ci: use LLVM 21

diff --git a/ci/test/00_setup_env_native_asan.sh b/ci/test/00_setup_env_native_asan.sh
index f750338a..a6f73854 100755
--- a/ci/test/00_setup_env_native_asan.sh
+++ b/ci/test/00_setup_env_native_asan.sh
@@ -19,7 +19,7 @@ else
 fi
 
 export CONTAINER_NAME=ci_native_asan
-export APT_LLVM_V="20"
+export APT_LLVM_V="21"
 export PACKAGES="systemtap-sdt-dev clang-${APT_LLVM_V} llvm-${APT_LLVM_V} libclang-rt-${APT_LLVM_V}-dev python3-zmq qt6-base-dev qt6-tools-dev qt6-l10n-tools libevent-dev libboost-dev libzmq3-dev libqrencode-dev libsqlite3-dev ${BPFCC_PACKAGE} libcapnp-dev capnproto"
 export NO_DEPENDS=1
 export GOAL="install"
diff --git a/ci/test/00_setup_env_native_fuzz.sh b/ci/test/00_setup_env_native_fuzz.sh
index fc0c6b78..b3ad36a8 100755
--- a/ci/test/00_setup_env_native_fuzz.sh
+++ b/ci/test/00_setup_env_native_fuzz.sh
@@ -8,7 +8,7 @@ export LC_ALL=C.UTF-8
 
 export CI_IMAGE_NAME_TAG="mirror.gcr.io/ubuntu:24.04"
 export CONTAINER_NAME=ci_native_fuzz
-export APT_LLVM_V="20"
+export APT_LLVM_V="21"
 export PACKAGES="clang-${APT_LLVM_V} llvm-${APT_LLVM_V} libclang-rt-${APT_LLVM_V}-dev libevent-dev libboost-dev libsqlite3-dev libcapnp-dev capnproto"
 export NO_DEPENDS=1
 export RUN_UNIT_TESTS=false
diff --git a/ci/test/00_setup_env_native_msan.sh b/ci/test/00_setup_env_native_msan.sh
index 80b25988..17ac78b4 100755
--- a/ci/test/00_setup_env_native_msan.sh
+++ b/ci/test/00_setup_env_native_msan.sh
@@ -7,7 +7,7 @@
 export LC_ALL=C.UTF-8
 
 export CI_IMAGE_NAME_TAG="mirror.gcr.io/ubuntu:24.04"
-export APT_LLVM_V="20"
+export APT_LLVM_V="21"
 LIBCXX_DIR="/cxx_build/"
 export MSAN_FLAGS="-fsanitize=memory -fsanitize-memory-track-origins=2 -fno-omit-frame-pointer -g -O1 -fno-optimize-sibling-calls"
 LIBCXX_FLAGS="-nostdinc++ -nostdlib++ -isystem ${LIBCXX_DIR}include/c++/v1 -L${LIBCXX_DIR}lib -Wl,-rpath,${LIBCXX_DIR}lib -lc++ -lc++abi -lpthread -Wno-unused-command-line-argument"
diff --git a/ci/test/00_setup_env_native_tsan.sh b/ci/test/00_setup_env_native_tsan.sh
index 2079ca73..3871c37f 100755
--- a/ci/test/00_setup_env_native_tsan.sh
+++ b/ci/test/00_setup_env_native_tsan.sh
@@ -8,7 +8,7 @@ export LC_ALL=C.UTF-8
 
 export CONTAINER_NAME=ci_native_tsan
 export CI_IMAGE_NAME_TAG="mirror.gcr.io/ubuntu:24.04"
-export APT_LLVM_V="20"
+export APT_LLVM_V="21"
 LIBCXX_DIR="/cxx_build/"
 LIBCXX_FLAGS="-fsanitize=thread -nostdinc++ -nostdlib++ -isystem ${LIBCXX_DIR}include/c++/v1 -L${LIBCXX_DIR}lib -Wl,-rpath,${LIBCXX_DIR}lib -lc++ -lc++abi -lpthread -Wno-unused-command-line-argument"
 export PACKAGES="clang-${APT_LLVM_V} llvm-${APT_LLVM_V} llvm-${APT_LLVM_V}-dev libclang-${APT_LLVM_V}-dev libclang-rt-${APT_LLVM_V}-dev python3-zmq"
diff --git a/ci/test/01_base_install.sh b/ci/test/01_base_install.sh
index b68dc778..b1a9d625 100755
--- a/ci/test/01_base_install.sh
+++ b/ci/test/01_base_install.sh
@@ -59,7 +59,7 @@ if [[ -n "${USE_INSTRUMENTED_LIBCPP}" ]]; then
   if [ -n "${APT_LLVM_V}" ]; then
     ${CI_RETRY_EXE} git clone --depth=1 https://github.com/llvm/llvm-project -b "llvmorg-$( clang --version | sed --silent 's@.*clang version \([0-9.]*\).*@\1@p' )" /llvm-project
   else
-    ${CI_RETRY_EXE} git clone --depth=1 https://github.com/llvm/llvm-project -b "llvmorg-20.1.8" /llvm-project
+    ${CI_RETRY_EXE} git clone --depth=1 https://github.com/llvm/llvm-project -b "llvmorg-21.1.0" /llvm-project
 
     cmake -G Ninja -B /clang_build/ \
       -DLLVM_ENABLE_PROJECTS="clang" \