diff --git a/services/clsi/app.js b/services/clsi/app.js
index f24ce5f924..6266c86b16 100644
--- a/services/clsi/app.js
+++ b/services/clsi/app.js
@@ -10,6 +10,7 @@ const Metrics = require('@overleaf/metrics')
 Metrics.initialize('clsi')
 
 const CompileController = require('./app/js/CompileController')
+const ContentController = require('./app/js/ContentController')
 const Settings = require('settings-sharelatex')
 const logger = require('logger-sharelatex')
 logger.initialize('clsi')
@@ -170,6 +171,15 @@ app.get(
   }
 )
 
+app.get(
+  '/project/:projectId/content/:contentId/:hash',
+  ContentController.getPdfRange
+)
+app.get(
+  '/project/:projectId/user/:userId/content/:contentId/:hash',
+  ContentController.getPdfRange
+)
+
 app.get('/project/:project_id/build/:build_id/output/*', function (
   req,
   res,
diff --git a/services/clsi/app/js/CompileController.js b/services/clsi/app/js/CompileController.js
index ddf83d7c8e..2813bca984 100644
--- a/services/clsi/app/js/CompileController.js
+++ b/services/clsi/app/js/CompileController.js
@@ -49,7 +49,9 @@ module.exports = CompileController = {
           }
           return CompileManager.doCompileWithLock(request, function (
             error,
-            outputFiles
+            outputFiles,
+            stats,
+            timings
           ) {
             let code, status
             if (outputFiles == null) {
@@ -118,18 +120,30 @@ module.exports = CompileController = {
               compile: {
                 status,
                 error: (error != null ? error.message : undefined) || error,
-                outputFiles: outputFiles.map((file) => ({
-                  url:
-                    `${Settings.apis.clsi.url}/project/${request.project_id}` +
-                    (request.user_id != null
-                      ? `/user/${request.user_id}`
-                      : '') +
-                    (file.build != null ? `/build/${file.build}` : '') +
-                    `/output/${file.path}`,
-                  path: file.path,
-                  type: file.type,
-                  build: file.build
-                }))
+                stats,
+                timings,
+                outputFiles: outputFiles.map((file) => {
+                  const record = {
+                    url:
+                      `${Settings.apis.clsi.url}/project/${request.project_id}` +
+                      (request.user_id != null
+                        ? `/user/${request.user_id}`
+                        : '') +
+                      (file.build != null ? `/build/${file.build}` : '') +
+                      `/output/${file.path}`,
+                    path: file.path,
+                    type: file.type,
+                    build: file.build,
+                    contentId: file.contentId
+                  }
+                  if (file.ranges != null) {
+                    record.ranges = file.ranges
+                  }
+                  if (file.size != null) {
+                    record.size = file.size
+                  }
+                  return record
+                })
               }
             })
           })
diff --git a/services/clsi/app/js/CompileManager.js b/services/clsi/app/js/CompileManager.js
index c801062595..c771082bfd 100644
--- a/services/clsi/app/js/CompileManager.js
+++ b/services/clsi/app/js/CompileManager.js
@@ -34,6 +34,7 @@ const os = require('os')
 const async = require('async')
 const Errors = require('./Errors')
 const CommandRunner = require('./CommandRunner')
+const { emitPdfStats } = require('./ContentCacheMetrics')
 
 const getCompileName = function (project_id, user_id) {
   if (user_id != null) {
@@ -77,6 +78,7 @@ module.exports = CompileManager = {
     const compileDir = getCompileDir(request.project_id, request.user_id)
     const outputDir = getOutputDir(request.project_id, request.user_id)
 
+    const timerE2E = new Metrics.Timer('compile-e2e')
     let timer = new Metrics.Timer('write-to-disk')
     logger.log(
       { project_id: request.project_id, user_id: request.user_id },
@@ -249,11 +251,13 @@ module.exports = CompileManager = {
                 return callback(error)
               }
               Metrics.inc('compiles-succeeded')
+              stats = stats || {}
               const object = stats || {}
               for (metric_key in object) {
                 metric_value = object[metric_key]
                 Metrics.count(metric_key, metric_value)
               }
+              timings = timings || {}
               const object1 = timings || {}
               for (metric_key in object1) {
                 metric_value = object1[metric_key]
@@ -297,10 +301,32 @@ module.exports = CompileManager = {
                     return callback(error)
                   }
                   return OutputCacheManager.saveOutputFiles(
+                    { request, stats, timings },
                     outputFiles,
                     compileDir,
                     outputDir,
-                    (error, newOutputFiles) => callback(null, newOutputFiles)
+                    (err, newOutputFiles) => {
+                      if (err) {
+                        const {
+                          project_id: projectId,
+                          user_id: userId
+                        } = request
+                        logger.err(
+                          { projectId, userId, err },
+                          'failed to save output files'
+                        )
+                      }
+
+                      // Emit compile time.
+                      timings.compile = ts
+                      timings.compileE2E = timerE2E.done()
+
+                      if (stats['pdf-size']) {
+                        emitPdfStats(stats, timings)
+                      }
+
+                      callback(null, newOutputFiles, stats, timings)
+                    }
                   )
                 }
               )
diff --git a/services/clsi/app/js/ContentCacheManager.js b/services/clsi/app/js/ContentCacheManager.js
new file mode 100644
index 0000000000..94ed9ebc00
--- /dev/null
+++ b/services/clsi/app/js/ContentCacheManager.js
@@ -0,0 +1,118 @@
+/**
+ * ContentCacheManager - maintains a cache of stream hashes from a PDF file
+ */
+
+const { callbackify } = require('util')
+const fs = require('fs')
+const crypto = require('crypto')
+const Path = require('path')
+const Settings = require('settings-sharelatex')
+
+const MIN_CHUNK_SIZE = Settings.pdfCachingMinChunkSize
+
+/**
+ *
+ * @param {String} contentDir path to directory where content hash files are cached
+ * @param {String} filePath the pdf file to scan for streams
+ */
+async function update(contentDir, filePath) {
+  const stream = fs.createReadStream(filePath)
+  const extractor = new PdfStreamsExtractor()
+  const ranges = []
+  const newRanges = []
+  for await (const chunk of stream) {
+    const pdfStreams = extractor.consume(chunk)
+    for (const pdfStream of pdfStreams) {
+      if (pdfStream.end - pdfStream.start < MIN_CHUNK_SIZE) continue
+      const hash = pdfStreamHash(pdfStream.buffers)
+      const range = { start: pdfStream.start, end: pdfStream.end, hash }
+      ranges.push(range)
+      if (await writePdfStream(contentDir, hash, pdfStream.buffers)) {
+        newRanges.push(range)
+      }
+    }
+  }
+  return [ranges, newRanges]
+}
+
+class PdfStreamsExtractor {
+  constructor() {
+    this.fileIndex = 0
+    this.inStream = false
+    this.streamStartIndex = 0
+    this.buffers = []
+  }
+
+  consume(chunk) {
+    let chunkIndex = 0
+    const pdfStreams = []
+    while (true) {
+      if (!this.inStream) {
+        // Not in a stream, look for stream start
+        const index = chunk.indexOf('stream', chunkIndex)
+        if (index === -1) {
+          // Couldn't find stream start
+          break
+        }
+        // Found stream start, start a stream
+        this.inStream = true
+        this.streamStartIndex = this.fileIndex + index
+        chunkIndex = index
+      } else {
+        // In a stream, look for stream end
+        const index = chunk.indexOf('endstream', chunkIndex)
+        if (index === -1) {
+          this.buffers.push(chunk.slice(chunkIndex))
+          break
+        }
+        // add "endstream" part
+        const endIndex = index + 9
+        this.buffers.push(chunk.slice(chunkIndex, endIndex))
+        pdfStreams.push({
+          start: this.streamStartIndex,
+          end: this.fileIndex + endIndex,
+          buffers: this.buffers
+        })
+        this.inStream = false
+        this.buffers = []
+        chunkIndex = endIndex
+      }
+    }
+    this.fileIndex += chunk.length
+    return pdfStreams
+  }
+}
+
+function pdfStreamHash(buffers) {
+  const hash = crypto.createHash('sha256')
+  for (const buffer of buffers) {
+    hash.update(buffer)
+  }
+  return hash.digest('hex')
+}
+
+async function writePdfStream(dir, hash, buffers) {
+  const filename = Path.join(dir, hash)
+  try {
+    await fs.promises.stat(filename)
+    // The file exists. Do not rewrite the content.
+    // It would change the modified-time of the file and hence invalidate the
+    //  ETags used for client side caching via browser internals.
+    return false
+  } catch (e) {}
+  const file = await fs.promises.open(filename, 'w')
+  if (Settings.enablePdfCachingDark) {
+    // Write an empty file in dark mode.
+    buffers = []
+  }
+  try {
+    for (const buffer of buffers) {
+      await file.write(buffer)
+    }
+  } finally {
+    await file.close()
+  }
+  return true
+}
+
+module.exports = { update: callbackify(update) }
diff --git a/services/clsi/app/js/ContentCacheMetrics.js b/services/clsi/app/js/ContentCacheMetrics.js
new file mode 100644
index 0000000000..04b475f827
--- /dev/null
+++ b/services/clsi/app/js/ContentCacheMetrics.js
@@ -0,0 +1,80 @@
+const Metrics = require('./Metrics')
+
+const ONE_MB = 1024 * 1024
+
+function emitPdfStats(stats, timings) {
+  if (timings['compute-pdf-caching']) {
+    emitPdfCachingStats(stats, timings)
+  } else {
+    // How much bandwidth will the pdf incur when downloaded in full?
+    Metrics.summary('pdf-bandwidth', stats['pdf-size'])
+  }
+}
+
+function emitPdfCachingStats(stats, timings) {
+  if (!stats['pdf-size']) return // double check
+
+  // How large is the overhead of hashing up-front?
+  const fraction =
+    timings.compileE2E - timings['compute-pdf-caching'] !== 0
+      ? timings.compileE2E /
+        (timings.compileE2E - timings['compute-pdf-caching'])
+      : 1
+  Metrics.summary('overhead-compute-pdf-ranges', fraction * 100 - 100)
+
+  // How does the hashing scale to pdf size in MB?
+  Metrics.timing(
+    'compute-pdf-caching-relative-to-pdf-size',
+    timings['compute-pdf-caching'] / (stats['pdf-size'] / ONE_MB)
+  )
+  if (stats['pdf-caching-total-ranges-size']) {
+    // How does the hashing scale to total ranges size in MB?
+    Metrics.timing(
+      'compute-pdf-caching-relative-to-total-ranges-size',
+      timings['compute-pdf-caching'] /
+        (stats['pdf-caching-total-ranges-size'] / ONE_MB)
+    )
+    // How fast is the hashing per range on average?
+    Metrics.timing(
+      'compute-pdf-caching-relative-to-ranges-count',
+      timings['compute-pdf-caching'] / stats['pdf-caching-n-ranges']
+    )
+
+    // How many ranges are new?
+    Metrics.summary(
+      'new-pdf-ranges-relative-to-total-ranges',
+      (stats['pdf-caching-n-new-ranges'] / stats['pdf-caching-n-ranges']) * 100
+    )
+  }
+
+  // How much content is cacheable?
+  Metrics.summary(
+    'cacheable-ranges-to-pdf-size',
+    (stats['pdf-caching-total-ranges-size'] / stats['pdf-size']) * 100
+  )
+
+  const sizeWhenDownloadedInFull =
+    // All of the pdf
+    stats['pdf-size'] -
+    // These ranges are potentially cached.
+    stats['pdf-caching-total-ranges-size'] +
+    // These ranges are not cached.
+    stats['pdf-caching-new-ranges-size']
+
+  // How much bandwidth can we save when downloading the pdf in full?
+  Metrics.summary(
+    'pdf-bandwidth-savings',
+    100 - (sizeWhenDownloadedInFull / stats['pdf-size']) * 100
+  )
+
+  // How much bandwidth will the pdf incur when downloaded in full?
+  Metrics.summary('pdf-bandwidth', sizeWhenDownloadedInFull)
+
+  // How much space do the ranges use?
+  // This will accumulate the ranges size over time, skipping already written ranges.
+  Metrics.summary('pdf-ranges-disk-size', stats['pdf-caching-new-ranges-size'])
+}
+
+module.exports = {
+  emitPdfStats
+}
diff --git a/services/clsi/app/js/ContentController.js b/services/clsi/app/js/ContentController.js
new file mode 100644
index 0000000000..76478defe8
--- /dev/null
+++ b/services/clsi/app/js/ContentController.js
@@ -0,0 +1,24 @@
+const Path = require('path')
+const send = require('send')
+const Settings = require('settings-sharelatex')
+const OutputCacheManager = require('./OutputCacheManager')
+
+const ONE_DAY_S = 24 * 60 * 60
+const ONE_DAY_MS = ONE_DAY_S * 1000
+
+function getPdfRange(req, res, next) {
+  const { projectId, userId, contentId, hash } = req.params
+  const perUserDir = userId ? `${projectId}-${userId}` : projectId
+  const path = Path.join(
+    Settings.path.outputDir,
+    perUserDir,
+    OutputCacheManager.CONTENT_SUBDIR,
+    contentId,
+    hash
+  )
+  res.setHeader('cache-control', `public, max-age=${ONE_DAY_S}`)
+  res.setHeader('expires', new Date(Date.now() + ONE_DAY_MS).toUTCString())
+  send(req, path).pipe(res)
+}
+
+module.exports = { getPdfRange }
diff --git a/services/clsi/app/js/OutputCacheManager.js b/services/clsi/app/js/OutputCacheManager.js
index 8aefb9b77a..cd1bd883a2 100644
--- a/services/clsi/app/js/OutputCacheManager.js
+++ b/services/clsi/app/js/OutputCacheManager.js
@@ -22,10 +22,13 @@ const logger = require('logger-sharelatex')
 const _ = require('lodash')
 const Settings = require('settings-sharelatex')
 const crypto = require('crypto')
+const Metrics = require('./Metrics')
 
 const OutputFileOptimiser = require('./OutputFileOptimiser')
+const ContentCacheManager = require('./ContentCacheManager')
 
 module.exports = OutputCacheManager = {
+  CONTENT_SUBDIR: 'content',
   CACHE_SUBDIR: 'generated-files',
   ARCHIVE_SUBDIR: 'archived-logs',
   // build id is HEXDATE-HEXRANDOM from Date.now()and RandomBytes
@@ -59,7 +62,13 @@ module.exports = OutputCacheManager = {
     })
   },
 
-  saveOutputFiles(outputFiles, compileDir, outputDir, callback) {
+  saveOutputFiles(
+    { request, stats, timings },
+    outputFiles,
+    compileDir,
+    outputDir,
+    callback
+  ) {
     if (callback == null) {
       callback = function (error) {}
     }
@@ -72,7 +81,31 @@ module.exports = OutputCacheManager = {
         compileDir,
         outputDir,
         buildId,
-        callback
+        function (err, result) {
+          if (err != null) {
+            return callback(err)
+          }
+          OutputCacheManager.collectOutputPdfSize(
+            result,
+            outputDir,
+            stats,
+            (err, result) => {
+              if (err) return callback(err, result)
+
+              if (!Settings.enablePdfCaching || !request.enablePdfCaching) {
+                return callback(null, result)
+              }
+
+              OutputCacheManager.saveStreamsInContentDir(
+                { stats, timings },
+                result,
+                compileDir,
+                outputDir,
+                callback
+              )
+            }
+          )
+        }
       )
     })
   },
@@ -206,6 +239,107 @@ module.exports = OutputCacheManager = {
     })
   },
 
+  collectOutputPdfSize(outputFiles, outputDir, stats, callback) {
+    const outputFile = outputFiles.find((x) => x.path === 'output.pdf')
+    if (!outputFile) return callback(null, outputFiles)
+    const outputFilePath = Path.join(
+      outputDir,
+      OutputCacheManager.path(outputFile.build, outputFile.path)
+    )
+    fs.stat(outputFilePath, (err, stat) => {
+      if (err) return callback(err, outputFiles)
+
+      outputFile.size = stat.size
+      stats['pdf-size'] = outputFile.size
+      callback(null, outputFiles)
+    })
+  },
+
+  saveStreamsInContentDir(
+    { stats, timings },
+    outputFiles,
+    compileDir,
+    outputDir,
+    callback
+  ) {
+    const cacheRoot = Path.join(outputDir, OutputCacheManager.CONTENT_SUBDIR)
+    // check if content dir exists
+    OutputCacheManager.ensureContentDir(cacheRoot, function (err, contentDir) {
+      if (err) return callback(err, outputFiles)
+
+      const outputFile = outputFiles.find((x) => x.path === 'output.pdf')
+      if (outputFile) {
+        // possibly we should copy the file from the build dir here
+        const outputFilePath = Path.join(
+          outputDir,
+          OutputCacheManager.path(outputFile.build, outputFile.path)
+        )
+        const timer = new Metrics.Timer('compute-pdf-ranges')
+        ContentCacheManager.update(contentDir, outputFilePath, function (
+          err,
+          ranges
+        ) {
+          if (err) return callback(err, outputFiles)
+          const [contentRanges, newContentRanges] = ranges
+
+          if (Settings.enablePdfCachingDark) {
+            // In dark mode we are doing the computation only and do not emit
+            //  any ranges to the frontend.
+          } else {
+            outputFile.contentId = Path.basename(contentDir)
+            outputFile.ranges = contentRanges
+          }
+
+          timings['compute-pdf-caching'] = timer.done()
+          stats['pdf-caching-n-ranges'] = contentRanges.length
+          stats['pdf-caching-total-ranges-size'] = contentRanges.reduce(
+            (sum, next) => sum + (next.end - next.start),
+            0
+          )
+          stats['pdf-caching-n-new-ranges'] = newContentRanges.length
+          stats['pdf-caching-new-ranges-size'] = newContentRanges.reduce(
+            (sum, next) => sum + (next.end - next.start),
+            0
+          )
+          callback(null, outputFiles)
+        })
+      } else {
+        callback(null, outputFiles)
+      }
+    })
+  },
+
+  ensureContentDir(contentRoot, callback) {
+    fse.ensureDir(contentRoot, function (err) {
+      if (err != null) {
+        return callback(err)
+      }
+      fs.readdir(contentRoot, function (err, results) {
+        const dirs = results.sort()
+        const contentId = dirs.find((dir) =>
+          OutputCacheManager.BUILD_REGEX.test(dir)
+        )
+        if (contentId) {
+          callback(null, Path.join(contentRoot, contentId))
+        } else {
+          // make a content directory
+          OutputCacheManager.generateBuildId(function (err, contentId) {
+            if (err) {
+              return callback(err)
+            }
+            const contentDir = Path.join(contentRoot, contentId)
+            fse.ensureDir(contentDir, function (err) {
+              if (err) {
+                return callback(err)
+              }
+              return callback(null, contentDir)
+            })
+          })
+        }
+      })
+    })
+  },
+
   archiveLogs(outputFiles, compileDir, outputDir, buildId, callback) {
     if (callback == null) {
       callback = function (error) {}
diff --git a/services/clsi/app/js/RequestParser.js b/services/clsi/app/js/RequestParser.js
index 4377204428..66c917aeed 100644
--- a/services/clsi/app/js/RequestParser.js
+++ b/services/clsi/app/js/RequestParser.js
@@ -50,6 +50,14 @@ module.exports = RequestParser = {
           type: 'string'
         }
       )
+      response.enablePdfCaching = this._parseAttribute(
+        'enablePdfCaching',
+        compile.options.enablePdfCaching,
+        {
+          default: false,
+          type: 'boolean'
+        }
+      )
       response.timeout = this._parseAttribute(
         'timeout',
         compile.options.timeout,
diff --git a/services/clsi/config/settings.defaults.js b/services/clsi/config/settings.defaults.js
index a0ad8433aa..b65a019365 100644
--- a/services/clsi/config/settings.defaults.js
+++ b/services/clsi/config/settings.defaults.js
@@ -63,7 +63,12 @@ module.exports = {
   texliveOpenoutAny: process.env.TEXLIVE_OPENOUT_ANY,
   sentry: {
     dsn: process.env.SENTRY_DSN
-  }
+  },
+
+  enablePdfCaching: process.env.ENABLE_PDF_CACHING === 'true',
+  enablePdfCachingDark: process.env.ENABLE_PDF_CACHING_DARK === 'true',
+  pdfCachingMinChunkSize:
+    parseInt(process.env.PDF_CACHING_MIN_CHUNK_SIZE, 10) || 1024
 }
 
 if (process.env.ALLOWED_COMPILE_GROUPS) {
diff --git a/services/clsi/docker-compose.ci.yml b/services/clsi/docker-compose.ci.yml
index 2237933754..245059ad98 100644
--- a/services/clsi/docker-compose.ci.yml
+++ b/services/clsi/docker-compose.ci.yml
@@ -29,6 +29,7 @@ services:
       NODE_ENV: test
       NODE_OPTIONS: "--unhandled-rejections=strict"
       TEXLIVE_IMAGE:
+      ENABLE_PDF_CACHING: "true"
     command: npm run test:acceptance:_run
 
 
diff --git a/services/clsi/docker-compose.yml b/services/clsi/docker-compose.yml
index 6688000204..ee68a7c0ee 100644
--- a/services/clsi/docker-compose.yml
+++ b/services/clsi/docker-compose.yml
@@ -38,5 +38,6 @@ services:
       LOG_LEVEL: ERROR
       NODE_ENV: test
       NODE_OPTIONS: "--unhandled-rejections=strict"
+      ENABLE_PDF_CACHING: "true"
     command: npm run --silent test:acceptance
 
diff --git a/services/clsi/test/acceptance/js/Stats.js b/services/clsi/test/acceptance/js/Stats.js
new file mode 100644
index 0000000000..87b20b1cc9
--- /dev/null
+++ b/services/clsi/test/acceptance/js/Stats.js
@@ -0,0 +1,16 @@
+const request = require('request')
+const Settings = require('settings-sharelatex')
+after(function (done) {
+  request(
+    {
+      url: `${Settings.apis.clsi.url}/metrics`
+    },
+    (err, response, body) => {
+      if (err) return done(err)
+      console.error('-- metrics --')
+      console.error(body)
+      console.error('-- metrics --')
+      done()
+    }
+  )
+})
diff --git a/services/clsi/test/acceptance/js/helpers/Client.js b/services/clsi/test/acceptance/js/helpers/Client.js
index 43825ae415..c5814ff3ef 100644
--- a/services/clsi/test/acceptance/js/helpers/Client.js
+++ b/services/clsi/test/acceptance/js/helpers/Client.js
@@ -30,6 +30,10 @@ module.exports = Client = {
     if (callback == null) {
       callback = function (error, res, body) {}
     }
+    if (data) {
+      // Enable pdf caching unless disabled explicitly.
+      data.options = Object.assign({}, { enablePdfCaching: true }, data.options)
+    }
     return request.post(
       {
         url: `${this.host}/project/${project_id}/compile`,
diff --git a/services/clsi/test/unit/js/CompileControllerTests.js b/services/clsi/test/unit/js/CompileControllerTests.js
index 6f256d2955..6d6b34ee58 100644
--- a/services/clsi/test/unit/js/CompileControllerTests.js
+++ b/services/clsi/test/unit/js/CompileControllerTests.js
@@ -113,6 +113,8 @@ describe('CompileController', function () {
       this.ProjectPersistenceManager.markProjectAsJustAccessed = sinon
         .stub()
         .callsArg(1)
+      this.stats = { foo: 1 }
+      this.timings = { bar: 2 }
       this.res.status = sinon.stub().returnsThis()
       return (this.res.send = sinon.stub())
     })
@@ -121,7 +123,7 @@ describe('CompileController', function () {
       beforeEach(function () {
         this.CompileManager.doCompileWithLock = sinon
           .stub()
-          .callsArgWith(1, null, this.output_files)
+          .yields(null, this.output_files, this.stats, this.timings)
         return this.CompileController.compile(this.req, this.res)
       })
 
@@ -150,12 +152,16 @@ describe('CompileController', function () {
             compile: {
               status: 'success',
               error: null,
+              stats: this.stats,
+              timings: this.timings,
               outputFiles: this.output_files.map((file) => {
                 return {
                   url: `${this.Settings.apis.clsi.url}/project/${this.project_id}/build/${file.build}/output/${file.path}`,
                   path: file.path,
                   type: file.type,
-                  build: file.build
+                  build: file.build,
+                  // gets dropped by JSON.stringify
+                  contentId: undefined
                 }
               })
             }
@@ -180,7 +186,7 @@ describe('CompileController', function () {
         ]
         this.CompileManager.doCompileWithLock = sinon
           .stub()
-          .callsArgWith(1, null, this.output_files)
+          .yields(null, this.output_files, this.stats, this.timings)
         this.CompileController.compile(this.req, this.res)
       })
 
@@ -191,12 +197,16 @@ describe('CompileController', function () {
             compile: {
               status: 'failure',
               error: null,
+              stats: this.stats,
+              timings: this.timings,
               outputFiles: this.output_files.map((file) => {
                 return {
                   url: `${this.Settings.apis.clsi.url}/project/${this.project_id}/build/${file.build}/output/${file.path}`,
                   path: file.path,
                   type: file.type,
-                  build: file.build
+                  build: file.build,
+                  // gets dropped by JSON.stringify
+                  contentId: undefined
                 }
               })
             }
@@ -220,7 +230,10 @@ describe('CompileController', function () {
             compile: {
               status: 'error',
               error: this.message,
-              outputFiles: []
+              outputFiles: [],
+              // JSON.stringify will omit these
+              stats: undefined,
+              timings: undefined
             }
           })
           .should.equal(true)
@@ -244,7 +257,10 @@ describe('CompileController', function () {
             compile: {
               status: 'timedout',
               error: this.message,
-              outputFiles: []
+              outputFiles: [],
+              // JSON.stringify will omit these
+              stats: undefined,
+              timings: undefined
             }
           })
           .should.equal(true)
@@ -266,7 +282,10 @@ describe('CompileController', function () {
             compile: {
               error: null,
               status: 'failure',
-              outputFiles: []
+              outputFiles: [],
+              // JSON.stringify will omit these
+              stats: undefined,
+              timings: undefined
             }
           })
           .should.equal(true)
diff --git a/services/clsi/test/unit/js/CompileManagerTests.js b/services/clsi/test/unit/js/CompileManagerTests.js
index 2d40bdd64a..97e318a4a6 100644
--- a/services/clsi/test/unit/js/CompileManagerTests.js
+++ b/services/clsi/test/unit/js/CompileManagerTests.js
@@ -71,7 +71,7 @@ describe('CompileManager', function () {
       this.compileDir = `${this.Settings.path.compilesDir}/${this.project_id}-${this.user_id}`
       this.CompileManager.doCompile = sinon
         .stub()
-        .callsArgWith(1, null, this.output_files)
+        .yields(null, this.output_files)
       return (this.LockManager.runWithLock = (lockFile, runner, callback) =>
         runner((err, ...result) => callback(err, ...Array.from(result))))
     })
@@ -172,10 +172,10 @@ describe('CompileManager', function () {
       this.LatexRunner.runLatex = sinon.stub().callsArg(2)
       this.OutputFileFinder.findOutputFiles = sinon
         .stub()
-        .callsArgWith(2, null, this.output_files)
+        .yields(null, this.output_files)
       this.OutputCacheManager.saveOutputFiles = sinon
         .stub()
-        .callsArgWith(3, null, this.build_files)
+        .yields(null, this.build_files)
       this.DraftModeManager.injectDraftMode = sinon.stub().callsArg(1)
       return (this.TikzManager.checkMainFile = sinon.stub().callsArg(3, false))
     })