diff --git a/mypy/typeshed/stubs/librt/librt/vecs.pyi b/mypy/typeshed/stubs/librt/librt/vecs.pyi
index a4e8c88e0e596..dbf199da9465c 100644
--- a/mypy/typeshed/stubs/librt/librt/vecs.pyi
+++ b/mypy/typeshed/stubs/librt/librt/vecs.pyi
@@ -14,6 +14,7 @@ class vec(Generic[T]):
     @overload
     def __getitem__(self, i: slice, /) -> vec[T]: ...
     def __setitem__(self, i: i64, o: T, /) -> None: ...
+    def __contains__(self, o: object, /) -> bool: ...
     def __iter__(self) -> Iterator[T]: ...
 
 def append(v: vec[T], o: T, /) -> vec[T]: ...
diff --git a/mypyc/lib-rt/vecs/vec_nested.c b/mypyc/lib-rt/vecs/vec_nested.c
index 459a40735744a..f877566c17e24 100644
--- a/mypyc/lib-rt/vecs/vec_nested.c
+++ b/mypyc/lib-rt/vecs/vec_nested.c
@@ -178,6 +178,24 @@ static int vec_ass_item(PyObject *self, Py_ssize_t i, PyObject *o) {
     }
 }
 
+static int vec_contains(PyObject *self, PyObject *value) {
+    VecNested v = ((VecNestedObject *)self)->vec;
+    for (Py_ssize_t i = 0; i < v.len; i++) {
+        PyObject *item = box_vec_item_by_index(v, i);
+        if (item == NULL)
+            return -1;
+        if (item == value) {
+            Py_DECREF(item);
+            return 1;
+        }
+        int cmp = PyObject_RichCompareBool(item, value, Py_EQ);
+        Py_DECREF(item);
+        if (cmp != 0)
+            return cmp;  // 1 if equal, -1 on error
+    }
+    return 0;
+}
+
 static PyObject *compare_vec_eq(VecNested x, VecNested y, int op) {
     int cmp = 1;
     PyObject *res;
@@ -414,6 +432,7 @@ static PyMappingMethods VecNestedMapping = {
 static PySequenceMethods VecNestedSequence = {
     .sq_item = vec_get_item,
     .sq_ass_item = vec_ass_item,
+    .sq_contains = vec_contains,
 };
 
 static PyMethodDef vec_methods[] = {
diff --git a/mypyc/lib-rt/vecs/vec_t.c b/mypyc/lib-rt/vecs/vec_t.c
index 79938cb9aade3..56188a42410e8 100644
--- a/mypyc/lib-rt/vecs/vec_t.c
+++ b/mypyc/lib-rt/vecs/vec_t.c
@@ -210,6 +210,22 @@ static int vec_ass_item(PyObject *self, Py_ssize_t i, PyObject *o) {
     }
 }
 
+static int vec_contains(PyObject *self, PyObject *value) {
+    VecT v = ((VecTObject *)self)->vec;
+    for (Py_ssize_t i = 0; i < v.len; i++) {
+        PyObject *item = v.buf->items[i];
+        if (item == value) {
+            return 1;
+        }
+        Py_INCREF(item);
+        int cmp = PyObject_RichCompareBool(item, value, Py_EQ);
+        Py_DECREF(item);
+        if (cmp != 0)
+            return cmp;  // 1 if equal, -1 on error
+    }
+    return 0;
+}
+
 static PyObject *vec_richcompare(PyObject *self, PyObject *other, int op) {
     PyObject *res;
     if (op == Py_EQ || op == Py_NE) {
@@ -410,6 +426,7 @@ static PyMappingMethods VecTMapping = {
 static PySequenceMethods VecTSequence = {
     .sq_item = vec_get_item,
     .sq_ass_item = vec_ass_item,
+    .sq_contains = vec_contains,
 };
 
 static PyMethodDef vec_methods[] = {
diff --git a/mypyc/lib-rt/vecs/vec_template.c b/mypyc/lib-rt/vecs/vec_template.c
index 7881bb496a88c..5978f4af5fb27 100644
--- a/mypyc/lib-rt/vecs/vec_template.c
+++ b/mypyc/lib-rt/vecs/vec_template.c
@@ -29,6 +29,7 @@
 #include <Python.h>
 #include "librt_vecs.h"
 #include "vecs_internal.h"
+#include "mypyc_util.h"
 
 inline static VEC vec_error() {
     VEC v = { .len = -1 };
@@ -235,6 +236,32 @@ static int vec_ass_item(PyObject *self, Py_ssize_t i, PyObject *o) {
     }
 }
 
+static int vec_contains(PyObject *self, PyObject *value) {
+    ITEM_C_TYPE x = UNBOX_ITEM(value);
+    if (unlikely(IS_UNBOX_ERROR(x))) {
+        if (PyErr_Occurred())
+            PyErr_Clear();
+        // Fall back to boxed comparison (e.g. 2.0 == 2)
+        VEC v = ((VEC_OBJECT *)self)->vec;
+        for (Py_ssize_t i = 0; i < v.len; i++) {
+            PyObject *boxed = BOX_ITEM(v.buf->items[i]);
+            if (boxed == NULL)
+                return -1;
+            int cmp = PyObject_RichCompareBool(boxed, value, Py_EQ);
+            Py_DECREF(boxed);
+            if (cmp != 0)
+                return cmp;  // 1 if equal, -1 on error
+        }
+        return 0;
+    }
+    VEC v = ((VEC_OBJECT *)self)->vec;
+    for (Py_ssize_t i = 0; i < v.len; i++) {
+        if (v.buf->items[i] == x)
+            return 1;
+    }
+    return 0;
+}
+
 static Py_ssize_t vec_length(PyObject *o) {
     return ((VEC_OBJECT *)o)->vec.len;
 }
@@ -348,6 +375,7 @@ static PyMappingMethods vec_mapping_methods = {
 static PySequenceMethods vec_sequence_methods = {
     .sq_item = vec_get_item,
     .sq_ass_item = vec_ass_item,
+    .sq_contains = vec_contains,
 };
 
 static PyMethodDef vec_methods[] = {
diff --git a/mypyc/test-data/run-vecs-i64-interp.test b/mypyc/test-data/run-vecs-i64-interp.test
index 166d6818a724c..5fd2c00d984fa 100644
--- a/mypyc/test-data/run-vecs-i64-interp.test
+++ b/mypyc/test-data/run-vecs-i64-interp.test
@@ -312,6 +312,41 @@ def test_contains() -> None:
     vv = vec[i64]()
     assert 3 not in vv
 
+def test_contains_boundary_values() -> None:
+    v = vec[i64]([0, 2**63 - 1, -2**63])
+    assert 0 in v
+    assert 2**63 - 1 in v
+    assert -2**63 in v
+    assert 1 not in v
+    assert -1 not in v
+
+def test_contains_wrong_type() -> None:
+    # Wrong type should return False, not raise
+    v: Any = vec[i64]([1, 2, 3])
+    assert 'x' not in v
+    assert None not in v
+    assert [] not in v
+    # Overflow should also return False
+    assert 2**63 not in v
+    assert -2**63 - 1 not in v
+
+def test_contains_float() -> None:
+    # float == int equality should work via boxed fallback
+    v: Any = vec[i64]([1, 2, 3])
+    assert 2.0 in v
+    assert 3.0 in v
+    assert 1.5 not in v
+    assert 0.0 not in v
+
+def test_contains_bool() -> None:
+    # bool is a subclass of int, so True/False should work
+    v: Any = vec[i64]([0, 1, 5])
+    assert True in v
+    assert False in v
+    v2: Any = vec[i64]([2, 3])
+    assert True not in v2
+    assert False not in v2
+
 def test_remove() -> None:
     a = [4, 7, 9]
     for i in a:
diff --git a/mypyc/test-data/run-vecs-nested-interp.test b/mypyc/test-data/run-vecs-nested-interp.test
index bd621e99498d1..50f8bca600b95 100644
--- a/mypyc/test-data/run-vecs-nested-interp.test
+++ b/mypyc/test-data/run-vecs-nested-interp.test
@@ -410,3 +410,48 @@ def test_iterator_length_hint() -> None:
     next(it)
     next(it)
     assert length_hint(it) == 0
+
+def test_contains() -> None:
+    v1 = vec[str](['a'])
+    v2 = vec[str](['b'])
+    v3 = vec[str](['c'])
+    v = vec[vec[str]]([v1, v2, v3])
+    assert v1 in v
+    assert v2 in v
+    assert v3 in v
+    assert vec[str]([]) not in v
+    assert vec[str](['d']) not in v
+
+def test_contains_empty() -> None:
+    v = vec[vec[str]]()
+    assert vec[str]([]) not in v
+    assert vec[str](['x']) not in v
+
+def test_contains_equality() -> None:
+    # Test that equality is used, not just identity
+    v = vec[vec[str]]([vec[str](['x', 'y'])])
+    assert vec[str](['x', 'y']) in v
+    assert vec[str](['x']) not in v
+    assert vec[str](['y']) not in v
+
+def test_contains_nested_i64() -> None:
+    v = vec[vec[i64]]([vec[i64]([1, 2]), vec[i64]([3])])
+    assert vec[i64]([1, 2]) in v
+    assert vec[i64]([3]) in v
+    assert vec[i64]([1]) not in v
+    assert vec[i64]([]) not in v
+
+def test_contains_wrong_type() -> None:
+    v: Any = vec[vec[str]]([vec[str](['x'])])
+    assert 'x' not in v
+    assert 123 not in v
+    assert None not in v
+    assert [] not in v
+
+def test_contains_deeply_nested() -> None:
+    inner = vec[vec[str]]([vec[str](['a'])])
+    v = vec[vec[vec[str]]]([inner])
+    assert inner in v
+    assert vec[vec[str]]([vec[str](['a'])]) in v
+    assert vec[vec[str]]([vec[str](['b'])]) not in v
+    assert vec[vec[str]]() not in v
diff --git a/mypyc/test-data/run-vecs-t-interp.test b/mypyc/test-data/run-vecs-t-interp.test
index 881530b50f7a6..76bb57bfdd571 100644
--- a/mypyc/test-data/run-vecs-t-interp.test
+++ b/mypyc/test-data/run-vecs-t-interp.test
@@ -419,6 +419,41 @@ def test_contains() -> None:
     assert None in v2
     assert '4' not in v2
 
+def test_contains_identity() -> None:
+    # Test that identity check works (short-circuits before __eq__)
+    o = ClassWithRaisingEq()
+    v = vec[object]([o])
+    assert o in v  # Should use identity, not __eq__
+
+def test_contains_equality() -> None:
+    # Test that equality is used when identity doesn't match
+    s = 'hello world!'
+    v = vec[str]([s])
+    # Create a new string object with same value (different identity)
+    s2 = 'hello' + str() + ' world!'
+    assert s2 in v
+
+def test_contains_exception_from_eq() -> None:
+    o1 = ClassWithRaisingEq()
+    o2 = ClassWithRaisingEq()
+    v = vec[object]([o1])
+    with assertRaises(RuntimeError):
+        o2 in v
+
+def test_contains_wrong_type() -> None:
+    # Wrong type should return False, not raise
+    v: Any = vec[str](['x'])
+    assert 123 not in v
+    assert b'x' not in v
+    assert None not in v
+    assert [] not in v
+
+def test_contains_subclass() -> None:
+    v = vec[str]([StringSubclass('abc')])
+    assert 'abc' in v
+    assert StringSubclass('abc') in v
+    assert 'xyz' not in v
+
 def test_remove() -> None:
     a = ['4x', '7x', '9x']
     for i in a: