diff --git a/vsintegration/src/FSharp.Editor/LanguageService/LanguageService.fs b/vsintegration/src/FSharp.Editor/LanguageService/LanguageService.fs
index dead969dd27..47ef037c255 100644
--- a/vsintegration/src/FSharp.Editor/LanguageService/LanguageService.fs
+++ b/vsintegration/src/FSharp.Editor/LanguageService/LanguageService.fs
@@ -126,10 +126,10 @@ type internal ProjectInfoManager
             // compiled and #r will refer to files on disk
             let referencedProjectFileNames = [| |] 
             let site = ProjectSitesAndFiles.CreateProjectSiteForScript(fileName, referencedProjectFileNames, options)
-            return ProjectSitesAndFiles.GetProjectOptionsForProjectSite(tryGetOptionsForReferencedProject,site,fileName,options.ExtraProjectInfo,serviceProvider, true)
+            return ProjectSitesAndFiles.GetProjectOptionsForProjectSite(Settings.IntelliSense.EnableInMemoryCrossProjectReferences, tryGetOptionsForReferencedProject,site,fileName,options.ExtraProjectInfo,serviceProvider, true)
         else
             let site = ProjectSitesAndFiles.ProjectSiteOfSingleFile(fileName)
-            return ProjectSitesAndFiles.GetProjectOptionsForProjectSite(tryGetOptionsForReferencedProject,site,fileName,extraProjectInfo,serviceProvider, true)
+            return ProjectSitesAndFiles.GetProjectOptionsForProjectSite(Settings.IntelliSense.EnableInMemoryCrossProjectReferences, tryGetOptionsForReferencedProject,site,fileName,extraProjectInfo,serviceProvider, true)
       }
 
     /// Update the info for a project in the project table
@@ -137,7 +137,7 @@ type internal ProjectInfoManager
         this.AddOrUpdateProject(projectId, (fun isRefresh -> 
             let extraProjectInfo = Some(box workspace)
             let tryGetOptionsForReferencedProject f = f |> tryGetOrCreateProjectId |> Option.bind this.TryGetOptionsForProject
-            let referencedProjects, options = ProjectSitesAndFiles.GetProjectOptionsForProjectSite(tryGetOptionsForReferencedProject, site, site.ProjectFileName(), extraProjectInfo, serviceProvider, true)
+            let referencedProjects, options = ProjectSitesAndFiles.GetProjectOptionsForProjectSite(Settings.IntelliSense.EnableInMemoryCrossProjectReferences, tryGetOptionsForReferencedProject, site, site.ProjectFileName(), extraProjectInfo, serviceProvider, true)
             let referencedProjectIds = referencedProjects |> Array.choose tryGetOrCreateProjectId
             checkerProvider.Checker.InvalidateConfiguration(options, startBackgroundCompileIfAlreadySeen = not isRefresh, userOpName= userOpName + ".UpdateProjectInfo")
             referencedProjectIds, options))
diff --git a/vsintegration/src/FSharp.Editor/Options/EditorOptions.fs b/vsintegration/src/FSharp.Editor/Options/EditorOptions.fs
index 88270cc7df4..4034d2db8fe 100644
--- a/vsintegration/src/FSharp.Editor/Options/EditorOptions.fs
+++ b/vsintegration/src/FSharp.Editor/Options/EditorOptions.fs
@@ -18,7 +18,8 @@ module DefaultTuning =
 // CLIMutable to make the record work also as a view model
 [<CLIMutable>]
 type IntelliSenseOptions =
-  { ShowAfterCharIsTyped: bool
+  { EnableInMemoryCrossProjectReferences: bool
+    ShowAfterCharIsTyped: bool
     ShowAfterCharIsDeleted: bool
     ShowAllSymbols : bool }
 
@@ -41,7 +42,8 @@ type internal Settings [<ImportingConstructor>](store: SettingsStore) =
     do  // Initialize default settings
         
         store.RegisterDefault
-            { ShowAfterCharIsTyped = true
+            { EnableInMemoryCrossProjectReferences = true
+              ShowAfterCharIsTyped = true
               ShowAfterCharIsDeleted = true
               ShowAllSymbols = true }
 
diff --git a/vsintegration/src/FSharp.LanguageService/BackgroundRequests.fs b/vsintegration/src/FSharp.LanguageService/BackgroundRequests.fs
index dc85178fe4b..8d2cfce4b92 100644
--- a/vsintegration/src/FSharp.LanguageService/BackgroundRequests.fs
+++ b/vsintegration/src/FSharp.LanguageService/BackgroundRequests.fs
@@ -83,7 +83,8 @@ type internal FSharpLanguageServiceBackgroundRequests
                     // This portion is executed on the UI thread.
                     let rdt = getServiceProvider().RunningDocumentTable
                     let projectSite = getProjectSitesAndFiles().FindOwningProject(rdt,fileName)
-                    let _, checkOptions = ProjectSitesAndFiles.GetProjectOptionsForProjectSite((fun _ -> None), projectSite, fileName, None, getServiceProvider(), false)                            
+                    let enableInMemoryCrossProjectReferences = true
+                    let _, checkOptions = ProjectSitesAndFiles.GetProjectOptionsForProjectSite(enableInMemoryCrossProjectReferences, (fun _ -> None), projectSite, fileName, None, getServiceProvider(), false)                            
                     let projectFileName = projectSite.ProjectFileName()
                     let data = 
                         {   ProjectSite = projectSite
diff --git a/vsintegration/src/FSharp.LanguageService/ProjectSitesAndFiles.fs b/vsintegration/src/FSharp.LanguageService/ProjectSitesAndFiles.fs
index 370e577a5f1..8b9c8ad77d8 100644
--- a/vsintegration/src/FSharp.LanguageService/ProjectSitesAndFiles.fs
+++ b/vsintegration/src/FSharp.LanguageService/ProjectSitesAndFiles.fs
@@ -123,7 +123,7 @@ type internal ProjectSitesAndFiles() =
             | None -> ()
         }
                     
-    static let rec referencedProjectsOf (tryGetOptionsForReferencedProject, projectSite:IProjectSite, extraProjectInfo, serviceProvider:System.IServiceProvider, useUniqueStamp) =
+    static let rec referencedProjectsOf (enableInMemoryCrossProjectReferences, tryGetOptionsForReferencedProject, projectSite:IProjectSite, extraProjectInfo, serviceProvider:System.IServiceProvider, useUniqueStamp) =
         [| for (p,ps) in referencedProvideProjectSites (projectSite, serviceProvider) do
               match fullOutputAssemblyPath p with 
               | None -> ()
@@ -132,14 +132,16 @@ type internal ProjectSitesAndFiles() =
                       // Lookup may not succeed if the project has not been established yet
                       // In this case we go and compute the options recursively.
                       match tryGetOptionsForReferencedProject p.FileName with 
-                      | None -> getProjectOptionsForProjectSite (tryGetOptionsForReferencedProject, ps.GetProjectSite(), p.FileName, extraProjectInfo, serviceProvider, useUniqueStamp) |> snd
+                      | None -> getProjectOptionsForProjectSite (enableInMemoryCrossProjectReferences, tryGetOptionsForReferencedProject, ps.GetProjectSite(), p.FileName, extraProjectInfo, serviceProvider, useUniqueStamp) |> snd
                       | Some options -> options
                   yield (p.FileName, (path, referencedProjectOptions)) |]
 
-    and getProjectOptionsForProjectSite(tryGetOptionsForReferencedProject, projectSite:IProjectSite, fileName, extraProjectInfo, serviceProvider, useUniqueStamp) =            
+    and getProjectOptionsForProjectSite(enableInMemoryCrossProjectReferences, tryGetOptionsForReferencedProject, projectSite:IProjectSite, fileName, extraProjectInfo, serviceProvider, useUniqueStamp) =            
         let referencedProjectFileNames, referencedProjectOptions = 
-            referencedProjectsOf(tryGetOptionsForReferencedProject, projectSite, extraProjectInfo, serviceProvider, useUniqueStamp) 
-            |> Array.unzip
+            if enableInMemoryCrossProjectReferences then
+                referencedProjectsOf(enableInMemoryCrossProjectReferences, tryGetOptionsForReferencedProject, projectSite, extraProjectInfo, serviceProvider, useUniqueStamp) 
+                |> Array.unzip
+            else [| |], [| |]
 
         let options = 
             {ProjectFileName = projectSite.ProjectFileName()
@@ -238,11 +240,11 @@ type internal ProjectSitesAndFiles() =
         |> Seq.toArray
 
     /// Create project options for this project site.
-    static member GetProjectOptionsForProjectSite(tryGetOptionsForReferencedProject, projectSite:IProjectSite,filename,extraProjectInfo,serviceProvider:System.IServiceProvider, useUniqueStamp) =
+    static member GetProjectOptionsForProjectSite(enableInMemoryCrossProjectReferences, tryGetOptionsForReferencedProject, projectSite:IProjectSite,filename,extraProjectInfo,serviceProvider:System.IServiceProvider, useUniqueStamp) =
         match projectSite with
         | :? IHaveCheckOptions as hco -> hco.OriginalCheckOptions()
         | _ ->             
-            getProjectOptionsForProjectSite(tryGetOptionsForReferencedProject, projectSite, filename, extraProjectInfo, serviceProvider, useUniqueStamp)
+            getProjectOptionsForProjectSite(enableInMemoryCrossProjectReferences, tryGetOptionsForReferencedProject, projectSite, filename, extraProjectInfo, serviceProvider, useUniqueStamp)
          
     /// Create project site for these project options
     static member CreateProjectSiteForScript (filename, referencedProjectFileNames, checkOptions) = 
diff --git a/vsintegration/src/FSharp.UIResources/IntelliSenseOptionControl.xaml b/vsintegration/src/FSharp.UIResources/IntelliSenseOptionControl.xaml
index d6d1858b54b..ecf48295c27 100644
--- a/vsintegration/src/FSharp.UIResources/IntelliSenseOptionControl.xaml
+++ b/vsintegration/src/FSharp.UIResources/IntelliSenseOptionControl.xaml
@@ -2,34 +2,40 @@
              x:ClassModifier="internal"
              xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
              xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
-             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
-             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
+             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
              xmlns:local="clr-namespace:Microsoft.VisualStudio.FSharp.UIResources"
-             mc:Ignorable="d" 
+             mc:Ignorable="d"
              d:DesignHeight="300" d:DesignWidth="400">
-    <UserControl.Resources>
-        <ResourceDictionary>
-            <ResourceDictionary.MergedDictionaries>
-                <ResourceDictionary Source="OptionPageStyle.xaml"/>
-            </ResourceDictionary.MergedDictionaries>
-        </ResourceDictionary>
-    </UserControl.Resources>
-    <Grid>
-        <ScrollViewer VerticalScrollBarVisibility="Auto">
-            <StackPanel>
-                <GroupBox Header="{x:Static local:Strings.Completion_Lists}">
-                    <StackPanel>
-                        <CheckBox x:Name="charTyped" IsChecked="{Binding ShowAfterCharIsTyped}"
-                                  Content="{x:Static local:Strings.Show_completion_list_after_a_character_is_typed}"/>
-                        <StackPanel Margin="15 0 0 0">
-                            <CheckBox x:Name="charDeleted" IsEnabled="{Binding IsChecked, ElementName=charTyped}" IsChecked="{Binding ShowAfterCharIsDeleted}"
-                                      Content="{x:Static local:Strings.Show_completion_list_after_a_character_is_deleted}"/>
-                        </StackPanel>
-                        <CheckBox x:Name="showAllSymbols" IsChecked="{Binding ShowAllSymbols}"
-                                  Content="{x:Static local:Strings.Show_all_symbols}"/>
-                    </StackPanel>
-                </GroupBox>
+  <UserControl.Resources>
+    <ResourceDictionary>
+      <ResourceDictionary.MergedDictionaries>
+        <ResourceDictionary Source="OptionPageStyle.xaml"/>
+      </ResourceDictionary.MergedDictionaries>
+    </ResourceDictionary>
+  </UserControl.Resources>
+  <Grid>
+    <ScrollViewer VerticalScrollBarVisibility="Auto">
+      <StackPanel>
+        <GroupBox Header="{x:Static local:Strings.Completion_Lists}">
+          <StackPanel>
+            <CheckBox x:Name="charTyped" IsChecked="{Binding ShowAfterCharIsTyped}"
+                      Content="{x:Static local:Strings.Show_completion_list_after_a_character_is_typed}"/>
+            <StackPanel Margin="15 0 0 0">
+              <CheckBox x:Name="charDeleted" IsEnabled="{Binding IsChecked, ElementName=charTyped}" IsChecked="{Binding ShowAfterCharIsDeleted}"
+                        Content="{x:Static local:Strings.Show_completion_list_after_a_character_is_deleted}"/>
             </StackPanel>
-        </ScrollViewer>
-    </Grid>
+            <CheckBox x:Name="showAllSymbols" IsChecked="{Binding ShowAllSymbols}"
+                      Content="{x:Static local:Strings.Show_all_symbols}"/>
+          </StackPanel>
+        </GroupBox>
+        <GroupBox Header="{x:Static local:Strings.Language_Service_Performance}">
+          <StackPanel>
+            <CheckBox x:Name="enableInMemoryCrossProjectReferences" IsChecked="{Binding EnableInMemoryCrossProjectReferences}"
+                      Content="{x:Static local:Strings.Enable_in_memory_cross_project_references}"/>
+          </StackPanel>
+        </GroupBox>
+      </StackPanel>
+    </ScrollViewer>
+  </Grid>
 </UserControl>
diff --git a/vsintegration/src/FSharp.UIResources/Strings.Designer.cs b/vsintegration/src/FSharp.UIResources/Strings.Designer.cs
index 1526ee21a06..4213081ecd3 100644
--- a/vsintegration/src/FSharp.UIResources/Strings.Designer.cs
+++ b/vsintegration/src/FSharp.UIResources/Strings.Designer.cs
@@ -105,6 +105,24 @@ public static string Dot_underline {
             }
         }
         
+        /// <summary>
+        ///   Looks up a localized string similar to _Enable in-memory cross project references.
+        /// </summary>
+        public static string Enable_in_memory_cross_project_references {
+            get {
+                return ResourceManager.GetString("Enable_in_memory_cross_project_references", resourceCulture);
+            }
+        }
+        
+        /// <summary>
+        ///   Looks up a localized string similar to Language Service Performance.
+        /// </summary>
+        public static string Language_Service_Performance {
+            get {
+                return ResourceManager.GetString("Language_Service_Performance", resourceCulture);
+            }
+        }
+        
         /// <summary>
         ///   Looks up a localized string similar to Navigation links.
         /// </summary>
diff --git a/vsintegration/src/FSharp.UIResources/Strings.resx b/vsintegration/src/FSharp.UIResources/Strings.resx
index 94860c1bf7e..c153f6bcafb 100644
--- a/vsintegration/src/FSharp.UIResources/Strings.resx
+++ b/vsintegration/src/FSharp.UIResources/Strings.resx
@@ -126,6 +126,9 @@
   <data name="Completion_Lists" xml:space="preserve">
     <value>Completion Lists</value>
   </data>
+  <data name="Language_Service_Performance" xml:space="preserve">
+    <value>Language Service Performance</value>
+  </data>
   <data name="Dash_underline" xml:space="preserve">
     <value>D_ash underline</value>
   </data>
@@ -144,6 +147,9 @@
   <data name="Show_completion_list_after_a_character_is_typed" xml:space="preserve">
     <value>_Show completion list after a character is typed</value>
   </data>
+  <data name="Enable_in_memory_cross_project_references" xml:space="preserve">
+    <value>_Enable in-memory cross project references</value>
+  </data>
   <data name="Show_navigation_links_as" xml:space="preserve">
     <value>S_how navigation links as</value>
   </data>
diff --git a/vsintegration/tests/Salsa/FSharpLanguageServiceTestable.fs b/vsintegration/tests/Salsa/FSharpLanguageServiceTestable.fs
index afafc5e835e..f0d61ee20fb 100644
--- a/vsintegration/tests/Salsa/FSharpLanguageServiceTestable.fs
+++ b/vsintegration/tests/Salsa/FSharpLanguageServiceTestable.fs
@@ -126,7 +126,8 @@ type internal FSharpLanguageServiceTestable() as this =
 
     /// Respond to project being cleaned/rebuilt (any live type providers in the project should be refreshed)
     member this.OnProjectCleaned(projectSite:IProjectSite) = 
-        let _, checkOptions = ProjectSitesAndFiles.GetProjectOptionsForProjectSite((fun _ -> None), projectSite, "" ,None, serviceProvider.Value, false)
+        let enableInMemoryCrossProjectReferences = true
+        let _, checkOptions = ProjectSitesAndFiles.GetProjectOptionsForProjectSite(enableInMemoryCrossProjectReferences, (fun _ -> None), projectSite, "" ,None, serviceProvider.Value, false)
         this.FSharpChecker.NotifyProjectCleaned(checkOptions) |> Async.RunSynchronously
 
     member this.OnActiveViewChanged(textView) =
@@ -167,8 +168,9 @@ type internal FSharpLanguageServiceTestable() as this =
     // For each change in dependency files, notify the language service of the change and propagate the update
     interface IDependencyFileChangeNotify with
         member this.DependencyFileCreated projectSite = 
+            let enableInMemoryCrossProjectReferences = true
             // Invalidate the configuration if we notice any add for any DependencyFiles 
-            let _, checkOptions = ProjectSitesAndFiles.GetProjectOptionsForProjectSite((fun _ -> None), projectSite, "", None, this.ServiceProvider, false)
+            let _, checkOptions = ProjectSitesAndFiles.GetProjectOptionsForProjectSite(enableInMemoryCrossProjectReferences, (fun _ -> None), projectSite, "", None, this.ServiceProvider, false)
             this.FSharpChecker.InvalidateConfiguration(checkOptions)
 
         member this.DependencyFileChanged (filename) = 
diff --git a/vsintegration/tests/unittests/CompletionProviderTests.fs b/vsintegration/tests/unittests/CompletionProviderTests.fs
index 3c6263b6172..5690c0087c0 100644
--- a/vsintegration/tests/unittests/CompletionProviderTests.fs
+++ b/vsintegration/tests/unittests/CompletionProviderTests.fs
@@ -87,7 +87,7 @@ let VerifyNoCompletionList(fileContents: string, marker: string) =
 
 [<OneTimeSetUp>]
 let usingDefaultSettings() = 
-    SettingsPersistence.setSettings { ShowAfterCharIsTyped = true; ShowAfterCharIsDeleted = false; ShowAllSymbols = true }
+    SettingsPersistence.setSettings { EnableInMemoryCrossProjectReferences=true; ShowAfterCharIsTyped = true; ShowAfterCharIsDeleted = false; ShowAllSymbols = true }
     
 [<Test>]
 let ShouldTriggerCompletionAtCorrectMarkers() =