diff --git a/src/base/bittorrent/session.h b/src/base/bittorrent/session.h
index 7d024d5db..5400f3843 100644
--- a/src/base/bittorrent/session.h
+++ b/src/base/bittorrent/session.h
@@ -165,8 +165,6 @@ namespace BitTorrent
         virtual bool addCategory(const QString &name, const CategoryOptions &options = {}) = 0;
         virtual bool editCategory(const QString &name, const CategoryOptions &options) = 0;
         virtual bool removeCategory(const QString &name) = 0;
-        virtual bool isSubcategoriesEnabled() const = 0;
-        virtual void setSubcategoriesEnabled(bool value) = 0;
         virtual bool useCategoryPathsInManualMode() const = 0;
         virtual void setUseCategoryPathsInManualMode(bool value) = 0;
 
diff --git a/src/base/bittorrent/sessionimpl.cpp b/src/base/bittorrent/sessionimpl.cpp
index 72f6e6a2a..7827b50e1 100644
--- a/src/base/bittorrent/sessionimpl.cpp
+++ b/src/base/bittorrent/sessionimpl.cpp
@@ -555,7 +555,6 @@ SessionImpl::SessionImpl(QObject *parent)
     , m_savePath(BITTORRENT_SESSION_KEY(u"DefaultSavePath"_s), specialFolderLocation(SpecialFolder::Downloads))
     , m_downloadPath(BITTORRENT_SESSION_KEY(u"TempPath"_s), (savePath() / Path(u"temp"_s)))
     , m_isDownloadPathEnabled(BITTORRENT_SESSION_KEY(u"TempPathEnabled"_s), false)
-    , m_isSubcategoriesEnabled(BITTORRENT_SESSION_KEY(u"SubcategoriesEnabled"_s), false)
     , m_useCategoryPathsInManualMode(BITTORRENT_SESSION_KEY(u"UseCategoryPathsInManualMode"_s), false)
     , m_isAutoTMMDisabledByDefault(BITTORRENT_SESSION_KEY(u"DisableAutoTMMByDefault"_s), true)
     , m_isDisableAutoTMMWhenCategoryChanged(BITTORRENT_SESSION_KEY(u"DisableAutoTMMTriggers/CategoryChanged"_s), false)
@@ -626,11 +625,6 @@ SessionImpl::SessionImpl(QObject *parent)
         enableBandwidthScheduler();
 
     loadCategories();
-    if (isSubcategoriesEnabled())
-    {
-        // if subcategories support changed manually
-        m_categories = expandCategories(m_categories);
-    }
 
     const QStringList storedTags = m_storedTags.get();
     for (const QString &tagStr : storedTags)
@@ -938,15 +932,8 @@ Path SessionImpl::categorySavePath(const QString &categoryName, const CategoryOp
     if (path.isEmpty())
     {
         // use implicit save path
-        if (isSubcategoriesEnabled())
-        {
-            path = Utils::Fs::toValidPath(subcategoryName(categoryName));
-            basePath = categorySavePath(parentCategoryName(categoryName));
-        }
-        else
-        {
-            path = Utils::Fs::toValidPath(categoryName);
-        }
+        path = Utils::Fs::toValidPath(subcategoryName(categoryName));
+        basePath = categorySavePath(parentCategoryName(categoryName));
     }
 
     return (path.isAbsolute() ? path : (basePath / path));
@@ -966,8 +953,7 @@ Path SessionImpl::categoryDownloadPath(const QString &categoryName, const Catego
     if (categoryName.isEmpty())
         return downloadPath();
 
-    const bool useSubcategories = isSubcategoriesEnabled();
-    const QString name = useSubcategories ? subcategoryName(categoryName) : categoryName;
+    const QString name = subcategoryName(categoryName);
     const Path path = !downloadPathOption.path.isEmpty()
             ? downloadPathOption.path
             : Utils::Fs::toValidPath(name); // use implicit download path
@@ -975,7 +961,7 @@ Path SessionImpl::categoryDownloadPath(const QString &categoryName, const Catego
     if (path.isAbsolute())
         return path;
 
-    const QString parentName = useSubcategories ? parentCategoryName(categoryName) : QString();
+    const QString parentName = parentCategoryName(categoryName);
     CategoryOptions parentOptions = categoryOptions(parentName);
     // Even if download path of parent category is disabled (directly or by inheritance)
     // we need to construct the one as if it would be enabled.
@@ -994,7 +980,7 @@ DownloadPathOption SessionImpl::resolveCategoryDownloadPathOption(const QString
     if (option.has_value())
         return *option;
 
-    const QString parentName = isSubcategoriesEnabled() ? parentCategoryName(categoryName) : QString();
+    const QString parentName = parentCategoryName(categoryName);
     return resolveCategoryDownloadPathOption(parentName, categoryOptions(parentName).downloadPath);
 }
 
@@ -1006,15 +992,12 @@ bool SessionImpl::addCategory(const QString &name, const CategoryOptions &option
     if (!isValidCategoryName(name) || m_categories.contains(name))
         return false;
 
-    if (isSubcategoriesEnabled())
+    for (const QString &parent : asConst(expandCategory(name)))
     {
-        for (const QString &parent : asConst(expandCategory(name)))
+        if ((parent != name) && !m_categories.contains(parent))
         {
-            if ((parent != name) && !m_categories.contains(parent))
-            {
-                m_categories[parent] = {};
-                emit categoryAdded(parent);
-            }
+            m_categories[parent] = {};
+            emit categoryAdded(parent);
         }
     }
 
@@ -1070,21 +1053,18 @@ bool SessionImpl::removeCategory(const QString &name)
 
     // remove stored category and its subcategories if exist
     bool result = false;
-    if (isSubcategoriesEnabled())
+    // remove subcategories
+    const QString test = name + u'/';
+    Algorithm::removeIf(m_categories, [this, &test, &result](const QString &category, const CategoryOptions &)
     {
-        // remove subcategories
-        const QString test = name + u'/';
-        Algorithm::removeIf(m_categories, [this, &test, &result](const QString &category, const CategoryOptions &)
+        if (category.startsWith(test))
         {
-            if (category.startsWith(test))
-            {
-                result = true;
-                emit categoryRemoved(category);
-                return true;
-            }
-            return false;
-        });
-    }
+            result = true;
+            emit categoryRemoved(category);
+            return true;
+        }
+        return false;
+    });
 
     result = (m_categories.remove(name) > 0) || result;
 
@@ -1098,32 +1078,6 @@ bool SessionImpl::removeCategory(const QString &name)
     return result;
 }
 
-bool SessionImpl::isSubcategoriesEnabled() const
-{
-    return m_isSubcategoriesEnabled;
-}
-
-void SessionImpl::setSubcategoriesEnabled(const bool value)
-{
-    if (isSubcategoriesEnabled() == value) return;
-
-    if (value)
-    {
-        // expand categories to include all parent categories
-        m_categories = expandCategories(m_categories);
-        // update stored categories
-        storeCategories();
-    }
-    else
-    {
-        // reload categories
-        loadCategories();
-    }
-
-    m_isSubcategoriesEnabled = value;
-    emit subcategoriesSupportChanged();
-}
-
 bool SessionImpl::useCategoryPathsInManualMode() const
 {
     return m_useCategoryPathsInManualMode;
@@ -5584,6 +5538,8 @@ void SessionImpl::loadCategories()
         const auto categoryOptions = CategoryOptions::fromJSON(it.value().toObject());
         m_categories[categoryName] = categoryOptions;
     }
+
+    m_categories = expandCategories(m_categories);
 }
 
 bool SessionImpl::hasPerTorrentRatioLimit() const
diff --git a/src/base/bittorrent/sessionimpl.h b/src/base/bittorrent/sessionimpl.h
index b40622a7f..a0daae281 100644
--- a/src/base/bittorrent/sessionimpl.h
+++ b/src/base/bittorrent/sessionimpl.h
@@ -156,8 +156,6 @@ namespace BitTorrent
         bool addCategory(const QString &name, const CategoryOptions &options = {}) override;
         bool editCategory(const QString &name, const CategoryOptions &options) override;
         bool removeCategory(const QString &name) override;
-        bool isSubcategoriesEnabled() const override;
-        void setSubcategoriesEnabled(bool value) override;
         bool useCategoryPathsInManualMode() const override;
         void setUseCategoryPathsInManualMode(bool value) override;
 
@@ -754,7 +752,6 @@ namespace BitTorrent
         CachedSettingValue<Path> m_savePath;
         CachedSettingValue<Path> m_downloadPath;
         CachedSettingValue<bool> m_isDownloadPathEnabled;
-        CachedSettingValue<bool> m_isSubcategoriesEnabled;
         CachedSettingValue<bool> m_useCategoryPathsInManualMode;
         CachedSettingValue<bool> m_isAutoTMMDisabledByDefault;
         CachedSettingValue<bool> m_isDisableAutoTMMWhenCategoryChanged;
diff --git a/src/base/bittorrent/torrentimpl.cpp b/src/base/bittorrent/torrentimpl.cpp
index 84450fe4f..b46107325 100644
--- a/src/base/bittorrent/torrentimpl.cpp
+++ b/src/base/bittorrent/torrentimpl.cpp
@@ -934,7 +934,7 @@ bool TorrentImpl::belongsToCategory(const QString &category) const
     if (m_category == category)
         return true;
 
-    return (m_session->isSubcategoriesEnabled() && m_category.startsWith(category + u'/'));
+    return m_category.startsWith(category + u'/');
 }
 
 TagSet TorrentImpl::tags() const
diff --git a/src/gui/optionsdialog.cpp b/src/gui/optionsdialog.cpp
index f1c3cca62..4f9d437bf 100644
--- a/src/gui/optionsdialog.cpp
+++ b/src/gui/optionsdialog.cpp
@@ -625,7 +625,6 @@ void OptionsDialog::loadDownloadsTabOptions()
     m_ui->comboCategoryChanged->setCurrentIndex(session->isDisableAutoTMMWhenCategorySavePathChanged());
     m_ui->comboCategoryDefaultPathChanged->setCurrentIndex(session->isDisableAutoTMMWhenDefaultSavePathChanged());
 
-    m_ui->checkUseSubcategories->setChecked(session->isSubcategoriesEnabled());
     m_ui->checkUseCategoryPaths->setChecked(session->useCategoryPathsInManualMode());
 
     m_ui->textSavePath->setDialogCaption(tr("Choose a save directory"));
@@ -730,7 +729,6 @@ void OptionsDialog::loadDownloadsTabOptions()
     connect(m_ui->comboCategoryChanged, qComboBoxCurrentIndexChanged, this, &ThisType::enableApplyButton);
     connect(m_ui->comboCategoryDefaultPathChanged, qComboBoxCurrentIndexChanged, this, &ThisType::enableApplyButton);
 
-    connect(m_ui->checkUseSubcategories, &QAbstractButton::toggled, this, &ThisType::enableApplyButton);
     connect(m_ui->checkUseCategoryPaths, &QAbstractButton::toggled, this, &ThisType::enableApplyButton);
 
     connect(m_ui->textSavePath, &FileSystemPathEdit::selectedPathChanged, this, &ThisType::enableApplyButton);
@@ -802,7 +800,6 @@ void OptionsDialog::saveDownloadsTabOptions() const
     session->setDisableAutoTMMWhenCategorySavePathChanged(m_ui->comboCategoryChanged->currentIndex() == 1);
     session->setDisableAutoTMMWhenDefaultSavePathChanged(m_ui->comboCategoryDefaultPathChanged->currentIndex() == 1);
 
-    session->setSubcategoriesEnabled(m_ui->checkUseSubcategories->isChecked());
     session->setUseCategoryPathsInManualMode(m_ui->checkUseCategoryPaths->isChecked());
 
     session->setSavePath(Path(m_ui->textSavePath->selectedPath()));
diff --git a/src/gui/optionsdialog.ui b/src/gui/optionsdialog.ui
index 21435d809..48dd071f8 100644
--- a/src/gui/optionsdialog.ui
+++ b/src/gui/optionsdialog.ui
@@ -1381,13 +1381,6 @@ Manual: Various torrent properties (e.g. save path) must be assigned manually</s
                  </item>
                 </layout>
                </item>
-               <item>
-                <widget class="QCheckBox" name="checkUseSubcategories">
-                 <property name="text">
-                  <string>Use Subcategories</string>
-                 </property>
-                </widget>
-               </item>
                <item>
                 <widget class="QCheckBox" name="checkUseCategoryPaths">
                  <property name="toolTip">
diff --git a/src/gui/transferlistfilters/categoryfiltermodel.cpp b/src/gui/transferlistfilters/categoryfiltermodel.cpp
index dfab6672e..ccbfa36e0 100644
--- a/src/gui/transferlistfilters/categoryfiltermodel.cpp
+++ b/src/gui/transferlistfilters/categoryfiltermodel.cpp
@@ -1,6 +1,6 @@
 /*
  * Bittorrent Client using Qt and libtorrent.
- * Copyright (C) 2016-2023  Vladimir Golovnev <glassez@yandex.ru>
+ * Copyright (C) 2016-2025  Vladimir Golovnev <glassez@yandex.ru>
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License
@@ -324,17 +324,17 @@ void CategoryFilterModel::categoryAdded(const QString &categoryName)
 {
     CategoryModelItem *parent = m_rootItem;
 
-    if (m_isSubcategoriesEnabled)
-    {
-        QStringList expanded = BitTorrent::Session::expandCategory(categoryName);
-        if (expanded.count() > 1)
-            parent = findItem(expanded[expanded.count() - 2]);
-    }
+    const QStringList expanded = BitTorrent::Session::expandCategory(categoryName);
+    if (expanded.count() > 1)
+        parent = findItem(expanded[expanded.count() - 2]);
+
+    Q_ASSERT(parent);
+    if (!parent) [[unlikely]]
+        return;
 
     const int row = parent->childCount();
     beginInsertRows(index(parent), row, row);
-    new CategoryModelItem(
-            parent, m_isSubcategoriesEnabled ? shortName(categoryName) : categoryName);
+    new CategoryModelItem(parent, shortName(categoryName));
     endInsertRows();
 }
 
@@ -426,7 +426,6 @@ void CategoryFilterModel::populate()
 
     const auto *session = BitTorrent::Session::instance();
     const auto torrents = session->torrents();
-    m_isSubcategoriesEnabled = session->isSubcategoriesEnabled();
 
     // All torrents
     m_rootItem->addChild(CategoryModelItem::UID_ALL
@@ -440,31 +439,19 @@ void CategoryFilterModel::populate()
             , new CategoryModelItem(nullptr, tr("Uncategorized"), torrentsCount));
 
     using BitTorrent::Torrent;
-    if (m_isSubcategoriesEnabled)
+    for (const QString &categoryName : asConst(session->categories()))
     {
-        for (const QString &categoryName : asConst(session->categories()))
+        CategoryModelItem *parent = m_rootItem;
+        for (const QString &subcat : asConst(BitTorrent::Session::expandCategory(categoryName)))
         {
-            CategoryModelItem *parent = m_rootItem;
-            for (const QString &subcat : asConst(BitTorrent::Session::expandCategory(categoryName)))
+            const QString subcatName = shortName(subcat);
+            if (!parent->hasChild(subcatName))
             {
-                const QString subcatName = shortName(subcat);
-                if (!parent->hasChild(subcatName))
-                {
-                    const int torrentsCount = std::ranges::count_if(torrents
-                            , [&subcat](const Torrent *torrent) { return torrent->category() == subcat; });
-                    new CategoryModelItem(parent, subcatName, torrentsCount);
-                }
-                parent = parent->child(subcatName);
+                const int torrentsCount = std::ranges::count_if(torrents
+                        , [&subcat](const Torrent *torrent) { return torrent->category() == subcat; });
+                new CategoryModelItem(parent, subcatName, torrentsCount);
             }
-        }
-    }
-    else
-    {
-        for (const QString &categoryName : asConst(session->categories()))
-        {
-            const int torrentsCount = std::ranges::count_if(torrents
-                    , [&categoryName](const Torrent *torrent) { return torrent->belongsToCategory(categoryName); });
-            new CategoryModelItem(m_rootItem, categoryName, torrentsCount);
+            parent = parent->child(subcatName);
         }
     }
 }
@@ -474,9 +461,6 @@ CategoryModelItem *CategoryFilterModel::findItem(const QString &fullName) const
     if (fullName.isEmpty())
         return m_rootItem->childAt(1); // "Uncategorized" item
 
-    if (!m_isSubcategoriesEnabled)
-        return m_rootItem->child(fullName);
-
     CategoryModelItem *item = m_rootItem;
     for (const QString &subcat : asConst(BitTorrent::Session::expandCategory(fullName)))
     {
diff --git a/src/gui/transferlistfilters/categoryfiltermodel.h b/src/gui/transferlistfilters/categoryfiltermodel.h
index fce28243d..3f5572d8b 100644
--- a/src/gui/transferlistfilters/categoryfiltermodel.h
+++ b/src/gui/transferlistfilters/categoryfiltermodel.h
@@ -1,6 +1,6 @@
 /*
  * Bittorrent Client using Qt and libtorrent.
- * Copyright (C) 2016-2023  Vladimir Golovnev <glassez@yandex.ru>
+ * Copyright (C) 2016-2025  Vladimir Golovnev <glassez@yandex.ru>
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License
@@ -72,6 +72,5 @@ private:
     QModelIndex index(CategoryModelItem *item) const;
     CategoryModelItem *findItem(const QString &fullName) const;
 
-    bool m_isSubcategoriesEnabled = false;
     CategoryModelItem *m_rootItem = nullptr;
 };
diff --git a/src/gui/transferlistfilters/categoryfilterwidget.cpp b/src/gui/transferlistfilters/categoryfilterwidget.cpp
index 49bab70c4..215e124f7 100644
--- a/src/gui/transferlistfilters/categoryfilterwidget.cpp
+++ b/src/gui/transferlistfilters/categoryfilterwidget.cpp
@@ -1,6 +1,6 @@
 /*
  * Bittorrent Client using Qt and libtorrent.
- * Copyright (C) 2016  Vladimir Golovnev <glassez@yandex.ru>
+ * Copyright (C) 2016-2025  Vladimir Golovnev <glassez@yandex.ru>
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License
@@ -72,9 +72,6 @@ CategoryFilterWidget::CategoryFilterWidget(QWidget *parent)
 #ifdef Q_OS_MACOS
     setAttribute(Qt::WA_MacShowFocusRect, false);
 #endif
-    m_defaultIndentation = indentation();
-    if (!BitTorrent::Session::instance()->isSubcategoriesEnabled())
-        setIndentation(0);
     setContextMenuPolicy(Qt::CustomContextMenu);
     sortByColumn(0, Qt::AscendingOrder);
     setCurrentIndex(model()->index(0, 0));
@@ -113,12 +110,8 @@ void CategoryFilterWidget::showMenu()
     const auto selectedRows = selectionModel()->selectedRows();
     if (!selectedRows.empty() && !CategoryFilterModel::isSpecialItem(selectedRows.first()))
     {
-        if (BitTorrent::Session::instance()->isSubcategoriesEnabled())
-        {
-            menu->addAction(UIThemeManager::instance()->getIcon(u"list-add"_s), tr("Add subcategory...")
-                , this, &CategoryFilterWidget::addSubcategory);
-        }
-
+        menu->addAction(UIThemeManager::instance()->getIcon(u"list-add"_s), tr("Add subcategory...")
+            , this, &CategoryFilterWidget::addSubcategory);
         menu->addAction(UIThemeManager::instance()->getIcon(u"edit-rename"_s, u"document-edit"_s), tr("Edit category...")
             , this, &CategoryFilterWidget::editCategory);
         menu->addAction(UIThemeManager::instance()->getIcon(u"edit-clear"_s, u"list-remove"_s), tr("Remove category")
@@ -140,11 +133,6 @@ void CategoryFilterWidget::showMenu()
 
 void CategoryFilterWidget::callUpdateGeometry()
 {
-    if (!BitTorrent::Session::instance()->isSubcategoriesEnabled())
-        setIndentation(0);
-    else
-        setIndentation(m_defaultIndentation);
-
     updateGeometry();
 }
 
diff --git a/src/gui/transferlistfilters/categoryfilterwidget.h b/src/gui/transferlistfilters/categoryfilterwidget.h
index d340d9337..93ef02182 100644
--- a/src/gui/transferlistfilters/categoryfilterwidget.h
+++ b/src/gui/transferlistfilters/categoryfilterwidget.h
@@ -1,6 +1,6 @@
 /*
  * Bittorrent Client using Qt and libtorrent.
- * Copyright (C) 2016  Vladimir Golovnev <glassez@yandex.ru>
+ * Copyright (C) 2016-2025  Vladimir Golovnev <glassez@yandex.ru>
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License
@@ -60,6 +60,4 @@ private:
     QSize sizeHint() const override;
     QSize minimumSizeHint() const override;
     void rowsInserted(const QModelIndex &parent, int start, int end) override;
-
-    int m_defaultIndentation;
 };
diff --git a/src/webui/api/appcontroller.cpp b/src/webui/api/appcontroller.cpp
index 11d6bee7e..a9f3dae6c 100644
--- a/src/webui/api/appcontroller.cpp
+++ b/src/webui/api/appcontroller.cpp
@@ -174,7 +174,6 @@ void AppController::preferencesAction()
     data[u"torrent_changed_tmm_enabled"_s] = !session->isDisableAutoTMMWhenCategoryChanged();
     data[u"save_path_changed_tmm_enabled"_s] = !session->isDisableAutoTMMWhenDefaultSavePathChanged();
     data[u"category_changed_tmm_enabled"_s] = !session->isDisableAutoTMMWhenCategorySavePathChanged();
-    data[u"use_subcategories"] = session->isSubcategoriesEnabled();
     data[u"save_path"_s] = session->savePath().toString();
     data[u"temp_path_enabled"_s] = session->isDownloadPathEnabled();
     data[u"temp_path"_s] = session->downloadPath().toString();
@@ -593,8 +592,6 @@ void AppController::setPreferencesAction()
         session->setDisableAutoTMMWhenDefaultSavePathChanged(!it.value().toBool());
     if (hasKey(u"category_changed_tmm_enabled"_s))
         session->setDisableAutoTMMWhenCategorySavePathChanged(!it.value().toBool());
-    if (hasKey(u"use_subcategories"_s))
-        session->setSubcategoriesEnabled(it.value().toBool());
     if (hasKey(u"save_path"_s))
         session->setSavePath(Path(it.value().toString()));
     if (hasKey(u"temp_path_enabled"_s))
diff --git a/src/webui/api/synccontroller.cpp b/src/webui/api/synccontroller.cpp
index 244b21b2f..4edf5f5c8 100644
--- a/src/webui/api/synccontroller.cpp
+++ b/src/webui/api/synccontroller.cpp
@@ -56,7 +56,6 @@ namespace
     const QString KEY_SYNC_MAINDATA_QUEUEING = u"queueing"_s;
     const QString KEY_SYNC_MAINDATA_REFRESH_INTERVAL = u"refresh_interval"_s;
     const QString KEY_SYNC_MAINDATA_USE_ALT_SPEED_LIMITS = u"use_alt_speed_limits"_s;
-    const QString KEY_SYNC_MAINDATA_USE_SUBCATEGORIES = u"use_subcategories"_s;
 
     // Sync torrent peers keys
     const QString KEY_SYNC_TORRENT_PEERS_SHOW_FLAGS = u"show_flags"_s;
@@ -617,7 +616,6 @@ void SyncController::makeMaindataSnapshot()
     m_maindataSnapshot.serverState[KEY_SYNC_MAINDATA_QUEUEING] = session->isQueueingSystemEnabled();
     m_maindataSnapshot.serverState[KEY_SYNC_MAINDATA_USE_ALT_SPEED_LIMITS] = session->isAltGlobalSpeedLimitEnabled();
     m_maindataSnapshot.serverState[KEY_SYNC_MAINDATA_REFRESH_INTERVAL] = session->refreshInterval();
-    m_maindataSnapshot.serverState[KEY_SYNC_MAINDATA_USE_SUBCATEGORIES] = session->isSubcategoriesEnabled();
 }
 
 QJsonObject SyncController::generateMaindataSyncData(const int id, const bool fullUpdate)
@@ -771,7 +769,6 @@ QJsonObject SyncController::generateMaindataSyncData(const int id, const bool fu
     serverState[KEY_SYNC_MAINDATA_QUEUEING] = session->isQueueingSystemEnabled();
     serverState[KEY_SYNC_MAINDATA_USE_ALT_SPEED_LIMITS] = session->isAltGlobalSpeedLimitEnabled();
     serverState[KEY_SYNC_MAINDATA_REFRESH_INTERVAL] = session->refreshInterval();
-    serverState[KEY_SYNC_MAINDATA_USE_SUBCATEGORIES] = session->isSubcategoriesEnabled();
     if (const QVariantMap syncData = processMap(m_maindataSnapshot.serverState, serverState); !syncData.isEmpty())
     {
         m_maindataSyncBuf.serverState = syncData;
diff --git a/src/webui/webapplication.h b/src/webui/webapplication.h
index ebac6207b..a752a3225 100644
--- a/src/webui/webapplication.h
+++ b/src/webui/webapplication.h
@@ -57,7 +57,7 @@
 
 using namespace std::chrono_literals;
 
-inline const Utils::Version<3, 2> API_VERSION {2, 14, 1};
+inline const Utils::Version<3, 2> API_VERSION {2, 15, 0};
 
 class APIController;
 class AuthController;
diff --git a/src/webui/www/private/scripts/client.js b/src/webui/www/private/scripts/client.js
index 3aecd3409..1afa3a852 100644
--- a/src/webui/www/private/scripts/client.js
+++ b/src/webui/www/private/scripts/client.js
@@ -222,7 +222,6 @@ let alternativeSpeedLimits = false;
 let queueing_enabled = true;
 let serverSyncMainDataInterval = 1500;
 let customSyncMainDataInterval = null;
-let useSubcategories = true;
 const useAutoHideZeroStatusFilters = localPreferences.get("hide_zero_status_filters", "false") === "true";
 const displayFullURLTrackerColumn = localPreferences.get("full_url_tracker_column", "false") === "true";
 
@@ -634,7 +633,7 @@ window.addEventListener("DOMContentLoaded", (event) => {
                 categoryName: category,
                 categoryCount: categoryData.torrents.size,
                 nameSegments: category.split("/"),
-                ...(useSubcategories && {
+                ...({
                     children: [],
                     isRoot: true,
                     forceExpand: localPreferences.get(`category_${category}_collapsed`) === null
@@ -659,32 +658,25 @@ window.addEventListener("DOMContentLoaded", (event) => {
         categoriesFragment.appendChild(createLink(CATEGORIES_ALL, "QBT_TR(All)QBT_TR[CONTEXT=CategoryFilterModel]", torrentsTable.getRowSize()));
         categoriesFragment.appendChild(createLink(CATEGORIES_UNCATEGORIZED, "QBT_TR(Uncategorized)QBT_TR[CONTEXT=CategoryFilterModel]", uncategorized));
 
-        if (useSubcategories) {
-            categoryList.classList.add("subcategories");
-            for (let i = 0; i < sortedCategories.length; ++i) {
-                const category = sortedCategories[i];
-                for (let j = (i + 1);
-                    ((j < sortedCategories.length) && sortedCategories[j].categoryName.startsWith(`${category.categoryName}/`)); ++j) {
-                    const subcategory = sortedCategories[j];
-                    category.categoryCount += subcategory.categoryCount;
-                    category.forceExpand ||= subcategory.forceExpand;
+        categoryList.classList.add("subcategories");
+        for (let i = 0; i < sortedCategories.length; ++i) {
+            const category = sortedCategories[i];
+            for (let j = (i + 1);
+                ((j < sortedCategories.length) && sortedCategories[j].categoryName.startsWith(`${category.categoryName}/`)); ++j) {
+                const subcategory = sortedCategories[j];
+                category.categoryCount += subcategory.categoryCount;
+                category.forceExpand ||= subcategory.forceExpand;
 
-                    const isDirectSubcategory = (subcategory.nameSegments.length - category.nameSegments.length) === 1;
-                    if (isDirectSubcategory) {
-                        subcategory.isRoot = false;
-                        category.children.push(subcategory);
-                    }
+                const isDirectSubcategory = (subcategory.nameSegments.length - category.nameSegments.length) === 1;
+                if (isDirectSubcategory) {
+                    subcategory.isRoot = false;
+                    category.children.push(subcategory);
                 }
             }
-            for (const category of sortedCategories) {
-                if (category.isRoot)
-                    createCategoryTree(category);
-            }
         }
-        else {
-            categoryList.classList.remove("subcategories");
-            for (const { categoryName, categoryCount } of sortedCategories)
-                categoriesFragment.appendChild(createLink(categoryName, categoryName, categoryCount));
+        for (const category of sortedCategories) {
+            if (category.isRoot)
+                createCategoryTree(category);
         }
 
         categoryList.appendChild(categoriesFragment);
@@ -1178,11 +1170,6 @@ window.addEventListener("DOMContentLoaded", (event) => {
             updateAltSpeedIcon(alternativeSpeedLimits);
         }
 
-        if (useSubcategories !== serverState.use_subcategories) {
-            useSubcategories = serverState.use_subcategories;
-            updateCategoryList();
-        }
-
         serverSyncMainDataInterval = Math.max(serverState.refresh_interval, 500);
     };
 
diff --git a/src/webui/www/private/scripts/contextmenu.js b/src/webui/www/private/scripts/contextmenu.js
index ce6c3756e..fcf44c936 100644
--- a/src/webui/www/private/scripts/contextmenu.js
+++ b/src/webui/www/private/scripts/contextmenu.js
@@ -585,10 +585,7 @@ window.qBittorrent.ContextMenu ??= (() => {
             if ((id !== CATEGORIES_ALL) && (id !== CATEGORIES_UNCATEGORIZED)) {
                 this.showItem("editCategory");
                 this.showItem("deleteCategory");
-                if (useSubcategories)
-                    this.showItem("createSubcategory");
-                else
-                    this.hideItem("createSubcategory");
+                this.showItem("createSubcategory");
             }
             else {
                 this.hideItem("editCategory");
diff --git a/src/webui/www/private/scripts/dynamicTable.js b/src/webui/www/private/scripts/dynamicTable.js
index 3465d7f03..d32c1ac9d 100644
--- a/src/webui/www/private/scripts/dynamicTable.js
+++ b/src/webui/www/private/scripts/dynamicTable.js
@@ -1621,21 +1621,16 @@ window.qBittorrent.DynamicTable ??= (() => {
                         return false;
                     break; // do nothing
 
-                default:
-                    if (!useSubcategories) {
-                        if (category !== row["full_data"].category)
+                default: {
+                    const selectedCategory = window.qBittorrent.Client.categoryMap.get(category);
+                    if (selectedCategory !== undefined) {
+                        const selectedCategoryName = `${category}/`;
+                        const torrentCategoryName = `${row["full_data"].category}/`;
+                        if (!torrentCategoryName.startsWith(selectedCategoryName))
                             return false;
                     }
-                    else {
-                        const selectedCategory = window.qBittorrent.Client.categoryMap.get(category);
-                        if (selectedCategory !== undefined) {
-                            const selectedCategoryName = `${category}/`;
-                            const torrentCategoryName = `${row["full_data"].category}/`;
-                            if (!torrentCategoryName.startsWith(selectedCategoryName))
-                                return false;
-                        }
-                    }
                     break;
+                }
             }
 
             switch (tag) {
diff --git a/src/webui/www/private/views/preferences.html b/src/webui/www/private/views/preferences.html
index 76257e9bb..f5cbfe3a8 100644
--- a/src/webui/www/private/views/preferences.html
+++ b/src/webui/www/private/views/preferences.html
@@ -229,10 +229,6 @@
                 </tr>
             </tbody>
         </table>
-        <div class="formRow">
-            <input type="checkbox" id="use_subcategories_checkbox">
-            <label for="use_subcategories_checkbox">QBT_TR(Use Subcategories)QBT_TR[CONTEXT=OptionsDialog]</label>
-        </div>
         <div class="formRow">
             <input type="checkbox" id="categoryPathsManualModeCheckbox" title="QBT_TR(Resolve relative Save Path against appropriate Category path instead of Default one)QBT_TR[CONTEXT=OptionsDialog]">
             <label for="categoryPathsManualModeCheckbox">QBT_TR(Use Category paths in Manual Mode)QBT_TR[CONTEXT=OptionsDialog]</label>
@@ -2332,7 +2328,6 @@ Use ';' to split multiple entries. Can use wildcard '*'.)QBT_TR[CONTEXT=OptionsD
                     document.getElementById("torrent_changed_tmm_combobox").value = pref.torrent_changed_tmm_enabled;
                     document.getElementById("save_path_changed_tmm_combobox").value = pref.save_path_changed_tmm_enabled;
                     document.getElementById("category_changed_tmm_combobox").value = pref.category_changed_tmm_enabled;
-                    document.getElementById("use_subcategories_checkbox").checked = pref.use_subcategories;
                     document.getElementById("categoryPathsManualModeCheckbox").checked = pref.use_category_paths_in_manual_mode;
                     document.getElementById("savepath_text").value = pref.save_path;
                     document.getElementById("temppath_checkbox").checked = pref.temp_path_enabled;
@@ -2754,7 +2749,6 @@ Use ';' to split multiple entries. Can use wildcard '*'.)QBT_TR[CONTEXT=OptionsD
             settings["torrent_changed_tmm_enabled"] = (document.getElementById("torrent_changed_tmm_combobox").value === "true");
             settings["save_path_changed_tmm_enabled"] = (document.getElementById("save_path_changed_tmm_combobox").value === "true");
             settings["category_changed_tmm_enabled"] = (document.getElementById("category_changed_tmm_combobox").value === "true");
-            settings["use_subcategories"] = document.getElementById("use_subcategories_checkbox").checked;
             settings["use_category_paths_in_manual_mode"] = document.getElementById("categoryPathsManualModeCheckbox").checked;
             settings["save_path"] = document.getElementById("savepath_text").value;
             settings["temp_path_enabled"] = document.getElementById("temppath_checkbox").checked;