diff --git a/capnp/__init__.py b/capnp/__init__.py
index a990f7b..b10d7cf 100644
--- a/capnp/__init__.py
+++ b/capnp/__init__.py
@@ -52,6 +52,8 @@ from .lib.capnp import (
     _write_message_to_fd,
     _write_packed_message_to_fd,
     _Promise as Promise,
+    _init_capnp_api,
 )
 
+_init_capnp_api()
 add_import_hook() # enable import hook by default
diff --git a/capnp/helpers/capabilityHelper.cpp b/capnp/helpers/capabilityHelper.cpp
new file mode 100644
index 0000000..05350ac
--- /dev/null
+++ b/capnp/helpers/capabilityHelper.cpp
@@ -0,0 +1,159 @@
+#include "capnp/helpers/capabilityHelper.h"
+#include "capnp/lib/capnp_api.h"
+
+::kj::Promise<PyObject *> convert_to_pypromise(capnp::RemotePromise<capnp::DynamicStruct> & promise) {
+    return promise.then([](capnp::Response<capnp::DynamicStruct>&& response) { return wrap_dynamic_struct_reader(response); } );
+}
+
+void reraise_kj_exception() {
+  GILAcquire gil;
+  try {
+    if (PyErr_Occurred())
+      ; // let the latest Python exn pass through and ignore the current one
+    else
+      throw;
+  }
+  catch (kj::Exception& exn) {
+    auto obj = wrap_kj_exception_for_reraise(exn);
+    PyErr_SetObject((PyObject*)obj->ob_type, obj);
+    Py_DECREF(obj);
+  }
+  catch (const std::exception& exn) {
+    PyErr_SetString(PyExc_RuntimeError, exn.what());
+  }
+  catch (...)
+  {
+    PyErr_SetString(PyExc_RuntimeError, "Unknown exception");
+  }
+}
+
+void check_py_error() {
+    GILAcquire gil;
+    PyObject * err = PyErr_Occurred();
+    if(err) {
+        PyObject * ptype, *pvalue, *ptraceback;
+        PyErr_Fetch(&ptype, &pvalue, &ptraceback);
+        if(ptype == NULL || pvalue == NULL || ptraceback == NULL)
+          throw kj::Exception(kj::Exception::Type::FAILED, kj::heapString("capabilityHelper.h"), 44, kj::heapString("Unknown error occurred"));
+
+        PyObject * info = get_exception_info(ptype, pvalue, ptraceback);
+
+        PyObject * py_filename = PyTuple_GetItem(info, 0);
+        kj::String filename(kj::heapString(PyBytes_AsString(py_filename)));
+
+        PyObject * py_line = PyTuple_GetItem(info, 1);
+        int line = PyLong_AsLong(py_line);
+
+        PyObject * py_description = PyTuple_GetItem(info, 2);
+        kj::String description(kj::heapString(PyBytes_AsString(py_description)));
+
+        Py_DECREF(ptype);
+        Py_DECREF(pvalue);
+        Py_DECREF(ptraceback);
+        Py_DECREF(info);
+        PyErr_Clear();
+
+        throw kj::Exception(kj::Exception::Type::FAILED, kj::mv(filename), line, kj::mv(description));
+    }
+}
+
+kj::Promise<PyObject *> wrapPyFunc(PyObject * func, PyObject * arg) {
+    GILAcquire gil;
+    auto arg_promise = extract_promise(arg);
+
+    if(arg_promise == NULL) {
+      PyObject * result = PyObject_CallFunctionObjArgs(func, arg, NULL);
+      Py_DECREF(arg);
+
+      check_py_error();
+
+      auto promise = extract_promise(result);
+      if(promise != NULL)
+        return kj::mv(*promise); // TODO: delete promise, see incref of containing promise in capnp.pyx
+      auto remote_promise = extract_remote_promise(result);
+      if(remote_promise != NULL)
+        return convert_to_pypromise(*remote_promise); // TODO: delete promise, see incref of containing promise in capnp.pyx
+      return result;
+    }
+    else {
+      return arg_promise->then([&](PyObject * new_arg){ return wrapPyFunc(func, new_arg); });// TODO: delete arg_promise?
+    }
+}
+
+kj::Promise<PyObject *> wrapPyFuncNoArg(PyObject * func) {
+    GILAcquire gil;
+    PyObject * result = PyObject_CallFunctionObjArgs(func, NULL);
+
+    check_py_error();
+
+    auto promise = extract_promise(result);
+    if(promise != NULL)
+      return kj::mv(*promise);
+    auto remote_promise = extract_remote_promise(result);
+    if(remote_promise != NULL)
+      return convert_to_pypromise(*remote_promise); // TODO: delete promise, see incref of containing promise in capnp.pyx
+    return result;
+}
+
+kj::Promise<PyObject *> wrapRemoteCall(PyObject * func, capnp::Response<capnp::DynamicStruct> & arg) {
+    GILAcquire gil;
+    PyObject * ret = wrap_remote_call(func, arg);
+
+    check_py_error();
+
+    auto promise = extract_promise(ret);
+    if(promise != NULL)
+      return kj::mv(*promise);
+    auto remote_promise = extract_remote_promise(ret);
+    if(remote_promise != NULL)
+      return convert_to_pypromise(*remote_promise); // TODO: delete promise, see incref of containing promise in capnp.pyx
+    return ret;
+}
+
+::kj::Promise<PyObject *> then(kj::Promise<PyObject *> & promise, PyObject * func, PyObject * error_func) {
+  if(error_func == Py_None)
+    return promise.then([func](PyObject * arg) { return wrapPyFunc(func, arg); } );
+  else
+    return promise.then([func](PyObject * arg) { return wrapPyFunc(func, arg); }
+                                     , [error_func](kj::Exception arg) { return wrapPyFunc(error_func, wrap_kj_exception(arg)); } );
+}
+
+::kj::Promise<PyObject *> then(::capnp::RemotePromise< ::capnp::DynamicStruct> & promise, PyObject * func, PyObject * error_func) {
+  if(error_func == Py_None)
+    return promise.then([func](capnp::Response<capnp::DynamicStruct>&& arg) { return wrapRemoteCall(func, arg); } );
+  else
+    return promise.then([func](capnp::Response<capnp::DynamicStruct>&& arg) { return  wrapRemoteCall(func, arg); }
+                                     , [error_func](kj::Exception arg) { return wrapPyFunc(error_func, wrap_kj_exception(arg)); } );
+}
+
+::kj::Promise<PyObject *> then(kj::Promise<void> & promise, PyObject * func, PyObject * error_func) {
+  if(error_func == Py_None)
+    return promise.then([func]() { return wrapPyFuncNoArg(func); } );
+  else
+    return promise.then([func]() { return wrapPyFuncNoArg(func); }
+                                     , [error_func](kj::Exception arg) { return wrapPyFunc(error_func, wrap_kj_exception(arg)); } );
+}
+
+::kj::Promise<PyObject *> then(kj::Promise<kj::Array<PyObject *> > && promise) {
+  return promise.then([](kj::Array<PyObject *>&& arg) { return convert_array_pyobject(arg); } );
+}
+
+kj::Promise<void> PythonInterfaceDynamicImpl::call(capnp::InterfaceSchema::Method method,
+                         capnp::CallContext< capnp::DynamicStruct, capnp::DynamicStruct> context) {
+    auto methodName = method.getProto().getName();
+
+    kj::Promise<void> * promise = call_server_method(py_server, const_cast<char *>(methodName.cStr()), context);
+
+    check_py_error();
+
+    if(promise == nullptr)
+      return kj::READY_NOW;
+
+    kj::Promise<void> ret(kj::mv(*promise));
+    delete promise;
+    return ret;
+};
+
+void init_capnp_api() {
+    import_capnp__lib__capnp();
+}
diff --git a/capnp/helpers/capabilityHelper.h b/capnp/helpers/capabilityHelper.h
index d6f7ff0..d45c511 100644
--- a/capnp/helpers/capabilityHelper.h
+++ b/capnp/helpers/capabilityHelper.h
@@ -4,18 +4,6 @@
 #include <stdexcept>
 #include "Python.h"
 
-extern "C" {
-   PyObject * wrap_remote_call(PyObject * func, capnp::Response<capnp::DynamicStruct> &);
-   PyObject * wrap_dynamic_struct_reader(capnp::Response<capnp::DynamicStruct> &);
-   ::kj::Promise<void> * call_server_method(PyObject * py_server, char * name, capnp::CallContext< capnp::DynamicStruct, capnp::DynamicStruct> & context);
-   PyObject * wrap_kj_exception(kj::Exception &);
-   PyObject * wrap_kj_exception_for_reraise(kj::Exception &);
-   PyObject * get_exception_info(PyObject *, PyObject *, PyObject *);
-   PyObject * convert_array_pyobject(kj::Array<PyObject *>&);
-   ::kj::Promise<PyObject *> * extract_promise(PyObject *);
-   ::capnp::RemotePromise< ::capnp::DynamicStruct> * extract_remote_promise(PyObject *);
- }
-
 class GILAcquire {
 public:
   GILAcquire() : gstate(PyGILState_Ensure()) {}
@@ -38,11 +26,9 @@ public:
   PyThreadState *_save; // The macros above read/write from this variable
 };
 
-::kj::Promise<PyObject *> convert_to_pypromise(capnp::RemotePromise<capnp::DynamicStruct> & promise) {
-    return promise.then([](capnp::Response<capnp::DynamicStruct>&& response) { return wrap_dynamic_struct_reader(response); } );
-}
+::kj::Promise<PyObject *> convert_to_pypromise(capnp::RemotePromise<capnp::DynamicStruct> & promise);
 
-::kj::Promise<PyObject *> convert_to_pypromise(kj::Promise<void> & promise) {
+inline ::kj::Promise<PyObject *> convert_to_pypromise(kj::Promise<void> & promise) {
     return promise.then([]() {
       GILAcquire gil;
       Py_INCREF( Py_None );
@@ -55,138 +41,22 @@ template<class T>
     return promise.then([](T) { } );
 }
 
-void reraise_kj_exception() {
-  GILAcquire gil;
-  try {
-    if (PyErr_Occurred())
-      ; // let the latest Python exn pass through and ignore the current one
-    else
-      throw;
-  }
-  catch (kj::Exception& exn) {
-    auto obj = wrap_kj_exception_for_reraise(exn);
-    PyErr_SetObject((PyObject*)obj->ob_type, obj);
-    Py_DECREF(obj);
-  }
-  catch (const std::exception& exn) {
-    PyErr_SetString(PyExc_RuntimeError, exn.what());
-  }
-  catch (...)
-  {
-    PyErr_SetString(PyExc_RuntimeError, "Unknown exception");
-  }
-}
+void reraise_kj_exception();
 
-void check_py_error() {
-    GILAcquire gil;
-    PyObject * err = PyErr_Occurred();
-    if(err) {
-        PyObject * ptype, *pvalue, *ptraceback;
-        PyErr_Fetch(&ptype, &pvalue, &ptraceback);
-        if(ptype == NULL || pvalue == NULL || ptraceback == NULL)
-          throw kj::Exception(kj::Exception::Type::FAILED, kj::heapString("capabilityHelper.h"), 44, kj::heapString("Unknown error occurred"));
+void check_py_error();
 
-        PyObject * info = get_exception_info(ptype, pvalue, ptraceback);
+kj::Promise<PyObject *> wrapPyFunc(PyObject * func, PyObject * arg);
 
-        PyObject * py_filename = PyTuple_GetItem(info, 0);
-        kj::String filename(kj::heapString(PyBytes_AsString(py_filename)));
+kj::Promise<PyObject *> wrapPyFuncNoArg(PyObject * func);
 
-        PyObject * py_line = PyTuple_GetItem(info, 1);
-        int line = PyInt_AsLong(py_line);
+kj::Promise<PyObject *> wrapRemoteCall(PyObject * func, capnp::Response<capnp::DynamicStruct> & arg);
 
-        PyObject * py_description = PyTuple_GetItem(info, 2);
-        kj::String description(kj::heapString(PyBytes_AsString(py_description)));
+::kj::Promise<PyObject *> then(kj::Promise<PyObject *> & promise, PyObject * func, PyObject * error_func);
+::kj::Promise<PyObject *> then(::capnp::RemotePromise< ::capnp::DynamicStruct> & promise, PyObject * func, PyObject * error_func);
 
-        Py_DECREF(ptype);
-        Py_DECREF(pvalue);
-        Py_DECREF(ptraceback);
-        Py_DECREF(info);
-        PyErr_Clear();
+::kj::Promise<PyObject *> then(kj::Promise<void> & promise, PyObject * func, PyObject * error_func);
 
-        throw kj::Exception(kj::Exception::Type::FAILED, kj::mv(filename), line, kj::mv(description));
-    }
-}
-
-kj::Promise<PyObject *> wrapPyFunc(PyObject * func, PyObject * arg) {
-    GILAcquire gil;
-    auto arg_promise = extract_promise(arg);
-
-    if(arg_promise == NULL) {
-      PyObject * result = PyObject_CallFunctionObjArgs(func, arg, NULL);
-      Py_DECREF(arg);
-
-      check_py_error();
-
-      auto promise = extract_promise(result);
-      if(promise != NULL)
-        return kj::mv(*promise); // TODO: delete promise, see incref of containing promise in capnp.pyx
-      auto remote_promise = extract_remote_promise(result);
-      if(remote_promise != NULL)
-        return convert_to_pypromise(*remote_promise); // TODO: delete promise, see incref of containing promise in capnp.pyx
-      return result;
-    }
-    else {
-      return arg_promise->then([&](PyObject * new_arg){ return wrapPyFunc(func, new_arg); });// TODO: delete arg_promise?
-    }
-}
-
-kj::Promise<PyObject *> wrapPyFuncNoArg(PyObject * func) {
-    GILAcquire gil;
-    PyObject * result = PyObject_CallFunctionObjArgs(func, NULL);
-
-    check_py_error();
-
-    auto promise = extract_promise(result);
-    if(promise != NULL)
-      return kj::mv(*promise);
-    auto remote_promise = extract_remote_promise(result);
-    if(remote_promise != NULL)
-      return convert_to_pypromise(*remote_promise); // TODO: delete promise, see incref of containing promise in capnp.pyx
-    return result;
-}
-
-kj::Promise<PyObject *> wrapRemoteCall(PyObject * func, capnp::Response<capnp::DynamicStruct> & arg) {
-    GILAcquire gil;
-    PyObject * ret = wrap_remote_call(func, arg);
-
-    check_py_error();
-
-    auto promise = extract_promise(ret);
-    if(promise != NULL)
-      return kj::mv(*promise);
-    auto remote_promise = extract_remote_promise(ret);
-    if(remote_promise != NULL)
-      return convert_to_pypromise(*remote_promise); // TODO: delete promise, see incref of containing promise in capnp.pyx
-    return ret;
-}
-
-::kj::Promise<PyObject *> then(kj::Promise<PyObject *> & promise, PyObject * func, PyObject * error_func) {
-  if(error_func == Py_None)
-    return promise.then([func](PyObject * arg) { return wrapPyFunc(func, arg); } );
-  else
-    return promise.then([func](PyObject * arg) { return wrapPyFunc(func, arg); }
-                                     , [error_func](kj::Exception arg) { return wrapPyFunc(error_func, wrap_kj_exception(arg)); } );
-}
-
-::kj::Promise<PyObject *> then(::capnp::RemotePromise< ::capnp::DynamicStruct> & promise, PyObject * func, PyObject * error_func) {
-  if(error_func == Py_None)
-    return promise.then([func](capnp::Response<capnp::DynamicStruct>&& arg) { return wrapRemoteCall(func, arg); } );
-  else
-    return promise.then([func](capnp::Response<capnp::DynamicStruct>&& arg) { return  wrapRemoteCall(func, arg); }
-                                     , [error_func](kj::Exception arg) { return wrapPyFunc(error_func, wrap_kj_exception(arg)); } );
-}
-
-::kj::Promise<PyObject *> then(kj::Promise<void> & promise, PyObject * func, PyObject * error_func) {
-  if(error_func == Py_None)
-    return promise.then([func]() { return wrapPyFuncNoArg(func); } );
-  else
-    return promise.then([func]() { return wrapPyFuncNoArg(func); }
-                                     , [error_func](kj::Exception arg) { return wrapPyFunc(error_func, wrap_kj_exception(arg)); } );
-}
-
-::kj::Promise<PyObject *> then(kj::Promise<kj::Array<PyObject *> > && promise) {
-  return promise.then([](kj::Array<PyObject *>&& arg) { return convert_array_pyobject(arg); } );
-}
+::kj::Promise<PyObject *> then(kj::Promise<kj::Array<PyObject *> > && promise);
 
 class PythonInterfaceDynamicImpl final: public capnp::DynamicCapability::Server {
 public:
@@ -204,20 +74,7 @@ public:
   }
 
   kj::Promise<void> call(capnp::InterfaceSchema::Method method,
-                         capnp::CallContext< capnp::DynamicStruct, capnp::DynamicStruct> context) {
-    auto methodName = method.getProto().getName();
-
-    kj::Promise<void> * promise = call_server_method(py_server, const_cast<char *>(methodName.cStr()), context);
-
-    check_py_error();
-
-    if(promise == nullptr)
-      return kj::READY_NOW;
-
-    kj::Promise<void> ret(kj::mv(*promise));
-    delete promise;
-    return ret;
-  }
+                         capnp::CallContext< capnp::DynamicStruct, capnp::DynamicStruct> context);
 };
 
 class PyRefCounter {
@@ -240,13 +97,15 @@ public:
   }
 };
 
-capnp::DynamicCapability::Client new_client(capnp::InterfaceSchema & schema, PyObject * server) {
+inline capnp::DynamicCapability::Client new_client(capnp::InterfaceSchema & schema, PyObject * server) {
   return capnp::DynamicCapability::Client(kj::heap<PythonInterfaceDynamicImpl>(schema, server));
 }
-capnp::DynamicValue::Reader new_server(capnp::InterfaceSchema & schema, PyObject * server) {
+inline capnp::DynamicValue::Reader new_server(capnp::InterfaceSchema & schema, PyObject * server) {
   return capnp::DynamicValue::Reader(kj::heap<PythonInterfaceDynamicImpl>(schema, server));
 }
 
-capnp::Capability::Client server_to_client(capnp::InterfaceSchema & schema, PyObject * server) {
+inline capnp::Capability::Client server_to_client(capnp::InterfaceSchema & schema, PyObject * server) {
   return kj::heap<PythonInterfaceDynamicImpl>(schema, server);
 }
+
+void init_capnp_api();
diff --git a/capnp/helpers/helpers.pxd b/capnp/helpers/helpers.pxd
index cde9bab..5304d5d 100644
--- a/capnp/helpers/helpers.pxd
+++ b/capnp/helpers/helpers.pxd
@@ -25,6 +25,7 @@ cdef extern from "capnp/helpers/capabilityHelper.h":
     PyPromise convert_to_pypromise(RemotePromise&)
     PyPromise convert_to_pypromise(VoidPromise&)
     VoidPromise convert_to_voidpromise(PyPromise&)
+    void init_capnp_api()
 
 cdef extern from "capnp/helpers/rpcHelper.h":
     Capability.Client bootstrapHelper(RpcSystem&)
diff --git a/capnp/lib/capnp.pxd b/capnp/lib/capnp.pxd
index 21c8950..55c8531 100644
--- a/capnp/lib/capnp.pxd
+++ b/capnp/lib/capnp.pxd
@@ -2,7 +2,7 @@
 
 from capnp.includes cimport capnp_cpp as capnp
 from capnp.includes cimport schema_cpp
-from capnp.includes.capnp_cpp cimport Schema as C_Schema, StructSchema as C_StructSchema, InterfaceSchema as C_InterfaceSchema, EnumSchema as C_EnumSchema, ListSchema as C_ListSchema, DynamicStruct as C_DynamicStruct, DynamicValue as C_DynamicValue, Type as C_Type, DynamicList as C_DynamicList, SchemaParser as C_SchemaParser, ParsedSchema as C_ParsedSchema, VOID, ArrayPtr, StringPtr, String, StringTree, DynamicOrphan as C_DynamicOrphan, AnyPointer as C_DynamicObject, DynamicCapability as C_DynamicCapability, Request, Response, RemotePromise, PyPromise, VoidPromise, CallContext, RpcSystem, makeRpcServerBootstrap, makeRpcClient, Capability as C_Capability, TwoPartyVatNetwork as C_TwoPartyVatNetwork, Side, AsyncIoStream, Own, makeTwoPartyVatNetwork, PromiseFulfillerPair as C_PromiseFulfillerPair, copyPromiseFulfillerPair, newPromiseAndFulfiller, PyArray, DynamicStruct_Builder, TwoWayPipe
+from capnp.includes.capnp_cpp cimport Schema as C_Schema, StructSchema as C_StructSchema, InterfaceSchema as C_InterfaceSchema, EnumSchema as C_EnumSchema, ListSchema as C_ListSchema, DynamicStruct as C_DynamicStruct, DynamicValue as C_DynamicValue, Type as C_Type, DynamicList as C_DynamicList, SchemaParser as C_SchemaParser, ParsedSchema as C_ParsedSchema, VOID, ArrayPtr, StringPtr, String, StringTree, DynamicOrphan as C_DynamicOrphan, AnyPointer as C_DynamicObject, DynamicCapability as C_DynamicCapability, Request, Response, RemotePromise, Promise, CallContext, RpcSystem, makeRpcServerBootstrap, makeRpcClient, Capability as C_Capability, TwoPartyVatNetwork as C_TwoPartyVatNetwork, Side, AsyncIoStream, Own, makeTwoPartyVatNetwork, PromiseFulfillerPair as C_PromiseFulfillerPair, copyPromiseFulfillerPair, newPromiseAndFulfiller, PyArray, DynamicStruct_Builder, TwoWayPipe
 from capnp.includes.schema_cpp cimport Node as C_Node, EnumNode as C_EnumNode
 from capnp.includes.types cimport *
 from capnp.helpers.non_circular cimport reraise_kj_exception
@@ -130,6 +130,15 @@ cdef class _DynamicListBuilder:
 
     cpdef init(self, index, size)
 
+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
+
 cdef to_python_reader(C_DynamicValue.Reader self, object parent)
 cdef to_python_builder(C_DynamicValue.Builder self, object parent)
 cdef _to_dict(msg, bint verbose, bint ordered)
@@ -137,3 +146,13 @@ cdef _from_list(_DynamicListBuilder msg, list d)
 cdef _from_tuple(_DynamicListBuilder msg, tuple d)
 cdef _setDynamicFieldWithField(DynamicStruct_Builder thisptr, _StructSchemaField field, value, parent)
 cdef _setDynamicFieldStatic(DynamicStruct_Builder thisptr, field, value, parent)
+
+cdef api object wrap_dynamic_struct_reader(Response & r) with gil
+cdef api PyObject * wrap_remote_call(PyObject * func, Response & r) except * with gil
+cdef api Promise[void] * call_server_method(PyObject * _server, char * _method_name, CallContext & _context) except * with gil
+cdef api convert_array_pyobject(PyArray & arr) with gil
+cdef api Promise[PyObject*] * extract_promise(object obj) with gil
+cdef api RemotePromise * extract_remote_promise(object obj) with gil
+cdef api object wrap_kj_exception(capnp.Exception & exception) with gil
+cdef api object wrap_kj_exception_for_reraise(capnp.Exception & exception) with gil
+cdef api object get_exception_info(object exc_type, object exc_obj, object exc_tb) with gil
diff --git a/capnp/lib/capnp.pyx b/capnp/lib/capnp.pyx
index 9cf03fd..b0d62a7 100644
--- a/capnp/lib/capnp.pyx
+++ b/capnp/lib/capnp.pyx
@@ -9,8 +9,8 @@
 
 cimport cython
 
-from capnp.helpers.helpers cimport AsyncIoStreamReadHelper
-from capnp.includes.capnp_cpp cimport AsyncIoStream, WaitScope
+from capnp.helpers.helpers cimport AsyncIoStreamReadHelper, init_capnp_api
+from capnp.includes.capnp_cpp cimport AsyncIoStream, WaitScope, PyPromise, VoidPromise
 
 from libc.stdlib cimport malloc, free
 from libc.string cimport memcpy
@@ -48,10 +48,10 @@ def deregister_all_types():
     _type_registry = {}
 
 # By making it public, we'll be able to call it from capabilityHelper.h
-cdef public object wrap_dynamic_struct_reader(Response & r) with gil:
+cdef api object wrap_dynamic_struct_reader(Response & r) with gil:
     return _Response()._init_childptr(new Response(moveResponse(r)), None)
 
-cdef public PyObject * wrap_remote_call(PyObject * func, Response & r) except * with gil:
+cdef api PyObject * wrap_remote_call(PyObject * func, Response & r) except * with gil:
     response = _Response()._init_childptr(new Response(moveResponse(r)), None)
 
     func_obj = <object>func
@@ -62,7 +62,7 @@ cdef public PyObject * wrap_remote_call(PyObject * func, Response & r) except *
 cdef _find_field_order(struct_node):
     return [f.name for f in sorted(struct_node.fields, key=_attrgetter('codeOrder'))]
 
-cdef public VoidPromise * call_server_method(PyObject * _server, char * _method_name, CallContext & _context) except * with gil:
+cdef api VoidPromise * call_server_method(PyObject * _server, char * _method_name, CallContext & _context) except * with gil:
     server = <object>_server
     method_name = <object>_method_name
 
@@ -117,10 +117,10 @@ cdef public VoidPromise * call_server_method(PyObject * _server, char * _method_
 
     return NULL
 
-cdef public convert_array_pyobject(PyArray & arr) with gil:
+cdef api convert_array_pyobject(PyArray & arr) with gil:
     return [<object>arr[i] for i in range(arr.size())]
 
-cdef public PyPromise * extract_promise(object obj) with gil:
+cdef api PyPromise * extract_promise(object obj) with gil:
     if type(obj) is _Promise:
         promise = <_Promise>obj
 
@@ -131,7 +131,7 @@ cdef public PyPromise * extract_promise(object obj) with gil:
 
     return NULL
 
-cdef public RemotePromise * extract_remote_promise(object obj) with gil:
+cdef api RemotePromise * extract_remote_promise(object obj) with gil:
     if type(obj) is _RemotePromise:
         promise = <_RemotePromise>obj
         promise.is_consumed = True
@@ -235,20 +235,20 @@ class KjException(Exception):
                 return AttributeError(message)
         return self
 
-cdef public object wrap_kj_exception(capnp.Exception & exception) with gil:
+cdef api object wrap_kj_exception(capnp.Exception & exception) with gil:
     PyErr_Clear()
     wrapper = _KjExceptionWrapper()._init(exception)
     ret = KjException(wrapper=wrapper)
 
     return ret
 
-cdef public object wrap_kj_exception_for_reraise(capnp.Exception & exception) with gil:
+cdef api object wrap_kj_exception_for_reraise(capnp.Exception & exception) with gil:
     wrapper = _KjExceptionWrapper()._init(exception)
 
     ret = KjException(wrapper=wrapper)
     return ret
 
-cdef public object get_exception_info(object exc_type, object exc_obj, object exc_tb) with gil:
+cdef api object get_exception_info(object exc_type, object exc_obj, object exc_tb) with gil:
     try:
         return (exc_tb.tb_frame.f_code.co_filename.encode(), exc_tb.tb_lineno, (repr(exc_type) + ':' + str(exc_obj)).encode())
     except:
@@ -3250,7 +3250,6 @@ cdef class _MessageBuilder:
 
     .. warning:: Don't ever instantiate this class directly. It is only used for inheritance.
     """
-    cdef schema_cpp.MessageBuilder * thisptr
     def __dealloc__(self):
         del self.thisptr
 
@@ -4080,3 +4079,7 @@ def remove_import_hook():
     if _importer is not None:
         _sys.meta_path.remove(_importer)
     _importer = None
+
+def _init_capnp_api():
+    """ Initialize static function pointers for cdef api functions. """
+    init_capnp_api()
diff --git a/setup.py b/setup.py
index 2c86de8..a6976de 100644
--- a/setup.py
+++ b/setup.py
@@ -168,7 +168,7 @@ if os.name == 'nt':
 import Cython.Build
 import Cython # noqa: F401
 extensions = [Extension(
-    '*', ['capnp/lib/*.pyx'],
+    '*', ['capnp/helpers/capabilityHelper.cpp', 'capnp/lib/*.pyx'],
     extra_compile_args=extra_compile_args,
     extra_link_args=extra_link_args,
     language='c++',