diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index a13ddec59..0bb0605b7 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -236,6 +236,30 @@ jobs:
             setenvs: export BUILDTARGET=clang-format
                             OPENIMAGEIO_CMAKE_FLAGS=-DUSE_PYTHON=0
 
+          # Test ABI stability. `abi_check` is the version or commit that we
+          # believe is the current standard against which we don't want to
+          # break the ABI. Basically, we will build that version as well as
+          # the current one, and compare the resulting libraries.
+          - desc: abi check
+            nametag: linux-vfx2023
+            runner: ubuntu-latest
+            container: aswftesting/ci-osl:2023-clang15
+            vfxyear: 2023
+            cc_compiler: gcc
+            cxx_compiler: g++
+            cxx_std: 17
+            # openimageio_ver: release
+            python_ver: "3.10"
+            simd: "avx2,f16c"
+            batched: b8_AVX2
+            fmt_ver: 10.1.1
+            pybind11_ver: v2.10.0
+            skip_tests: 1
+            abi_check: 8374278a07d88358a6931dc2492f98ca49b21038
+            setenvs: export OSL_CMAKE_FLAGS="-DOSL_BUILD_TESTS=0 -DBUILD_TESTING=OFF -DUSE_QT=0"
+                            OPENIMAGEIO_CMAKE_FLAGS="-DUSE_PYTHON=0"
+                            CMAKE_BUILD_TYPE=RelWithDebInfo
+
     runs-on: ${{matrix.runner}}
     container:
         image: ${{ matrix.container }}
@@ -250,6 +274,7 @@ jobs:
       PYTHON_VERSION: ${{matrix.python_ver}}
       USE_BATCHED: ${{matrix.batched}}
       USE_SIMD: ${{matrix.simd}}
+      ABI_CHECK: ${{matrix.abi_check}}
     steps:
       # We would like to use harden-runner, but it flags too many false
       # positives, every time we download a dependency. We should use it only
@@ -290,11 +315,31 @@ jobs:
       - name: Testsuite
         if: matrix.skip_tests != '1'
         run: src/build-scripts/ci-test.bash
+      - name: Check out ABI standard
+        if: matrix.abi_check != ''
+        uses: actions/checkout@3df4ab11eba7bda6032a0b82a6bb43b11571feac # v4.0.0
+        with:
+          ref: ${{matrix.abi_check}}
+          path: abi_standard
+      - name: Build ABI standard
+        if: matrix.abi_check != ''
+        run: |
+            mkdir -p abi_standard/build
+            pushd abi_standard
+            src/build-scripts/ci-build.bash
+            popd
+      - name: Check ABI
+        if: matrix.abi_check != ''
+        run: |
+            src/build-scripts/ci-abicheck.bash ./build abi_standard/build \
+                  liboslexec liboslcomp liboslquery liboslnoise
       - uses: actions/upload-artifact@3cea5372237819ed00197afe530f5a7ea3e805c8 # v3.1.0
         if: failure()
         with:
           name: osl-${{github.job}}-${{matrix.nametag}}
           path: |
+            build/cmake-save
+            build/compat_reports
             build/*.cmake
             build/CMake*
             build/testsuite/*/*.*
@@ -433,6 +478,7 @@ jobs:
         with:
           name: osl-${{github.job}}-${{matrix.nametag}}
           path: |
+            build/cmake-save
             build/*.cmake
             build/CMake*
             build/testsuite/*/*.*
@@ -520,6 +566,7 @@ jobs:
         with:
           name: osl-${{github.job}}-${{matrix.nametag}}
           path: |
+            build/cmake-save
             build/*.cmake
             build/CMake*
             build/testsuite/*/*.*
diff --git a/CMakeLists.txt b/CMakeLists.txt
index a0e49d01e..efb21ca13 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -219,7 +219,7 @@ add_subdirectory (src/liboslnoise)
 add_subdirectory (src/oslc)
 add_subdirectory (src/oslinfo)
 
-if (OSL_BUILD_TESTS)
+if (OSL_BUILD_TESTS AND BUILD_TESTING)
     add_subdirectory (src/testshade)
     add_subdirectory (src/testrender)
 endif ()
@@ -228,7 +228,7 @@ if (OSL_BUILD_PLUGINS)
     add_subdirectory (src/osl.imageio)
 endif ()
 
-if (USE_QT AND (Qt5_FOUND OR Qt6_FOUND))
+if (USE_QT AND (Qt5_FOUND OR Qt6_FOUND) AND NOT DISABLE_OSLTOY)
     add_subdirectory (src/osltoy)
 endif ()
 
@@ -309,7 +309,7 @@ install (EXPORT OSL_EXPORTED_TARGETS
         FILE ${OSL_TARGETS_EXPORT_NAME}
         NAMESPACE ${PROJECT_NAME}::)
 
-if (${PROJECT_NAME}_BUILD_TESTS AND PROJECT_IS_TOP_LEVEL)
+if (PROJECT_IS_TOP_LEVEL AND BUILD_TESTING AND ${PROJECT_NAME}_BUILD_TESTS)
 	osl_add_all_tests()
 endif ()
 
diff --git a/src/build-scripts/build_abi_tools.bash b/src/build-scripts/build_abi_tools.bash
new file mode 100755
index 000000000..1b9e8c8ad
--- /dev/null
+++ b/src/build-scripts/build_abi_tools.bash
@@ -0,0 +1,31 @@
+#!/usr/bin/env bash
+
+# Utility script to download and build abi checking tools
+#
+# Copyright Contributors to the Open Shading Language project.
+# SPDX-License-Identifier: BSD-3-Clause
+# https://github.com/AcademySoftwareFoundation/OpenShadingLanguage
+
+# Exit the whole script if any command fails.
+set -ex
+
+# Where to install the final results
+: ${LOCAL_DEPS_DIR:=${PWD}/ext}
+: ${ABITOOLS_INSTALL_DIR:=${LOCAL_DEPS_DIR}/dist}
+
+mkdir -p ${LOCAL_DEPS_DIR}
+pushd ${LOCAL_DEPS_DIR}
+
+git clone https://github.com/lvc/vtable-dumper
+pushd vtable-dumper ; make install prefix=${ABITOOLS_INSTALL_DIR} ; popd
+
+git clone https://github.com/lvc/abi-dumper
+pushd abi-dumper ; make install prefix=${ABITOOLS_INSTALL_DIR} ; popd
+
+git clone https://github.com/lvc/abi-compliance-checker
+pushd abi-compliance-checker ; make install prefix=${ABITOOLS_INSTALL_DIR} ; popd
+
+popd
+
+# ls -R ${LOCAL_DEPS_DIR}
+export PATH=${PATH}:${ABITOOLS_INSTALL_DIR}/bin
diff --git a/src/build-scripts/ci-abicheck.bash b/src/build-scripts/ci-abicheck.bash
new file mode 100755
index 000000000..9d52dd633
--- /dev/null
+++ b/src/build-scripts/ci-abicheck.bash
@@ -0,0 +1,54 @@
+#!/usr/bin/env bash
+
+# Copyright Contributors to the Open Shading Language project.
+# SPDX-License-Identifier: BSD-3-Clause
+# https://github.com/AcademySoftwareFoundation/OpenShadingLanguage
+
+# Important: set -ex causes this whole script to terminate with error if
+# any command in it fails. This is crucial for CI tests.
+set -e
+
+# Arguments to this script are: 
+#      BUILDDIR_NEW BUILDDIR_OLD LIBRARIES...
+
+BUILDDIR_NEW=$1
+shift
+BUILDDIR_OLD=$1
+shift
+LIBS=$*
+
+#
+# First, create ABI dumps from both builds
+#
+ABI_ARGS="-bin-only -skip-cxx -public-headers $PWD/dist/include/OSL "
+echo "ABI_CHECK: PWD=${PWD} "
+ls -l $BUILDDIR_NEW
+ls -l $BUILDDIR_OLD
+for dir in $BUILDDIR_NEW $BUILDDIR_OLD ; do
+    for lib in $LIBS ; do
+        abi-dumper $ABI_ARGS ${dir}/lib/${lib}.so -o ${dir}/abi-${lib}.dump
+    done
+done
+echo "Saved ABI dumps"
+
+#
+# Run the ABI compliance checker, saving the outputs to files
+#
+for lib in $LIBS ; do
+    abi-compliance-checker -l $lib -old $BUILDDIR_OLD/abi-$lib.dump -new $BUILDDIR_NEW/abi-$lib.dump | tee ${lib}-abi-results.txt || true
+    echo -e "\x1b[33;1m"
+    echo -e "$lib"
+    fgrep "Binary compatibility:" ${lib}-abi-results.txt
+    echo -e "\x1b[33;0m"
+done
+
+#
+# If the "Binary compatibility" summary results say anything other than 100%,
+# we fail!
+#
+for lib in $LIBS ; do
+    if [[ `fgrep "Binary compatibility:" ${lib}-abi-results.txt | grep -v 100\%` != "" ]] ; then
+        cp -r compat_reports ${BUILDDIR_NEW}/compat_reports
+        exit 1
+    fi
+done
diff --git a/src/build-scripts/gh-installdeps.bash b/src/build-scripts/gh-installdeps.bash
index 4ab5e9dab..b40201e23 100755
--- a/src/build-scripts/gh-installdeps.bash
+++ b/src/build-scripts/gh-installdeps.bash
@@ -186,14 +186,18 @@ if [[ "$OPENIMAGEIO_VERSION" != "" ]] ; then
     # Don't let warnings in OIIO break OSL's CI run
     export OPENIMAGEIO_CMAKE_FLAGS+=" -DSTOP_ON_WARNING=OFF"
     export OPENIMAGEIO_CMAKE_FLAGS+=" -DUSE_OPENGL=0"
-    if [[ $OPENIMAGEIO_VERSION == master && "${OPENIMAGEIO_UNITY:-1}" != "0" ]] ; then
+    export OPENIMAGEIO_CMAKE_FLAGS+=" -DUSE_OPENCV=0 -DUSE_FFMPEG=0 -DUSE_QT=0"
+    if [[ "${OPENIMAGEIO_UNITY:-1}" != "0" ]] ; then
         # Speed up the OIIO build by doing a "unity" build. (Note: this is
-        # only a savings in CI where there are only 1-2 cores available, and
-        # is only supported for OIIO 2.3.14 and later)
+        # only a savings in CI where there are only 1-2 cores available.)
         export OPENIMAGEIO_CMAKE_FLAGS+=" -DCMAKE_UNITY_BUILD=ON -DCMAKE_UNITY_BUILD_MODE=BATCH"
     fi
     source src/build-scripts/build_openimageio.bash
 fi
 
+if [[ "$ABI_CHECK" != "" ]] ; then
+    source src/build-scripts/build_abi_tools.bash
+fi
+
 # Save the env for use by other stages
 src/build-scripts/save-env.bash
diff --git a/src/liboslexec/CMakeLists.txt b/src/liboslexec/CMakeLists.txt
index b04da7b9c..29f6ca729 100644
--- a/src/liboslexec/CMakeLists.txt
+++ b/src/liboslexec/CMakeLists.txt
@@ -592,7 +592,7 @@ endforeach(batched_target_lib)
 install_targets (${local_lib})
 
 # Unit tests
-if (OSL_BUILD_TESTS)
+if (OSL_BUILD_TESTS AND BUILD_TESTING)
     add_executable (accum_test accum_test.cpp)
     target_link_libraries (accum_test PRIVATE oslexec ${Boost_LIBRARIES} ${CMAKE_DL_LIBS})
     set_target_properties (accum_test PROPERTIES FOLDER "Unit Tests")
diff --git a/src/liboslnoise/CMakeLists.txt b/src/liboslnoise/CMakeLists.txt
index 903d027fa..0bae6689f 100644
--- a/src/liboslnoise/CMakeLists.txt
+++ b/src/liboslnoise/CMakeLists.txt
@@ -51,7 +51,7 @@ set_target_properties (${local_lib}
 install_targets (${local_lib})
 
 
-if (OSL_BUILD_TESTS)
+if (OSL_BUILD_TESTS AND BUILD_TESTING)
     add_executable (oslnoise_test oslnoise_test.cpp)
     set_target_properties (oslnoise_test PROPERTIES FOLDER "Unit Tests")
     target_link_libraries (oslnoise_test PRIVATE oslnoise)