WebView caches keyed by the app bundle id (ai.unsloth.studio) hold copies
+# of the previous frontend, so an install/update must clear them or the app can
+# keep rendering old styles. Clearing must be cache-only: LocalStorage,
+# IndexedDB, app data, and unrelated apps' caches stay intact.
+#
+# Follows the extract-via-sed pattern of test_uninstall_shared_icon.sh; uname
+# is overridden per test with a shell function to select the OS branch.
+# shellcheck disable=SC2329  # uname stubs are invoked inside the extracted function
+set -e
+
+SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
+SETUP_SH="$SCRIPT_DIR/../../studio/setup.sh"
+BID="ai.unsloth.studio"
+PASS=0
+FAIL=0
+
+_TMP_ROOT=$(mktemp -d)
+trap 'rm -rf "$_TMP_ROOT"' EXIT
+
+assert_gone()    { _l="$1"; if [ -e "$2" ]; then echo "  FAIL: $_l (still present: $2)"; FAIL=$((FAIL+1)); else echo "  PASS: $_l"; PASS=$((PASS+1)); fi; }
+assert_present() { _l="$1"; if [ -e "$2" ]; then echo "  PASS: $_l"; PASS=$((PASS+1)); else echo "  FAIL: $_l (missing: $2)"; FAIL=$((FAIL+1)); fi; }
+
+# Extract just the function definition (top-level, closes at column 0).
+FUNC_FILE=$(mktemp -p "$_TMP_ROOT")
+sed -n '/^_clear_webview_caches() {/,/^}/p' "$SETUP_SH" > "$FUNC_FILE"
+# shellcheck disable=SC1090
+. "$FUNC_FILE"
+substep() { :; }  # stub the setup.sh logger
+
+# ── 1. macOS: cache paths removed, user-facing storage kept ──
+H=$(mktemp -d -p "$_TMP_ROOT")
+mkdir -p "$H/Library/Caches/$BID/WebKit/NetworkCache" \
+         "$H/Library/WebKit/$BID/WebsiteData/CacheStorage" \
+         "$H/Library/WebKit/$BID/WebsiteData/ServiceWorkers" \
+         "$H/Library/WebKit/$BID/WebsiteData/DiskCache" \
+         "$H/Library/WebKit/$BID/WebsiteData/LocalStorage" \
+         "$H/Library/WebKit/$BID/WebsiteData/IndexedDB" \
+         "$H/Library/Application Support/$BID" \
+         "$H/Library/Caches/com.other.app"
+uname() { echo Darwin; }
+HOME="$H" _clear_webview_caches
+assert_gone    "macOS: Caches/$BID removed"              "$H/Library/Caches/$BID"
+assert_gone    "macOS: WebsiteData/CacheStorage removed" "$H/Library/WebKit/$BID/WebsiteData/CacheStorage"
+assert_gone    "macOS: WebsiteData/ServiceWorkers removed" "$H/Library/WebKit/$BID/WebsiteData/ServiceWorkers"
+assert_gone    "macOS: WebsiteData/DiskCache removed"    "$H/Library/WebKit/$BID/WebsiteData/DiskCache"
+assert_present "macOS: LocalStorage kept"                "$H/Library/WebKit/$BID/WebsiteData/LocalStorage"
+assert_present "macOS: IndexedDB kept"                   "$H/Library/WebKit/$BID/WebsiteData/IndexedDB"
+assert_present "macOS: Application Support kept"         "$H/Library/Application Support/$BID"
+assert_present "macOS: unrelated app cache kept"         "$H/Library/Caches/com.other.app"
+
+# ── 2. Linux: cache paths removed (XDG cache dir AND the cache subdirs wry
+# keys to the app data dir), user-facing storage kept ──
+H=$(mktemp -d -p "$_TMP_ROOT")
+D="$H/.local/share/$BID"
+mkdir -p "$H/.cache/$BID" "$D/WebKitCache" "$D/CacheStorage" "$D/serviceworkers" \
+         "$D/localstorage" "$D/indexeddb" "$H/.config/$BID" "$H/.cache/other.app"
+: > "$D/cookies.sqlite"
+uname() { echo Linux; }
+HOME="$H" XDG_CACHE_HOME="" XDG_DATA_HOME="" _clear_webview_caches
+assert_gone    "linux: ~/.cache/$BID removed"          "$H/.cache/$BID"
+assert_gone    "linux: data-dir WebKitCache removed"   "$D/WebKitCache"
+assert_gone    "linux: data-dir CacheStorage removed"  "$D/CacheStorage"
+assert_gone    "linux: data-dir serviceworkers removed" "$D/serviceworkers"
+assert_present "linux: localstorage kept"              "$D/localstorage"
+assert_present "linux: indexeddb kept"                 "$D/indexeddb"
+assert_present "linux: cookies kept"                   "$D/cookies.sqlite"
+assert_present "linux: ~/.config/$BID kept"            "$H/.config/$BID"
+assert_present "linux: unrelated app cache kept"       "$H/.cache/other.app"
+
+# ── 3. Linux: XDG_CACHE_HOME / XDG_DATA_HOME overrides honored ──
+H=$(mktemp -d -p "$_TMP_ROOT")
+XDG=$(mktemp -d -p "$_TMP_ROOT")
+mkdir -p "$XDG/cache/$BID" "$XDG/data/$BID/WebKitCache" "$XDG/data/$BID/localstorage" "$H/.cache/$BID"
+HOME="$H" XDG_CACHE_HOME="$XDG/cache" XDG_DATA_HOME="$XDG/data" _clear_webview_caches
+assert_gone    "linux: XDG_CACHE_HOME/$BID removed"          "$XDG/cache/$BID"
+assert_gone    "linux: XDG_DATA_HOME WebKitCache removed"    "$XDG/data/$BID/WebKitCache"
+assert_present "linux: XDG_DATA_HOME localstorage kept"      "$XDG/data/$BID/localstorage"
+assert_present "linux: ~/.cache/$BID kept under override"    "$H/.cache/$BID"
+
+# ── 4. Nothing to clear is a clean no-op ──
+H=$(mktemp -d -p "$_TMP_ROOT")
+uname() { echo Darwin; }
+if HOME="$H" _clear_webview_caches; then
+    echo "  PASS: empty HOME -> no-op exit 0"; PASS=$((PASS+1))
+else
+    echo "  FAIL: empty HOME -> nonzero exit"; FAIL=$((FAIL+1))
+fi
+
+# ── 5. Unknown OS is a no-op ──
+H=$(mktemp -d -p "$_TMP_ROOT")
+mkdir -p "$H/Library/Caches/$BID"
+uname() { echo SunOS; }
+HOME="$H" _clear_webview_caches
+assert_present "unknown OS: nothing removed" "$H/Library/Caches/$BID"
+
+echo ""
+echo "Results: $PASS passed, $FAIL failed"
+[ "$FAIL" = 0 ]
diff --git a/tests/studio/playwright_ui_font_scale.py b/tests/studio/playwright_ui_font_scale.py
index 7dbe36127c..89c7894929 100644
--- a/tests/studio/playwright_ui_font_scale.py
+++ b/tests/studio/playwright_ui_font_scale.py
@@ -38,7 +38,11 @@ def fail(m):
     raise AssertionError(f"[font-scale] FAIL: {m}")
 
 
-def near(a, b, tol = 0.35):
+def near(
+    a,
+    b,
+    tol = 0.35,
+):
     return a is not None and b is not None and abs(a - b) <= tol
 
 
@@ -86,9 +90,7 @@ def open_appearance(page):
         page.wait_for_timeout(700)
     if page.get_by_role("dialog").count() == 0:
         fail("settings dialog did not open")
-    page.get_by_role("dialog").get_by_role("button").filter(
-        has_text = "Appearance"
-    ).first.click()
+    page.get_by_role("dialog").get_by_role("button").filter(has_text = "Appearance").first.click()
     page.wait_for_timeout(600)
 
 
@@ -153,9 +155,7 @@ def main():
         page.wait_for_timeout(400)
 
         step("overflowing select scrolls its Radix viewport")
-        page.get_by_role("dialog").get_by_role("button").filter(
-            has_text = "Voice"
-        ).first.click()
+        page.get_by_role("dialog").get_by_role("button").filter(has_text = "Voice").first.click()
         page.wait_for_timeout(600)
         page.set_viewport_size({"width": 1440, "height": 480})
         page.locator("[aria-label='Dictation language']").click()
@@ -194,9 +194,7 @@ def main():
         page.wait_for_timeout(400)
 
         step("default restores exactly")
-        page.get_by_role("dialog").get_by_role("button").filter(
-            has_text = "Appearance"
-        ).first.click()
+        page.get_by_role("dialog").get_by_role("button").filter(has_text = "Appearance").first.click()
         page.wait_for_timeout(500)
         set_input(page, "UI font size", DEFAULT)
         final = measure(page)
diff --git a/tests/studio/test_ui_font_scale_contract.py b/tests/studio/test_ui_font_scale_contract.py
index 62bf80e82b..393c60dd6b 100644
--- a/tests/studio/test_ui_font_scale_contract.py
+++ b/tests/studio/test_ui_font_scale_contract.py
@@ -15,9 +15,7 @@ from pathlib import Path
 REPO = Path(__file__).resolve().parents[2]
 SRC = REPO / "studio/frontend/src"
 INDEX_CSS = (SRC / "index.css").read_text(encoding = "utf-8")
-STORE = (SRC / "features/settings/stores/appearance-custom-store.ts").read_text(
-    encoding = "utf-8"
-)
+STORE = (SRC / "features/settings/stores/appearance-custom-store.ts").read_text(encoding = "utf-8")
 SELECT = (SRC / "components/ui/select.tsx").read_text(encoding = "utf-8")
 
 # Raw numeric fontSize props are only allowed where a scaled stylesheet rule
@@ -70,9 +68,7 @@ def test_ui_token_families_exist():
 
 
 def test_explicit_code_font_size_is_never_multiplied():
-    match = re.search(
-        r"html\[data-code-font-size\][^{]*\{([^}]*)\}", INDEX_CSS
-    )
+    match = re.search(r"html\[data-code-font-size\][^{]*\{([^}]*)\}", INDEX_CSS)
     assert match is not None
     body = match.group(1)
     assert "var(--custom-code-font-size)" in body
@@ -83,7 +79,9 @@ def test_radix_select_viewport_owns_the_scroll_state():
     viewport = SELECT[SELECT.index("SelectPrimitive.Viewport") :]
     assert "overflow-y-auto" in viewport.split("</SelectPrimitive.Viewport>")[0]
     # The rounded surface itself must not scroll (WebKit squares its corners).
-    content_cls = re.search(r"SelectPrimitive\.Content[\s\S]*?className=\{cn\(\s*\"([^\"]+)\"", SELECT)
+    content_cls = re.search(
+        r"SelectPrimitive\.Content[\s\S]*?className=\{cn\(\s*\"([^\"]+)\"", SELECT
+    )
     assert content_cls is not None
     assert "overflow-hidden" in content_cls.group(1)
     assert "overflow-y-auto" not in content_cls.group(1)