diff --git a/cmake/dotnet.cmake b/cmake/dotnet.cmake
index 16cbf47215..a0978c5b2d 100644
--- a/cmake/dotnet.cmake
+++ b/cmake/dotnet.cmake
@@ -67,6 +67,10 @@ message(STATUS ".Net runtime project: ${DOTNET_NATIVE_PROJECT}")
 set(DOTNET_NATIVE_PROJECT_DIR ${PROJECT_BINARY_DIR}/dotnet/${DOTNET_NATIVE_PROJECT})
 message(STATUS ".Net runtime project build path: ${DOTNET_NATIVE_PROJECT_DIR}")
 
+# Language Version
+# see: https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/configure-language-version
+set(DOTNET_LANG "9.0")
+message(STATUS ".Net C# language version: ${DOTNET_LANG}")
 # see: Platform
 if(CMAKE_SYSTEM_PROCESSOR MATCHES "^(aarch64|arm64)")
   set(DOTNET_PLATFORM arm64)
diff --git a/makefiles/Makefile.dotnet.mk b/makefiles/Makefile.dotnet.mk
index 850e54786c..770730cc8a 100644
--- a/makefiles/Makefile.dotnet.mk
+++ b/makefiles/Makefile.dotnet.mk
@@ -108,6 +108,8 @@ $(TEMP_DOTNET_DIR)/$1/%/%.csproj: \
 	$(SED) -e "s/@DOTNET_PACKAGES_DIR@/..\/..\/..\/$(BUILD_DIR)\/dotnet\/packages/" \
  ortools$Sdotnet$SSample.csproj.in \
  > $(TEMP_DOTNET_DIR)$S$1$S$$*$S$$*.csproj
+	$(SED) -i -e 's/@DOTNET_LANG@/9.0/' \
+ $(TEMP_DOTNET_DIR)$S$1$S$$*$S$$*.csproj
 ifeq ($(USE_DOTNET_6)_$(USE_DOTNET_CORE_31),ON_ON)
 	$(SED) -i -e 's/@DOTNET_TFM@/<TargetFrameworks>netcoreapp3.1;net6.0<\/TargetFrameworks>/' \
  $(TEMP_DOTNET_DIR)$S$1$S$$*$S$$*.csproj
@@ -178,6 +180,8 @@ $(TEMP_DOTNET_DIR)/$1/%/%.csproj: \
 	$(SED) -e "s/@DOTNET_PACKAGES_DIR@/..\/..\/..\/$(BUILD_DIR)\/dotnet\/packages/" \
  ortools$Sdotnet$SSample.csproj.in \
  > $(TEMP_DOTNET_DIR)$S$1$S$$*$S$$*.csproj
+	$(SED) -i -e 's/@DOTNET_LANG@/9.0/' \
+ $(TEMP_DOTNET_DIR)$S$1$S$$*$S$$*.csproj
 ifeq ($(USE_DOTNET_6)_$(USE_DOTNET_CORE_31),ON_ON)
 	$(SED) -i -e 's/@DOTNET_TFM@/<TargetFrameworks>netcoreapp3.1;net6.0<\/TargetFrameworks>/' \
  $(TEMP_DOTNET_DIR)$S$1$S$$*$S$$*.csproj
@@ -245,6 +249,8 @@ $(TEMP_DOTNET_DIR)/$1/%/%.csproj: \
 	$(SED) -e "s/@DOTNET_PACKAGES_DIR@/..\/..\/..\/$(BUILD_DIR)\/dotnet\/packages/" \
  ortools$Sdotnet$STest.csproj.in \
  > $(TEMP_DOTNET_DIR)$S$1$S$$*$S$$*.csproj
+	$(SED) -i -e 's/@DOTNET_LANG@/9.0/' \
+ $(TEMP_DOTNET_DIR)$S$1$S$$*$S$$*.csproj
 ifeq ($(USE_DOTNET_6)_$(USE_DOTNET_CORE_31),ON_ON)
 	$(SED) -i -e 's/@DOTNET_TFM@/<TargetFrameworks>netcoreapp3.1;net6.0<\/TargetFrameworks>/' \
  $(TEMP_DOTNET_DIR)$S$1$S$$*$S$$*.csproj
@@ -646,6 +652,8 @@ $(TEMP_DOTNET_DIR)/ortools_examples/examples/dotnet/%.csproj: \
 	$(SED) -i -e 's/@PROJECT_VERSION_PATCH@/$(OR_TOOLS_PATCH)/' \
  $(TEMP_DOTNET_DIR)$Sortools_examples$Sexamples$Sdotnet$S$$*.csproj
 	$(SED) -i -e 's/@DOTNET_PACKAGES_DIR@/./' \
+ $(TEMP_DOTNET_DIR)$Sortools_examples$Sexamples$Sdotnet$S$$*.csproj
+	$(SED) -i -e 's/@DOTNET_LANG@/9.0/' \
  $(TEMP_DOTNET_DIR)$Sortools_examples$Sexamples$Sdotnet$S$$*.csproj
 	$(SED) -i -e 's/@DOTNET_TFM@/<TargetFrameworks>netcoreapp3.1;net6.0<\/TargetFrameworks>/' \
  $(TEMP_DOTNET_DIR)$Sortools_examples$Sexamples$Sdotnet$S$$*.csproj
@@ -677,6 +685,8 @@ $(TEMP_DOTNET_DIR)/ortools_examples/examples/dotnet/%.csproj: \
 	$(SED) -i -e 's/@PROJECT_VERSION_PATCH@/$(OR_TOOLS_PATCH)/' \
  $(TEMP_DOTNET_DIR)$Sortools_examples$Sexamples$Sdotnet$S$$*.csproj
 	$(SED) -i -e 's/@DOTNET_PACKAGES_DIR@/./' \
+ $(TEMP_DOTNET_DIR)$Sortools_examples$Sexamples$Sdotnet$S$$*.csproj
+	$(SED) -i -e 's/@DOTNET_LANG@/9.0/' \
  $(TEMP_DOTNET_DIR)$Sortools_examples$Sexamples$Sdotnet$S$$*.csproj
 	$(SED) -i -e 's/@DOTNET_TFM@/<TargetFrameworks>netcoreapp3.1;net6.0<\/TargetFrameworks>/' \
  $(TEMP_DOTNET_DIR)$Sortools_examples$Sexamples$Sdotnet$S$$*.csproj
diff --git a/ortools/dotnet/Google.OrTools-full.csproj.in b/ortools/dotnet/Google.OrTools-full.csproj.in
index 0273979cd0..9562248be2 100644
--- a/ortools/dotnet/Google.OrTools-full.csproj.in
+++ b/ortools/dotnet/Google.OrTools-full.csproj.in
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <OutputType>Library</OutputType>
-    <LangVersion>9.0</LangVersion>
+    <LangVersion>@DOTNET_LANG@</LangVersion>
     @DOTNET_TFM@
     <RuntimeIdentifiers>linux-x64;osx-x64;win-x64;linux-arm64;osx-arm64</RuntimeIdentifiers>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
diff --git a/ortools/dotnet/Google.OrTools-local.csproj.in b/ortools/dotnet/Google.OrTools-local.csproj.in
index b096480696..25c053b7c7 100644
--- a/ortools/dotnet/Google.OrTools-local.csproj.in
+++ b/ortools/dotnet/Google.OrTools-local.csproj.in
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <OutputType>Library</OutputType>
-    <LangVersion>9.0</LangVersion>
+    <LangVersion>@DOTNET_LANG@</LangVersion>
     @DOTNET_TFM@
     <RuntimeIdentifier>@RUNTIME_IDENTIFIER@</RuntimeIdentifier>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
diff --git a/ortools/dotnet/Test.csproj.in b/ortools/dotnet/Test.csproj.in
index 4385fb72c4..48b486f4c2 100644
--- a/ortools/dotnet/Test.csproj.in
+++ b/ortools/dotnet/Test.csproj.in
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <LangVersion>8.0</LangVersion>
+    <LangVersion>@DOTNET_LANG@</LangVersion>
     @DOTNET_TFM@
     <EnableDefaultItems>false</EnableDefaultItems>
     <EnableDefaultCompileItems>false</EnableDefaultCompileItems>