diff --git a/fcs/fcs-fable/System.Collections.fs b/fcs/fcs-fable/System.Collections.fs
index b9776db3afa..c9cb4b270a3 100644
--- a/fcs/fcs-fable/System.Collections.fs
+++ b/fcs/fcs-fable/System.Collections.fs
@@ -34,6 +34,7 @@ module Immutable =
     type ImmutableArray<'T> =
         static member CreateBuilder() = ResizeArray<'T>()
 
+    [<Sealed>]
     type ImmutableHashSet<'T>(values: 'T seq) =
         let xs = HashSet<'T>(values)
 
@@ -62,13 +63,21 @@ module Immutable =
             member _.GetEnumerator(): IEnumerator<'T> =
                 xs.GetEnumerator()
 
-    type ImmutableDictionary<'Key, 'Value when 'Key: equality>(pairs: KeyValuePair<'Key, 'Value> seq) =
-        let xs = Dictionary<'Key, 'Value>()
-        do for pair in pairs do xs.Add(pair.Key, pair.Value)
+    [<Sealed>]
+    type ImmutableDictionary<'Key, 'Value when 'Key: equality>(xs: Dictionary<'Key, 'Value>) =
+        static member Create(comparer: IEqualityComparer<'Key>) =
+            ImmutableDictionary<'Key, 'Value>(Dictionary(comparer))
 
-        static member CreateRange(items) = ImmutableDictionary<'Key, 'Value>(items)
-        static member Empty = ImmutableDictionary<'Key, 'Value>(Array.empty)
+        static member CreateRange(items: IEnumerable<KeyValuePair<'Key, 'Value>>) =
+            let xs = Dictionary<'Key, 'Value>()
+            for pair in items do
+                xs.Add(pair.Key, pair.Value)
+            ImmutableDictionary<'Key, 'Value>(xs)
 
+        static member Empty =
+            ImmutableDictionary<'Key, 'Value>(Dictionary())
+
+        member _.IsEmpty = xs.Count = 0
         member _.Item with get (key: 'Key): 'Value = xs[key]
         member _.ContainsKey (key: 'Key) = xs.ContainsKey(key)
 
diff --git a/fcs/fcs-fable/TcImports_shim.fs b/fcs/fcs-fable/TcImports_shim.fs
index 226695c7aaf..b3eda77d9a2 100644
--- a/fcs/fcs-fable/TcImports_shim.fs
+++ b/fcs/fcs-fable/TcImports_shim.fs
@@ -176,7 +176,7 @@ module TcImports =
                     XmlDocumentationInfo = None
                   }
 
-            let optdata = lazy (
+            let optdata = InterruptibleLazy(fun _ ->
                 match memoize_opt.Apply ccuName with 
                 | None -> None
                 | Some data ->
diff --git a/fcs/fcs-fable/fcs-fable.fsproj b/fcs/fcs-fable/fcs-fable.fsproj
index 9099407ed47..f12e26d9774 100644
--- a/fcs/fcs-fable/fcs-fable.fsproj
+++ b/fcs/fcs-fable/fcs-fable.fsproj
@@ -93,8 +93,8 @@
     <!-- <Compile Include="$(FSharpSourcesRoot)/Facilities/CompilerLocation.fs" /> -->
     <Compile Include="$(FSharpSourcesRoot)/Facilities/BuildGraph.fsi" />
     <Compile Include="$(FSharpSourcesRoot)/Facilities/BuildGraph.fs" />
-    <Compile Include="$(FSharpSourcesRoot)/Utilities/ReadOnlySpan.fsi" />
-    <Compile Include="$(FSharpSourcesRoot)/Utilities/ReadOnlySpan.fs" />
+    <!-- <Compile Include="$(FSharpSourcesRoot)/Utilities/ReadOnlySpan.fsi" /> -->
+    <!-- <Compile Include="$(FSharpSourcesRoot)/Utilities/ReadOnlySpan.fs" /> -->
     <!-- <FsLex Include="$(FSharpSourcesRoot)/AbstractIL/illex.fsl" /> -->
     <!-- <None Include="$(FSharpSourcesRoot)/AbstractIL/illex.fsl" /> -->
     <!-- <FsYacc Include="$(FSharpSourcesRoot)/AbstractIL/ilpars.fsy" /> -->
diff --git a/fcs/fcs-fable/test/fcs-fable-test.fsproj b/fcs/fcs-fable/test/fcs-fable-test.fsproj
index bcc9b5414e2..ccaf13c1aaa 100644
--- a/fcs/fcs-fable/test/fcs-fable-test.fsproj
+++ b/fcs/fcs-fable/test/fcs-fable-test.fsproj
@@ -20,7 +20,7 @@
   <ItemGroup>
     <!-- <PackageReference Include="FSharp.Core" Version="8.0.0" /> -->
     <!-- <Reference Include="../../../artifacts/bin/FSharp.Compiler.Service/Release/netstandard2.0/FSharp.Core.dll" /> -->
-    <PackageReference Include="Fable.Core" Version="4.1.0" />
+    <PackageReference Include="Fable.Core" Version="4.2.0" />
   </ItemGroup>
 
 </Project>
diff --git a/global.json b/global.json
index 365652e8f7e..95f24805cb6 100644
--- a/global.json
+++ b/global.json
@@ -1,10 +1,10 @@
 {
   "sdk": {
-    "version": "8.0.100-rc.1.23463.5",
+    "version": "8.0.100",
     "allowPrerelease": true
   },
   "tools": {
-    "dotnet": "8.0.100-rc.1.23463.5",
+    "dotnet": "8.0.100",
     "vs": {
       "version": "17.6",
       "components": [
diff --git a/src/Compiler/AbstractIL/ilread.fs b/src/Compiler/AbstractIL/ilread.fs
index bf84f039b60..854f6e0be9a 100644
--- a/src/Compiler/AbstractIL/ilread.fs
+++ b/src/Compiler/AbstractIL/ilread.fs
@@ -1219,19 +1219,14 @@ type ISeekReadIndexedRowReader<'RowT, 'KeyT, 'T when 'RowT: struct> =
     abstract CompareKey: 'KeyT -> int
     abstract ConvertRow: ref<'RowT> -> 'T
 
-#if FABLE_COMPILER
 [<Struct>]
 type CustomAttributeRow =
     val mutable parentIndex: TaggedIndex<HasCustomAttributeTag>
     val mutable typeIndex: TaggedIndex<CustomAttributeTypeTag>
     val mutable valueIndex: int
 
-let seekReadIndexedRowsRange numRows binaryChop (reader: ISeekReadIndexedRowReader<CustomAttributeRow, 'KeyT, 'T>) =
+let seekReadIndexedRowsRange numRows binaryChop (reader: ISeekReadIndexedRowReader<CustomAttributeRow, _, _>) =
     let mutable row = ref Unchecked.defaultof<CustomAttributeRow>
-#else
-let seekReadIndexedRowsRange numRows binaryChop (reader: ISeekReadIndexedRowReader<'RowT, _, _>) =
-    let mutable row = Unchecked.defaultof<'RowT>
-#endif
 
     let mutable startRid = -1
     let mutable endRid = -1
@@ -1310,9 +1305,9 @@ let seekReadIndexedRowsRange numRows binaryChop (reader: ISeekReadIndexedRowRead
         let mutable fin = false
 
         while rid <= numRows && not fin do
-            reader.GetRow(rid, &row)
+            reader.GetRow(rid, row)
 
-            if reader.CompareKey(reader.GetKey(&row)) = 0 then
+            if reader.CompareKey(reader.GetKey(row)) = 0 then
                 endRid <- rid
             else
                 fin <- true
@@ -1321,7 +1316,7 @@ let seekReadIndexedRowsRange numRows binaryChop (reader: ISeekReadIndexedRowRead
 
     startRid, endRid
 
-let seekReadIndexedRowsByInterface numRows binaryChop (reader: ISeekReadIndexedRowReader<'RowT, _, _>) =
+let seekReadIndexedRowsByInterface numRows binaryChop (reader: ISeekReadIndexedRowReader<CustomAttributeRow, _, _>) =
     let startRid, endRid = seekReadIndexedRowsRange numRows binaryChop reader
 
     if startRid <= 0 || endRid < startRid then
@@ -1329,9 +1324,9 @@ let seekReadIndexedRowsByInterface numRows binaryChop (reader: ISeekReadIndexedR
     else
 
         Array.init (endRid - startRid + 1) (fun i ->
-            let mutable row = Unchecked.defaultof<'RowT>
-            reader.GetRow(startRid + i, &row)
-            reader.ConvertRow(&row))
+            let mutable row = ref Unchecked.defaultof<CustomAttributeRow>
+            reader.GetRow(startRid + i, row)
+            reader.ConvertRow(row))
 
 let inline rowAddr (ctxt: ILMetadataReader) (tn: TableName) (idx: int) =
     ref (ctxt.rowAddr tn idx)
diff --git a/src/Compiler/Checking/QuotationTranslator.fs b/src/Compiler/Checking/QuotationTranslator.fs
index 04f69016123..b7dd2b1c7f3 100644
--- a/src/Compiler/Checking/QuotationTranslator.fs
+++ b/src/Compiler/Checking/QuotationTranslator.fs
@@ -718,13 +718,9 @@ and private ConvExprCore cenv (env : QuotationTranslationEnv) (expr: Expr) : QP.
             let witnessArgInfo = 
                 if g.generateWitnesses && inWitnessPassingScope then 
                     let witnessInfo = traitInfo.GetWitnessInfo()
-#if FABLE_COMPILER
-                    env.witnessesInScope.TryFind witnessInfo
-#else
                     match env.witnessesInScope.TryGetValue witnessInfo with 
                     | true, storage -> Some storage
                     | _ -> None
-#endif
                 else
                     None
 
diff --git a/src/Compiler/CodeGen/IlxGen.fs b/src/Compiler/CodeGen/IlxGen.fs
index 89179f27cd1..b7492a6836b 100644
--- a/src/Compiler/CodeGen/IlxGen.fs
+++ b/src/Compiler/CodeGen/IlxGen.fs
@@ -1318,13 +1318,9 @@ let ComputeGenerateWitnesses (g: TcGlobals) eenv =
     && not eenv.suppressWitnesses
 
 let TryStorageForWitness (_g: TcGlobals) eenv (w: TraitWitnessInfo) =
-#if FABLE_COMPILER
-    eenv.witnessesInScope.TryFind w
-#else
     match eenv.witnessesInScope.TryGetValue w with
     | true, storage -> Some storage
     | _ -> None
-#endif
 
 let IsValRefIsDllImport g (vref: ValRef) =
     vref.Attribs |> HasFSharpAttributeOpt g g.attrib_DllImportAttribute
diff --git a/src/Compiler/TypedTree/TypedTreeOps.fs b/src/Compiler/TypedTree/TypedTreeOps.fs
index a0253933a1d..2034d5ecb20 100644
--- a/src/Compiler/TypedTree/TypedTreeOps.fs
+++ b/src/Compiler/TypedTree/TypedTreeOps.fs
@@ -10293,23 +10293,6 @@ let CombineCcuContentFragments l =
 /// An immutable mappping from witnesses to some data.
 ///
 /// Note: this uses an immutable HashMap/Dictionary with an IEqualityComparer that captures TcGlobals, see EmptyTraitWitnessInfoHashMap
-#if FABLE_COMPILER
-type TraitWitnessInfoHashMap<'T> = Internal.Utilities.Collections.Tagged.Map<TraitWitnessInfo, 'T>
-
-/// Create an empty immutable mapping from witnesses to some data
-let EmptyTraitWitnessInfoHashMap g : TraitWitnessInfoHashMap<'T> =
-    let comparer =
-        { new IComparer<TraitWitnessInfo> with
-            member _.Compare(x, y) =
-                let xhash = hash x
-                let yhash = hash y
-                let equals x y = traitKeysAEquiv g TypeEquivEnv.Empty x y
-                if xhash = yhash
-                then if equals x y then 0 else -1
-                else if xhash < yhash then -1 else 1
-        }
-    Internal.Utilities.Collections.Tagged.Map<_,_>.FromList(comparer, [])
-#else //!FABLE_COMPILER
 type TraitWitnessInfoHashMap<'T> = ImmutableDictionary<TraitWitnessInfo, 'T>
 
 /// Create an empty immutable mapping from witnesses to some data
@@ -10319,7 +10302,6 @@ let EmptyTraitWitnessInfoHashMap g : TraitWitnessInfoHashMap<'T> =
             member _.Equals(a, b) = traitKeysAEquiv g TypeEquivEnv.Empty a b
             member _.GetHashCode(a) = hash a.MemberName
         })
-#endif //!FABLE_COMPILER
 
 let (|WhileExpr|_|) expr = 
     match expr with 
diff --git a/src/Compiler/TypedTree/TypedTreeOps.fsi b/src/Compiler/TypedTree/TypedTreeOps.fsi
index 1dde299a1ff..f2fa42412e7 100755
--- a/src/Compiler/TypedTree/TypedTreeOps.fsi
+++ b/src/Compiler/TypedTree/TypedTreeOps.fsi
@@ -2585,11 +2585,7 @@ val GetTraitWitnessInfosOfTypars: TcGlobals -> numParentTypars: int -> typars: T
 /// An immutable mappping from witnesses to some data.
 ///
 /// Note: this uses an immutable HashMap/Dictionary with an IEqualityComparer that captures TcGlobals, see EmptyTraitWitnessInfoHashMap
-#if FABLE_COMPILER
-type TraitWitnessInfoHashMap<'T> = Internal.Utilities.Collections.Tagged.Map<TraitWitnessInfo, 'T>
-#else
 type TraitWitnessInfoHashMap<'T> = ImmutableDictionary<TraitWitnessInfo, 'T>
-#endif
 
 /// Create an empty immutable mapping from witnesses to some data
 val EmptyTraitWitnessInfoHashMap: TcGlobals -> TraitWitnessInfoHashMap<'T>
diff --git a/src/Compiler/Utilities/Cancellable.fs b/src/Compiler/Utilities/Cancellable.fs
index 81bb140f6ef..ec5036027bd 100644
--- a/src/Compiler/Utilities/Cancellable.fs
+++ b/src/Compiler/Utilities/Cancellable.fs
@@ -47,10 +47,14 @@ module Cancellable =
         if ct.IsCancellationRequested then
             ValueOrCancelled.Cancelled(OperationCanceledException ct)
         else
+#if FABLE_COMPILER
+            oper ct
+#else
             try
                 oper ct
             with :? OperationCanceledException as e ->
                 ValueOrCancelled.Cancelled(OperationCanceledException e.CancellationToken)
+#endif
 
     let fold f acc seq =
         Cancellable(fun ct ->
@@ -142,7 +146,11 @@ type CancellableBuilder() =
                 | Choice2Of2 err -> Cancellable.run ct (handler err)
             | ValueOrCancelled.Cancelled err1 -> ValueOrCancelled.Cancelled err1)
 
+#if FABLE_COMPILER
+    member inline _.Using(resource: 'Resource when 'Resource :> IDisposable, [<InlineIfLambda>] comp) =
+#else
     member inline _.Using(resource, [<InlineIfLambda>] comp) =
+#endif
         Cancellable(fun ct ->
 #if !FSHARPCORE_USE_PACKAGE
             __debugPoint ""