diff --git a/newsfragments/5064.added.md b/newsfragments/5064.added.md
new file mode 100644
index 00000000000..21e2cce6430
--- /dev/null
+++ b/newsfragments/5064.added.md
@@ -0,0 +1 @@
+Add FFI definition `PY_INVALID_STACK_EFFECT`.
diff --git a/newsfragments/5064.changed.md b/newsfragments/5064.changed.md
new file mode 100644
index 00000000000..0ca3ad7d542
--- /dev/null
+++ b/newsfragments/5064.changed.md
@@ -0,0 +1,3 @@
+Reduce visibility of some CPython implementation details:
+- The FFI definition `PyCodeObject` is now an opaque struct on all Python versions.
+- The FFI definition `PyFutureFeatures` is now only defined up until Python 3.10 (it was present in CPython headers but unused in 3.11 and 3.12).
diff --git a/newsfragments/5064.removed.md b/newsfragments/5064.removed.md
new file mode 100644
index 00000000000..f1a04a78aa7
--- /dev/null
+++ b/newsfragments/5064.removed.md
@@ -0,0 +1,2 @@
+Remove private types from `pyo3-ffi` (i.e. starting with `_Py`) which are not referenced by public APIs: `_PyLocalMonitors`, `_Py_GlobalMonitors`, `_PyCoCached`, `_PyCoLineInstrumentationData`, `_PyCoMonitoringData`, `_PyCompilerSrcLocation`, `_PyErr_StackItem`.
+Remove FFI definition `PyCode_GetNumFree` (PyO3 cannot support it due to knowledge of the code object).
diff --git a/pyo3-ffi-check/macro/src/lib.rs b/pyo3-ffi-check/macro/src/lib.rs
index c6cee5c7ec3..41092b9020e 100644
--- a/pyo3-ffi-check/macro/src/lib.rs
+++ b/pyo3-ffi-check/macro/src/lib.rs
@@ -9,11 +9,6 @@ const PY_3_12: PythonVersion = PythonVersion {
     minor: 12,
 };
 
-const PY_3_13: PythonVersion = PythonVersion {
-    major: 3,
-    minor: 13,
-};
-
 /// Macro which expands to multiple macro calls, one per pyo3-ffi struct.
 #[proc_macro]
 pub fn for_all_structs(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
@@ -55,16 +50,6 @@ pub fn for_all_structs(input: proc_macro::TokenStream) -> proc_macro::TokenStrea
             .strip_suffix(".html")
             .unwrap();
 
-        if struct_name == "_PyCoLineInstrumentationData"
-            && pyo3_build_config::get().version == PY_3_13
-        {
-            // private type, fields changed name in 3.13.2 -> 3.13.3
-            //
-            // PyO3 0.25 will remove this struct, ignoring temporarily just to unblock CI
-            // changed, the size stayed the same.
-            continue;
-        }
-
         let struct_ident = Ident::new(struct_name, Span::call_site());
         output.extend(quote!(#macro_name!(#struct_ident);));
     }
diff --git a/pyo3-ffi/src/bytearrayobject.rs b/pyo3-ffi/src/bytearrayobject.rs
index 24a97bcc31b..d27dfa8b0ec 100644
--- a/pyo3-ffi/src/bytearrayobject.rs
+++ b/pyo3-ffi/src/bytearrayobject.rs
@@ -17,7 +17,7 @@ pub struct PyByteArrayObject {
 }
 
 #[cfg(any(PyPy, GraalPy, Py_LIMITED_API))]
-opaque_struct!(PyByteArrayObject);
+opaque_struct!(pub PyByteArrayObject);
 
 #[cfg_attr(windows, link(name = "pythonXY"))]
 extern "C" {
diff --git a/pyo3-ffi/src/code.rs b/pyo3-ffi/src/code.rs
index d28f68cded7..296b17f6aa4 100644
--- a/pyo3-ffi/src/code.rs
+++ b/pyo3-ffi/src/code.rs
@@ -1,4 +1,4 @@
 // This header doesn't exist in CPython, but Include/cpython/code.h does. We add
 // this here so that PyCodeObject has a definition under the limited API.
 
-opaque_struct!(PyCodeObject);
+opaque_struct!(pub PyCodeObject);
diff --git a/pyo3-ffi/src/cpython/bytesobject.rs b/pyo3-ffi/src/cpython/bytesobject.rs
index 306702de25e..dd78e646a12 100644
--- a/pyo3-ffi/src/cpython/bytesobject.rs
+++ b/pyo3-ffi/src/cpython/bytesobject.rs
@@ -17,7 +17,7 @@ pub struct PyBytesObject {
 }
 
 #[cfg(any(PyPy, GraalPy, Py_LIMITED_API))]
-opaque_struct!(PyBytesObject);
+opaque_struct!(pub PyBytesObject);
 
 extern "C" {
     #[cfg_attr(PyPy, link_name = "_PyPyBytes_Resize")]
diff --git a/pyo3-ffi/src/cpython/code.rs b/pyo3-ffi/src/cpython/code.rs
index 60989901052..3d47a1bc8c3 100644
--- a/pyo3-ffi/src/cpython/code.rs
+++ b/pyo3-ffi/src/cpython/code.rs
@@ -1,209 +1,43 @@
 use crate::object::*;
 use crate::pyport::Py_ssize_t;
 
-#[allow(unused_imports)]
-use std::os::raw::{c_char, c_int, c_short, c_uchar, c_void};
+#[cfg(not(GraalPy))]
+use std::os::raw::c_char;
+use std::os::raw::{c_int, c_void};
 #[cfg(not(any(PyPy, GraalPy)))]
 use std::ptr::addr_of_mut;
 
-#[cfg(all(Py_3_8, not(any(PyPy, GraalPy)), not(Py_3_11)))]
-opaque_struct!(_PyOpcache);
+// skipped private _PY_MONITORING_LOCAL_EVENTS
+// skipped private _PY_MONITORING_UNGROUPED_EVENTS
+// skipped private _PY_MONITORING_EVENTS
 
-#[cfg(Py_3_12)]
-pub const _PY_MONITORING_LOCAL_EVENTS: usize = 10;
-#[cfg(Py_3_12)]
-pub const _PY_MONITORING_UNGROUPED_EVENTS: usize = 15;
-#[cfg(Py_3_12)]
-pub const _PY_MONITORING_EVENTS: usize = 17;
+// skipped private _PyLocalMonitors
+// skipped private _Py_GlobalMonitors
 
-#[cfg(Py_3_12)]
-#[repr(C)]
-#[derive(Clone, Copy)]
-pub struct _Py_LocalMonitors {
-    pub tools: [u8; if cfg!(Py_3_13) {
-        _PY_MONITORING_LOCAL_EVENTS
-    } else {
-        _PY_MONITORING_UNGROUPED_EVENTS
-    }],
-}
-
-#[cfg(Py_3_12)]
-#[repr(C)]
-#[derive(Clone, Copy)]
-pub struct _Py_GlobalMonitors {
-    pub tools: [u8; _PY_MONITORING_UNGROUPED_EVENTS],
-}
-
-// skipped _Py_CODEUNIT
+// skipped private _Py_CODEUNIT
 
-// skipped _Py_OPCODE
-// skipped _Py_OPARG
+// skipped private _Py_OPCODE
+// skipped private _Py_OPARG
 
-// skipped _py_make_codeunit
+// skipped private _py_make_codeunit
 
-// skipped _py_set_opcode
+// skipped private _py_set_opcode
 
-// skipped _Py_MAKE_CODEUNIT
-// skipped _Py_SET_OPCODE
-
-#[cfg(Py_3_12)]
-#[repr(C)]
-#[derive(Copy, Clone)]
-pub struct _PyCoCached {
-    pub _co_code: *mut PyObject,
-    pub _co_varnames: *mut PyObject,
-    pub _co_cellvars: *mut PyObject,
-    pub _co_freevars: *mut PyObject,
-}
-
-#[cfg(Py_3_12)]
-#[repr(C)]
-#[derive(Copy, Clone)]
-pub struct _PyCoLineInstrumentationData {
-    pub original_opcode: u8,
-    pub line_delta: i8,
-}
+// skipped private _Py_MAKE_CODEUNIT
+// skipped private _Py_SET_OPCODE
 
-#[cfg(Py_3_12)]
-#[repr(C)]
-#[derive(Copy, Clone)]
-pub struct _PyCoMonitoringData {
-    pub local_monitors: _Py_LocalMonitors,
-    pub active_monitors: _Py_LocalMonitors,
-    pub tools: *mut u8,
-    pub lines: *mut _PyCoLineInstrumentationData,
-    pub line_tools: *mut u8,
-    pub per_instruction_opcodes: *mut u8,
-    pub per_instruction_tools: *mut u8,
-}
-
-#[cfg(all(not(any(PyPy, GraalPy)), not(Py_3_7)))]
-opaque_struct!(PyCodeObject);
-
-#[cfg(all(not(any(PyPy, GraalPy)), Py_3_7, not(Py_3_8)))]
-#[repr(C)]
-pub struct PyCodeObject {
-    pub ob_base: PyObject,
-    pub co_argcount: c_int,
-    pub co_kwonlyargcount: c_int,
-    pub co_nlocals: c_int,
-    pub co_stacksize: c_int,
-    pub co_flags: c_int,
-    pub co_firstlineno: c_int,
-    pub co_code: *mut PyObject,
-    pub co_consts: *mut PyObject,
-    pub co_names: *mut PyObject,
-    pub co_varnames: *mut PyObject,
-    pub co_freevars: *mut PyObject,
-    pub co_cellvars: *mut PyObject,
-    pub co_cell2arg: *mut Py_ssize_t,
-    pub co_filename: *mut PyObject,
-    pub co_name: *mut PyObject,
-    pub co_lnotab: *mut PyObject,
-    pub co_zombieframe: *mut c_void,
-    pub co_weakreflist: *mut PyObject,
-    pub co_extra: *mut c_void,
-}
-
-#[cfg(Py_3_13)]
-opaque_struct!(_PyExecutorArray);
-
-#[cfg(all(not(any(PyPy, GraalPy)), Py_3_8, not(Py_3_11)))]
-#[repr(C)]
-pub struct PyCodeObject {
-    pub ob_base: PyObject,
-    pub co_argcount: c_int,
-    pub co_posonlyargcount: c_int,
-    pub co_kwonlyargcount: c_int,
-    pub co_nlocals: c_int,
-    pub co_stacksize: c_int,
-    pub co_flags: c_int,
-    pub co_firstlineno: c_int,
-    pub co_code: *mut PyObject,
-    pub co_consts: *mut PyObject,
-    pub co_names: *mut PyObject,
-    pub co_varnames: *mut PyObject,
-    pub co_freevars: *mut PyObject,
-    pub co_cellvars: *mut PyObject,
-    pub co_cell2arg: *mut Py_ssize_t,
-    pub co_filename: *mut PyObject,
-    pub co_name: *mut PyObject,
-    #[cfg(not(Py_3_10))]
-    pub co_lnotab: *mut PyObject,
-    #[cfg(Py_3_10)]
-    pub co_linetable: *mut PyObject,
-    pub co_zombieframe: *mut c_void,
-    pub co_weakreflist: *mut PyObject,
-    pub co_extra: *mut c_void,
-    pub co_opcache_map: *mut c_uchar,
-    pub co_opcache: *mut _PyOpcache,
-    pub co_opcache_flag: c_int,
-    pub co_opcache_size: c_uchar,
-}
+// skipped private _PyCoCached
+// skipped private _PyCoLineInstrumentationData
+// skipped private _PyCoMontoringData
 
-#[cfg(all(not(any(PyPy, GraalPy)), Py_3_11))]
-#[repr(C)]
-pub struct PyCodeObject {
-    pub ob_base: PyVarObject,
-    pub co_consts: *mut PyObject,
-    pub co_names: *mut PyObject,
-    pub co_exceptiontable: *mut PyObject,
-    pub co_flags: c_int,
-    #[cfg(not(Py_3_12))]
-    pub co_warmup: c_int,
+// skipped private _PyExecutorArray
 
-    pub co_argcount: c_int,
-    pub co_posonlyargcount: c_int,
-    pub co_kwonlyargcount: c_int,
-    pub co_stacksize: c_int,
-    pub co_firstlineno: c_int,
-
-    pub co_nlocalsplus: c_int,
-    #[cfg(Py_3_12)]
-    pub co_framesize: c_int,
-    pub co_nlocals: c_int,
-    #[cfg(not(Py_3_12))]
-    pub co_nplaincellvars: c_int,
-    pub co_ncellvars: c_int,
-    pub co_nfreevars: c_int,
-    #[cfg(Py_3_12)]
-    pub co_version: u32,
-
-    pub co_localsplusnames: *mut PyObject,
-    pub co_localspluskinds: *mut PyObject,
-    pub co_filename: *mut PyObject,
-    pub co_name: *mut PyObject,
-    pub co_qualname: *mut PyObject,
-    pub co_linetable: *mut PyObject,
-    pub co_weakreflist: *mut PyObject,
-    #[cfg(not(Py_3_12))]
-    pub _co_code: *mut PyObject,
-    #[cfg(not(Py_3_12))]
-    pub _co_linearray: *mut c_char,
-    #[cfg(Py_3_13)]
-    pub co_executors: *mut _PyExecutorArray,
-    #[cfg(Py_3_12)]
-    pub _co_cached: *mut _PyCoCached,
-    #[cfg(all(Py_3_12, not(Py_3_13)))]
-    pub _co_instrumentation_version: u64,
-    #[cfg(Py_3_13)]
-    pub _co_instrumentation_version: libc::uintptr_t,
-    #[cfg(Py_3_12)]
-    pub _co_monitoring: *mut _PyCoMonitoringData,
-    pub _co_firsttraceable: c_int,
-    pub co_extra: *mut c_void,
-    pub co_code_adaptive: [c_char; 1],
-}
-
-#[cfg(PyPy)]
-#[repr(C)]
-pub struct PyCodeObject {
-    pub ob_base: PyObject,
-    pub co_name: *mut PyObject,
-    pub co_filename: *mut PyObject,
-    pub co_argcount: c_int,
-    pub co_flags: c_int,
-}
+opaque_struct!(
+    #[doc = "A Python code object.\n"]
+    #[doc = "\n"]
+    #[doc = "`pyo3-ffi` does not expose the contents of this struct, as it has no stability guarantees."]
+    pub PyCodeObject
+);
 
 /* Masks for co_flags */
 pub const CO_OPTIMIZED: c_int = 0x0001;
@@ -249,28 +83,14 @@ pub unsafe fn PyCode_Check(op: *mut PyObject) -> c_int {
     (Py_TYPE(op) == addr_of_mut!(PyCode_Type)) as c_int
 }
 
-#[inline]
-#[cfg(all(not(any(PyPy, GraalPy)), Py_3_10, not(Py_3_11)))]
-pub unsafe fn PyCode_GetNumFree(op: *mut PyCodeObject) -> Py_ssize_t {
-    crate::PyTuple_GET_SIZE((*op).co_freevars)
-}
-
-#[inline]
-#[cfg(all(not(Py_3_10), Py_3_11, not(any(PyPy, GraalPy))))]
-pub unsafe fn PyCode_GetNumFree(op: *mut PyCodeObject) -> c_int {
-    (*op).co_nfreevars
-}
-
 extern "C" {
     #[cfg(PyPy)]
     #[link_name = "PyPyCode_Check"]
     pub fn PyCode_Check(op: *mut PyObject) -> c_int;
-
-    #[cfg(PyPy)]
-    #[link_name = "PyPyCode_GetNumFree"]
-    pub fn PyCode_GetNumFree(op: *mut PyCodeObject) -> Py_ssize_t;
 }
 
+// skipped PyCode_GetNumFree (requires knowledge of code object layout)
+
 extern "C" {
     #[cfg(not(GraalPy))]
     #[cfg_attr(PyPy, link_name = "PyPyCode_New")]
diff --git a/pyo3-ffi/src/cpython/compile.rs b/pyo3-ffi/src/cpython/compile.rs
index 79f06c92003..078b5e0d675 100644
--- a/pyo3-ffi/src/cpython/compile.rs
+++ b/pyo3-ffi/src/cpython/compile.rs
@@ -6,19 +6,21 @@ use crate::pyarena::*;
 use crate::pythonrun::*;
 #[cfg(not(any(PyPy, Py_3_10)))]
 use crate::PyCodeObject;
+use crate::INT_MAX;
 #[cfg(not(any(PyPy, Py_3_10)))]
 use std::os::raw::c_char;
 use std::os::raw::c_int;
 
-// skipped non-limited PyCF_MASK
-// skipped non-limited PyCF_MASK_OBSOLETE
-// skipped non-limited PyCF_SOURCE_IS_UTF8
-// skipped non-limited PyCF_DONT_IMPLY_DEDENT
-// skipped non-limited PyCF_ONLY_AST
-// skipped non-limited PyCF_IGNORE_COOKIE
-// skipped non-limited PyCF_TYPE_COMMENTS
-// skipped non-limited PyCF_ALLOW_TOP_LEVEL_AWAIT
-// skipped non-limited PyCF_COMPILE_MASK
+// skipped PyCF_MASK
+// skipped PyCF_MASK_OBSOLETE
+// skipped PyCF_SOURCE_IS_UTF8
+// skipped PyCF_DONT_IMPLY_DEDENT
+// skipped PyCF_ONLY_AST
+// skipped PyCF_IGNORE_COOKIE
+// skipped PyCF_TYPE_COMMENTS
+// skipped PyCF_ALLOW_TOP_LEVEL_AWAIT
+// skipped PyCF_OPTIMIZED_AST
+// skipped PyCF_COMPILE_MASK
 
 #[repr(C)]
 #[derive(Copy, Clone)]
@@ -28,31 +30,23 @@ pub struct PyCompilerFlags {
     pub cf_feature_version: c_int,
 }
 
-// skipped non-limited _PyCompilerFlags_INIT
+// skipped _PyCompilerFlags_INIT
 
-#[cfg(all(Py_3_12, not(any(Py_3_13, PyPy, GraalPy))))]
-#[repr(C)]
-#[derive(Copy, Clone)]
-pub struct _PyCompilerSrcLocation {
-    pub lineno: c_int,
-    pub end_lineno: c_int,
-    pub col_offset: c_int,
-    pub end_col_offset: c_int,
-}
-
-// skipped SRC_LOCATION_FROM_AST
-
-#[cfg(not(any(PyPy, GraalPy, Py_3_13)))]
+// NB this type technically existed in the header until 3.13, when it was
+// moved to the internal CPython headers.
+//
+// We choose not to expose it in the public API past 3.10, as it is
+// not used in the public API past that point.
+#[cfg(not(any(PyPy, GraalPy, Py_3_10)))]
 #[repr(C)]
 #[derive(Copy, Clone)]
 pub struct PyFutureFeatures {
     pub ff_features: c_int,
-    #[cfg(not(Py_3_12))]
     pub ff_lineno: c_int,
-    #[cfg(Py_3_12)]
-    pub ff_location: _PyCompilerSrcLocation,
 }
 
+// FIXME: these constants should probably be &CStr, if they are used at all
+
 pub const FUTURE_NESTED_SCOPES: &str = "nested_scopes";
 pub const FUTURE_GENERATORS: &str = "generators";
 pub const FUTURE_DIVISION: &str = "division";
@@ -62,13 +56,12 @@ pub const FUTURE_PRINT_FUNCTION: &str = "print_function";
 pub const FUTURE_UNICODE_LITERALS: &str = "unicode_literals";
 pub const FUTURE_BARRY_AS_BDFL: &str = "barry_as_FLUFL";
 pub const FUTURE_GENERATOR_STOP: &str = "generator_stop";
-// skipped non-limited FUTURE_ANNOTATIONS
+pub const FUTURE_ANNOTATIONS: &str = "annotations";
 
+#[cfg(not(any(PyPy, GraalPy, Py_3_10)))]
 extern "C" {
-    #[cfg(not(any(PyPy, Py_3_10)))]
     pub fn PyNode_Compile(arg1: *mut _node, arg2: *const c_char) -> *mut PyCodeObject;
 
-    #[cfg(not(any(PyPy, Py_3_10)))]
     pub fn PyAST_CompileEx(
         _mod: *mut _mod,
         filename: *const c_char,
@@ -77,7 +70,6 @@ extern "C" {
         arena: *mut PyArena,
     ) -> *mut PyCodeObject;
 
-    #[cfg(not(any(PyPy, Py_3_10)))]
     pub fn PyAST_CompileObject(
         _mod: *mut _mod,
         filename: *mut PyObject,
@@ -86,23 +78,20 @@ extern "C" {
         arena: *mut PyArena,
     ) -> *mut PyCodeObject;
 
-    #[cfg(not(any(PyPy, Py_3_10)))]
     pub fn PyFuture_FromAST(_mod: *mut _mod, filename: *const c_char) -> *mut PyFutureFeatures;
 
-    #[cfg(not(any(PyPy, Py_3_10)))]
     pub fn PyFuture_FromASTObject(
         _mod: *mut _mod,
         filename: *mut PyObject,
     ) -> *mut PyFutureFeatures;
+}
 
-    // skipped non-limited _Py_Mangle
-    // skipped non-limited PY_INVALID_STACK_EFFECT
+pub const PY_INVALID_STACK_EFFECT: c_int = INT_MAX;
+
+extern "C" {
 
     pub fn PyCompile_OpcodeStackEffect(opcode: c_int, oparg: c_int) -> c_int;
 
     #[cfg(Py_3_8)]
     pub fn PyCompile_OpcodeStackEffectWithJump(opcode: c_int, oparg: c_int, jump: c_int) -> c_int;
-
-    // skipped non-limited _PyASTOptimizeState
-    // skipped non-limited _PyAST_Optimize
 }
diff --git a/pyo3-ffi/src/cpython/critical_section.rs b/pyo3-ffi/src/cpython/critical_section.rs
index 97b2f5e0559..808dba870c6 100644
--- a/pyo3-ffi/src/cpython/critical_section.rs
+++ b/pyo3-ffi/src/cpython/critical_section.rs
@@ -17,10 +17,10 @@ pub struct PyCriticalSection2 {
 }
 
 #[cfg(not(Py_GIL_DISABLED))]
-opaque_struct!(PyCriticalSection);
+opaque_struct!(pub PyCriticalSection);
 
 #[cfg(not(Py_GIL_DISABLED))]
-opaque_struct!(PyCriticalSection2);
+opaque_struct!(pub PyCriticalSection2);
 
 extern "C" {
     pub fn PyCriticalSection_Begin(c: *mut PyCriticalSection, op: *mut PyObject);
diff --git a/pyo3-ffi/src/cpython/dictobject.rs b/pyo3-ffi/src/cpython/dictobject.rs
index 79dcbfdb62e..93ce560c573 100644
--- a/pyo3-ffi/src/cpython/dictobject.rs
+++ b/pyo3-ffi/src/cpython/dictobject.rs
@@ -2,10 +2,10 @@ use crate::object::*;
 use crate::pyport::Py_ssize_t;
 use std::os::raw::c_int;
 
-opaque_struct!(PyDictKeysObject);
+opaque_struct!(pub PyDictKeysObject);
 
 #[cfg(Py_3_11)]
-opaque_struct!(PyDictValues);
+opaque_struct!(pub PyDictValues);
 
 #[cfg(not(GraalPy))]
 #[repr(C)]
diff --git a/pyo3-ffi/src/cpython/frameobject.rs b/pyo3-ffi/src/cpython/frameobject.rs
index e9b9c183f37..993e93c838b 100644
--- a/pyo3-ffi/src/cpython/frameobject.rs
+++ b/pyo3-ffi/src/cpython/frameobject.rs
@@ -53,7 +53,7 @@ pub struct PyFrameObject {
 }
 
 #[cfg(any(PyPy, GraalPy, Py_3_11))]
-opaque_struct!(PyFrameObject);
+opaque_struct!(pub PyFrameObject);
 
 // skipped _PyFrame_IsRunnable
 // skipped _PyFrame_IsExecuting
diff --git a/pyo3-ffi/src/cpython/genobject.rs b/pyo3-ffi/src/cpython/genobject.rs
index c9d419e3782..51c80f1a212 100644
--- a/pyo3-ffi/src/cpython/genobject.rs
+++ b/pyo3-ffi/src/cpython/genobject.rs
@@ -1,7 +1,5 @@
 use crate::object::*;
 use crate::PyFrameObject;
-#[cfg(not(any(PyPy, GraalPy)))]
-use crate::_PyErr_StackItem;
 #[cfg(all(Py_3_11, not(any(PyPy, GraalPy))))]
 use std::os::raw::c_char;
 use std::os::raw::c_int;
@@ -20,7 +18,7 @@ pub struct PyGenObject {
     pub gi_weakreflist: *mut PyObject,
     pub gi_name: *mut PyObject,
     pub gi_qualname: *mut PyObject,
-    pub gi_exc_state: _PyErr_StackItem,
+    pub gi_exc_state: crate::cpython::pystate::_PyErr_StackItem,
     #[cfg(Py_3_11)]
     pub gi_origin_or_finalizer: *mut PyObject,
     #[cfg(Py_3_11)]
diff --git a/pyo3-ffi/src/cpython/pyframe.rs b/pyo3-ffi/src/cpython/pyframe.rs
index 5e1e16a7d08..f0c38be47be 100644
--- a/pyo3-ffi/src/cpython/pyframe.rs
+++ b/pyo3-ffi/src/cpython/pyframe.rs
@@ -1,2 +1,3 @@
+// NB used in `_PyEval_EvalFrameDefault`, maybe we remove this too.
 #[cfg(all(Py_3_11, not(PyPy)))]
-opaque_struct!(_PyInterpreterFrame);
+opaque_struct!(pub _PyInterpreterFrame);
diff --git a/pyo3-ffi/src/cpython/pystate.rs b/pyo3-ffi/src/cpython/pystate.rs
index 650cd6a1f7f..b8f6fd667b7 100644
--- a/pyo3-ffi/src/cpython/pystate.rs
+++ b/pyo3-ffi/src/cpython/pystate.rs
@@ -27,16 +27,18 @@ pub const PyTrace_OPCODE: c_int = 7;
 // skipped PyTraceInfo
 // skipped CFrame
 
+/// Private structure used inline in `PyGenObject`
 #[cfg(not(PyPy))]
 #[repr(C)]
 #[derive(Clone, Copy)]
+#[doc(hidden)] // TODO should be able to make pub(crate) after MSRV 1.74
 pub struct _PyErr_StackItem {
     #[cfg(not(Py_3_11))]
-    pub exc_type: *mut PyObject,
-    pub exc_value: *mut PyObject,
+    exc_type: *mut PyObject,
+    exc_value: *mut PyObject,
     #[cfg(not(Py_3_11))]
-    pub exc_traceback: *mut PyObject,
-    pub previous_item: *mut _PyErr_StackItem,
+    exc_traceback: *mut PyObject,
+    previous_item: *mut _PyErr_StackItem,
 }
 
 // skipped _PyStackChunk
diff --git a/pyo3-ffi/src/cpython/weakrefobject.rs b/pyo3-ffi/src/cpython/weakrefobject.rs
index 88bb501bcc5..1c50c7a759f 100644
--- a/pyo3-ffi/src/cpython/weakrefobject.rs
+++ b/pyo3-ffi/src/cpython/weakrefobject.rs
@@ -1,3 +1,4 @@
+// NB publicly re-exported in `src/weakrefobject.rs`
 #[cfg(not(any(PyPy, GraalPy)))]
 pub struct _PyWeakReference {
     pub ob_base: crate::PyObject,
diff --git a/pyo3-ffi/src/dictobject.rs b/pyo3-ffi/src/dictobject.rs
index 710be80243f..e609352ac1b 100644
--- a/pyo3-ffi/src/dictobject.rs
+++ b/pyo3-ffi/src/dictobject.rs
@@ -118,4 +118,4 @@ extern "C" {
 
 #[cfg(any(PyPy, GraalPy, Py_LIMITED_API))]
 // TODO: remove (see https://github.com/PyO3/pyo3/pull/1341#issuecomment-751515985)
-opaque_struct!(PyDictObject);
+opaque_struct!(pub PyDictObject);
diff --git a/pyo3-ffi/src/floatobject.rs b/pyo3-ffi/src/floatobject.rs
index 65fc1d4c316..4e1d6476f58 100644
--- a/pyo3-ffi/src/floatobject.rs
+++ b/pyo3-ffi/src/floatobject.rs
@@ -4,7 +4,7 @@ use std::ptr::addr_of_mut;
 
 #[cfg(Py_LIMITED_API)]
 // TODO: remove (see https://github.com/PyO3/pyo3/pull/1341#issuecomment-751515985)
-opaque_struct!(PyFloatObject);
+opaque_struct!(pub PyFloatObject);
 
 #[cfg_attr(windows, link(name = "pythonXY"))]
 extern "C" {
diff --git a/pyo3-ffi/src/lib.rs b/pyo3-ffi/src/lib.rs
index aba8866b266..9b98d08c3c5 100644
--- a/pyo3-ffi/src/lib.rs
+++ b/pyo3-ffi/src/lib.rs
@@ -341,9 +341,10 @@
 // model opaque types:
 // https://doc.rust-lang.org/nomicon/ffi.html#representing-opaque-structs
 macro_rules! opaque_struct {
-    ($name:ident) => {
+    ($(#[$attrs:meta])* $pub:vis $name:ident) => {
+        $(#[$attrs])*
         #[repr(C)]
-        pub struct $name([u8; 0]);
+        $pub struct $name([u8; 0]);
     };
 }
 
diff --git a/pyo3-ffi/src/longobject.rs b/pyo3-ffi/src/longobject.rs
index 68b4ecba540..eca0af3d0a5 100644
--- a/pyo3-ffi/src/longobject.rs
+++ b/pyo3-ffi/src/longobject.rs
@@ -4,7 +4,7 @@ use libc::size_t;
 use std::os::raw::{c_char, c_double, c_int, c_long, c_longlong, c_ulong, c_ulonglong, c_void};
 use std::ptr::addr_of_mut;
 
-opaque_struct!(PyLongObject);
+opaque_struct!(pub PyLongObject);
 
 #[inline]
 pub unsafe fn PyLong_Check(op: *mut PyObject) -> c_int {
diff --git a/pyo3-ffi/src/object.rs b/pyo3-ffi/src/object.rs
index 087cd32920c..38f79ba111a 100644
--- a/pyo3-ffi/src/object.rs
+++ b/pyo3-ffi/src/object.rs
@@ -10,7 +10,7 @@ use std::ptr;
 use std::sync::atomic::{AtomicIsize, AtomicU32, AtomicU8, Ordering::Relaxed};
 
 #[cfg(Py_LIMITED_API)]
-opaque_struct!(PyTypeObject);
+opaque_struct!(pub PyTypeObject);
 
 #[cfg(not(Py_LIMITED_API))]
 pub use crate::cpython::object::PyTypeObject;
diff --git a/pyo3-ffi/src/pyarena.rs b/pyo3-ffi/src/pyarena.rs
index 87d5f28a7a5..1200de3df48 100644
--- a/pyo3-ffi/src/pyarena.rs
+++ b/pyo3-ffi/src/pyarena.rs
@@ -1 +1 @@
-opaque_struct!(PyArena);
+opaque_struct!(pub PyArena);
diff --git a/pyo3-ffi/src/pyframe.rs b/pyo3-ffi/src/pyframe.rs
index 4dd3d2b31a5..1693b20b0af 100644
--- a/pyo3-ffi/src/pyframe.rs
+++ b/pyo3-ffi/src/pyframe.rs
@@ -6,7 +6,7 @@ use crate::PyFrameObject;
 use std::os::raw::c_int;
 
 #[cfg(Py_LIMITED_API)]
-opaque_struct!(PyFrameObject);
+opaque_struct!(pub PyFrameObject);
 
 extern "C" {
     pub fn PyFrame_GetLineNumber(f: *mut PyFrameObject) -> c_int;
diff --git a/pyo3-ffi/src/pyport.rs b/pyo3-ffi/src/pyport.rs
index a144c67fb1b..e524831d80d 100644
--- a/pyo3-ffi/src/pyport.rs
+++ b/pyo3-ffi/src/pyport.rs
@@ -1,3 +1,8 @@
+// NB libc does not define this constant on all platforms, so we hard code it
+// like CPython does.
+// https://github.com/python/cpython/blob/d8b9011702443bb57579f8834f3effe58e290dfc/Include/pyport.h#L372
+pub const INT_MAX: std::os::raw::c_int = 2147483647;
+
 pub type PY_UINT32_T = u32;
 pub type PY_UINT64_T = u64;
 
@@ -11,8 +16,8 @@ pub type Py_ssize_t = ::libc::ssize_t;
 pub type Py_hash_t = Py_ssize_t;
 pub type Py_uhash_t = ::libc::size_t;
 
-pub const PY_SSIZE_T_MIN: Py_ssize_t = isize::MIN as Py_ssize_t;
-pub const PY_SSIZE_T_MAX: Py_ssize_t = isize::MAX as Py_ssize_t;
+pub const PY_SSIZE_T_MIN: Py_ssize_t = Py_ssize_t::MIN;
+pub const PY_SSIZE_T_MAX: Py_ssize_t = Py_ssize_t::MAX;
 
 #[cfg(target_endian = "big")]
 pub const PY_BIG_ENDIAN: usize = 1;
diff --git a/pyo3-ffi/src/pystate.rs b/pyo3-ffi/src/pystate.rs
index a6caf421ff6..e97cca94ed5 100644
--- a/pyo3-ffi/src/pystate.rs
+++ b/pyo3-ffi/src/pystate.rs
@@ -9,8 +9,8 @@ use std::os::raw::c_long;
 
 pub const MAX_CO_EXTRA_USERS: c_int = 255;
 
-opaque_struct!(PyThreadState);
-opaque_struct!(PyInterpreterState);
+opaque_struct!(pub PyThreadState);
+opaque_struct!(pub PyInterpreterState);
 
 extern "C" {
     #[cfg(not(PyPy))]
diff --git a/pyo3-ffi/src/pythonrun.rs b/pyo3-ffi/src/pythonrun.rs
index e7ea2d2efd0..80209b5875a 100644
--- a/pyo3-ffi/src/pythonrun.rs
+++ b/pyo3-ffi/src/pythonrun.rs
@@ -49,12 +49,12 @@ pub const PYOS_STACK_MARGIN: c_int = 2048;
 // skipped PyOS_CheckStack under Microsoft C
 
 #[cfg(not(any(PyPy, Py_LIMITED_API, Py_3_10)))]
-opaque_struct!(_mod);
+opaque_struct!(pub _mod);
 
 #[cfg(not(any(PyPy, Py_3_10)))]
-opaque_struct!(symtable);
+opaque_struct!(pub symtable);
 #[cfg(not(any(PyPy, Py_3_10)))]
-opaque_struct!(_node);
+opaque_struct!(pub _node);
 
 #[cfg(not(any(PyPy, Py_LIMITED_API, Py_3_10)))]
 #[cfg_attr(Py_3_9, deprecated(note = "Python 3.9"))]
diff --git a/pyo3-ffi/src/weakrefobject.rs b/pyo3-ffi/src/weakrefobject.rs
index 305dc290fa8..0a1afe1a619 100644
--- a/pyo3-ffi/src/weakrefobject.rs
+++ b/pyo3-ffi/src/weakrefobject.rs
@@ -4,7 +4,7 @@ use std::os::raw::c_int;
 use std::ptr::addr_of_mut;
 
 #[cfg(all(not(PyPy), Py_LIMITED_API, not(GraalPy)))]
-opaque_struct!(PyWeakReference);
+opaque_struct!(pub PyWeakReference);
 
 #[cfg(all(not(PyPy), not(Py_LIMITED_API), not(GraalPy)))]
 pub use crate::_PyWeakReference as PyWeakReference;