diff --git a/subprojects/sim/include/sim/submissions/old_submission.hh b/subprojects/sim/include/sim/submissions/old_submission.hh
index 058445b5..1bafb87a 100644
--- a/subprojects/sim/include/sim/submissions/old_submission.hh
+++ b/subprojects/sim/include/sim/submissions/old_submission.hh
@@ -35,6 +35,7 @@ struct OldSubmission {
         (PYTHON, 5, "python")
         (RUST, 6, "rust")
         (CPP20, 7, "cpp20")
+        (CPP23, 8, "cpp23")
     );
 
     // Initial and final values may be combined, but special not
@@ -96,6 +97,7 @@ constexpr const char* to_string(OldSubmission::Language x) {
     case OldSubmission::Language::CPP14: return "C++14";
     case OldSubmission::Language::CPP17: return "C++17";
     case OldSubmission::Language::CPP20: return "C++20";
+    case OldSubmission::Language::CPP23: return "C++23";
     case OldSubmission::Language::PASCAL: return "Pascal";
     case OldSubmission::Language::PYTHON: return "Python";
     case OldSubmission::Language::RUST: return "Rust";
@@ -109,7 +111,8 @@ constexpr const char* to_extension(OldSubmission::Language x) {
     case OldSubmission::Language::CPP11:
     case OldSubmission::Language::CPP14:
     case OldSubmission::Language::CPP17:
-    case OldSubmission::Language::CPP20: return ".cpp";
+    case OldSubmission::Language::CPP20:
+    case OldSubmission::Language::CPP23: return ".cpp";
     case OldSubmission::Language::PASCAL: return ".pas";
     case OldSubmission::Language::PYTHON: return ".py";
     case OldSubmission::Language::RUST: return ".rs";
@@ -123,7 +126,8 @@ constexpr const char* to_mime(OldSubmission::Language x) {
     case OldSubmission::Language::CPP11:
     case OldSubmission::Language::CPP14:
     case OldSubmission::Language::CPP17:
-    case OldSubmission::Language::CPP20: return "text/x-c++src";
+    case OldSubmission::Language::CPP20:
+    case OldSubmission::Language::CPP23: return "text/x-c++src";
     case OldSubmission::Language::PASCAL: return "text/x-pascal";
     case OldSubmission::Language::PYTHON: return "text/x-python";
     case OldSubmission::Language::RUST: return "text/x-rust";
diff --git a/subprojects/sim/include/sim/submissions/submission.hh b/subprojects/sim/include/sim/submissions/submission.hh
index c43dea8d..a3bfd031 100644
--- a/subprojects/sim/include/sim/submissions/submission.hh
+++ b/subprojects/sim/include/sim/submissions/submission.hh
@@ -31,6 +31,7 @@ struct Submission {
         (PYTHON, 5, "python")
         (RUST, 6, "rust")
         (CPP20, 7, "cpp20")
+        (CPP23, 8, "cpp23")
     );
 
     // Initial and final values may be combined, but special not
diff --git a/subprojects/sim/src/job_server/job_handlers/add_or_reupload_problem/add_or_reupload_problem.cc b/subprojects/sim/src/job_server/job_handlers/add_or_reupload_problem/add_or_reupload_problem.cc
index a8786c84..4ce6f1c5 100644
--- a/subprojects/sim/src/job_server/job_handlers/add_or_reupload_problem/add_or_reupload_problem.cc
+++ b/subprojects/sim/src/job_server/job_handlers/add_or_reupload_problem/add_or_reupload_problem.cc
@@ -185,6 +185,7 @@ std::vector<FileRemover> submit_solutions(
             case sim::SolutionLanguage::CPP14: return Submission::Language::CPP14;
             case sim::SolutionLanguage::CPP17: return Submission::Language::CPP17;
             case sim::SolutionLanguage::CPP20: return Submission::Language::CPP20;
+            case sim::SolutionLanguage::CPP23: return Submission::Language::CPP23;
             case sim::SolutionLanguage::PASCAL: return Submission::Language::PASCAL;
             case sim::SolutionLanguage::PYTHON: return Submission::Language::PYTHON;
             case sim::SolutionLanguage::RUST: return Submission::Language::RUST;
diff --git a/subprojects/sim/src/job_server/job_handlers/judge_or_rejudge_submission.cc b/subprojects/sim/src/job_server/job_handlers/judge_or_rejudge_submission.cc
index 432f8144..b428feb4 100644
--- a/subprojects/sim/src/job_server/job_handlers/judge_or_rejudge_submission.cc
+++ b/subprojects/sim/src/job_server/job_handlers/judge_or_rejudge_submission.cc
@@ -149,6 +149,7 @@ void judge_or_rejudge_submission(
         case Submission::Language::CPP14: return sim::SolutionLanguage::CPP14;
         case Submission::Language::CPP17: return sim::SolutionLanguage::CPP17;
         case Submission::Language::CPP20: return sim::SolutionLanguage::CPP20;
+        case Submission::Language::CPP23: return sim::SolutionLanguage::CPP23;
         case Submission::Language::PASCAL: return sim::SolutionLanguage::PASCAL;
         case Submission::Language::PYTHON: return sim::SolutionLanguage::PYTHON;
         case Submission::Language::RUST: return sim::SolutionLanguage::RUST;
diff --git a/subprojects/sim/src/web_server/old/submissions_api.cc b/subprojects/sim/src/web_server/old/submissions_api.cc
index 0b9dc0c1..4d8ba85c 100644
--- a/subprojects/sim/src/web_server/old/submissions_api.cc
+++ b/subprojects/sim/src/web_server/old/submissions_api.cc
@@ -902,6 +902,8 @@ void Sim::api_submission_add() {
         slang = OldSubmission::Language::CPP17;
     } else if (slang_str == "cpp20") {
         slang = OldSubmission::Language::CPP20;
+    } else if (slang_str == "cpp23") {
+        slang = OldSubmission::Language::CPP23;
     } else if (slang_str == "pascal") {
         slang = OldSubmission::Language::PASCAL;
     } else if (slang_str == "python") {
diff --git a/subprojects/sim/src/web_server/static/kit/scripts.js b/subprojects/sim/src/web_server/static/kit/scripts.js
index b620f005..8ca64315 100644
--- a/subprojects/sim/src/web_server/static/kit/scripts.js
+++ b/subprojects/sim/src/web_server/static/kit/scripts.js
@@ -2061,6 +2061,7 @@ function submission_language_to_user_string(submission_language) {
 		case 'python': return 'Python';
 		case 'rust': return 'Rust';
 		case 'cpp20': return 'C++20';
+		case 'cpp23': return 'C++23';
 		default: assert(false, 'unexpected submission_language: ' + submission_language);
 	}
 }
@@ -4579,6 +4580,9 @@ function add_submission_impl(as_oldmodal, url, api_url, problem_field_elem, mayb
 					}).add('<option>', {
 						value: 'cpp20',
 						text: 'C++20',
+					}).add('<option>', {
+						value: 'cpp23',
+						text: 'C++23',
 						selected: true
 					}).add('<option>', {
 						value: 'pascal',
diff --git a/subprojects/simlib/include/simlib/sim/judge_worker.hh b/subprojects/simlib/include/simlib/sim/judge_worker.hh
index 9013918c..020a9f1c 100644
--- a/subprojects/simlib/include/simlib/sim/judge_worker.hh
+++ b/subprojects/simlib/include/simlib/sim/judge_worker.hh
@@ -156,7 +156,8 @@ enum class SolutionLanguage {
     CPP14,
     CPP17,
     CPP20,
-    CPP = CPP20,
+    CPP23,
+    CPP = CPP23,
     PASCAL,
     PYTHON,
     RUST,
@@ -192,7 +193,8 @@ inline SolutionLanguage filename_to_lang(const StringView& filename) {
         return res;
     case SolutionLanguage::CPP11:
     case SolutionLanguage::CPP14:
-    case SolutionLanguage::CPP17: break;
+    case SolutionLanguage::CPP17:
+    case SolutionLanguage::CPP20: break;
     }
 
     THROW("Should not reach here");
diff --git a/subprojects/simlib/src/sim/judge_worker.cc b/subprojects/simlib/src/sim/judge_worker.cc
index 7165e80e..b5bcfe68 100644
--- a/subprojects/simlib/src/sim/judge_worker.cc
+++ b/subprojects/simlib/src/sim/judge_worker.cc
@@ -124,6 +124,11 @@ std::unique_ptr<judge::language_suite::Suite> lang_to_suite(SolutionLanguage lan
             judge::language_suite::Cpp_GCC::Standard::Cpp20
         );
     } break;
+    case SolutionLanguage::CPP23: {
+        return std::make_unique<judge::language_suite::Cpp_GCC>(
+            judge::language_suite::Cpp_GCC::Standard::Cpp23
+        );
+    } break;
     case SolutionLanguage::PASCAL: {
         return std::make_unique<judge::language_suite::Pascal>();
     } break;
diff --git a/subprojects/simlib/test/sim/judge/language_suite/cpp_clang.cc b/subprojects/simlib/test/sim/judge/language_suite/cpp_clang.cc
index ad4069ad..5649d6d0 100644
--- a/subprojects/simlib/test/sim/judge/language_suite/cpp_clang.cc
+++ b/subprojects/simlib/test/sim/judge/language_suite/cpp_clang.cc
@@ -21,7 +21,7 @@ int main() {
 )";
 
 // NOLINTNEXTLINE
-TEST(sim_judge_compiler, cpp_clang) {
+TEST(sim_judge_compiler, cpp_clang_cpp20) {
     auto suite = Cpp_Clang{Cpp_Clang::Standard::Cpp20};
     ASSERT_EQ(suite.is_supported(), path_exists("/usr/bin/clang++"));
     if (suite.is_supported()) {
@@ -30,3 +30,14 @@ TEST(sim_judge_compiler, cpp_clang) {
         );
     }
 }
+
+// NOLINTNEXTLINE
+TEST(sim_judge_compiler, cpp_clang_cpp23) {
+    auto suite = Cpp_Clang{Cpp_Clang::Standard::Cpp23};
+    ASSERT_EQ(suite.is_supported(), path_exists("/usr/bin/clang++"));
+    if (suite.is_supported()) {
+        test_compiled_language_suite(
+            suite, test_prog_ok, test_prog_invalid, "error: use of undeclared identifier 'p'"
+        );
+    }
+}
diff --git a/subprojects/simlib/test/sim/judge/language_suite/cpp_gcc.cc b/subprojects/simlib/test/sim/judge/language_suite/cpp_gcc.cc
index 3a6ca71b..e9cb16f8 100644
--- a/subprojects/simlib/test/sim/judge/language_suite/cpp_gcc.cc
+++ b/subprojects/simlib/test/sim/judge/language_suite/cpp_gcc.cc
@@ -21,7 +21,7 @@ int main() {
 )";
 
 // NOLINTNEXTLINE
-TEST(sim_judge_compiler, cpp_gcc) {
+TEST(sim_judge_compiler, cpp_gcc_cpp20) {
     auto suite = Cpp_GCC{Cpp_GCC::Standard::Cpp20};
     ASSERT_EQ(suite.is_supported(), path_exists("/usr/bin/g++"));
     if (suite.is_supported()) {
@@ -30,3 +30,14 @@ TEST(sim_judge_compiler, cpp_gcc) {
         );
     }
 }
+
+// NOLINTNEXTLINE
+TEST(sim_judge_compiler, cpp_gcc_cpp23) {
+    auto suite = Cpp_GCC{Cpp_GCC::Standard::Cpp23};
+    ASSERT_EQ(suite.is_supported(), path_exists("/usr/bin/g++"));
+    if (suite.is_supported()) {
+        test_compiled_language_suite(
+            suite, test_prog_ok, test_prog_invalid, "error: 'p' was not declared in this scope"
+        );
+    }
+}