diff --git a/crates/vm/src/builtins/mod.rs b/crates/vm/src/builtins/mod.rs
index c40f09bde..e9ca1f8b4 100644
--- a/crates/vm/src/builtins/mod.rs
+++ b/crates/vm/src/builtins/mod.rs
@@ -92,7 +92,7 @@ pub(crate) mod zip;
 pub use zip::PyZip;
 #[path = "union.rs"]
 pub(crate) mod union_;
-pub use union_::PyUnion;
+pub use union_::{PyUnion, make_union};
 pub(crate) mod descriptor;
 
 pub use float::try_to_bigint as try_f64_to_bigint;
diff --git a/crates/vm/src/stdlib/_abc.rs b/crates/vm/src/stdlib/_abc.rs
new file mode 100644
index 000000000..06b403206
--- /dev/null
+++ b/crates/vm/src/stdlib/_abc.rs
@@ -0,0 +1,498 @@
+//! Implementation of the `_abc` module.
+//!
+//! This module provides the C implementation of Abstract Base Classes (ABCs)
+//! as defined in PEP 3119.
+
+pub(crate) use _abc::make_module;
+
+#[pymodule]
+mod _abc {
+    use crate::{
+        AsObject, PyObject, PyObjectRef, PyPayload, PyRef, PyResult, VirtualMachine,
+        builtins::{PyFrozenSet, PyList, PySet, PyStr, PyTupleRef, PyTypeRef, PyWeak},
+        common::lock::PyRwLock,
+        convert::ToPyObject,
+        protocol::PyIterReturn,
+        types::Constructor,
+    };
+    use std::sync::atomic::{AtomicU64, Ordering};
+
+    // Global invalidation counter
+    static ABC_INVALIDATION_COUNTER: AtomicU64 = AtomicU64::new(0);
+
+    fn get_invalidation_counter() -> u64 {
+        ABC_INVALIDATION_COUNTER.load(Ordering::SeqCst)
+    }
+
+    fn increment_invalidation_counter() {
+        ABC_INVALIDATION_COUNTER.fetch_add(1, Ordering::SeqCst);
+    }
+
+    /// Internal state held by ABC machinery.
+    #[pyattr]
+    #[pyclass(name = "_abc_data", module = "_abc")]
+    #[derive(Debug, PyPayload)]
+    struct AbcData {
+        // WeakRef sets for registry and caches
+        registry: PyRwLock<Option<PyRef<PySet>>>,
+        cache: PyRwLock<Option<PyRef<PySet>>>,
+        negative_cache: PyRwLock<Option<PyRef<PySet>>>,
+        negative_cache_version: AtomicU64,
+    }
+
+    #[pyclass(with(Constructor))]
+    impl AbcData {
+        fn new() -> Self {
+            AbcData {
+                registry: PyRwLock::new(None),
+                cache: PyRwLock::new(None),
+                negative_cache: PyRwLock::new(None),
+                negative_cache_version: AtomicU64::new(get_invalidation_counter()),
+            }
+        }
+
+        fn get_cache_version(&self) -> u64 {
+            self.negative_cache_version.load(Ordering::SeqCst)
+        }
+
+        fn set_cache_version(&self, version: u64) {
+            self.negative_cache_version.store(version, Ordering::SeqCst);
+        }
+    }
+
+    impl Constructor for AbcData {
+        type Args = ();
+
+        fn py_new(
+            _cls: &crate::Py<crate::builtins::PyType>,
+            _args: Self::Args,
+            _vm: &VirtualMachine,
+        ) -> PyResult<Self> {
+            Ok(AbcData::new())
+        }
+    }
+
+    /// Get the _abc_impl attribute from an ABC class
+    fn get_impl(cls: &PyObject, vm: &VirtualMachine) -> PyResult<PyRef<AbcData>> {
+        let impl_obj = cls.get_attr("_abc_impl", vm)?;
+        impl_obj
+            .downcast::<AbcData>()
+            .map_err(|_| vm.new_type_error("_abc_impl is set to a wrong type".to_owned()))
+    }
+
+    /// Check if obj is in the weak set
+    fn in_weak_set(
+        set_lock: &PyRwLock<Option<PyRef<PySet>>>,
+        obj: &PyObject,
+        vm: &VirtualMachine,
+    ) -> PyResult<bool> {
+        let set_opt = set_lock.read();
+        let set = match &*set_opt {
+            Some(s) if !s.elements().is_empty() => s.clone(),
+            _ => return Ok(false),
+        };
+        drop(set_opt);
+
+        // Create a weak reference to the object
+        let weak_ref = match obj.downgrade(None, vm) {
+            Ok(w) => w,
+            Err(e) => {
+                // If we can't create a weakref (e.g., TypeError), the object can't be in the set
+                if e.class().is(vm.ctx.exceptions.type_error) {
+                    return Ok(false);
+                }
+                return Err(e);
+            }
+        };
+
+        // Use vm.call_method to call __contains__
+        let weak_ref_obj: PyObjectRef = weak_ref.into();
+        vm.call_method(set.as_ref(), "__contains__", (weak_ref_obj,))?
+            .try_to_bool(vm)
+    }
+
+    /// Add obj to the weak set
+    fn add_to_weak_set(
+        set_lock: &PyRwLock<Option<PyRef<PySet>>>,
+        obj: &PyObject,
+        vm: &VirtualMachine,
+    ) -> PyResult<()> {
+        let mut set_opt = set_lock.write();
+        let set = match &*set_opt {
+            Some(s) => s.clone(),
+            None => {
+                let new_set = PySet::default().into_ref(&vm.ctx);
+                *set_opt = Some(new_set.clone());
+                new_set
+            }
+        };
+        drop(set_opt);
+
+        // Create a weak reference to the object
+        let weak_ref = obj.downgrade(None, vm)?;
+        set.add(weak_ref.into(), vm)?;
+        Ok(())
+    }
+
+    /// Returns the current ABC cache token.
+    #[pyfunction]
+    fn get_cache_token() -> u64 {
+        get_invalidation_counter()
+    }
+
+    /// Compute set of abstract method names.
+    fn compute_abstract_methods(cls: &PyObject, vm: &VirtualMachine) -> PyResult<()> {
+        let mut abstracts = Vec::new();
+
+        // Stage 1: direct abstract methods
+        let ns = cls.get_attr("__dict__", vm)?;
+        let items = vm.call_method(&ns, "items", ())?;
+        let iter = items.get_iter(vm)?;
+
+        loop {
+            match iter.next(vm)? {
+                PyIterReturn::Return(item) => {
+                    let tuple: PyTupleRef = item
+                        .downcast()
+                        .map_err(|_| vm.new_type_error("items() returned non-tuple".to_owned()))?;
+                    let elements = tuple.as_slice();
+                    if elements.len() != 2 {
+                        return Err(vm.new_type_error(
+                            "items() returned item which size is not 2".to_owned(),
+                        ));
+                    }
+                    let key = &elements[0];
+                    let value = &elements[1];
+
+                    // Check if value has __isabstractmethod__ = True
+                    if let Ok(is_abstract) = value.get_attr("__isabstractmethod__", vm) {
+                        if is_abstract.try_to_bool(vm)? {
+                            abstracts.push(key.clone());
+                        }
+                    }
+                }
+                PyIterReturn::StopIteration(_) => break,
+            }
+        }
+
+        // Stage 2: inherited abstract methods
+        let bases: PyTupleRef = cls
+            .get_attr("__bases__", vm)?
+            .downcast()
+            .map_err(|_| vm.new_type_error("__bases__ is not a tuple".to_owned()))?;
+
+        for base in bases.iter() {
+            if let Ok(base_abstracts) = base.get_attr("__abstractmethods__", vm) {
+                let iter = base_abstracts.get_iter(vm)?;
+                loop {
+                    match iter.next(vm)? {
+                        PyIterReturn::Return(key) => {
+                            // Try to get the attribute from cls - key should be a string
+                            if let Some(key_str) = key.downcast_ref::<PyStr>() {
+                                if let Some(value) =
+                                    vm.get_attribute_opt(cls.to_owned(), key_str)?
+                                {
+                                    if let Ok(is_abstract) =
+                                        value.get_attr("__isabstractmethod__", vm)
+                                    {
+                                        if is_abstract.try_to_bool(vm)? {
+                                            abstracts.push(key);
+                                        }
+                                    }
+                                }
+                            }
+                        }
+                        PyIterReturn::StopIteration(_) => break,
+                    }
+                }
+            }
+        }
+
+        // Set __abstractmethods__
+        let abstracts_set = PyFrozenSet::from_iter(vm, abstracts.into_iter())?;
+        cls.set_attr("__abstractmethods__", abstracts_set.into_pyobject(vm), vm)?;
+
+        Ok(())
+    }
+
+    /// Internal ABC helper for class set-up. Should be never used outside abc module.
+    #[pyfunction]
+    fn _abc_init(cls: PyObjectRef, vm: &VirtualMachine) -> PyResult<()> {
+        compute_abstract_methods(&cls, vm)?;
+
+        // Set up inheritance registry
+        let data = AbcData::new();
+        cls.set_attr("_abc_impl", data.to_pyobject(vm), vm)?;
+
+        Ok(())
+    }
+
+    /// Internal ABC helper for subclass registration. Should be never used outside abc module.
+    #[pyfunction]
+    fn _abc_register(
+        cls: PyObjectRef,
+        subclass: PyObjectRef,
+        vm: &VirtualMachine,
+    ) -> PyResult<PyObjectRef> {
+        // Type check
+        if !subclass.class().fast_issubclass(vm.ctx.types.type_type) {
+            return Err(vm.new_type_error("Can only register classes".to_owned()));
+        }
+
+        // Check if already a subclass
+        if subclass.is_subclass(&cls, vm)? {
+            return Ok(subclass);
+        }
+
+        // Check for cycles
+        if cls.is_subclass(&subclass, vm)? {
+            return Err(vm.new_runtime_error("Refusing to create an inheritance cycle".to_owned()));
+        }
+
+        // Add to registry
+        let impl_data = get_impl(&cls, vm)?;
+        add_to_weak_set(&impl_data.registry, &subclass, vm)?;
+
+        // Invalidate negative cache
+        increment_invalidation_counter();
+
+        Ok(subclass)
+    }
+
+    /// Internal ABC helper for instance checks. Should be never used outside abc module.
+    #[pyfunction]
+    fn _abc_instancecheck(
+        cls: PyObjectRef,
+        instance: PyObjectRef,
+        vm: &VirtualMachine,
+    ) -> PyResult<PyObjectRef> {
+        let impl_data = get_impl(&cls, vm)?;
+
+        // Get instance.__class__
+        let subclass = instance.get_attr("__class__", vm)?;
+
+        // Check cache
+        if in_weak_set(&impl_data.cache, &subclass, vm)? {
+            return Ok(vm.ctx.true_value.clone().into());
+        }
+
+        let subtype: PyObjectRef = instance.class().to_owned().into();
+        if subtype.is(&subclass) {
+            let invalidation_counter = get_invalidation_counter();
+            if impl_data.get_cache_version() == invalidation_counter {
+                if in_weak_set(&impl_data.negative_cache, &subclass, vm)? {
+                    return Ok(vm.ctx.false_value.clone().into());
+                }
+            }
+            // Fall back to __subclasscheck__
+            return vm.call_method(&cls, "__subclasscheck__", (subclass,));
+        }
+
+        // Call __subclasscheck__ on subclass
+        let result = vm.call_method(&cls, "__subclasscheck__", (subclass.clone(),))?;
+
+        match result.clone().try_to_bool(vm) {
+            Ok(true) => Ok(result),
+            Ok(false) => {
+                // Also try with subtype
+                vm.call_method(&cls, "__subclasscheck__", (subtype,))
+            }
+            Err(e) => Err(e),
+        }
+    }
+
+    /// Check if subclass is in registry (recursive)
+    fn subclasscheck_check_registry(
+        impl_data: &AbcData,
+        subclass: &PyObject,
+        vm: &VirtualMachine,
+    ) -> PyResult<Option<bool>> {
+        // Fast path: check if subclass is in weakref directly
+        if in_weak_set(&impl_data.registry, subclass, vm)? {
+            return Ok(Some(true));
+        }
+
+        let registry_opt = impl_data.registry.read();
+        let registry = match &*registry_opt {
+            Some(s) => s.clone(),
+            None => return Ok(None),
+        };
+        drop(registry_opt);
+
+        // Make a local copy to protect against concurrent modifications
+        let registry_copy = PyFrozenSet::from_iter(vm, registry.elements().into_iter())?;
+
+        for weak_ref_obj in registry_copy.elements() {
+            if let Ok(weak_ref) = weak_ref_obj.downcast::<PyWeak>() {
+                if let Some(rkey) = weak_ref.upgrade() {
+                    if subclass.to_owned().is_subclass(&rkey, vm)? {
+                        add_to_weak_set(&impl_data.cache, subclass, vm)?;
+                        return Ok(Some(true));
+                    }
+                }
+            }
+        }
+
+        Ok(None)
+    }
+
+    /// Internal ABC helper for subclass checks. Should be never used outside abc module.
+    #[pyfunction]
+    fn _abc_subclasscheck(
+        cls: PyObjectRef,
+        subclass: PyObjectRef,
+        vm: &VirtualMachine,
+    ) -> PyResult<bool> {
+        // Type check
+        if !subclass.class().fast_issubclass(vm.ctx.types.type_type) {
+            return Err(vm.new_type_error("issubclass() arg 1 must be a class".to_owned()));
+        }
+
+        let impl_data = get_impl(&cls, vm)?;
+
+        // 1. Check cache
+        if in_weak_set(&impl_data.cache, &subclass, vm)? {
+            return Ok(true);
+        }
+
+        // 2. Check negative cache; may have to invalidate
+        let invalidation_counter = get_invalidation_counter();
+        if impl_data.get_cache_version() < invalidation_counter {
+            // Invalidate the negative cache
+            // Clone set ref and drop lock before calling into VM to avoid reentrancy
+            let set = impl_data.negative_cache.read().clone();
+            if let Some(ref set) = set {
+                vm.call_method(set.as_ref(), "clear", ())?;
+            }
+            impl_data.set_cache_version(invalidation_counter);
+        } else if in_weak_set(&impl_data.negative_cache, &subclass, vm)? {
+            return Ok(false);
+        }
+
+        // 3. Check the subclass hook
+        let ok = vm.call_method(&cls, "__subclasshook__", (subclass.clone(),))?;
+        if ok.is(&vm.ctx.true_value) {
+            add_to_weak_set(&impl_data.cache, &subclass, vm)?;
+            return Ok(true);
+        }
+        if ok.is(&vm.ctx.false_value) {
+            add_to_weak_set(&impl_data.negative_cache, &subclass, vm)?;
+            return Ok(false);
+        }
+        if !ok.is(&vm.ctx.not_implemented) {
+            return Err(vm.new_exception_msg(
+                vm.ctx.exceptions.assertion_error.to_owned(),
+                "__subclasshook__ must return either False, True, or NotImplemented".to_owned(),
+            ));
+        }
+
+        // 4. Check if it's a direct subclass
+        let subclass_type: PyTypeRef = subclass
+            .clone()
+            .downcast()
+            .map_err(|_| vm.new_type_error("expected a type object".to_owned()))?;
+        let cls_type: PyTypeRef = cls
+            .clone()
+            .downcast()
+            .map_err(|_| vm.new_type_error("expected a type object".to_owned()))?;
+        if subclass_type.fast_issubclass(&cls_type) {
+            add_to_weak_set(&impl_data.cache, &subclass, vm)?;
+            return Ok(true);
+        }
+
+        // 5. Check if it's a subclass of a registered class (recursive)
+        if let Some(result) = subclasscheck_check_registry(&impl_data, &subclass, vm)? {
+            return Ok(result);
+        }
+
+        // 6. Check if it's a subclass of a subclass (recursive)
+        let subclasses: PyRef<PyList> = vm
+            .call_method(&cls, "__subclasses__", ())?
+            .downcast()
+            .map_err(|_| vm.new_type_error("__subclasses__() must return a list".to_owned()))?;
+
+        for scls in subclasses.borrow_vec().iter() {
+            if subclass.is_subclass(scls, vm)? {
+                add_to_weak_set(&impl_data.cache, &subclass, vm)?;
+                return Ok(true);
+            }
+        }
+
+        // No dice; update negative cache
+        add_to_weak_set(&impl_data.negative_cache, &subclass, vm)?;
+        Ok(false)
+    }
+
+    /// Internal ABC helper for cache and registry debugging.
+    #[pyfunction]
+    fn _get_dump(cls: PyObjectRef, vm: &VirtualMachine) -> PyResult<PyTupleRef> {
+        let impl_data = get_impl(&cls, vm)?;
+
+        let registry = {
+            let r = impl_data.registry.read();
+            match &*r {
+                Some(s) => {
+                    // Use copy method to get a shallow copy
+                    vm.call_method(s.as_ref(), "copy", ())?
+                }
+                None => PySet::default().to_pyobject(vm),
+            }
+        };
+
+        let cache = {
+            let c = impl_data.cache.read();
+            match &*c {
+                Some(s) => vm.call_method(s.as_ref(), "copy", ())?,
+                None => PySet::default().to_pyobject(vm),
+            }
+        };
+
+        let negative_cache = {
+            let nc = impl_data.negative_cache.read();
+            match &*nc {
+                Some(s) => vm.call_method(s.as_ref(), "copy", ())?,
+                None => PySet::default().to_pyobject(vm),
+            }
+        };
+
+        let version = impl_data.get_cache_version();
+
+        Ok(vm.ctx.new_tuple(vec![
+            registry,
+            cache,
+            negative_cache,
+            vm.ctx.new_int(version).into(),
+        ]))
+    }
+
+    /// Internal ABC helper to reset registry of a given class.
+    #[pyfunction]
+    fn _reset_registry(cls: PyObjectRef, vm: &VirtualMachine) -> PyResult<()> {
+        let impl_data = get_impl(&cls, vm)?;
+        // Clone set ref and drop lock before calling into VM to avoid reentrancy
+        let set = impl_data.registry.read().clone();
+        if let Some(ref set) = set {
+            vm.call_method(set.as_ref(), "clear", ())?;
+        }
+        Ok(())
+    }
+
+    /// Internal ABC helper to reset both caches of a given class.
+    #[pyfunction]
+    fn _reset_caches(cls: PyObjectRef, vm: &VirtualMachine) -> PyResult<()> {
+        let impl_data = get_impl(&cls, vm)?;
+
+        // Clone set refs and drop locks before calling into VM to avoid reentrancy
+        let cache = impl_data.cache.read().clone();
+        if let Some(ref set) = cache {
+            vm.call_method(set.as_ref(), "clear", ())?;
+        }
+
+        let negative_cache = impl_data.negative_cache.read().clone();
+        if let Some(ref set) = negative_cache {
+            vm.call_method(set.as_ref(), "clear", ())?;
+        }
+
+        Ok(())
+    }
+}
diff --git a/crates/vm/src/stdlib/mod.rs b/crates/vm/src/stdlib/mod.rs
index e46f333a2..85c28983d 100644
--- a/crates/vm/src/stdlib/mod.rs
+++ b/crates/vm/src/stdlib/mod.rs
@@ -1,3 +1,4 @@
+mod _abc;
 #[cfg(feature = "ast")]
 pub(crate) mod ast;
 pub mod atexit;
@@ -87,6 +88,7 @@ pub fn get_module_inits() -> StdlibMap {
     modules! {
         #[cfg(all())]
         {
+            "_abc" => _abc::make_module,
             "atexit" => atexit::make_module,
             "_codecs" => codecs::make_module,
             "_collections" => collections::make_module,
diff --git a/crates/vm/src/stdlib/typevar.rs b/crates/vm/src/stdlib/typevar.rs
index 65249bfd0..5d5b1fc7b 100644
--- a/crates/vm/src/stdlib/typevar.rs
+++ b/crates/vm/src/stdlib/typevar.rs
@@ -1,7 +1,7 @@
 // spell-checker:ignore typevarobject funcobj
 use crate::{
     AsObject, Context, Py, PyObject, PyObjectRef, PyPayload, PyRef, PyResult, VirtualMachine,
-    builtins::{PyTupleRef, PyType, PyTypeRef, pystr::AsPyStr},
+    builtins::{PyTuple, PyTupleRef, PyType, PyTypeRef, make_union, pystr::AsPyStr},
     common::lock::PyMutex,
     function::{FuncArgs, IntoFuncArgs, PyComparisonValue},
     protocol::PyNumberMethods,
@@ -250,7 +250,8 @@ impl AsNumber for TypeVar {
     fn as_number() -> &'static PyNumberMethods {
         static AS_NUMBER: PyNumberMethods = PyNumberMethods {
             or: Some(|a, b, vm| {
-                _call_typing_func_object(vm, "_make_union", (a.to_owned(), b.to_owned()))
+                let args = PyTuple::new_ref(vec![a.to_owned(), b.to_owned()], &vm.ctx);
+                Ok(make_union(&args, vm))
             }),
             ..PyNumberMethods::NOT_IMPLEMENTED
         };
@@ -525,7 +526,8 @@ impl AsNumber for ParamSpec {
     fn as_number() -> &'static PyNumberMethods {
         static AS_NUMBER: PyNumberMethods = PyNumberMethods {
             or: Some(|a, b, vm| {
-                _call_typing_func_object(vm, "_make_union", (a.to_owned(), b.to_owned()))
+                let args = PyTuple::new_ref(vec![a.to_owned(), b.to_owned()], &vm.ctx);
+                Ok(make_union(&args, vm))
             }),
             ..PyNumberMethods::NOT_IMPLEMENTED
         };