diff --git a/ci/build.linux.gitlab-ci.yml b/ci/build.linux.gitlab-ci.yml
index 198c01f67..e0075eaa8 100644
--- a/ci/build.linux.gitlab-ci.yml
+++ b/ci/build.linux.gitlab-ci.yml
@@ -98,6 +98,21 @@ build:linux:cross:x86-64:clang-19:generic:avx512dq:
     EIGEN_CI_ADDITIONAL_ARGS: >
       -DEIGEN_TEST_CUSTOM_CXX_FLAGS=-mfma;-mavx512dq;-DEIGEN_VECTORIZE_GENERIC=1
 
+# Nightly full test suite in C++20 mode.
+build:linux:cross:x86-64:clang-19:cxx20:nightly:
+  extends: .build:linux:cross:x86-64
+  image: ubuntu:24.04
+  variables:
+    EIGEN_CI_INSTALL: clang-19
+    EIGEN_CI_C_COMPILER: clang-19
+    EIGEN_CI_CXX_COMPILER: clang++-19
+    EIGEN_CI_CROSS_INSTALL: g++-14-x86-64-linux-gnu clang-19
+    EIGEN_CI_ADDITIONAL_ARGS: -DCMAKE_CXX_STANDARD=20
+  rules:
+    - if: $CI_PIPELINE_SOURCE == "schedule" && $CI_PROJECT_NAMESPACE == "libeigen" && $CI_COMMIT_BRANCH == $CI_DEFAULT_BRANCH
+    - if: $CI_PIPELINE_SOURCE == "web" && $CI_PROJECT_NAMESPACE == "libeigen"
+    - if: $CI_PIPELINE_SOURCE == "merge_request_event" && $CI_PROJECT_NAMESPACE == "libeigen" && $CI_MERGE_REQUEST_LABELS =~ "/all-tests/"
+
 build:linux:docs:
   extends: .build:linux:cross
   variables:
diff --git a/ci/test.linux.gitlab-ci.yml b/ci/test.linux.gitlab-ci.yml
index f7f312198..1d2a25176 100644
--- a/ci/test.linux.gitlab-ci.yml
+++ b/ci/test.linux.gitlab-ci.yml
@@ -202,6 +202,27 @@ test:linux:x86-64:clang-19:generic:avx512dq:unsupported:
   variables:
     EIGEN_CI_CTEST_LABEL: Unsupported
 
+.test:linux:x86-64:clang-19:cxx20:nightly:
+  image: ubuntu:24.04
+  extends: .test:linux:x86-64
+  needs: [ build:linux:cross:x86-64:clang-19:cxx20:nightly ]
+  variables:
+    EIGEN_CI_INSTALL: clang-19
+  rules:
+    - if: $CI_PIPELINE_SOURCE == "schedule" && $CI_PROJECT_NAMESPACE == "libeigen" && $CI_COMMIT_BRANCH == $CI_DEFAULT_BRANCH
+    - if: $CI_PIPELINE_SOURCE == "web" && $CI_PROJECT_NAMESPACE == "libeigen"
+    - if: $CI_PIPELINE_SOURCE == "merge_request_event" && $CI_PROJECT_NAMESPACE == "libeigen" && $CI_MERGE_REQUEST_LABELS =~ "/all-tests/"
+
+test:linux:x86-64:clang-19:cxx20:nightly:official:
+  extends: .test:linux:x86-64:clang-19:cxx20:nightly
+  variables:
+    EIGEN_CI_CTEST_LABEL: Official
+
+test:linux:x86-64:clang-19:cxx20:nightly:unsupported:
+  extends: .test:linux:x86-64:clang-19:cxx20:nightly
+  variables:
+    EIGEN_CI_CTEST_LABEL: Unsupported
+
 ##### Sanitizers ###############################################################
 
 .test:linux:x86-64:clang-19:default:asan-ubsan: