diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 9b67bc95..7429928b 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -55,11 +55,23 @@ jobs:
 
     - name: Configure
       run: >
-        cmake -S . -B build -DNB_TEST_STABLE_ABI=ON -DNB_TEST_SHARED_BUILD="$(python3 -c 'import sys; print(int(sys.version_info.minor>=11))')"
+        cmake -S . -B build -DNB_TEST_STABLE_ABI=ON -DNB_TEST_SHARED_BUILD="$(python -c 'import sys; print(int(sys.version_info.minor>=11))')"
 
     - name: Build C++
       run: cmake --build build -j 2
 
+    - name: Check ABI tag
+      if: ${{ !startsWith(matrix.os, 'windows')  }}
+      run: >
+        cd build/tests;
+        python -c 'import test_functions_ext as t; print(f"ABI tag is \"{ t.abi_tag() }\"")'
+
+    - name: Check ABI tag
+      if: ${{ startsWith(matrix.os, 'windows')  }}
+      run: >
+        cd build/tests/Debug;
+        python -c 'import test_functions_ext as t; print(f"ABI tag is \"{ t.abi_tag() }\"")'
+
     - name: Run tests
       run: >
         cd build;
@@ -85,6 +97,11 @@ jobs:
     - name: Build C++
       run: cmake --build build -j 2
 
+    - name: Check ABI tag
+      run: >
+        cd build/tests;
+        python3 -c 'import test_functions_ext as t; print(f"ABI tag is \"{ t.abi_tag() }\"")'
+
     - name: Run tests
       run: >
         cd build;
@@ -134,6 +151,11 @@ jobs:
     - name: Build C++
       run: cmake --build build -j 2
 
+    - name: Check ABI tag
+      run: >
+        cd build/tests;
+        python -c 'import test_functions_ext as t; print(f"ABI tag is \"{ t.abi_tag() }\"")'
+
     - name: Run tests
       run: >
         cd build;
@@ -165,7 +187,13 @@ jobs:
         cmake -S . -B build -DNB_TEST_FREE_THREADED=ON
 
     - name: Build C++
-      run: cmake --build build -j 2
+      run: >
+        cmake --build build -j 2
+
+    - name: Check ABI tag
+      run: >
+        cd build/tests;
+        python -c 'import test_functions_ext as t; print(f"ABI tag is \"{ t.abi_tag() }\"")'
 
     - name: Run tests
       run: >
diff --git a/include/nanobind/nb_lib.h b/include/nanobind/nb_lib.h
index 7ea1703c..b02f10fd 100644
--- a/include/nanobind/nb_lib.h
+++ b/include/nanobind/nb_lib.h
@@ -557,6 +557,8 @@ NB_CORE void *type_get_slot(PyTypeObject *t, int slot_id);
 
 NB_CORE PyObject *dict_get_item_ref_or_fail(PyObject *d, PyObject *k);
 
+NB_CORE const char *abi_tag();
+
 NAMESPACE_END(detail)
 
 using detail::raise;
diff --git a/src/nb_abi.h b/src/nb_abi.h
new file mode 100644
index 00000000..da704d99
--- /dev/null
+++ b/src/nb_abi.h
@@ -0,0 +1,102 @@
+/*
+   src/nb_abi.h: this file computes tags that are used to isolate extensions
+   from each other in the case of platform or nanobind-related ABI
+   incompatibilities. The file is included by ``nb_internals.cpp`` and should
+   not be used directly.
+
+   The implementation of this file (specifically, the NB_PLATFORM_ABI_TAG) is
+   designed to be compatible with @rwgk's
+   https://github.com/pybind/pybind11/blob/master/include/pybind11/conduit/pybind11_platform_abi_id.h
+
+   Use of this source code is governed by a BSD-style license that can be found
+   in the LICENSE file.
+*/
+
+/// Tracks the version of nanobind's internal data structures
+#ifndef NB_INTERNALS_VERSION
+#  define NB_INTERNALS_VERSION 16
+#endif
+
+#if defined(__MINGW32__)
+#  define NB_COMPILER_TYPE "mingw"
+#elif defined(__CYGWIN__)
+#  define NB_COMPILER_TYPE "gcc_cygwin"
+#elif defined(_MSC_VER)
+#  define NB_COMPILER_TYPE "msvc"
+#elif defined(__clang__) || defined(__GNUC__)
+#  define NB_COMPILER_TYPE "system" // Assumed compatible with system compiler.
+#else
+#  error "Unknown compiler type. Please revise this code."
+#endif
+
+// Catch other conditions that imply ABI incompatibility
+// - MSVC builds with different CRT versions
+// - An anticipated MSVC ABI break ("vNext")
+// - Builds using libc++ with unstable ABIs
+// - Builds using libstdc++ with the legacy (pre-C++11) ABI, etc.
+#if defined(_MSC_VER)
+#  if defined(_MT) && defined(_DLL) // Corresponding to CL command line options /MD or /MDd.
+#    if (_MSC_VER) / 100 == 19
+#      define NB_BUILD_ABI "_md_mscver19"
+#    else
+#      error "Unknown MSVC major version. Please revise this code."
+#    endif
+#  elif defined(_MT) // Corresponding to CL command line options /MT or /MTd.
+#    define NB_BUILD_ABI "_mt_mscver" NB_TOSTRING(_MSC_VER)
+#  else
+#    if (_MSC_VER) / 100 == 19
+#      define NB_BUILD_ABI "_none_mscver19"
+#    else
+#      error "Unknown MSVC major version. Please revise this code."
+#    endif
+#  endif
+#elif defined(_LIBCPP_ABI_VERSION) // https://libcxx.llvm.org/DesignDocs/ABIVersioning.html
+#    define NB_BUILD_ABI "_libcpp_abi" NB_TOSTRING(_LIBCPP_ABI_VERSION)
+#elif defined(_GLIBCXX_USE_CXX11_ABI)
+#  if defined(__NVCOMPILER) && !defined(__GXX_ABI_VERSION)
+#    error  "Unknown platform or compiler (_GLIBCXX_USE_CXX11_ABI). Please revise this code."
+#  endif
+#  if defined(__GXX_ABI_VERSION) && __GXX_ABI_VERSION < 1002 || __GXX_ABI_VERSION >= 2000
+#    error "Unknown platform or compiler (__GXX_ABI_VERSION). Please revise this code."
+#  endif
+#  define NB_BUILD_ABI "_libstdcpp_gxx_abi_1xxx_use_cxx11_abi_" NB_TOSTRING(_GLIBCXX_USE_CXX11_ABI)
+#else
+#  error "Unknown platform or compiler. Please revise this code."
+#endif
+
+// On MSVC, debug and release builds are not ABI-compatible!
+#if defined(_MSC_VER) && defined(_DEBUG)
+#  define NB_BUILD_TYPE "_debug"
+#else
+#  define NB_BUILD_TYPE ""
+#endif
+
+// Tag to determine if inter-library C++ function can be safely dispatched
+#define NB_PLATFORM_ABI_TAG \
+    NB_COMPILER_TYPE NB_BUILD_ABI NB_BUILD_TYPE
+
+// Can have limited and non-limited-API extensions in the same process.
+// Nanobind data structures will differ, so these can't talk to each other
+#if defined(Py_LIMITED_API)
+#  define NB_STABLE_ABI "_stable"
+#else
+#  define NB_STABLE_ABI ""
+#endif
+
+// As above, but for free-threaded extensions
+#if defined(NB_FREE_THREADED)
+#  define NB_FREE_THREADED_ABI "_ft"
+#else
+#  define NB_FREE_THREADED_ABI ""
+#endif
+
+#if NB_VERSION_DEV > 0
+  #define NB_VERSION_DEV_STR "_dev" NB_TOSTRING(NB_VERSION_DEV)
+#else
+  #define NB_VERSION_DEV_STR ""
+#endif
+
+#define NB_ABI_TAG                                                             \
+    "v" NB_TOSTRING(NB_INTERNALS_VERSION)                                      \
+        NB_VERSION_DEV_STR "_" NB_PLATFORM_ABI_TAG NB_STABLE_ABI               \
+            NB_FREE_THREADED_ABI
diff --git a/src/nb_internals.cpp b/src/nb_internals.cpp
index b4a3f1d9..2ccae09e 100644
--- a/src/nb_internals.cpp
+++ b/src/nb_internals.cpp
@@ -10,86 +10,13 @@
 #include <nanobind/nanobind.h>
 #include <structmember.h>
 #include "nb_internals.h"
+#include "nb_abi.h"
 #include <thread>
 
 #if defined(__GNUC__) && !defined(__clang__)
 #  pragma GCC diagnostic ignored "-Wmissing-field-initializers"
 #endif
 
-/// Tracks the ABI of nanobind
-#ifndef NB_INTERNALS_VERSION
-#  define NB_INTERNALS_VERSION 15
-#endif
-
-/// On MSVC, debug and release builds are not ABI-compatible!
-#if defined(_MSC_VER) && defined(_DEBUG)
-#  define NB_BUILD_TYPE "_debug"
-#else
-#  define NB_BUILD_TYPE ""
-#endif
-
-/// Let's assume that different compilers are ABI-incompatible.
-#if defined(_MSC_VER)
-#  define NB_COMPILER_TYPE "_msvc"
-#elif defined(__INTEL_COMPILER)
-#  define NB_COMPILER_TYPE "_icc"
-#elif defined(__clang__)
-#  define NB_COMPILER_TYPE "_clang"
-#elif defined(__PGI)
-#  define NB_COMPILER_TYPE "_pgi"
-#elif defined(__MINGW32__)
-#  define NB_COMPILER_TYPE "_mingw"
-#elif defined(__CYGWIN__)
-#  define NB_COMPILER_TYPE "_gcc_cygwin"
-#elif defined(__GNUC__)
-#  define NB_COMPILER_TYPE "_gcc"
-#else
-#  define NB_COMPILER_TYPE "_unknown"
-#endif
-
-/// Also standard libs
-#if defined(_LIBCPP_VERSION)
-#  define NB_STDLIB "_libcpp"
-#elif defined(__GLIBCXX__) || defined(__GLIBCPP__)
-#  define NB_STDLIB "_libstdcpp"
-#else
-#  define NB_STDLIB ""
-#endif
-
-/// On Linux/OSX, changes in __GXX_ABI_VERSION__ indicate ABI incompatibility.
-/// Also keep potentially ABI-incompatible visual studio builds apart.
-#if defined(__GXX_ABI_VERSION)
-#  define NB_BUILD_ABI "_cxxabi" NB_TOSTRING(__GXX_ABI_VERSION)
-#elif defined(_MSC_VER)
-#  define NB_BUILD_ABI "_mscver" NB_TOSTRING(_MSC_VER)
-#else
-#  define NB_BUILD_ABI ""
-#endif
-
-// Can have limited and non-limited-API extensions in the same process, and they might be incompatible
-#if defined(Py_LIMITED_API)
-#  define NB_STABLE_ABI "_stable"
-#else
-#  define NB_STABLE_ABI ""
-#endif
-
-#if defined(NB_FREE_THREADED)
-#  define NB_FREE_THREADED_ABI "_ft"
-#else
-#  define NB_FREE_THREADED_ABI ""
-#endif
-
-#if NB_VERSION_DEV > 0
-  #define NB_VERSION_DEV_STR "_dev" NB_TOSTRING(NB_VERSION_DEV)
-#else
-  #define NB_VERSION_DEV_STR ""
-#endif
-
-#define NB_INTERNALS_ID                                                        \
-    "v" NB_TOSTRING(NB_INTERNALS_VERSION)                                      \
-        NB_VERSION_DEV_STR NB_COMPILER_TYPE NB_STDLIB NB_BUILD_ABI             \
-            NB_BUILD_TYPE NB_STABLE_ABI NB_FREE_THREADED_ABI
-
 NAMESPACE_BEGIN(NB_NAMESPACE)
 NAMESPACE_BEGIN(detail)
 
@@ -241,6 +168,8 @@ static bool is_alive_value = false;
 static bool *is_alive_ptr = &is_alive_value;
 bool is_alive() noexcept { return *is_alive_ptr; }
 
+const char *abi_tag() { return NB_ABI_TAG; }
+
 static void internals_cleanup() {
     nb_internals *p = internals;
     if (!p)
@@ -382,7 +311,7 @@ NB_NOINLINE void init(const char *name) {
     check(dict, "nanobind::detail::init(): could not access internals dictionary!");
 
     PyObject *key = PyUnicode_FromFormat("__nb_internals_%s_%s__",
-                                         NB_INTERNALS_ID, name ? name : "");
+                                         abi_tag(), name ? name : "");
     check(key, "nanobind::detail::init(): could not create dictionary key!");
 
     PyObject *capsule = dict_get_item_ref_or_fail(dict, key);
diff --git a/tests/test_functions.cpp b/tests/test_functions.cpp
index 66718737..51136785 100644
--- a/tests/test_functions.cpp
+++ b/tests/test_functions.cpp
@@ -479,4 +479,6 @@ NB_MODULE(test_functions_ext, m) {
               auto ret = std::move(example_policy::calls);
               return ret;
           });
+
+    m.def("abi_tag", [](){ return nb::detail::abi_tag(); });
 }
diff --git a/tests/test_functions_ext.pyi.ref b/tests/test_functions_ext.pyi.ref
index 773c3868..81ca9a6e 100644
--- a/tests/test_functions_ext.pyi.ref
+++ b/tests/test_functions_ext.pyi.ref
@@ -3,6 +3,8 @@ import types
 from typing import Annotated, Any, overload
 
 
+def abi_tag() -> str: ...
+
 def call_guard_value() -> int: ...
 
 def call_policy_record() -> list[tuple[tuple, object]]: ...