diff --git a/server/controllers/LibraryController.js b/server/controllers/LibraryController.js
index 97cf6fbd5..9b9a63760 100644
--- a/server/controllers/LibraryController.js
+++ b/server/controllers/LibraryController.js
@@ -640,7 +640,7 @@ class LibraryController {
       }
       const { libraryItems, count } = await libraryItemsBookFilters.getCollapsedSeriesWindow(req.library.id, seriesId, req.user, include, payload, collapsedSeriesWindow)
       payload.total = count
-      payload.results = await libraryHelpers.toCollapsedSeriesPayload(libraryItems, seriesId)
+      payload.results = await libraryHelpers.toCollapsedSeriesPayload(libraryItems, seriesId, req.library.settings.hideSingleBookSeries)
     } else {
       const { libraryItems, count, nextCursor, paginationMode, countMode, isCountDeferred } = await Database.libraryItemModel.getByFilterAndSort(req.library, req.user, payload)
       payload.results = libraryItems
diff --git a/server/utils/libraryHelpers.js b/server/utils/libraryHelpers.js
index 602aba7da..1baee56e6 100644
--- a/server/utils/libraryHelpers.js
+++ b/server/utils/libraryHelpers.js
@@ -1,7 +1,101 @@
+const { createNewSortInstance } = require('../libs/fastSort')
+const { getTitlePrefixAtEnd, isNullOrNaN, getTitleIgnorePrefix } = require('../utils/index')
+
+const naturalSort = createNewSortInstance({
+  comparer: new Intl.Collator(undefined, { numeric: true, sensitivity: 'base' }).compare
+})
+
+function getSeriesFromBooks(libraryItems, filterSeries, hideSingleBookSeries) {
+  const seriesById = {}
+
+  libraryItems.forEach((libraryItem) => {
+    const allBookSeries = libraryItem.media.series || []
+    if (!allBookSeries.length) return
+
+    allBookSeries.forEach((bookSeries) => {
+      const itemJson = libraryItem.toOldJSONMinified()
+      itemJson.sequence = bookSeries.bookSeries.sequence
+      if (filterSeries) {
+        const filteredSeries = libraryItem.media.series.find((series) => series.id === filterSeries)
+        itemJson.filterSeriesSequence = filteredSeries?.bookSeries?.sequence
+      }
+
+      if (!seriesById[bookSeries.id]) {
+        seriesById[bookSeries.id] = {
+          id: bookSeries.id,
+          name: bookSeries.name,
+          nameIgnorePrefix: getTitlePrefixAtEnd(bookSeries.name),
+          nameIgnorePrefixSort: getTitleIgnorePrefix(bookSeries.name),
+          type: 'series',
+          books: [itemJson],
+          totalDuration: isNullOrNaN(itemJson.media.duration) ? 0 : Number(itemJson.media.duration)
+        }
+      } else {
+        seriesById[bookSeries.id].books.push(itemJson)
+        seriesById[bookSeries.id].totalDuration += isNullOrNaN(itemJson.media.duration) ? 0 : Number(itemJson.media.duration)
+      }
+    })
+  })
+
+  let seriesItems = Object.values(seriesById)
+  if (hideSingleBookSeries) {
+    seriesItems = seriesItems.filter((series) => series.books.length > 1)
+  }
+
+  return seriesItems.map((series) => {
+    series.books = naturalSort(series.books).asc((libraryItem) => libraryItem.sequence)
+    return series
+  })
+}
+
+function collapseBookSeries(libraryItems, filterSeries, hideSingleBookSeries) {
+  const seriesObjects = getSeriesFromBooks(libraryItems, filterSeries, hideSingleBookSeries).filter((series) => series.id !== filterSeries)
+  const filteredLibraryItems = []
+
+  libraryItems.forEach((libraryItem) => {
+    if (libraryItem.mediaType && libraryItem.mediaType !== 'book') return
+
+    seriesObjects
+      .filter((series) => series.books[0].id === libraryItem.id)
+      .forEach((series) => {
+        filteredLibraryItems.push(Object.assign(Object.create(Object.getPrototypeOf(libraryItem)), libraryItem, { collapsedSeries: series }))
+      })
+
+    if (!seriesObjects.some((series) => series.books.some((book) => book.id === libraryItem.id))) {
+      filteredLibraryItems.push(libraryItem)
+    }
+  })
+
+  return filteredLibraryItems
+}
+
+function getSeriesSequenceList(collapsedSeries) {
+  return naturalSort(collapsedSeries.books.filter((book) => book.filterSeriesSequence).map((book) => book.filterSeriesSequence))
+    .asc()
+    .reduce((ranges, currentSequence) => {
+      const lastRange = ranges.at(-1)
+      const isNumber = /^(\d+|\d+\.\d*|\d*\.\d+)$/.test(currentSequence)
+      const normalizedSequence = isNumber ? parseFloat(currentSequence) : currentSequence
+
+      if (lastRange && isNumber && lastRange.isNumber && lastRange.end + 1 === normalizedSequence) {
+        lastRange.end = normalizedSequence
+      } else {
+        ranges.push({ start: normalizedSequence, end: normalizedSequence, isNumber })
+      }
+
+      return ranges
+    }, [])
+    .map((range) => (range.start === range.end ? range.start : `${range.start}-${range.end}`))
+    .join(', ')
+}
+
 module.exports = {
-  async toCollapsedSeriesPayload(libraryItems, seriesId) {
+  async toCollapsedSeriesPayload(libraryItems, seriesId, hideSingleBookSeries = false) {
+    const collapsedItems = collapseBookSeries(libraryItems, seriesId, hideSingleBookSeries)
+    const shapedItems = !(collapsedItems.length === 1 && collapsedItems[0].collapsedSeries) ? collapsedItems : libraryItems
+
     return Promise.all(
-      libraryItems.map(async (libraryItem) => {
+      shapedItems.map(async (libraryItem) => {
         const filteredSeries = libraryItem.media.series.find((series) => series.id === seriesId)
         const json = libraryItem.toOldJSONMinified()
 
@@ -13,6 +107,21 @@ module.exports = {
           }
         }
 
+        if (libraryItem.collapsedSeries) {
+          json.collapsedSeries = {
+            id: libraryItem.collapsedSeries.id,
+            name: libraryItem.collapsedSeries.name,
+            nameIgnorePrefix: libraryItem.collapsedSeries.nameIgnorePrefix,
+            libraryItemIds: libraryItem.collapsedSeries.books.map((book) => book.id),
+            numBooks: libraryItem.collapsedSeries.books.length,
+            seriesSequenceList: getSeriesSequenceList(libraryItem.collapsedSeries)
+          }
+        }
+
+        if (libraryItem.rssFeed?.toOldJSONMinified) {
+          json.rssFeed = libraryItem.rssFeed.toOldJSONMinified()
+        }
+
         return json
       })
     )
diff --git a/server/utils/queries/libraryItemsBookFilters.js b/server/utils/queries/libraryItemsBookFilters.js
index e76ed3438..accd9f419 100644
--- a/server/utils/queries/libraryItemsBookFilters.js
+++ b/server/utils/queries/libraryItemsBookFilters.js
@@ -917,13 +917,14 @@ module.exports = {
     }
 
     const userPermissionBookWhere = this.getUserPermissionBookWhereQuery(user)
+    const collapsedSortBy = payload.sortBy || 'sequence'
     const direction = payload.sortDesc ? 'DESC' : 'ASC'
-    const sortOrder = payload.sortBy === 'sequence'
+    const sortOrder = collapsedSortBy === 'sequence'
       ? [
           [Sequelize.literal(`${dialectHelpers.getSafeSequenceCast(Database.getDialect(), '"bookSeries"."sequence"')} ${direction} NULLS LAST`)],
-          [Sequelize.literal('"libraryItem"."id"'), 'ASC']
+          ...this.getOrder('media.metadata.title', payload.sortDesc, false)
         ]
-      : this.getOrder(payload.sortBy, payload.sortDesc, false)
+      : this.getOrder(collapsedSortBy, payload.sortDesc, false)
 
     const findOptions = {
       where: userPermissionBookWhere.bookWhere,
@@ -949,6 +950,13 @@ module.exports = {
             attributes: ['id', 'name', 'nameIgnorePrefix']
           }
         },
+        {
+          model: Database.seriesModel,
+          attributes: ['id', 'name', 'nameIgnorePrefix'],
+          through: {
+            attributes: ['sequence']
+          }
+        },
         {
           model: Database.bookAuthorModel,
           attributes: ['authorId', 'createdAt'],
@@ -966,10 +974,28 @@ module.exports = {
     }
 
     const countOptions = {
-      ...findOptions,
-      distinct: true
+      where: userPermissionBookWhere.bookWhere,
+      replacements: userPermissionBookWhere.replacements,
+      include: [
+        {
+          model: Database.libraryItemModel,
+          required: true,
+          where: {
+            libraryId
+          },
+          include: libraryItemIncludes
+        },
+        {
+          model: Database.bookSeriesModel,
+          required: true,
+          where: {
+            seriesId
+          }
+        }
+      ],
+      distinct: true,
+      subQuery: false
     }
-    delete countOptions.order
 
     const { books, count } = await loadCollapsedSeriesWindow({
       findOptions,
@@ -985,13 +1011,7 @@ module.exports = {
 
         delete book.libraryItem
 
-        book.series =
-          book.bookSeries?.map((bs) => {
-            const series = bs.series
-            delete bs.series
-            series.bookSeries = bs
-            return series
-          }) || []
+        book.series = book.series || []
         delete book.bookSeries
 
         book.authors = book.bookAuthors?.map((ba) => ba.author) || []
diff --git a/test/server/controllers/LibraryController.largeLibraryBrowse.test.js b/test/server/controllers/LibraryController.largeLibraryBrowse.test.js
index a4e2e88aa..d04b78b44 100644
--- a/test/server/controllers/LibraryController.largeLibraryBrowse.test.js
+++ b/test/server/controllers/LibraryController.largeLibraryBrowse.test.js
@@ -9,6 +9,7 @@ const { decodeBrowseCursor } = require('../../../server/utils/queries/libraryBro
 const { getLibraryBrowseStrategy } = require('../../../server/utils/queries/libraryBrowseStrategy')
 const libraryItemsBookFilters = require('../../../server/utils/queries/libraryItemsBookFilters')
 const libraryItemsPodcastFilters = require('../../../server/utils/queries/libraryItemsPodcastFilters')
+const libraryHelpers = require('../../../server/utils/libraryHelpers')
 
 describe('LibraryController large-library browse contract', () => {
   const buildBookPredicateSql = (where, replacements = {}) => {
@@ -321,6 +322,68 @@ describe('LibraryController large-library browse contract', () => {
     expect(findAllStub.firstCall.args[0].offset).to.equal(20)
   })
 
+  it('restores collapsed-series payload fields and preserves rssfeed serialization', async () => {
+    const payload = await libraryHelpers.toCollapsedSeriesPayload([
+      {
+        media: {
+          series: [{ id: 'series_1', name: 'Main Series', bookSeries: { sequence: '5' } }]
+        },
+        collapsedSeries: {
+          id: 'subseries_1',
+          name: 'Subseries',
+          nameIgnorePrefix: 'Subseries',
+          books: [
+            { id: 'li_2', filterSeriesSequence: '2' },
+            { id: 'li_3', filterSeriesSequence: '3' },
+            { id: 'li_5', filterSeriesSequence: '5' }
+          ]
+        },
+        rssFeed: {
+          toOldJSONMinified: () => ({ id: 'feed_1' })
+        },
+        toOldJSONMinified() {
+          return {
+            id: 'li_1',
+            media: { metadata: {} }
+          }
+        }
+      }
+    ], 'series_1')
+
+    expect(payload[0].media.metadata.series).to.deep.equal({
+      id: 'series_1',
+      name: 'Main Series',
+      sequence: '5'
+    })
+    expect(payload[0].collapsedSeries).to.deep.equal({
+      id: 'subseries_1',
+      name: 'Subseries',
+      nameIgnorePrefix: 'Subseries',
+      libraryItemIds: ['li_2', 'li_3', 'li_5'],
+      numBooks: 3,
+      seriesSequenceList: '2-3, 5'
+    })
+    expect(payload[0].rssFeed).to.deep.equal({ id: 'feed_1' })
+  })
+
+  it('uses a deterministic default collapsed-series order when sort is omitted', async () => {
+    const findAllStub = sinon.stub(Database.bookModel, 'findAll').resolves([])
+    sinon.stub(Database.bookModel, 'count').resolves(0)
+
+    await libraryItemsBookFilters.getCollapsedSeriesWindow(
+      'lib_1',
+      'series_1',
+      { id: 'user_1', canAccessExplicitContent: true, accessAllTags: true },
+      [],
+      { sortBy: null, sortDesc: false },
+      { limit: 20, offset: 0 }
+    )
+
+    expect(findAllStub.firstCall.args[0].order).to.have.length.greaterThan(0)
+    expect(findAllStub.firstCall.args[0].order[0][0].val || findAllStub.firstCall.args[0].order[0][0]).to.include('bookSeries')
+    expect(findAllStub.firstCall.args[0].order[0][0].val || findAllStub.firstCall.args[0].order[0][0]).to.include('sequence')
+  })
+
   it('adds a deterministic libraryItem.id tie-breaker for keyset title browse with duplicate titles', async () => {
     global.ServerSettings = { sortingIgnorePrefix: true }