diff --git a/capnp/helpers/helpers.pxd b/capnp/helpers/helpers.pxd
index dde61f0..fe98ebf 100644
--- a/capnp/helpers/helpers.pxd
+++ b/capnp/helpers/helpers.pxd
@@ -16,20 +16,17 @@ cdef extern from "capnp/helpers/fixMaybe.h":
 
 cdef extern from "capnp/helpers/capabilityHelper.h":
     PyPromise then(PyPromise promise, Own[PyRefCounter] func, Own[PyRefCounter] error_func)
-    DynamicCapability.Client new_client(InterfaceSchema&, PyObject *)
-    DynamicValue.Reader new_server(InterfaceSchema&, PyObject *)
-    Capability.Client server_to_client(InterfaceSchema&, PyObject *)
     PyPromise convert_to_pypromise(RemotePromise)
     PyPromise convert_to_pypromise(VoidPromise)
     VoidPromise taskToPromise(Own[PyRefCounter] coroutine, PyObject* callback)
     void init_capnp_api()
 
 cdef extern from "capnp/helpers/rpcHelper.h":
-    Capability.Client bootstrapHelper(RpcSystem&)
-    Capability.Client bootstrapHelperServer(RpcSystem&)
+    Own[Capability.Client] bootstrapHelper(RpcSystem&) except +reraise_kj_exception
+    Own[Capability.Client] bootstrapHelperServer(RpcSystem&) except +reraise_kj_exception
 
 cdef extern from "capnp/helpers/serialize.h":
-    ByteArray messageToPackedBytes(MessageBuilder &, size_t wordCount)
+    ByteArray messageToPackedBytes(MessageBuilder &, size_t wordCount) except +reraise_kj_exception
 
 cdef extern from "capnp/helpers/deserialize.h":
     Node.Reader toReader(DynamicStruct.Reader reader) except +reraise_kj_exception
diff --git a/capnp/helpers/rpcHelper.h b/capnp/helpers/rpcHelper.h
index 0681039..c017ba3 100644
--- a/capnp/helpers/rpcHelper.h
+++ b/capnp/helpers/rpcHelper.h
@@ -6,16 +6,16 @@
 #include "Python.h"
 #include "capabilityHelper.h"
 
-capnp::Capability::Client bootstrapHelper(capnp::RpcSystem<capnp::rpc::twoparty::SturdyRefHostId>& client) {
+kj::Own<capnp::Capability::Client> bootstrapHelper(capnp::RpcSystem<capnp::rpc::twoparty::SturdyRefHostId>& client) {
     capnp::MallocMessageBuilder hostIdMessage(8);
     auto hostId = hostIdMessage.initRoot<capnp::rpc::twoparty::SturdyRefHostId>();
     hostId.setSide(capnp::rpc::twoparty::Side::SERVER);
-    return client.bootstrap(hostId);
+    return kj::heap<capnp::Capability::Client>(client.bootstrap(hostId));
 }
 
-capnp::Capability::Client bootstrapHelperServer(capnp::RpcSystem<capnp::rpc::twoparty::SturdyRefHostId>& client) {
+kj::Own<capnp::Capability::Client> bootstrapHelperServer(capnp::RpcSystem<capnp::rpc::twoparty::SturdyRefHostId>& client) {
     capnp::MallocMessageBuilder hostIdMessage(8);
     auto hostId = hostIdMessage.initRoot<capnp::rpc::twoparty::SturdyRefHostId>();
     hostId.setSide(capnp::rpc::twoparty::Side::CLIENT);
-    return client.bootstrap(hostId);
+    return kj::heap<capnp::Capability::Client>(client.bootstrap(hostId));
 }
diff --git a/capnp/includes/capnp_cpp.pxd b/capnp/includes/capnp_cpp.pxd
index 335b172..9e559b7 100644
--- a/capnp/includes/capnp_cpp.pxd
+++ b/capnp/includes/capnp_cpp.pxd
@@ -57,26 +57,12 @@ cdef extern from "kj/async.h" namespace " ::kj":
     cdef cppclass Promise[T] nogil:
         Promise(Promise)
         Promise(T)
-        T wait(WaitScope) except +reraise_kj_exception
-        bool poll(WaitScope) except +reraise_kj_exception
-        # ForkedPromise<T> fork()
-        # Promise<T> exclusiveJoin(Promise<T>&& other)
-        # Promise[T] eagerlyEvaluate()
-        # void detach(ErrorFunc)
         String trace()
         Promise[T] attach(Own[PyRefCounter] &)
         Promise[T] attach(Own[PyRefCounter] &, Own[PyRefCounter] &)
         Promise[T] attach(Own[PyRefCounter] &, Own[PyRefCounter] &, Own[PyRefCounter] &)
         Promise[T] attach(Own[PyRefCounter] &, Own[PyRefCounter] &, Own[PyRefCounter] &, Own[PyRefCounter] &)
 
-    cdef cppclass Canceler nogil:
-        Canceler()
-        Promise[T] wrap[T](Promise[T] promise)
-        void cancel(StringPtr cancelReason)
-        void cancel(Exception& exception)
-        void release()
-        bool isEmpty()
-
 ctypedef Promise[Own[PyRefCounter]] PyPromise
 ctypedef Promise[void] VoidPromise
 
@@ -109,8 +95,8 @@ cdef extern from "kj/array.h" namespace " ::kj":
 
 cdef extern from "kj/async-io.h" namespace " ::kj":
     cdef cppclass AsyncIoStream nogil:
-        Promise[size_t] read(void*, size_t, size_t)
-        Promise[void] write(const void*, size_t)
+        Promise[size_t] read(void*, size_t, size_t) except +reraise_kj_exception
+        Promise[void] write(const void*, size_t) except +reraise_kj_exception
 
 cdef extern from "capnp/schema.capnp.h" namespace " ::capnp":
     enum TypeWhich" ::capnp::schema::Type::Which":
@@ -297,7 +283,7 @@ cdef extern from "capnp/dynamic.h" namespace " ::capnp":
             Client()
             Client(Client&)
             Client(Own[PythonInterfaceDynamicImpl])
-            Client upcast(InterfaceSchema requestedSchema)
+            Client upcast(InterfaceSchema requestedSchema) except +reraise_kj_exception
             DynamicCapability.Client castAs"castAs< ::capnp::DynamicCapability>"(InterfaceSchema)
             InterfaceSchema getSchema()
             Request newRequest(char * methodName)
@@ -447,7 +433,7 @@ cdef extern from "capnp/dynamic.h" namespace " ::capnp":
             Type getType()
 
 cdef extern from "capnp/schema-loader.h" namespace " ::capnp":
-    cdef cppclass SchemaLoader:
+    cdef cppclass SchemaLoader nogil:
         SchemaLoader()
         Schema load(Node.Reader reader) except +reraise_kj_exception
         Schema get(uint64_t id_) except +reraise_kj_exception
diff --git a/capnp/includes/schema_cpp.pxd b/capnp/includes/schema_cpp.pxd
index e552089..6f8d559 100644
--- a/capnp/includes/schema_cpp.pxd
+++ b/capnp/includes/schema_cpp.pxd
@@ -673,7 +673,7 @@ cdef extern from "capnp/message.h" namespace " ::capnp":
         Annotation.Builder getRootAnnotation'getRoot< ::capnp::schema::Annotation>'()
         Annotation.Builder initRootAnnotation'initRoot< ::capnp::schema::Annotation>'()
 
-        DynamicStruct_Builder getRootDynamicStruct'getRoot< ::capnp::DynamicStruct>'(StructSchema)
+        DynamicStruct_Builder getRootDynamicStruct'getRoot< ::capnp::DynamicStruct>'(StructSchema) except +reraise_kj_exception
         DynamicStruct_Builder initRootDynamicStruct'initRoot< ::capnp::DynamicStruct>'(StructSchema)
         void setRootDynamicStruct'setRoot< ::capnp::DynamicStruct::Reader>'(DynamicStruct.Reader)
 
@@ -696,7 +696,7 @@ cdef extern from "capnp/message.h" namespace " ::capnp":
         StructNode.Reader getRootStructNode'getRoot< ::capnp::schema::StructNode>'()
         Annotation.Reader getRootAnnotation'getRoot< ::capnp::schema::Annotation>'()
 
-        DynamicStruct.Reader getRootDynamicStruct'getRoot< ::capnp::DynamicStruct>'(StructSchema)
+        DynamicStruct.Reader getRootDynamicStruct'getRoot< ::capnp::DynamicStruct>'(StructSchema) except +reraise_kj_exception
         AnyPointer.Reader getRootAnyPointer'getRoot< ::capnp::AnyPointer>'()
 
     cdef cppclass MallocMessageBuilder(MessageBuilder) nogil:
@@ -798,7 +798,7 @@ cdef extern from "capnp/serialize.h" namespace " ::capnp":
         FlatArrayMessageReader(WordArrayPtr array, ReaderOptions) except +reraise_kj_exception
         const word* getEnd() const
 
-    void writeMessageToFd(int, MessageBuilder&) nogil except +reraise_kj_exception
+    void writeMessageToFd(int, MessageBuilder&) except +reraise_kj_exception nogil
 
     WordArray messageToFlatArray(MessageBuilder &) nogil
 
@@ -816,6 +816,6 @@ cdef extern from "capnp/serialize-packed.h" namespace " ::capnp":
         PackedFdMessageReader(int) except +reraise_kj_exception
         PackedFdMessageReader(int, ReaderOptions) except +reraise_kj_exception
 
-    void writePackedMessage(BufferedOutputStream&, MessageBuilder&) nogil except +reraise_kj_exception
-    void writePackedMessage(OutputStream&, MessageBuilder&) nogil except +reraise_kj_exception
-    void writePackedMessageToFd(int, MessageBuilder&) nogil except +reraise_kj_exception
+    void writePackedMessage(BufferedOutputStream&, MessageBuilder&) except +reraise_kj_exception nogil
+    void writePackedMessage(OutputStream&, MessageBuilder&) except +reraise_kj_exception nogil
+    void writePackedMessageToFd(int, MessageBuilder&) except +reraise_kj_exception nogil
diff --git a/capnp/lib/capnp.pxd b/capnp/lib/capnp.pxd
index 1ddd6b8..bb235a3 100644
--- a/capnp/lib/capnp.pxd
+++ b/capnp/lib/capnp.pxd
@@ -28,7 +28,7 @@ cdef class _StringArrayPtr:
     cdef StringPtr * thisptr
     cdef object parent
     cdef size_t size
-    cdef ArrayPtr[StringPtr] asArrayPtr(self) except +reraise_kj_exception
+    cdef ArrayPtr[StringPtr] asArrayPtr(self)
 
 cdef class SchemaLoader:
     cdef C_SchemaLoader * thisptr
@@ -38,7 +38,7 @@ cdef class SchemaParser:
     cdef public dict modules_by_id
     cdef list _all_imports
     cdef _StringArrayPtr _last_import_array
-    cpdef _parse_disk_file(self, displayName, diskPath, imports) except +reraise_kj_exception
+    cpdef _parse_disk_file(self, displayName, diskPath, imports)
 
 cdef class _DynamicOrphan:
     cdef C_DynamicOrphan thisptr
@@ -79,10 +79,10 @@ cdef class _DynamicStructBuilder:
     cdef _init(self, DynamicStruct_Builder other, object parent, bint isRoot=?, bint tryRegistry=?)
 
     cdef _check_write(self)
-    cpdef to_bytes(_DynamicStructBuilder self) except +reraise_kj_exception
-    cpdef to_segments(_DynamicStructBuilder self) except +reraise_kj_exception
-    cpdef _to_bytes_packed_helper(_DynamicStructBuilder self, word_count) except +reraise_kj_exception
-    cpdef to_bytes_packed(_DynamicStructBuilder self) except +reraise_kj_exception
+    cpdef to_bytes(_DynamicStructBuilder self)
+    cpdef to_segments(_DynamicStructBuilder self)
+    cpdef _to_bytes_packed_helper(_DynamicStructBuilder self, word_count)
+    cpdef to_bytes_packed(_DynamicStructBuilder self)
 
     cpdef _get(self, field)
     cpdef _set(self, field, value)
@@ -128,7 +128,7 @@ cdef class _DynamicEnum:
     cdef public object _parent
 
     cdef _init(self, capnp.DynamicEnum other, object parent)
-    cpdef _as_str(self) except +reraise_kj_exception
+    cpdef _as_str(self)
 
 cdef class _DynamicListBuilder:
     cdef C_DynamicList.Builder thisptr
@@ -146,11 +146,11 @@ cdef class _DynamicListBuilder:
 cdef class _MessageBuilder:
     cdef schema_cpp.MessageBuilder * thisptr
     cpdef init_root(self, schema)
-    cpdef get_root(self, schema) except +reraise_kj_exception
-    cpdef get_root_as_any(self) except +reraise_kj_exception
-    cpdef set_root(self, value) except +reraise_kj_exception
-    cpdef get_segments_for_output(self) except +reraise_kj_exception
-    cpdef new_orphan(self, schema) except +reraise_kj_exception
+    cpdef get_root(self, schema)
+    cpdef get_root_as_any(self)
+    cpdef set_root(self, value)
+    cpdef get_segments_for_output(self)
+    cpdef new_orphan(self, schema)
 
 cdef to_python_reader(C_DynamicValue.Reader self, object parent)
 cdef to_python_builder(C_DynamicValue.Builder self, object parent)
diff --git a/capnp/lib/capnp.pyx b/capnp/lib/capnp.pyx
index dbb92b7..850f9bb 100644
--- a/capnp/lib/capnp.pyx
+++ b/capnp/lib/capnp.pyx
@@ -10,11 +10,12 @@
 cimport cython  # noqa: E402
 
 from capnp.helpers.helpers cimport init_capnp_api
-from capnp.includes.capnp_cpp cimport AsyncIoStream, WaitScope, PyPromise, VoidPromise, EventPort, EventLoop, Canceler, PyAsyncIoStream, PromiseFulfiller, VoidPromiseFulfiller, tryReadMessage, writeMessage, makeException, PythonInterfaceDynamicImpl
+from capnp.includes.capnp_cpp cimport AsyncIoStream, WaitScope, PyPromise, VoidPromise, EventPort, EventLoop, PyAsyncIoStream, PromiseFulfiller, VoidPromiseFulfiller, tryReadMessage, writeMessage, makeException, PythonInterfaceDynamicImpl
 from capnp.includes.schema_cpp cimport (MessageReader,)
 
-from cpython cimport array, Py_buffer, PyObject_CheckBuffer, memoryview, buffer
-from cpython.buffer cimport PyBUF_SIMPLE, PyBUF_WRITABLE
+from cpython cimport array, Py_buffer, PyObject_CheckBuffer
+from cpython.buffer cimport PyBUF_SIMPLE, PyBUF_WRITABLE, PyBUF_WRITE, PyBUF_READ
+from cpython.memoryview cimport PyMemoryView_FromMemory
 from cpython.exc cimport PyErr_Clear
 from cython.operator cimport dereference as deref
 from libc.stdlib cimport malloc, free
@@ -120,10 +121,10 @@ def fill_context(method_name, context, returned_data):
     for arg_name, arg_val in zip(names, returned_data):
         setattr(results, arg_name, arg_val)
 
-cdef api VoidPromise * call_server_method(object server,
+cdef api Promise[void]* call_server_method(object server,
                                           char * _method_name,
                                           CallContext & _context,
-                                          object _kj_loop) except * with gil:
+                                          object _kj_loop) except* with gil:
     method_name = <object>_method_name
     kj_loop = <_EventLoop>_kj_loop
     kj_loop.check()
@@ -290,7 +291,7 @@ cdef api object get_exception_info(object exc_type, object exc_obj, object exc_t
         return (b'', 0, b"Couldn't determine python exception")
 
 
-cdef schema_cpp.ReaderOptions make_reader_opts(traversal_limit_in_words, nesting_limit) with gil:
+cdef schema_cpp.ReaderOptions make_reader_opts(traversal_limit_in_words, nesting_limit):
     cdef schema_cpp.ReaderOptions opts
     if traversal_limit_in_words is not None:
         opts.traversalLimitInWords = traversal_limit_in_words
@@ -992,7 +993,7 @@ cdef class _DynamicEnum:
         self._parent = parent
         return self
 
-    cpdef _as_str(self) except +reraise_kj_exception:
+    cpdef _as_str(self):
         return <char*>helpers.fixMaybe(self.thisptr.getEnumerant()).getProto().getName().cStr()
 
     property raw:
@@ -1302,7 +1303,7 @@ cdef class _DynamicStructBuilder:
         _write_packed_message_to_fd(file.fileno(), self._parent)
         self._is_written = True
 
-    cpdef to_bytes(_DynamicStructBuilder self) except +reraise_kj_exception:
+    cpdef to_bytes(_DynamicStructBuilder self):
         """Returns the struct's containing message as a Python bytes object in the unpacked binary format.
 
         This is inefficient; it makes several copies.
@@ -1319,7 +1320,7 @@ cdef class _DynamicStructBuilder:
         self._is_written = True
         return ret
 
-    cpdef to_segments(_DynamicStructBuilder self) except +reraise_kj_exception:
+    cpdef to_segments(_DynamicStructBuilder self):
         """Returns the struct's containing message as a Python list of Python bytes objects.
 
         This avoids making copies.
@@ -1333,14 +1334,14 @@ cdef class _DynamicStructBuilder:
         segments = builder.get_segments_for_output()
         return segments
 
-    cpdef _to_bytes_packed_helper(_DynamicStructBuilder self, word_count) except +reraise_kj_exception:
+    cpdef _to_bytes_packed_helper(_DynamicStructBuilder self, word_count):
         cdef _MessageBuilder builder = self._parent
         array = helpers.messageToPackedBytes(deref(builder.thisptr), word_count)
         cdef const char* ptr = <const char *>array.begin()
         cdef bytes ret = ptr[:array.size()]
         return ret
 
-    cpdef to_bytes_packed(_DynamicStructBuilder self) except +reraise_kj_exception:
+    cpdef to_bytes_packed(_DynamicStructBuilder self):
         self._check_write()
         word_count = self.total_size.word_count + 2
 
@@ -1610,7 +1611,7 @@ cdef class _DynamicStructPipeline:
     def __dealloc__(self):
         del self.thisptr
 
-    cpdef _get(self, field) except +reraise_kj_exception:
+    cpdef _get(self, field):
         cdef int type = (<C_DynamicValue.Pipeline>self.thisptr.get(field)).getType()
         if type == capnp.TYPE_CAPABILITY:
             return _DynamicCapabilityClient()._init(
@@ -1680,7 +1681,7 @@ cdef class _DynamicObjectReader:
         self._parent = parent
         return self
 
-    cpdef as_struct(self, schema) except +reraise_kj_exception:
+    cpdef as_struct(self, schema):
         cdef _StructSchema s
         if hasattr(schema, 'schema'):
             s = schema.schema
@@ -1689,7 +1690,7 @@ cdef class _DynamicObjectReader:
 
         return _DynamicStructReader()._init(self.thisptr.getAs(s._thisptr()), self._parent)
 
-    cpdef as_interface(self, schema) except +reraise_kj_exception:
+    cpdef as_interface(self, schema):
         cdef _InterfaceSchema s
         if hasattr(schema, 'schema'):
             s = schema.schema
@@ -1698,7 +1699,7 @@ cdef class _DynamicObjectReader:
 
         return _DynamicCapabilityClient()._init(self.thisptr.getAsCapability(s.thisptr), self._parent)
 
-    cpdef as_list(self, schema) except +reraise_kj_exception:
+    cpdef as_list(self, schema):
         cdef _ListSchema s
         if hasattr(schema, 'schema'):
             s = schema.schema
@@ -1707,7 +1708,7 @@ cdef class _DynamicObjectReader:
 
         return _DynamicListReader()._init(self.thisptr.getAsList(s.thisptr), self._parent)
 
-    cpdef as_text(self) except +reraise_kj_exception:
+    cpdef as_text(self):
         return (<char*>self.thisptr.getAsText().cStr())[:]
 
 
@@ -1723,7 +1724,7 @@ cdef class _DynamicObjectBuilder:
     def __dealloc__(self):
         del self.thisptr
 
-    cpdef as_struct(self, schema) except +reraise_kj_exception:
+    cpdef as_struct(self, schema):
         cdef _StructSchema s
         if hasattr(schema, 'schema'):
             s = schema.schema
@@ -1732,7 +1733,7 @@ cdef class _DynamicObjectBuilder:
 
         return _DynamicStructBuilder()._init(self.thisptr.getAs(s._thisptr()), self._parent)
 
-    cpdef as_interface(self, schema) except +reraise_kj_exception:
+    cpdef as_interface(self, schema):
         cdef _InterfaceSchema s
         if hasattr(schema, 'schema'):
             s = schema.schema
@@ -1741,7 +1742,7 @@ cdef class _DynamicObjectBuilder:
 
         return _DynamicCapabilityClient()._init(self.thisptr.getAsCapability(s.thisptr), self._parent)
 
-    cpdef as_list(self, schema) except +reraise_kj_exception:
+    cpdef as_list(self, schema):
         cdef _ListSchema s
         if hasattr(schema, 'schema'):
             s = schema.schema
@@ -1767,13 +1768,13 @@ cdef class _DynamicObjectBuilder:
 
         return _DynamicListBuilder()._init(self.thisptr.initAsList(s.thisptr, size), self._parent)
 
-    cpdef as_text(self) except +reraise_kj_exception:
+    cpdef as_text(self):
         return (<char*>self.thisptr.getAsText().cStr())[:]
 
     cpdef as_reader(self):
         return _DynamicObjectReader()._init(self.thisptr.asReader(), self._parent)
 
-cdef void kjloop_runnable_callback(void* data) with gil:
+cdef kjloop_runnable_callback(void* data):
     cdef AsyncIoEventPort *port = <AsyncIoEventPort*>data
     assert port.runHandle is not None
     port.kjLoop.run()
@@ -1823,7 +1824,7 @@ cdef class _EventLoop:
     cdef object active_tasks
     cdef cbool closed
 
-    cdef _init(self, asyncio_loop) except +reraise_kj_exception:
+    cdef _init(self, asyncio_loop):
         self.event_port = capnp.heap[AsyncIoEventPort](<PyObject*>asyncio_loop)
         kj_loop = deref(self.event_port).getKjLoop()
         self.wait_scope = capnp.heap[WaitScope](deref(kj_loop))
@@ -1941,7 +1942,7 @@ cdef class _Promise:
         self.thisptr = capnp.heap[PyPromise](move(other))
         return self
 
-    cpdef cancel(self) except +reraise_kj_exception:
+    cpdef cancel(self):
         self.thisptr = Own[PyPromise]()
 
 
@@ -1956,7 +1957,7 @@ cdef class _RemotePromise:
         self._parent = parent
         return self
 
-    cdef void _check_consumed(self) except*:
+    cdef _check_consumed(self):
         if self.thisptr.get() == NULL:
             raise KjException(
                 "Promise was already used in a consuming operation. You can no longer use this Promise object")
@@ -1969,7 +1970,7 @@ cdef class _RemotePromise:
             .attach(capnp.heap[PyRefCounter](<PyObject*>self._parent))
             ).__await__()
 
-    cpdef _get(self, field) except +reraise_kj_exception:
+    cpdef _get(self, field):
         self._check_consumed()
         cdef int type = (<C_DynamicValue.Pipeline>self.thisptr.get().get(field)).getType()
         if type == capnp.TYPE_CAPABILITY:
@@ -2002,7 +2003,7 @@ cdef class _RemotePromise:
     def to_dict(self, verbose=False, ordered=False):
         return _to_dict(self, verbose, ordered)
 
-    cpdef cancel(self) except +reraise_kj_exception:
+    cpdef cancel(self):
         self.thisptr = Own[RemotePromise]()
         self._parent = None # We don't need parent anymore. Setting to none allows quicker garbage collection
 
@@ -2105,7 +2106,7 @@ cdef class _DynamicCapabilityClient:
             for key, val in kwargs.items():
                 _setDynamicField(<DynamicStruct_Builder>deref(request), key, val, self)
 
-    cpdef _send_helper(self, name, word_count, args, kwargs) except +reraise_kj_exception:
+    cpdef _send_helper(self, name, word_count, args, kwargs):
         # if word_count is None:
         #     word_count = 0
         C_DEFAULT_EVENT_LOOP_GETTER() # Make sure the event loop is running
@@ -2115,7 +2116,7 @@ cdef class _DynamicCapabilityClient:
 
         return _RemotePromise()._init(request.send(), self)
 
-    cpdef _request_helper(self, name, firstSegmentWordSize, args, kwargs) except +reraise_kj_exception:
+    cpdef _request_helper(self, name, firstSegmentWordSize, args, kwargs):
         # if word_count is None:
         #     word_count = 0
         cdef _Request req = _Request()._init_child(self.thisptr.newRequest(name), self)
@@ -2144,7 +2145,7 @@ cdef class _DynamicCapabilityClient:
         except KjException as e:
             raise e._to_python(), None, _sys.exc_info()[2]
 
-    cpdef upcast(self, schema) except +reraise_kj_exception:
+    cpdef upcast(self, schema):
         cdef _InterfaceSchema s
         if hasattr(schema, 'schema'):
             s = schema.schema
@@ -2153,7 +2154,7 @@ cdef class _DynamicCapabilityClient:
 
         return _DynamicCapabilityClient()._init(self.thisptr.upcast(s.thisptr), self._parent)
 
-    cpdef cast_as(self, schema) except +reraise_kj_exception:
+    cpdef cast_as(self, schema):
         cdef _InterfaceSchema s
         if hasattr(schema, 'schema'):
             s = schema.schema
@@ -2173,24 +2174,21 @@ cdef class _DynamicCapabilityClient:
 
 
 cdef class _CapabilityClient:
-    cdef C_Capability.Client * thisptr
+    cdef Own[C_Capability.Client] thisptr
     cdef public object _parent
 
-    cdef _init(self, C_Capability.Client other, object parent):
-        self.thisptr = new C_Capability.Client(other)
+    cdef _init(self, Own[C_Capability.Client] other, object parent):
+        self.thisptr = move(other)
         self._parent = parent
         return self
 
-    def __dealloc__(self):
-        del self.thisptr
-
     cpdef cast_as(self, schema):
         cdef _InterfaceSchema s
         if hasattr(schema, 'schema'):
             s = schema.schema
         else:
             s = schema
-        return _DynamicCapabilityClient()._init(self.thisptr.castAs(s.thisptr), self._parent)
+        return _DynamicCapabilityClient()._init(deref(self.thisptr).castAs(s.thisptr), self._parent)
 
 
 cdef class _TwoPartyVatNetwork:
@@ -2205,7 +2203,7 @@ cdef class _TwoPartyVatNetwork:
         self.thisptr = capnp.heap[C_TwoPartyVatNetwork](deref(stream.thisptr), side, opts)
         return self
 
-    cpdef on_disconnect(self) except +reraise_kj_exception:
+    cpdef on_disconnect(self):
         return _voidpromise_to_asyncio(deref(self.thisptr).onDisconnect())
 
 
@@ -2244,12 +2242,12 @@ cdef class TwoPartyClient:
 
         self.thisptr = capnp.heap[RpcSystem](makeRpcClient(deref(self._network.thisptr)))
 
-    cpdef bootstrap(self) except +reraise_kj_exception:
+    cpdef bootstrap(self):
         if self.closed:
             raise RuntimeError("This client is closed")
         return _CapabilityClient()._init(helpers.bootstrapHelper(deref(self.thisptr)), self)
 
-    cpdef on_disconnect(self) except +reraise_kj_exception:
+    cpdef on_disconnect(self):
         if self.closed:
             raise RuntimeError("This client is closed")
         return self._network.on_disconnect()
@@ -2299,12 +2297,12 @@ cdef class TwoPartyServer:
                 capnp.heap[PyRefCounter](<PyObject*>bootstrap),
                 capnp.heap[PyRefCounter](<PyObject*>loop)))))
 
-    cpdef bootstrap(self) except +reraise_kj_exception:
+    cpdef bootstrap(self):
         if self.closed:
             raise RuntimeError("This server is closed")
         return _CapabilityClient()._init(helpers.bootstrapHelperServer(deref(self.thisptr)), self)
 
-    cpdef on_disconnect(self) except +reraise_kj_exception:
+    cpdef on_disconnect(self):
         if self.closed:
             raise RuntimeError("This server is closed")
         return _voidpromise_to_asyncio(deref(self._network.thisptr).onDisconnect()
@@ -2496,7 +2494,7 @@ cdef class _PyAsyncIoStreamProtocol(DummyBaseClass, asyncio.BufferedProtocol):
             self.read_overflow_buffer_current = bytearray(size)
             return self.read_overflow_buffer_current
         else:
-            return memoryview.PyMemoryView_FromMemory(self.read_buffer, self.read_max_bytes, buffer.PyBUF_WRITE)
+            return PyMemoryView_FromMemory(self.read_buffer, self.read_max_bytes, PyBUF_WRITE)
 
     def buffer_updated(self, size):
         if self.read_buffer == NULL: # Should not happen, but for SSL it does, see comment above
@@ -2531,7 +2529,7 @@ cdef class _PyAsyncIoStreamProtocol(DummyBaseClass, asyncio.BufferedProtocol):
                 self.write_index = i
                 break
             piece = &self.write_pieces[i]
-            view = memoryview.PyMemoryView_FromMemory(<char*>piece.begin(), piece.size(), buffer.PyBUF_READ)
+            view = PyMemoryView_FromMemory(<char*>piece.begin(), piece.size(), PyBUF_READ)
             self.transport.write(view)
         if not self.write_paused:
             self.write_fulfiller.fulfill()
@@ -2582,7 +2580,7 @@ cdef api void _asyncio_stream_read_start(
     # Begin of draining the overflow buffer, which is created because of a bug in SSL, see comment above.
     # Can be removed once Python < 3.11 is not longer supported.
     if self.read_overflow_buffer:
-        to_copy = min(len(self.read_overflow_buffer), max_bytes)
+        to_copy = min(<size_t>len(self.read_overflow_buffer), max_bytes)
         memcpy(buffer, <char*>self.read_overflow_buffer, to_copy)
         del self.read_overflow_buffer[:to_copy]
         self.read_buffer += to_copy
@@ -3316,7 +3314,7 @@ cdef class _StringArrayPtr:
     def __dealloc__(self):
         free(self.thisptr)
 
-    cdef ArrayPtr[StringPtr] asArrayPtr(self) except +reraise_kj_exception:
+    cdef ArrayPtr[StringPtr] asArrayPtr(self):
         return ArrayPtr[StringPtr](self.thisptr, self.size)
 
 
@@ -3363,7 +3361,7 @@ cdef class SchemaParser:
     def __dealloc__(self):
         del self.thisptr
 
-    cpdef _parse_disk_file(self, displayName, diskPath, imports) except +reraise_kj_exception:
+    cpdef _parse_disk_file(self, displayName, diskPath, imports):
         cdef _StringArrayPtr importArray
 
         if self._last_import_array and self._last_import_array.parent == imports:
@@ -3531,7 +3529,7 @@ cdef class _MessageBuilder:
             s = schema
         return _DynamicStructBuilder()._init(self.thisptr.initRootDynamicStruct(s._thisptr()), self, True)
 
-    cpdef get_root(self, schema) except +reraise_kj_exception:
+    cpdef get_root(self, schema):
         """A method for instantiating Cap'n Proto structs, from an already pre-written buffer
 
         Don't use this method unless you know what you're doing. You probably
@@ -3556,7 +3554,7 @@ cdef class _MessageBuilder:
             s = schema
         return _DynamicStructBuilder()._init(self.thisptr.getRootDynamicStruct(s._thisptr()), self, True)
 
-    cpdef get_root_as_any(self) except +reraise_kj_exception:
+    cpdef get_root_as_any(self):
         """A method for getting a Cap'n Proto AnyPointer, from an already pre-written buffer
 
         Don't use this method unless you know what you're doing.
@@ -3566,7 +3564,7 @@ cdef class _MessageBuilder:
         """
         return _DynamicObjectBuilder()._init(self.thisptr.getRootAnyPointer(), self)
 
-    cpdef set_root(self, value) except +reraise_kj_exception:
+    cpdef set_root(self, value):
         """A method for instantiating Cap'n Proto structs by copying from an existing struct
 
         :type value: :class:`_DynamicStructReader`
@@ -3582,7 +3580,7 @@ cdef class _MessageBuilder:
             self.thisptr.setRootDynamicStruct((<_DynamicStructReader>value).thisptr)
             return self.get_root(value.schema)
 
-    cpdef get_segments_for_output(self) except +reraise_kj_exception:
+    cpdef get_segments_for_output(self):
         segments = self.thisptr.getSegmentsForOutput()
         res = []
         cdef const char* ptr
@@ -3594,7 +3592,7 @@ cdef class _MessageBuilder:
             res.append(segment_bytes)
         return res
 
-    cpdef new_orphan(self, schema) except +reraise_kj_exception:
+    cpdef new_orphan(self, schema):
         """A method for instantiating Cap'n Proto orphans
 
         Don't use this method unless you know what you're doing.
@@ -3652,7 +3650,7 @@ cdef class _MessageReader:
     def __init__(self):
         raise NotImplementedError("This is an abstract base class")
 
-    cpdef get_root(self, schema) except +reraise_kj_exception:
+    cpdef get_root(self, schema):
         """A method for instantiating Cap'n Proto structs
 
         You will need to pass in a schema to specify which struct to
@@ -3676,7 +3674,7 @@ cdef class _MessageReader:
             s = schema
         return _DynamicStructReader()._init(self.thisptr.getRootDynamicStruct(s._thisptr()), self)
 
-    cpdef get_root_as_any(self) except +reraise_kj_exception:
+    cpdef get_root_as_any(self):
         """A method for getting a Cap'n Proto AnyPointer, from an already pre-written buffer
 
         Don't use this method unless you know what you're doing.
diff --git a/pyproject.toml b/pyproject.toml
index 1551bd2..a59ee2b 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -1,5 +1,5 @@
 [build-system]
-requires = ["setuptools", "wheel", "pkgconfig", "cython<3"]
+requires = ["setuptools", "wheel", "pkgconfig", "cython>=3.0"]
 build-backend = "backend"
 backend-path = ["_custom_build"]