diff --git a/tools/SourceKit/tools/sourcekitd/lib/API/CMakeLists.txt b/tools/SourceKit/tools/sourcekitd/lib/API/CMakeLists.txt
index f04952857afcf..086dcbe7e3a42 100644
--- a/tools/SourceKit/tools/sourcekitd/lib/API/CMakeLists.txt
+++ b/tools/SourceKit/tools/sourcekitd/lib/API/CMakeLists.txt
@@ -7,11 +7,16 @@ set(sourcekitdAPI_sources
   TokenAnnotationsArray.cpp
 )
 
-set(sourcekitdAPI_Darwin_sources
-  sourcekitdAPI-XPC.cpp)
-set(LLVM_OPTIONAL_SOURCES ${sourcekitdAPI_Darwin_sources})
-if(APPLE)
-  list(APPEND sourcekitdAPI_sources ${sourcekitdAPI_Darwin_sources})
+set(sourcekitdAPI_InProc_sources sourcekitdAPI-InProc.cpp)
+set(sourcekitdAPI_XPC_sources sourcekitdAPI-XPC.cpp)
+
+set(LLVM_OPTIONAL_SOURCES ${sourcekitdAPI_InProc_sources})
+set(LLVM_OPTIONAL_SOURCES ${sourcekitdAPI_XPC_sources})
+
+if(SWIFT_SOURCEKIT_USE_INPROC_LIBRARY)
+  list(APPEND sourcekitdAPI_sources ${sourcekitdAPI_InProc_sources})
+else()
+  list(APPEND sourcekitdAPI_sources ${sourcekitdAPI_XPC_sources})
 endif()
 
 add_sourcekit_library(sourcekitdAPI
diff --git a/tools/SourceKit/tools/sourcekitd/lib/API/sourcekitdAPI-InProc.cpp b/tools/SourceKit/tools/sourcekitd/lib/API/sourcekitdAPI-InProc.cpp
new file mode 100644
index 0000000000000..816d60a2084a9
--- /dev/null
+++ b/tools/SourceKit/tools/sourcekitd/lib/API/sourcekitdAPI-InProc.cpp
@@ -0,0 +1,239 @@
+//===--- sourcekitdAPI-InProc.cpp -----------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2016 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See http://swift.org/LICENSE.txt for license information
+// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+#include "sourcekitd/sourcekitd.h"
+#include "sourcekitd/Internal.h"
+#include "SourceKit/Support/UIdent.h"
+#include "llvm/ADT/ArrayRef.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/Support/ErrorHandling.h"
+
+using namespace SourceKit;
+using namespace sourcekitd;
+using llvm::ArrayRef;
+using llvm::StringRef;
+using llvm::raw_ostream;
+
+// The following functions are declared in sourcekitd/sourcekitd.h.
+// These are their "in-process" implementations.
+
+sourcekitd_uid_t
+sourcekitd_uid_get_from_buf(const char *buf, size_t length) {
+  llvm::report_fatal_error("not yet implemented");
+}
+
+size_t
+sourcekitd_uid_get_length(sourcekitd_uid_t uid) {
+  llvm::report_fatal_error("not yet implemented");
+}
+
+const char *
+sourcekitd_uid_get_string_ptr(sourcekitd_uid_t uid) {
+  llvm::report_fatal_error("not yet implemented");
+}
+
+sourcekitd_object_t
+sourcekitd_request_retain(sourcekitd_object_t object) {
+  llvm::report_fatal_error("not yet implemented");
+}
+
+void sourcekitd_request_release(sourcekitd_object_t object) {
+  llvm::report_fatal_error("not yet implemented");
+}
+
+sourcekitd_object_t
+sourcekitd_request_dictionary_create(const sourcekitd_uid_t *keys,
+                                     const sourcekitd_object_t *values,
+                                     size_t count) {
+  llvm::report_fatal_error("not yet implemented");
+}
+
+void
+sourcekitd_request_dictionary_set_value(sourcekitd_object_t dict,
+                                        sourcekitd_uid_t key,
+                                        sourcekitd_object_t value) {
+  llvm::report_fatal_error("not yet implemented");
+}
+
+sourcekitd_object_t
+sourcekitd_request_array_create(const sourcekitd_object_t *objects,
+                                size_t count) {
+  llvm::report_fatal_error("not yet implemented");
+}
+
+void
+sourcekitd_request_array_set_value(sourcekitd_object_t array, size_t index,
+                                   sourcekitd_object_t value) {
+  llvm::report_fatal_error("not yet implemented");
+}
+
+sourcekitd_object_t
+sourcekitd_request_int64_create(int64_t val) {
+  llvm::report_fatal_error("not yet implemented");
+}
+
+sourcekitd_object_t
+sourcekitd_request_string_create(const char *string) {
+  llvm::report_fatal_error("not yet implemented");
+}
+
+sourcekitd_object_t
+sourcekitd_request_uid_create(sourcekitd_uid_t uid) {
+  llvm::report_fatal_error("not yet implemented");
+}
+
+void
+sourcekitd_response_dispose(sourcekitd_response_t obj) {
+  llvm::report_fatal_error("not yet implemented");
+}
+
+bool
+sourcekitd_response_is_error(sourcekitd_response_t obj) {
+  llvm::report_fatal_error("not yet implemented");
+}
+
+sourcekitd_error_t
+sourcekitd_response_error_get_kind(sourcekitd_response_t obj) {
+  llvm::report_fatal_error("not yet implemented");
+}
+
+const char *
+sourcekitd_response_error_get_description(sourcekitd_response_t obj) {
+  llvm::report_fatal_error("not yet implemented");
+}
+
+sourcekitd_variant_t
+sourcekitd_response_get_value(sourcekitd_response_t resp) {
+  llvm::report_fatal_error("not yet implemented");
+}
+
+// The following functions are declared in sourcekitd/Internal.h.
+// These are their "in-process" implementations.
+
+void sourcekitd::printRequestObject(sourcekitd_object_t Obj, raw_ostream &OS) {
+  llvm::report_fatal_error("not yet implemented");
+}
+
+ResponseBuilder::ResponseBuilder() {
+  llvm::report_fatal_error("not yet implemented");
+}
+
+ResponseBuilder::~ResponseBuilder() {
+  llvm::report_fatal_error("not yet implemented");
+}
+
+ResponseBuilder::Dictionary ResponseBuilder::getDictionary() {
+  llvm::report_fatal_error("not yet implemented");
+}
+
+sourcekitd_response_t ResponseBuilder::createResponse() {
+  llvm::report_fatal_error("not yet implemented");
+}
+
+void ResponseBuilder::Dictionary::set(UIdent Key, SourceKit::UIdent UID) {
+  llvm::report_fatal_error("not yet implemented");
+}
+
+void ResponseBuilder::Dictionary::set(UIdent Key, sourcekitd_uid_t UID) {
+  llvm::report_fatal_error("not yet implemented");
+}
+
+void ResponseBuilder::Dictionary::set(UIdent Key, const char *Str) {
+  llvm::report_fatal_error("not yet implemented");
+}
+
+void ResponseBuilder::Dictionary::set(UIdent Key, llvm::StringRef Str) {
+  llvm::report_fatal_error("not yet implemented");
+}
+
+void ResponseBuilder::Dictionary::set(UIdent Key, int64_t val) {
+  llvm::report_fatal_error("not yet implemented");
+}
+
+void ResponseBuilder::Dictionary::set(SourceKit::UIdent Key,
+                                      ArrayRef<StringRef> Strs) {
+  llvm::report_fatal_error("not yet implemented");
+}
+
+void ResponseBuilder::Dictionary::setBool(UIdent Key, bool val) {
+  llvm::report_fatal_error("not yet implemented");
+}
+
+ResponseBuilder::Dictionary
+ResponseBuilder::Dictionary::setDictionary(UIdent Key) {
+  llvm::report_fatal_error("not yet implemented");
+}
+
+void ResponseBuilder::Dictionary::setCustomBuffer(
+      SourceKit::UIdent Key,
+      CustomBufferKind Kind, std::unique_ptr<llvm::MemoryBuffer> MemBuf) {
+  llvm::report_fatal_error("not yet implemented");
+}
+
+ResponseBuilder::Array
+ResponseBuilder::Dictionary::setArray(UIdent Key) {
+  llvm::report_fatal_error("not yet implemented");
+}
+
+ResponseBuilder::Dictionary ResponseBuilder::Array::appendDictionary() {
+  llvm::report_fatal_error("not yet implemented");
+}
+
+sourcekitd_uid_t RequestDict::getUID(UIdent Key) {
+  llvm::report_fatal_error("not yet implemented");
+}
+
+
+Optional<StringRef> RequestDict::getString(UIdent Key) {
+  llvm::report_fatal_error("not yet implemented");
+}
+
+Optional<RequestDict> RequestDict::getDictionary(SourceKit::UIdent Key) {
+  llvm::report_fatal_error("not yet implemented");
+}
+
+bool RequestDict::getStringArray(SourceKit::UIdent Key,
+                                 llvm::SmallVectorImpl<const char *> &Arr,
+                                 bool isOptional) {
+  llvm::report_fatal_error("not yet implemented");
+}
+
+bool RequestDict::getUIDArray(SourceKit::UIdent Key,
+                              llvm::SmallVectorImpl<sourcekitd_uid_t> &Arr,
+                              bool isOptional) {
+  llvm::report_fatal_error("not yet implemented");
+}
+
+bool RequestDict::dictionaryArrayApply(
+    SourceKit::UIdent key, llvm::function_ref<bool(RequestDict)> applier) {
+  llvm::report_fatal_error("not yet implemented");
+}
+
+bool RequestDict::getInt64(SourceKit::UIdent Key, int64_t &Val,
+                           bool isOptional) {
+  llvm::report_fatal_error("not yet implemented");
+}
+
+sourcekitd_response_t
+sourcekitd::createErrorRequestInvalid(const char *Description) {
+  llvm::report_fatal_error("not yet implemented");
+}
+
+sourcekitd_response_t
+sourcekitd::createErrorRequestFailed(const char *Description) {
+  llvm::report_fatal_error("not yet implemented");
+}
+
+sourcekitd_response_t
+sourcekitd::createErrorRequestCancelled() {
+  llvm::report_fatal_error("not yet implemented");
+}
diff --git a/tools/SourceKit/tools/sourcekitd/lib/API/sourcekitdAPI-XPC.cpp b/tools/SourceKit/tools/sourcekitd/lib/API/sourcekitdAPI-XPC.cpp
index 72ce190202fd6..cbd03b0805a32 100644
--- a/tools/SourceKit/tools/sourcekitd/lib/API/sourcekitdAPI-XPC.cpp
+++ b/tools/SourceKit/tools/sourcekitd/lib/API/sourcekitdAPI-XPC.cpp
@@ -195,6 +195,10 @@ class SKDObjectPrinter : public SKDObjectVisitor<SKDObjectPrinter> {
 
 } // anonymous namespace.
 
+//===----------------------------------------------------------------------===//
+// Internal API
+//===----------------------------------------------------------------------===//
+
 void sourcekitd::printRequestObject(sourcekitd_object_t Obj, raw_ostream &OS) {
   if (!Obj) {
     OS << "<<NULL>>";
@@ -204,10 +208,6 @@ void sourcekitd::printRequestObject(sourcekitd_object_t Obj, raw_ostream &OS) {
   SKDObjectPrinter(OS).visit(Obj);
 }
 
-//===----------------------------------------------------------------------===//
-// Internal API
-//===----------------------------------------------------------------------===//
-
 ResponseBuilder::ResponseBuilder() {
   Impl = xpc_dictionary_create(nullptr, nullptr, 0);
 }