diff --git a/lib/cadet/assessments/library.ex b/lib/cadet/assessments/library.ex
index e81e42028..00a7f3d2d 100644
--- a/lib/cadet/assessments/library.ex
+++ b/lib/cadet/assessments/library.ex
@@ -9,12 +9,14 @@ defmodule Cadet.Assessments.Library do
   @primary_key false
   embedded_schema do
     field(:chapter, :integer, default: 1)
+    field(:variant, :string, default: nil)
+    field(:exec_time_ms, :integer, default: 1000)
     field(:globals, :map, default: %{})
     embeds_one(:external, ExternalLibrary, on_replace: :update)
   end
 
   @required_fields ~w(chapter)a
-  @optional_fields ~w(globals)a
+  @optional_fields ~w(globals variant exec_time_ms)a
   @required_embeds ~w(external)a
 
   def changeset(library, params \\ %{}) do
@@ -24,6 +26,8 @@ defmodule Cadet.Assessments.Library do
     |> put_default_external()
     |> validate_required(@required_fields ++ @required_embeds)
     |> validate_globals()
+    |> validate_chapter()
+    |> validate_chapter_variant()
   end
 
   defp validate_globals(changeset) do
@@ -40,6 +44,45 @@ defmodule Cadet.Assessments.Library do
     end
   end
 
+  defp validate_chapter(changeset) do
+    case changeset |> fetch_change(:chapter) do
+      {:ok, c} when c in 1..4 -> changeset
+      :error -> changeset
+      _ -> add_error(changeset, :chapter, "invalid chapter")
+    end
+  end
+
+  @valid_chapter_variants [
+    {1, "wasm"},
+    {1, "lazy"},
+    {2, "lazy"},
+    {3, "concurrent"},
+    {3, "non-det"},
+    {4, "gpu"}
+  ]
+
+  defp validate_chapter_variant(changeset) do
+    chapter = changeset |> fetch_field(:chapter)
+    variant = changeset |> fetch_field(:variant)
+
+    case {chapter, variant} do
+      # no changes
+      {{:data, _}, {:data, _}} ->
+        changeset
+
+      # default variant
+      {{_, _c}, {_, v}} when is_nil(v) or v == "default" ->
+        changeset
+
+      {{_, chapter}, {_, variant}} ->
+        if {chapter, variant} in @valid_chapter_variants do
+          changeset
+        else
+          add_error(changeset, :variant, "invalid variant for given chapter")
+        end
+    end
+  end
+
   def put_default_external(changeset) do
     external = get_change(changeset, :external)
 
diff --git a/lib/cadet/jobs/xml_parser.ex b/lib/cadet/jobs/xml_parser.ex
index 1b67fa56b..003091b84 100644
--- a/lib/cadet/jobs/xml_parser.ex
+++ b/lib/cadet/jobs/xml_parser.ex
@@ -308,7 +308,9 @@ defmodule Cadet.Updater.XMLParser do
     library_entity
     |> xpath(
       ~x"."e,
-      chapter: ~x"./@interpreter"i
+      chapter: ~x"./@interpreter"i,
+      exec_time_ms: ~x"./@exectime"oi,
+      variant: ~x"./@variant"os
     )
     |> Map.put(:globals, globals)
     |> Map.put(:external, external)
diff --git a/lib/cadet_web/views/assessments_helpers.ex b/lib/cadet_web/views/assessments_helpers.ex
index bbe4c0cee..77dfc44c8 100644
--- a/lib/cadet_web/views/assessments_helpers.ex
+++ b/lib/cadet_web/views/assessments_helpers.ex
@@ -7,6 +7,8 @@ defmodule CadetWeb.AssessmentsHelpers do
   defp build_library(%{library: library}) do
     transform_map_for_view(library, %{
       chapter: :chapter,
+      variant: :variant,
+      execTimeMs: :exec_time_ms,
       globals: :globals,
       external: &build_external_library(%{external_library: &1.external})
     })
diff --git a/test/cadet/assessments/library_test.exs b/test/cadet/assessments/library_test.exs
index 94c4ecf40..4608eafdd 100644
--- a/test/cadet/assessments/library_test.exs
+++ b/test/cadet/assessments/library_test.exs
@@ -25,6 +25,65 @@ defmodule Cadet.Assessments.LibraryTest do
       end
     end
 
+    test "invalid changeset invalid chapter", %{valid_params: params} do
+      params
+      |> Map.put(:chapter, 100)
+      |> assert_changeset(:invalid)
+
+      params
+      |> Map.put(:chapter, 0)
+      |> assert_changeset(:invalid)
+    end
+
+    test "valid changeset valid chapter-variant", %{valid_params: params} do
+      variants = [
+        {1, "default"},
+        {1, "wasm"},
+        {1, "lazy"},
+        {2, "default"},
+        {2, "lazy"},
+        {3, "default"},
+        {3, "concurrent"},
+        {3, "non-det"},
+        {4, "default"},
+        {4, "gpu"}
+      ]
+
+      for {c, v} <- variants do
+        params
+        |> Map.merge(%{chapter: c, variant: v})
+        |> assert_changeset(:valid)
+      end
+
+      # no variant
+      params
+      |> Map.merge(%{chapter: 1})
+      |> assert_changeset(:valid)
+    end
+
+    test "valid changeset invalid chapter-variant", %{valid_params: params} do
+      variants = [
+        {1, "hello"},
+        {1, "concurrent"},
+        {1, "non-det"},
+        {2, "undefault"},
+        {2, "eager"},
+        {3, "concurren"},
+        {4, "geforce rtx 3080"}
+      ]
+
+      for {c, v} <- variants do
+        params
+        |> Map.merge(%{chapter: c, variant: v})
+        |> assert_changeset(:invalid)
+      end
+    end
+
+    test "invalid changeset empty" do
+      refute (%Library{chapter: nil}
+              |> Library.changeset(%{})).valid?
+    end
+
     test "valid changeset without globals", %{valid_params: params} do
       params
       |> Map.delete(:globals)
diff --git a/test/cadet_web/admin_controllers/admin_grading_controller_test.exs b/test/cadet_web/admin_controllers/admin_grading_controller_test.exs
index ca1b87995..dfe691e7b 100644
--- a/test/cadet_web/admin_controllers/admin_grading_controller_test.exs
+++ b/test/cadet_web/admin_controllers/admin_grading_controller_test.exs
@@ -268,7 +268,9 @@ defmodule CadetWeb.AdminGradingControllerTest do
                     "external" => %{
                       "name" => "#{&1.question.library.external.name}",
                       "symbols" => &1.question.library.external.symbols
-                    }
+                    },
+                    "execTimeMs" => &1.question.library.exec_time_ms,
+                    "variant" => &1.question.library.variant
                   },
                   "maxXp" => &1.question.max_xp,
                   "content" => &1.question.question.content,
@@ -305,7 +307,9 @@ defmodule CadetWeb.AdminGradingControllerTest do
                     "external" => %{
                       "name" => "#{&1.question.library.external.name}",
                       "symbols" => &1.question.library.external.symbols
-                    }
+                    },
+                    "execTimeMs" => &1.question.library.exec_time_ms,
+                    "variant" => &1.question.library.variant
                   },
                   "maxXp" => &1.question.max_xp,
                   "content" => &1.question.question.content,
@@ -352,7 +356,9 @@ defmodule CadetWeb.AdminGradingControllerTest do
                     "external" => %{
                       "name" => "#{&1.question.library.external.name}",
                       "symbols" => &1.question.library.external.symbols
-                    }
+                    },
+                    "execTimeMs" => &1.question.library.exec_time_ms,
+                    "variant" => &1.question.library.variant
                   },
                   "maxXp" => &1.question.max_xp,
                   "content" => &1.question.question.content,
@@ -902,7 +908,9 @@ defmodule CadetWeb.AdminGradingControllerTest do
                     "external" => %{
                       "name" => "#{&1.question.library.external.name}",
                       "symbols" => &1.question.library.external.symbols
-                    }
+                    },
+                    "execTimeMs" => &1.question.library.exec_time_ms,
+                    "variant" => &1.question.library.variant
                   },
                   "maxXp" => &1.question.max_xp,
                   "content" => &1.question.question.content,
@@ -939,7 +947,9 @@ defmodule CadetWeb.AdminGradingControllerTest do
                     "external" => %{
                       "name" => "#{&1.question.library.external.name}",
                       "symbols" => &1.question.library.external.symbols
-                    }
+                    },
+                    "execTimeMs" => &1.question.library.exec_time_ms,
+                    "variant" => &1.question.library.variant
                   },
                   "content" => &1.question.question.content,
                   "answer" => &1.answer.choice_id,
@@ -986,7 +996,9 @@ defmodule CadetWeb.AdminGradingControllerTest do
                     "external" => %{
                       "name" => "#{&1.question.library.external.name}",
                       "symbols" => &1.question.library.external.symbols
-                    }
+                    },
+                    "execTimeMs" => &1.question.library.exec_time_ms,
+                    "variant" => &1.question.library.variant
                   },
                   "maxXp" => &1.question.max_xp,
                   "content" => &1.question.question.content,
diff --git a/test/factories/assessments/library_factory.ex b/test/factories/assessments/library_factory.ex
index 29d73db3f..e0eab6a9e 100644
--- a/test/factories/assessments/library_factory.ex
+++ b/test/factories/assessments/library_factory.ex
@@ -9,7 +9,7 @@ defmodule Cadet.Assessments.LibraryFactory do
 
       def library_factory do
         %{
-          chapter: Enum.random(1..20),
+          chapter: Enum.random(1..4),
           globals:
             Enum.reduce(
               0..5,