diff --git a/include/pybind11/cast.h b/include/pybind11/cast.h
index e41ad2abfa..0f3091f686 100644
--- a/include/pybind11/cast.h
+++ b/include/pybind11/cast.h
@@ -794,11 +794,11 @@ struct copyable_holder_caster : public type_caster_base<type> {
         }
     }
 
-    bool load_value(value_and_holder &&v_h) {
+    void load_value(value_and_holder &&v_h) {
         if (v_h.holder_constructed()) {
             value = v_h.value_ptr();
             holder = v_h.template holder<holder_type>();
-            return true;
+            return;
         }
         throw cast_error("Unable to cast from non-held to held instance (T& to Holder<T>) "
 #if !defined(PYBIND11_DETAILED_ERROR_MESSAGES)
diff --git a/include/pybind11/detail/class.h b/include/pybind11/detail/class.h
index d30621c88c..b990507d62 100644
--- a/include/pybind11/detail/class.h
+++ b/include/pybind11/detail/class.h
@@ -9,8 +9,10 @@
 
 #pragma once
 
-#include "../attr.h"
-#include "../options.h"
+#include <pybind11/attr.h>
+#include <pybind11/options.h>
+
+#include "exception_translation.h"
 
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
 PYBIND11_NAMESPACE_BEGIN(detail)
@@ -591,7 +593,18 @@ extern "C" inline int pybind11_getbuffer(PyObject *obj, Py_buffer *view, int fla
         return -1;
     }
     std::memset(view, 0, sizeof(Py_buffer));
-    buffer_info *info = tinfo->get_buffer(obj, tinfo->get_buffer_data);
+    buffer_info *info = nullptr;
+    try {
+        info = tinfo->get_buffer(obj, tinfo->get_buffer_data);
+    } catch (...) {
+        try_translate_exceptions();
+        raise_from(PyExc_BufferError, "Error getting buffer");
+        return -1;
+    }
+    if (info == nullptr) {
+        pybind11_fail("FATAL UNEXPECTED SITUATION: tinfo->get_buffer() returned nullptr.");
+    }
+
     if ((flags & PyBUF_WRITABLE) == PyBUF_WRITABLE && info->readonly) {
         delete info;
         // view->obj = nullptr;  // Was just memset to 0, so not necessary
diff --git a/include/pybind11/detail/common.h b/include/pybind11/detail/common.h
index fc66e6f756..c51d1d60bc 100644
--- a/include/pybind11/detail/common.h
+++ b/include/pybind11/detail/common.h
@@ -10,12 +10,12 @@
 #pragma once
 
 #define PYBIND11_VERSION_MAJOR 2
-#define PYBIND11_VERSION_MINOR 14
-#define PYBIND11_VERSION_PATCH 0.dev1
+#define PYBIND11_VERSION_MINOR 13
+#define PYBIND11_VERSION_PATCH 6
 
 // Similar to Python's convention: https://docs.python.org/3/c-api/apiabiversion.html
 // Additional convention: 0xD = dev
-#define PYBIND11_VERSION_HEX 0x020E00D1
+#define PYBIND11_VERSION_HEX 0x020D0600
 
 // Define some generic pybind11 helper macros for warning management.
 //
@@ -462,7 +462,25 @@ PYBIND11_WARNING_POP
                 return "Hello, World!";
             });
         }
+
+    The third macro argument is optional (available since 2.13.0), and can be used to
+    mark the extension module as safe to run without the GIL under a free-threaded CPython
+    interpreter. Passing this argument has no effect on other interpreters.
+
+    .. code-block:: cpp
+
+        PYBIND11_MODULE(example, m, py::mod_gil_not_used()) {
+            m.doc() = "pybind11 example module safe to run without the GIL";
+
+            // Add bindings here
+            m.def("foo", []() {
+                return "Hello, Free-threaded World!";
+            });
+        }
+
 \endrst */
+PYBIND11_WARNING_PUSH
+PYBIND11_WARNING_DISABLE_CLANG("-Wgnu-zero-variadic-macro-arguments")
 #define PYBIND11_MODULE(name, variable, ...)                                                      \
     static ::pybind11::module_::module_def PYBIND11_CONCAT(pybind11_module_def_, name)            \
         PYBIND11_MAYBE_UNUSED;                                                                    \
@@ -483,6 +501,7 @@ PYBIND11_WARNING_POP
         PYBIND11_CATCH_INIT_EXCEPTIONS                                                            \
     }                                                                                             \
     void PYBIND11_CONCAT(pybind11_init_, name)(::pybind11::module_ & (variable))
+PYBIND11_WARNING_POP
 
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
 
@@ -538,7 +557,7 @@ enum class return_value_policy : uint8_t {
         object without taking ownership similar to the above
         return_value_policy::reference policy. In contrast to that policy, the
         function or property's implicit this argument (called the parent) is
-        considered to be the the owner of the return value (the child).
+        considered to be the owner of the return value (the child).
         pybind11 then couples the lifetime of the parent to the child via a
         reference relationship that ensures that the parent cannot be garbage
         collected while Python is still using the child. More advanced
diff --git a/include/pybind11/detail/cpp_conduit.h b/include/pybind11/detail/cpp_conduit.h
new file mode 100644
index 0000000000..b66c2d39c0
--- /dev/null
+++ b/include/pybind11/detail/cpp_conduit.h
@@ -0,0 +1,77 @@
+// Copyright (c) 2024 The pybind Community.
+
+#pragma once
+
+#include <pybind11/pytypes.h>
+
+#include "common.h"
+#include "internals.h"
+
+#include <typeinfo>
+
+PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
+PYBIND11_NAMESPACE_BEGIN(detail)
+
+// Forward declaration needed here: Refactoring opportunity.
+extern "C" inline PyObject *pybind11_object_new(PyTypeObject *type, PyObject *, PyObject *);
+
+inline bool type_is_managed_by_our_internals(PyTypeObject *type_obj) {
+#if defined(PYPY_VERSION)
+    auto &internals = get_internals();
+    return bool(internals.registered_types_py.find(type_obj)
+                != internals.registered_types_py.end());
+#else
+    return bool(type_obj->tp_new == pybind11_object_new);
+#endif
+}
+
+inline bool is_instance_method_of_type(PyTypeObject *type_obj, PyObject *attr_name) {
+    PyObject *descr = _PyType_Lookup(type_obj, attr_name);
+    return bool((descr != nullptr) && PyInstanceMethod_Check(descr));
+}
+
+inline object try_get_cpp_conduit_method(PyObject *obj) {
+    if (PyType_Check(obj)) {
+        return object();
+    }
+    PyTypeObject *type_obj = Py_TYPE(obj);
+    str attr_name("_pybind11_conduit_v1_");
+    bool assumed_to_be_callable = false;
+    if (type_is_managed_by_our_internals(type_obj)) {
+        if (!is_instance_method_of_type(type_obj, attr_name.ptr())) {
+            return object();
+        }
+        assumed_to_be_callable = true;
+    }
+    PyObject *method = PyObject_GetAttr(obj, attr_name.ptr());
+    if (method == nullptr) {
+        PyErr_Clear();
+        return object();
+    }
+    if (!assumed_to_be_callable && PyCallable_Check(method) == 0) {
+        Py_DECREF(method);
+        return object();
+    }
+    return reinterpret_steal<object>(method);
+}
+
+inline void *try_raw_pointer_ephemeral_from_cpp_conduit(handle src,
+                                                        const std::type_info *cpp_type_info) {
+    object method = try_get_cpp_conduit_method(src.ptr());
+    if (method) {
+        capsule cpp_type_info_capsule(const_cast<void *>(static_cast<const void *>(cpp_type_info)),
+                                      typeid(std::type_info).name());
+        object cpp_conduit = method(bytes(PYBIND11_PLATFORM_ABI_ID),
+                                    cpp_type_info_capsule,
+                                    bytes("raw_pointer_ephemeral"));
+        if (isinstance<capsule>(cpp_conduit)) {
+            return reinterpret_borrow<capsule>(cpp_conduit).get_pointer();
+        }
+    }
+    return nullptr;
+}
+
+#define PYBIND11_HAS_CPP_CONDUIT 1
+
+PYBIND11_NAMESPACE_END(detail)
+PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)
diff --git a/include/pybind11/detail/exception_translation.h b/include/pybind11/detail/exception_translation.h
new file mode 100644
index 0000000000..2764180bb0
--- /dev/null
+++ b/include/pybind11/detail/exception_translation.h
@@ -0,0 +1,71 @@
+/*
+    pybind11/detail/exception_translation.h: means to translate C++ exceptions to Python exceptions
+
+    Copyright (c) 2024 The Pybind Development Team.
+
+    All rights reserved. Use of this source code is governed by a
+    BSD-style license that can be found in the LICENSE file.
+*/
+
+#pragma once
+
+#include "common.h"
+#include "internals.h"
+
+PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
+PYBIND11_NAMESPACE_BEGIN(detail)
+
+// Apply all the extensions translators from a list
+// Return true if one of the translators completed without raising an exception
+// itself. Return of false indicates that if there are other translators
+// available, they should be tried.
+inline bool apply_exception_translators(std::forward_list<ExceptionTranslator> &translators) {
+    auto last_exception = std::current_exception();
+
+    for (auto &translator : translators) {
+        try {
+            translator(last_exception);
+            return true;
+        } catch (...) {
+            last_exception = std::current_exception();
+        }
+    }
+    return false;
+}
+
+inline void try_translate_exceptions() {
+    /* When an exception is caught, give each registered exception
+        translator a chance to translate it to a Python exception. First
+        all module-local translators will be tried in reverse order of
+        registration. If none of the module-locale translators handle
+        the exception (or there are no module-locale translators) then
+        the global translators will be tried, also in reverse order of
+        registration.
+
+        A translator may choose to do one of the following:
+
+        - catch the exception and call py::set_error()
+            to set a standard (or custom) Python exception, or
+        - do nothing and let the exception fall through to the next translator, or
+        - delegate translation to the next translator by throwing a new type of exception.
+        */
+
+    bool handled = with_internals([&](internals &internals) {
+        auto &local_exception_translators = get_local_internals().registered_exception_translators;
+        if (detail::apply_exception_translators(local_exception_translators)) {
+            return true;
+        }
+        auto &exception_translators = internals.registered_exception_translators;
+        if (detail::apply_exception_translators(exception_translators)) {
+            return true;
+        }
+        return false;
+    });
+
+    if (!handled) {
+        set_error(PyExc_SystemError, "Exception escaped from default exception translator!");
+    }
+}
+
+PYBIND11_NAMESPACE_END(detail)
+PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)
diff --git a/include/pybind11/detail/init.h b/include/pybind11/detail/init.h
index 4509bd131e..79cc930c8d 100644
--- a/include/pybind11/detail/init.h
+++ b/include/pybind11/detail/init.h
@@ -128,11 +128,13 @@ void construct(value_and_holder &v_h, Cpp<Class> *ptr, bool need_alias) {
         // the holder and destruction happens when we leave the C++ scope, and the holder
         // class gets to handle the destruction however it likes.
         v_h.value_ptr() = ptr;
-        v_h.set_instance_registered(true);          // To prevent init_instance from registering it
-        v_h.type->init_instance(v_h.inst, nullptr); // Set up the holder
+        v_h.set_instance_registered(true); // Trick to prevent init_instance from registering it
+        // DANGER ZONE BEGIN: exceptions will leave v_h in an invalid state.
+        v_h.type->init_instance(v_h.inst, nullptr);                        // Set up the holder
         Holder<Class> temp_holder(std::move(v_h.holder<Holder<Class>>())); // Steal the holder
         v_h.type->dealloc(v_h); // Destroys the moved-out holder remains, resets value ptr to null
         v_h.set_instance_registered(false);
+        // DANGER ZONE END.
 
         construct_alias_from_cpp<Class>(is_alias_constructible<Class>{}, v_h, std::move(*ptr));
     } else {
diff --git a/include/pybind11/detail/internals.h b/include/pybind11/detail/internals.h
index 3f0a6a9492..232bc32d82 100644
--- a/include/pybind11/detail/internals.h
+++ b/include/pybind11/detail/internals.h
@@ -12,10 +12,10 @@
 #include "common.h"
 
 #if defined(PYBIND11_SIMPLE_GIL_MANAGEMENT)
-#    include "../gil.h"
+#    include <pybind11/gil.h>
 #endif
 
-#include "../pytypes.h"
+#include <pybind11/pytypes.h>
 
 #include <exception>
 #include <mutex>
@@ -321,15 +321,17 @@ struct type_info {
 #    define PYBIND11_INTERNALS_KIND ""
 #endif
 
+#define PYBIND11_PLATFORM_ABI_ID                                                                  \
+    PYBIND11_INTERNALS_KIND PYBIND11_COMPILER_TYPE PYBIND11_STDLIB PYBIND11_BUILD_ABI             \
+        PYBIND11_BUILD_TYPE
+
 #define PYBIND11_INTERNALS_ID                                                                     \
     "__pybind11_internals_v" PYBIND11_TOSTRING(PYBIND11_INTERNALS_VERSION)                        \
-        PYBIND11_INTERNALS_KIND PYBIND11_COMPILER_TYPE PYBIND11_STDLIB                            \
-            PYBIND11_BUILD_ABI PYBIND11_BUILD_TYPE "__"
+        PYBIND11_PLATFORM_ABI_ID "__"
 
 #define PYBIND11_MODULE_LOCAL_ID                                                                  \
     "__pybind11_module_local_v" PYBIND11_TOSTRING(PYBIND11_INTERNALS_VERSION)                     \
-        PYBIND11_INTERNALS_KIND PYBIND11_COMPILER_TYPE PYBIND11_STDLIB                            \
-            PYBIND11_BUILD_ABI PYBIND11_BUILD_TYPE "__"
+        PYBIND11_PLATFORM_ABI_ID "__"
 
 /// Each module locally stores a pointer to the `internals` data. The data
 /// itself is shared among modules with the same `PYBIND11_INTERNALS_ID`.
@@ -553,7 +555,7 @@ PYBIND11_NOINLINE internals &get_internals() {
         }
 #endif
         internals_ptr->istate = tstate->interp;
-        state_dict[PYBIND11_INTERNALS_ID] = capsule(internals_pp);
+        state_dict[PYBIND11_INTERNALS_ID] = capsule(reinterpret_cast<void *>(internals_pp));
         internals_ptr->registered_exception_translators.push_front(&translate_exception);
         internals_ptr->static_property_type = make_static_property_type();
         internals_ptr->default_metaclass = make_default_metaclass();
diff --git a/include/pybind11/detail/type_caster_base.h b/include/pybind11/detail/type_caster_base.h
index fd8c81b9ac..e40e44ba6c 100644
--- a/include/pybind11/detail/type_caster_base.h
+++ b/include/pybind11/detail/type_caster_base.h
@@ -9,15 +9,20 @@
 
 #pragma once
 
-#include "../pytypes.h"
+#include <pybind11/pytypes.h>
+
 #include "common.h"
+#include "cpp_conduit.h"
 #include "descr.h"
 #include "internals.h"
 #include "typeid.h"
+#include "value_and_holder.h"
 
 #include <cstdint>
+#include <cstring>
 #include <iterator>
 #include <new>
+#include <stdexcept>
 #include <string>
 #include <type_traits>
 #include <typeindex>
@@ -259,67 +264,6 @@ PYBIND11_NOINLINE handle find_registered_python_instance(void *src,
     });
 }
 
-struct value_and_holder {
-    instance *inst = nullptr;
-    size_t index = 0u;
-    const detail::type_info *type = nullptr;
-    void **vh = nullptr;
-
-    // Main constructor for a found value/holder:
-    value_and_holder(instance *i, const detail::type_info *type, size_t vpos, size_t index)
-        : inst{i}, index{index}, type{type},
-          vh{inst->simple_layout ? inst->simple_value_holder
-                                 : &inst->nonsimple.values_and_holders[vpos]} {}
-
-    // Default constructor (used to signal a value-and-holder not found by get_value_and_holder())
-    value_and_holder() = default;
-
-    // Used for past-the-end iterator
-    explicit value_and_holder(size_t index) : index{index} {}
-
-    template <typename V = void>
-    V *&value_ptr() const {
-        return reinterpret_cast<V *&>(vh[0]);
-    }
-    // True if this `value_and_holder` has a non-null value pointer
-    explicit operator bool() const { return value_ptr() != nullptr; }
-
-    template <typename H>
-    H &holder() const {
-        return reinterpret_cast<H &>(vh[1]);
-    }
-    bool holder_constructed() const {
-        return inst->simple_layout
-                   ? inst->simple_holder_constructed
-                   : (inst->nonsimple.status[index] & instance::status_holder_constructed) != 0u;
-    }
-    // NOLINTNEXTLINE(readability-make-member-function-const)
-    void set_holder_constructed(bool v = true) {
-        if (inst->simple_layout) {
-            inst->simple_holder_constructed = v;
-        } else if (v) {
-            inst->nonsimple.status[index] |= instance::status_holder_constructed;
-        } else {
-            inst->nonsimple.status[index] &= (std::uint8_t) ~instance::status_holder_constructed;
-        }
-    }
-    bool instance_registered() const {
-        return inst->simple_layout
-                   ? inst->simple_instance_registered
-                   : ((inst->nonsimple.status[index] & instance::status_instance_registered) != 0);
-    }
-    // NOLINTNEXTLINE(readability-make-member-function-const)
-    void set_instance_registered(bool v = true) {
-        if (inst->simple_layout) {
-            inst->simple_instance_registered = v;
-        } else if (v) {
-            inst->nonsimple.status[index] |= instance::status_instance_registered;
-        } else {
-            inst->nonsimple.status[index] &= (std::uint8_t) ~instance::status_instance_registered;
-        }
-    }
-};
-
 // Container for accessing and iterating over an instance's values/holders
 struct values_and_holders {
 private:
@@ -488,7 +432,7 @@ PYBIND11_NOINLINE void instance::allocate_layout() {
 // NOLINTNEXTLINE(readability-make-member-function-const)
 PYBIND11_NOINLINE void instance::deallocate_layout() {
     if (!simple_layout) {
-        PyMem_Free(nonsimple.values_and_holders);
+        PyMem_Free(reinterpret_cast<void *>(nonsimple.values_and_holders));
     }
 }
 
@@ -670,6 +614,13 @@ class type_caster_generic {
         }
         return false;
     }
+    bool try_cpp_conduit(handle src) {
+        value = try_raw_pointer_ephemeral_from_cpp_conduit(src, cpptype);
+        if (value != nullptr) {
+            return true;
+        }
+        return false;
+    }
     void check_holder_compat() {}
 
     PYBIND11_NOINLINE static void *local_load(PyObject *src, const type_info *ti) {
@@ -801,6 +752,10 @@ class type_caster_generic {
             return true;
         }
 
+        if (convert && cpptype && this_.try_cpp_conduit(src)) {
+            return true;
+        }
+
         return false;
     }
 
@@ -828,6 +783,32 @@ class type_caster_generic {
     void *value = nullptr;
 };
 
+inline object cpp_conduit_method(handle self,
+                                 const bytes &pybind11_platform_abi_id,
+                                 const capsule &cpp_type_info_capsule,
+                                 const bytes &pointer_kind) {
+#ifdef PYBIND11_HAS_STRING_VIEW
+    using cpp_str = std::string_view;
+#else
+    using cpp_str = std::string;
+#endif
+    if (cpp_str(pybind11_platform_abi_id) != PYBIND11_PLATFORM_ABI_ID) {
+        return none();
+    }
+    if (std::strcmp(cpp_type_info_capsule.name(), typeid(std::type_info).name()) != 0) {
+        return none();
+    }
+    if (cpp_str(pointer_kind) != "raw_pointer_ephemeral") {
+        throw std::runtime_error("Invalid pointer_kind: \"" + std::string(pointer_kind) + "\"");
+    }
+    const auto *cpp_type_info = cpp_type_info_capsule.get_pointer<const std::type_info>();
+    type_caster_generic caster(*cpp_type_info);
+    if (!caster.load(self, false)) {
+        return none();
+    }
+    return capsule(caster.value, cpp_type_info->name());
+}
+
 /**
  * Determine suitable casting operator for pointer-or-lvalue-casting type casters.  The type caster
  * needs to provide `operator T*()` and `operator T&()` operators.
diff --git a/include/pybind11/detail/value_and_holder.h b/include/pybind11/detail/value_and_holder.h
new file mode 100644
index 0000000000..ca37d70ad2
--- /dev/null
+++ b/include/pybind11/detail/value_and_holder.h
@@ -0,0 +1,77 @@
+// Copyright (c) 2016-2024 The Pybind Development Team.
+// All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+#pragma once
+
+#include "common.h"
+
+#include <cstddef>
+#include <typeinfo>
+
+PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
+PYBIND11_NAMESPACE_BEGIN(detail)
+
+struct value_and_holder {
+    instance *inst = nullptr;
+    size_t index = 0u;
+    const detail::type_info *type = nullptr;
+    void **vh = nullptr;
+
+    // Main constructor for a found value/holder:
+    value_and_holder(instance *i, const detail::type_info *type, size_t vpos, size_t index)
+        : inst{i}, index{index}, type{type},
+          vh{inst->simple_layout ? inst->simple_value_holder
+                                 : &inst->nonsimple.values_and_holders[vpos]} {}
+
+    // Default constructor (used to signal a value-and-holder not found by get_value_and_holder())
+    value_and_holder() = default;
+
+    // Used for past-the-end iterator
+    explicit value_and_holder(size_t index) : index{index} {}
+
+    template <typename V = void>
+    V *&value_ptr() const {
+        return reinterpret_cast<V *&>(vh[0]);
+    }
+    // True if this `value_and_holder` has a non-null value pointer
+    explicit operator bool() const { return value_ptr() != nullptr; }
+
+    template <typename H>
+    H &holder() const {
+        return reinterpret_cast<H &>(vh[1]);
+    }
+    bool holder_constructed() const {
+        return inst->simple_layout
+                   ? inst->simple_holder_constructed
+                   : (inst->nonsimple.status[index] & instance::status_holder_constructed) != 0u;
+    }
+    // NOLINTNEXTLINE(readability-make-member-function-const)
+    void set_holder_constructed(bool v = true) {
+        if (inst->simple_layout) {
+            inst->simple_holder_constructed = v;
+        } else if (v) {
+            inst->nonsimple.status[index] |= instance::status_holder_constructed;
+        } else {
+            inst->nonsimple.status[index] &= (std::uint8_t) ~instance::status_holder_constructed;
+        }
+    }
+    bool instance_registered() const {
+        return inst->simple_layout
+                   ? inst->simple_instance_registered
+                   : ((inst->nonsimple.status[index] & instance::status_instance_registered) != 0);
+    }
+    // NOLINTNEXTLINE(readability-make-member-function-const)
+    void set_instance_registered(bool v = true) {
+        if (inst->simple_layout) {
+            inst->simple_instance_registered = v;
+        } else if (v) {
+            inst->nonsimple.status[index] |= instance::status_instance_registered;
+        } else {
+            inst->nonsimple.status[index] &= (std::uint8_t) ~instance::status_instance_registered;
+        }
+    }
+};
+
+PYBIND11_NAMESPACE_END(detail)
+PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)
diff --git a/include/pybind11/eigen/matrix.h b/include/pybind11/eigen/matrix.h
index 8d4342f81b..5cf1f0a2a0 100644
--- a/include/pybind11/eigen/matrix.h
+++ b/include/pybind11/eigen/matrix.h
@@ -9,7 +9,8 @@
 
 #pragma once
 
-#include "../numpy.h"
+#include <pybind11/numpy.h>
+
 #include "common.h"
 
 /* HINT: To suppress warnings originating from the Eigen headers, use -isystem.
diff --git a/include/pybind11/eigen/tensor.h b/include/pybind11/eigen/tensor.h
index d4ed6c0ca8..0a9d7c2522 100644
--- a/include/pybind11/eigen/tensor.h
+++ b/include/pybind11/eigen/tensor.h
@@ -7,7 +7,8 @@
 
 #pragma once
 
-#include "../numpy.h"
+#include <pybind11/numpy.h>
+
 #include "common.h"
 
 #if defined(__GNUC__) && !defined(__clang__) && !defined(__INTEL_COMPILER)
@@ -469,9 +470,6 @@ struct type_caster<Eigen::TensorMap<Type, Options>,
                 parent_object = reinterpret_borrow<object>(parent);
                 break;
 
-            case return_value_policy::take_ownership:
-                delete src;
-                // fallthrough
             default:
                 // move, take_ownership don't make any sense for a ref/map:
                 pybind11_fail("Invalid return_value_policy for Eigen Map type, must be either "
diff --git a/include/pybind11/functional.h b/include/pybind11/functional.h
index 6856119cde..4b3610117c 100644
--- a/include/pybind11/functional.h
+++ b/include/pybind11/functional.h
@@ -9,12 +9,55 @@
 
 #pragma once
 
+#define PYBIND11_HAS_TYPE_CASTER_STD_FUNCTION_SPECIALIZATIONS
+
 #include "pybind11.h"
 
 #include <functional>
 
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
 PYBIND11_NAMESPACE_BEGIN(detail)
+PYBIND11_NAMESPACE_BEGIN(type_caster_std_function_specializations)
+
+// ensure GIL is held during functor destruction
+struct func_handle {
+    function f;
+#if !(defined(_MSC_VER) && _MSC_VER == 1916 && defined(PYBIND11_CPP17))
+    // This triggers a syntax error under very special conditions (very weird indeed).
+    explicit
+#endif
+        func_handle(function &&f_) noexcept
+        : f(std::move(f_)) {
+    }
+    func_handle(const func_handle &f_) { operator=(f_); }
+    func_handle &operator=(const func_handle &f_) {
+        gil_scoped_acquire acq;
+        f = f_.f;
+        return *this;
+    }
+    ~func_handle() {
+        gil_scoped_acquire acq;
+        function kill_f(std::move(f));
+    }
+};
+
+// to emulate 'move initialization capture' in C++11
+struct func_wrapper_base {
+    func_handle hfunc;
+    explicit func_wrapper_base(func_handle &&hf) noexcept : hfunc(hf) {}
+};
+
+template <typename Return, typename... Args>
+struct func_wrapper : func_wrapper_base {
+    using func_wrapper_base::func_wrapper_base;
+    Return operator()(Args... args) const {
+        gil_scoped_acquire acq;
+        // casts the returned object as a rvalue to the return type
+        return hfunc.f(std::forward<Args>(args)...).template cast<Return>();
+    }
+};
+
+PYBIND11_NAMESPACE_END(type_caster_std_function_specializations)
 
 template <typename Return, typename... Args>
 struct type_caster<std::function<Return(Args...)>> {
@@ -77,40 +120,8 @@ struct type_caster<std::function<Return(Args...)>> {
             // See PR #1413 for full details
         }
 
-        // ensure GIL is held during functor destruction
-        struct func_handle {
-            function f;
-#if !(defined(_MSC_VER) && _MSC_VER == 1916 && defined(PYBIND11_CPP17))
-            // This triggers a syntax error under very special conditions (very weird indeed).
-            explicit
-#endif
-                func_handle(function &&f_) noexcept
-                : f(std::move(f_)) {
-            }
-            func_handle(const func_handle &f_) { operator=(f_); }
-            func_handle &operator=(const func_handle &f_) {
-                gil_scoped_acquire acq;
-                f = f_.f;
-                return *this;
-            }
-            ~func_handle() {
-                gil_scoped_acquire acq;
-                function kill_f(std::move(f));
-            }
-        };
-
-        // to emulate 'move initialization capture' in C++11
-        struct func_wrapper {
-            func_handle hfunc;
-            explicit func_wrapper(func_handle &&hf) noexcept : hfunc(std::move(hf)) {}
-            Return operator()(Args... args) const {
-                gil_scoped_acquire acq;
-                // casts the returned object as a rvalue to the return type
-                return hfunc.f(std::forward<Args>(args)...).template cast<Return>();
-            }
-        };
-
-        value = func_wrapper(func_handle(std::move(func)));
+        value = type_caster_std_function_specializations::func_wrapper<Return, Args...>(
+            type_caster_std_function_specializations::func_handle(std::move(func)));
         return true;
     }
 
diff --git a/include/pybind11/numpy.h b/include/pybind11/numpy.h
index 05ef3918b1..09894cf74f 100644
--- a/include/pybind11/numpy.h
+++ b/include/pybind11/numpy.h
@@ -901,7 +901,11 @@ class array : public buffer {
 
     template <typename T>
     array(ShapeContainer shape, StridesContainer strides, const T *ptr, handle base = handle())
-        : array(pybind11::dtype::of<T>(), std::move(shape), std::move(strides), ptr, base) {}
+        : array(pybind11::dtype::of<T>(),
+                std::move(shape),
+                std::move(strides),
+                reinterpret_cast<const void *>(ptr),
+                base) {}
 
     template <typename T>
     array(ShapeContainer shape, const T *ptr, handle base = handle())
@@ -1986,7 +1990,7 @@ struct vectorize_helper {
         // Pointers to values the function was called with; the vectorized ones set here will start
         // out as array_t<T> pointers, but they will be changed them to T pointers before we make
         // call the wrapped function.  Non-vectorized pointers are left as-is.
-        std::array<void *, N> params{{&args...}};
+        std::array<void *, N> params{{reinterpret_cast<void *>(&args)...}};
 
         // The array of `buffer_info`s of vectorized arguments:
         std::array<buffer_info, NVectorized> buffers{
diff --git a/include/pybind11/pybind11.h b/include/pybind11/pybind11.h
index 74919a7d52..5219c0ff85 100644
--- a/include/pybind11/pybind11.h
+++ b/include/pybind11/pybind11.h
@@ -9,8 +9,8 @@
 */
 
 #pragma once
-
 #include "detail/class.h"
+#include "detail/exception_translation.h"
 #include "detail/init.h"
 #include "attr.h"
 #include "gil.h"
@@ -95,24 +95,6 @@ inline std::string replace_newlines_and_squash(const char *text) {
     return result.substr(str_begin, str_range);
 }
 
-// Apply all the extensions translators from a list
-// Return true if one of the translators completed without raising an exception
-// itself. Return of false indicates that if there are other translators
-// available, they should be tried.
-inline bool apply_exception_translators(std::forward_list<ExceptionTranslator> &translators) {
-    auto last_exception = std::current_exception();
-
-    for (auto &translator : translators) {
-        try {
-            translator(last_exception);
-            return true;
-        } catch (...) {
-            last_exception = std::current_exception();
-        }
-    }
-    return false;
-}
-
 #if defined(_MSC_VER)
 #    define PYBIND11_COMPAT_STRDUP _strdup
 #else
@@ -610,7 +592,8 @@ class cpp_function : public function {
         int index = 0;
         /* Create a nice pydoc rec including all signatures and
            docstrings of the functions in the overload chain */
-        if (chain && options::show_function_signatures()) {
+        if (chain && options::show_function_signatures()
+            && std::strcmp(rec->name, "_pybind11_conduit_v1_") != 0) {
             // First a generic signature
             signatures += rec->name;
             signatures += "(*args, **kwargs)\n";
@@ -619,7 +602,8 @@ class cpp_function : public function {
         // Then specific overload signatures
         bool first_user_def = true;
         for (auto *it = chain_start; it != nullptr; it = it->next) {
-            if (options::show_function_signatures()) {
+            if (options::show_function_signatures()
+                && std::strcmp(rec->name, "_pybind11_conduit_v1_") != 0) {
                 if (index > 0) {
                     signatures += '\n';
                 }
@@ -1038,40 +1022,7 @@ class cpp_function : public function {
             throw;
 #endif
         } catch (...) {
-            /* When an exception is caught, give each registered exception
-               translator a chance to translate it to a Python exception. First
-               all module-local translators will be tried in reverse order of
-               registration. If none of the module-locale translators handle
-               the exception (or there are no module-locale translators) then
-               the global translators will be tried, also in reverse order of
-               registration.
-
-               A translator may choose to do one of the following:
-
-                - catch the exception and call py::set_error()
-                  to set a standard (or custom) Python exception, or
-                - do nothing and let the exception fall through to the next translator, or
-                - delegate translation to the next translator by throwing a new type of exception.
-             */
-
-            bool handled = with_internals([&](internals &internals) {
-                auto &local_exception_translators
-                    = get_local_internals().registered_exception_translators;
-                if (detail::apply_exception_translators(local_exception_translators)) {
-                    return true;
-                }
-                auto &exception_translators = internals.registered_exception_translators;
-                if (detail::apply_exception_translators(exception_translators)) {
-                    return true;
-                }
-                return false;
-            });
-
-            if (handled) {
-                return nullptr;
-            }
-
-            set_error(PyExc_SystemError, "Exception escaped from default exception translator!");
+            try_translate_exceptions();
             return nullptr;
         }
 
@@ -1652,6 +1603,7 @@ class class_ : public detail::generic_type {
                     = instances[std::type_index(typeid(type))];
             });
         }
+        def("_pybind11_conduit_v1_", cpp_conduit_method);
     }
 
     template <typename Base, detail::enable_if_t<is_base<Base>::value, int> = 0>
diff --git a/include/pybind11/pytypes.h b/include/pybind11/pytypes.h
index f26c307a87..1e76d7bc13 100644
--- a/include/pybind11/pytypes.h
+++ b/include/pybind11/pytypes.h
@@ -1259,6 +1259,7 @@ class sequence_fast_readonly {
     using pointer = arrow_proxy<const handle>;
 
     sequence_fast_readonly(handle obj, ssize_t n) : ptr(PySequence_Fast_ITEMS(obj.ptr()) + n) {}
+    sequence_fast_readonly() = default;
 
     // NOLINTNEXTLINE(readability-const-return-type) // PR #3263
     reference dereference() const { return *ptr; }
@@ -1281,6 +1282,7 @@ class sequence_slow_readwrite {
     using pointer = arrow_proxy<const sequence_accessor>;
 
     sequence_slow_readwrite(handle obj, ssize_t index) : obj(obj), index(index) {}
+    sequence_slow_readwrite() = default;
 
     reference dereference() const { return {obj, static_cast<size_t>(index)}; }
     void increment() { ++index; }
diff --git a/include/pybind11/stl/filesystem.h b/include/pybind11/stl/filesystem.h
index 85c131efe4..c16a9ae5c2 100644
--- a/include/pybind11/stl/filesystem.h
+++ b/include/pybind11/stl/filesystem.h
@@ -4,11 +4,11 @@
 
 #pragma once
 
-#include "../pybind11.h"
-#include "../detail/common.h"
-#include "../detail/descr.h"
-#include "../cast.h"
-#include "../pytypes.h"
+#include <pybind11/cast.h>
+#include <pybind11/detail/common.h>
+#include <pybind11/detail/descr.h>
+#include <pybind11/pybind11.h>
+#include <pybind11/pytypes.h>
 
 #include <string>
 
@@ -33,6 +33,13 @@
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
 PYBIND11_NAMESPACE_BEGIN(detail)
 
+#ifdef PYPY_VERSION
+#    define PYBIND11_REINTERPRET_CAST_VOID_PTR_IF_NOT_PYPY(...) (__VA_ARGS__)
+#else
+#    define PYBIND11_REINTERPRET_CAST_VOID_PTR_IF_NOT_PYPY(...)                                   \
+        (reinterpret_cast<void *>(__VA_ARGS__))
+#endif
+
 #if defined(PYBIND11_HAS_FILESYSTEM) || defined(PYBIND11_HAS_EXPERIMENTAL_FILESYSTEM)
 template <typename T>
 struct path_caster {
@@ -72,7 +79,8 @@ struct path_caster {
         }
         PyObject *native = nullptr;
         if constexpr (std::is_same_v<typename T::value_type, char>) {
-            if (PyUnicode_FSConverter(buf, &native) != 0) {
+            if (PyUnicode_FSConverter(buf, PYBIND11_REINTERPRET_CAST_VOID_PTR_IF_NOT_PYPY(&native))
+                != 0) {
                 if (auto *c_str = PyBytes_AsString(native)) {
                     // AsString returns a pointer to the internal buffer, which
                     // must not be free'd.
@@ -80,7 +88,8 @@ struct path_caster {
                 }
             }
         } else if constexpr (std::is_same_v<typename T::value_type, wchar_t>) {
-            if (PyUnicode_FSDecoder(buf, &native) != 0) {
+            if (PyUnicode_FSDecoder(buf, PYBIND11_REINTERPRET_CAST_VOID_PTR_IF_NOT_PYPY(&native))
+                != 0) {
                 if (auto *c_str = PyUnicode_AsWideCharString(native, nullptr)) {
                     // AsWideCharString returns a new string that must be free'd.
                     value = c_str; // Copies the string.
diff --git a/include/pybind11/stl_bind.h b/include/pybind11/stl_bind.h
index 66c452ea79..fcb48dea33 100644
--- a/include/pybind11/stl_bind.h
+++ b/include/pybind11/stl_bind.h
@@ -180,7 +180,7 @@ void vector_modifiers(
                         v.end());
                 try {
                     v.shrink_to_fit();
-                } catch (const std::exception &) {
+                } catch (const std::exception &) { // NOLINT(bugprone-empty-catch)
                     // Do nothing
                 }
                 throw;
diff --git a/include/pybind11/typing.h b/include/pybind11/typing.h
index b0feb9464a..84aaf9f702 100644
--- a/include/pybind11/typing.h
+++ b/include/pybind11/typing.h
@@ -100,9 +100,7 @@ class Never : public none {
     using none::none;
 };
 
-#if defined(__cpp_nontype_template_parameter_class)                                               \
-    && (/* See #5201 */ !defined(__GNUC__)                                                        \
-        || (__GNUC__ > 10 || (__GNUC__ == 10 && __GNUC_MINOR__ >= 3)))
+#if defined(__cpp_nontype_template_args) && __cpp_nontype_template_args >= 201911L
 #    define PYBIND11_TYPING_H_HAS_STRING_LITERAL
 template <size_t N>
 struct StringLiteral {