diff --git a/integration_test/Dialect/ESI/runtime/basic_mmio.sv.py b/integration_test/Dialect/ESI/runtime/basic_mmio.sv.py
index 9a883f771e6f..15f6e79d67c5 100644
--- a/integration_test/Dialect/ESI/runtime/basic_mmio.sv.py
+++ b/integration_test/Dialect/ESI/runtime/basic_mmio.sv.py
@@ -1,8 +1,7 @@
 import esi
-import os
 import sys
 
-acc = esi.Accelerator(sys.argv[1], sys.argv[2])
+acc = esi.AcceleratorConnection(sys.argv[1], sys.argv[2])
 
 mmio = acc.get_service_mmio()
 
diff --git a/integration_test/Dialect/ESI/runtime/loopback.mlir.py b/integration_test/Dialect/ESI/runtime/loopback.mlir.py
index ffc57b5e03e2..662dcc6ea21b 100644
--- a/integration_test/Dialect/ESI/runtime/loopback.mlir.py
+++ b/integration_test/Dialect/ESI/runtime/loopback.mlir.py
@@ -3,7 +3,7 @@
 import sys
 
 platform = sys.argv[1]
-acc = esi.Accelerator(platform, sys.argv[2])
+acc = esi.AcceleratorConnection(platform, sys.argv[2])
 
 assert acc.sysinfo().esi_version() == 1
 m = acc.manifest()
@@ -36,7 +36,7 @@ def strType(t: esi.Type) -> str:
   print(f"{esiType}:")
   print(f"  {strType(esiType)}")
 
-d = m.build_design(acc)
+d = m.build_accelerator(acc)
 
 loopback = d.children[esi.AppID("loopback_inst", 0)]
 appid = loopback.id
diff --git a/lib/Dialect/ESI/CMakeLists.txt b/lib/Dialect/ESI/CMakeLists.txt
index 51f9f9de7c02..9533448fd809 100644
--- a/lib/Dialect/ESI/CMakeLists.txt
+++ b/lib/Dialect/ESI/CMakeLists.txt
@@ -72,19 +72,20 @@ set(ESI_RUNTIME_SRCS
 
   runtime/cpp/include/esi/backends/Cosim.h
   runtime/cpp/include/esi/backends/Trace.h
+  runtime/cpp/include/esi/Utils.h
   runtime/cpp/include/esi/Accelerator.h
-  runtime/cpp/include/esi/Design.h
   runtime/cpp/include/esi/Manifest.h
-  runtime/cpp/include/esi/StdServices.h
   runtime/cpp/include/esi/Types.h
-  runtime/cpp/include/esi/Utils.h
+  runtime/cpp/include/esi/Ports.h
+  runtime/cpp/include/esi/Services.h
+  runtime/cpp/include/esi/Common.h
   runtime/cpp/lib/backends/Cosim.cpp
   runtime/cpp/lib/backends/Trace.cpp
-  runtime/cpp/lib/Accelerator.cpp
-  runtime/cpp/lib/Design.cpp
-  runtime/cpp/lib/Manifest.cpp
-  runtime/cpp/lib/StdServices.cpp
   runtime/cpp/lib/Utils.cpp
+  runtime/cpp/lib/Manifest.cpp
+  runtime/cpp/lib/Services.cpp
+  runtime/cpp/lib/Accelerator.cpp
+  runtime/cpp/lib/Ports.cpp
   runtime/cpp/tools/esiquery.cpp
   runtime/cosim/CMakeLists.txt
   runtime/cosim/Cosim_MMIO.sv
@@ -100,10 +101,10 @@ set(ESI_RUNTIME_SRCS
   runtime/cosim/include/cosim/Server.h
   runtime/cosim/include/cosim/dpi.h
   runtime/cosim/include/dpi/svdpi.h
-  runtime/cosim/Cosim_Endpoint.sv
-  runtime/cosim/CosimDpi.capnp
   runtime/cosim/Cosim_DpiPkg.sv
   runtime/cosim/Cosim_Manifest.sv
+  runtime/cosim/Cosim_Endpoint.sv
+  runtime/cosim/CosimDpi.capnp
   runtime/python/esi/__init__.py
   runtime/python/esi/accelerator.py
   runtime/python/esi/esiCppAccel.cpp
diff --git a/lib/Dialect/ESI/runtime/CMakeLists.txt b/lib/Dialect/ESI/runtime/CMakeLists.txt
index 678778967aaa..c1b4df0f09db 100644
--- a/lib/Dialect/ESI/runtime/CMakeLists.txt
+++ b/lib/Dialect/ESI/runtime/CMakeLists.txt
@@ -44,9 +44,9 @@ include_directories(cpp/include)
 
 set(ESIRuntimeSources
   cpp/lib/Accelerator.cpp
-  cpp/lib/Design.cpp
   cpp/lib/Manifest.cpp
-  cpp/lib/StdServices.cpp
+  cpp/lib/Services.cpp
+  cpp/lib/Ports.cpp
   cpp/lib/Utils.cpp
 
   cpp/lib/backends/Trace.cpp
diff --git a/lib/Dialect/ESI/runtime/cpp/include/esi/Accelerator.h b/lib/Dialect/ESI/runtime/cpp/include/esi/Accelerator.h
index 694a3667f7c4..1cb7853a23fb 100644
--- a/lib/Dialect/ESI/runtime/cpp/include/esi/Accelerator.h
+++ b/lib/Dialect/ESI/runtime/cpp/include/esi/Accelerator.h
@@ -21,8 +21,9 @@
 #ifndef ESI_ACCELERATOR_H
 #define ESI_ACCELERATOR_H
 
-#include "esi/Design.h"
 #include "esi/Manifest.h"
+#include "esi/Ports.h"
+#include "esi/Services.h"
 
 #include <any>
 #include <cstdint>
@@ -34,92 +35,89 @@
 
 namespace esi {
 
+//===----------------------------------------------------------------------===//
+// Constants used by low-level APIs.
+//===----------------------------------------------------------------------===//
+
 constexpr uint32_t MagicNumOffset = 16;
 constexpr uint32_t MagicNumberLo = 0xE5100E51;
 constexpr uint32_t MagicNumberHi = 0x207D98E5;
 constexpr uint32_t VersionNumberOffset = MagicNumOffset + 8;
 constexpr uint32_t ExpectedVersionNumber = 0;
 
-/// Unidirectional channels are the basic communication primitive between the
-/// host and accelerator. A 'ChannelPort' is the host side of a channel. It can
-/// be either read or write but not both. At this level, channels are untyped --
-/// just streams of bytes. They are not intended to be used directly by users
-/// but used by higher level APIs which add types.
-class ChannelPort {
-public:
-  ChannelPort(const Type &type) : type(type) {}
-  virtual ~ChannelPort() = default;
-
-  virtual void connect() {}
-  virtual void disconnect() {}
-
-  const Type &getType() const { return type; }
+//===----------------------------------------------------------------------===//
+// Accelerator design hierarchy.
+//===----------------------------------------------------------------------===//
 
-private:
-  const Type &type;
-};
+class Instance;
 
-/// A ChannelPort which sends data to the accelerator.
-class WriteChannelPort : public ChannelPort {
+class HWModule {
 public:
-  using ChannelPort::ChannelPort;
+  HWModule(std::optional<ModuleInfo> info,
+           std::vector<std::unique_ptr<Instance>> children,
+           std::vector<services::Service *> services,
+           std::vector<BundlePort> ports);
+
+  std::optional<ModuleInfo> getInfo() const { return info; }
+  const std::vector<std::unique_ptr<Instance>> &getChildrenOrdered() const {
+    return children;
+  }
+  const std::map<AppID, Instance *> &getChildren() const { return childIndex; }
+  const std::vector<BundlePort> &getPortsOrdered() const { return ports; }
+  const std::map<AppID, const BundlePort &> &getPorts() const {
+    return portIndex;
+  }
 
-  /// A very basic write API. Will likely change for performance reasons.
-  virtual void write(const void *data, size_t size) = 0;
+protected:
+  const std::optional<ModuleInfo> info;
+  const std::vector<std::unique_ptr<Instance>> children;
+  const std::map<AppID, Instance *> childIndex;
+  const std::vector<services::Service *> services;
+  const std::vector<BundlePort> ports;
+  const std::map<AppID, const BundlePort &> portIndex;
 };
 
-/// A ChannelPort which reads data from the accelerator.
-class ReadChannelPort : public ChannelPort {
+class Instance : public HWModule {
 public:
-  using ChannelPort::ChannelPort;
+  Instance() = delete;
+  Instance(const Instance &) = delete;
+  ~Instance() = default;
+  Instance(AppID id, std::optional<ModuleInfo> info,
+           std::vector<std::unique_ptr<Instance>> children,
+           std::vector<services::Service *> services,
+           std::vector<BundlePort> ports)
+      : HWModule(info, std::move(children), services, ports), id(id) {}
 
-  /// Specify a buffer to read into and a maximum size to read. Returns the
-  /// number of bytes read, or -1 on error. Basic API, will likely change for
-  /// performance reasons.
-  virtual std::ptrdiff_t read(void *data, size_t maxSize) = 0;
-};
-
-namespace services {
-/// Parent class of all APIs modeled as 'services'. May or may not map to a
-/// hardware side 'service'.
-class Service {
-public:
-  using Type = const std::type_info &;
-  virtual ~Service() = default;
+  const AppID getID() const { return id; }
 
-  virtual std::string getServiceSymbol() const = 0;
+protected:
+  const AppID id;
 };
 
-/// A service for which there are no standard services registered. Requires
-/// ports be added to the design hierarchy instead of high level interfaces like
-/// the ones in StdServices.h.
-class CustomService : public Service {
+class Accelerator : public HWModule {
 public:
-  CustomService(AppIDPath idPath, const ServiceImplDetails &details,
-                const HWClientDetails &clients);
-  virtual ~CustomService() = default;
-
-  virtual std::string getServiceSymbol() const override {
-    return serviceSymbol;
-  }
+  Accelerator() = delete;
+  Accelerator(const Accelerator &) = delete;
+  ~Accelerator() = default;
+  Accelerator(std::optional<ModuleInfo> info,
+              std::vector<std::unique_ptr<Instance>> children,
+              std::vector<services::Service *> services,
+              std::vector<BundlePort> ports,
+              std::shared_ptr<Manifest::Impl> manifestImpl)
+      : HWModule(info, std::move(children), services, ports),
+        manifestImpl(manifestImpl) {}
 
-  /// Request the host side channel ports for a particular instance (identified
-  /// by the AppID path). For convenience, provide the bundle type and direction
-  /// of the bundle port.
-  virtual std::map<std::string, ChannelPort &>
-  requestChannelsFor(AppIDPath, const BundleType &,
-                     BundlePort::Direction portDir) = 0;
-
-protected:
-  std::string serviceSymbol;
-  AppIDPath id;
+private:
+  std::shared_ptr<Manifest::Impl> manifestImpl;
 };
-} // namespace services
 
-/// An ESI accelerator system.
-class Accelerator {
+//===----------------------------------------------------------------------===//
+// Connection to the accelerator and its services.
+//===----------------------------------------------------------------------===//
+
+class AcceleratorConnection {
 public:
-  virtual ~Accelerator() = default;
+  virtual ~AcceleratorConnection() = default;
 
   using Service = services::Service;
   /// Get a typed reference to a particular service type. Caller does *not* take
@@ -159,13 +157,14 @@ namespace registry {
 
 // Connect to an ESI accelerator given a backend name and connection specifier.
 // Alternatively, instantiate the backend directly (if you're using C++).
-std::unique_ptr<Accelerator> connect(std::string backend,
-                                     std::string connection);
+std::unique_ptr<AcceleratorConnection> connect(std::string backend,
+                                               std::string connection);
 
 namespace internal {
 
 /// Backends can register themselves to be connected via a connection string.
-using BackendCreate = std::function<std::unique_ptr<Accelerator>(std::string)>;
+using BackendCreate =
+    std::function<std::unique_ptr<AcceleratorConnection>(std::string)>;
 void registerBackend(std::string name, BackendCreate create);
 
 // Helper struct to
diff --git a/lib/Dialect/ESI/runtime/cpp/include/esi/Common.h b/lib/Dialect/ESI/runtime/cpp/include/esi/Common.h
new file mode 100644
index 000000000000..62667444a8c9
--- /dev/null
+++ b/lib/Dialect/ESI/runtime/cpp/include/esi/Common.h
@@ -0,0 +1,88 @@
+//===- Common.h - Commonly used classes w/o dependencies --------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// DO NOT EDIT!
+// This file is distributed as part of an ESI package. The source for this file
+// should always be modified within CIRCT.
+//
+//===----------------------------------------------------------------------===//
+
+// NOLINTNEXTLINE(llvm-header-guard)
+#ifndef ESI_COMMON_H
+#define ESI_COMMON_H
+
+#include <any>
+#include <map>
+#include <memory>
+#include <optional>
+#include <string>
+#include <vector>
+
+namespace esi {
+
+//===----------------------------------------------------------------------===//
+// Common accelerator description types.
+//===----------------------------------------------------------------------===//
+
+struct AppID {
+  std::string name;
+  std::optional<uint32_t> idx;
+
+  AppID(const AppID &) = default;
+  AppID(const std::string &name, std::optional<uint32_t> idx = std::nullopt)
+      : name(name), idx(idx) {}
+
+  bool operator==(const AppID &other) const {
+    return name == other.name && idx == other.idx;
+  }
+  bool operator!=(const AppID &other) const { return !(*this == other); }
+};
+bool operator<(const AppID &a, const AppID &b);
+
+class AppIDPath : public std::vector<AppID> {
+public:
+  using std::vector<AppID>::vector;
+
+  AppIDPath operator+(const AppIDPath &b);
+  std::string toStr() const;
+};
+bool operator<(const AppIDPath &a, const AppIDPath &b);
+std::ostream &operator<<(std::ostream &, const esi::AppIDPath &);
+
+struct ModuleInfo {
+  const std::optional<std::string> name;
+  const std::optional<std::string> summary;
+  const std::optional<std::string> version;
+  const std::optional<std::string> repo;
+  const std::optional<std::string> commitHash;
+  const std::map<std::string, std::any> extra;
+};
+
+/// A description of a service port. Used pretty exclusively in setting up the
+/// design.
+struct ServicePortDesc {
+  std::string name;
+  std::string portName;
+};
+
+/// A description of a hardware client. Used pretty exclusively in setting up
+/// the design.
+struct HWClientDetail {
+  AppIDPath relPath;
+  ServicePortDesc port;
+  std::map<std::string, std::any> implOptions;
+};
+using HWClientDetails = std::vector<HWClientDetail>;
+using ServiceImplDetails = std::map<std::string, std::any>;
+
+} // namespace esi
+
+std::ostream &operator<<(std::ostream &, const esi::ModuleInfo &);
+std::ostream &operator<<(std::ostream &, const esi::AppID &);
+
+#endif // ESI_COMMON_H
diff --git a/lib/Dialect/ESI/runtime/cpp/include/esi/Design.h b/lib/Dialect/ESI/runtime/cpp/include/esi/Design.h
deleted file mode 100644
index 9669fdaf29d0..000000000000
--- a/lib/Dialect/ESI/runtime/cpp/include/esi/Design.h
+++ /dev/null
@@ -1,127 +0,0 @@
-//===- Design.h - Dynamic accelerator API -----------------------*- C++ -*-===//
-//
-// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
-// See https://llvm.org/LICENSE.txt for license information.
-// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-//
-//===----------------------------------------------------------------------===//
-//
-// The dynamic API into an accelerator allows access to the accelerator's design
-// and communication channels through various stl containers (e.g. std::vector,
-// std::map, etc.). This allows runtime reflection against the accelerator and
-// can be pybind'd to create a Python API.
-//
-// The static API, in contrast, is a compile-time API that allows access to the
-// design and communication channels symbolically. It will be generated once
-// (not here) then compiled into the host software.
-//
-// DO NOT EDIT!
-// This file is distributed as part of an ESI package. The source for this file
-// should always be modified within CIRCT.
-//
-//===----------------------------------------------------------------------===//
-
-// NOLINTNEXTLINE(llvm-header-guard)
-#ifndef ESI_DESIGN_H
-#define ESI_DESIGN_H
-
-#include "esi/Manifest.h"
-
-#include <any>
-#include <cstdint>
-#include <string>
-
-namespace esi {
-// Forward declarations.
-class Instance;
-class ChannelPort;
-class WriteChannelPort;
-class ReadChannelPort;
-namespace services {
-class Service;
-}
-
-/// Services provide connections to 'bundles' -- collections of named,
-/// unidirectional communication channels. This class provides access to those
-/// ChannelPorts.
-class BundlePort {
-public:
-  /// Direction of a bundle. This -- combined with the channel direction in the
-  /// bundle -- can be used to determine if a channel should be writing to or
-  /// reading from the accelerator.
-  enum Direction { ToServer, ToClient };
-
-  /// Compute the direction of a channel given the bundle direction and the
-  /// bundle port's direction.
-  static bool isWrite(BundleType::Direction bundleDir, Direction svcDir) {
-    if (svcDir == Direction::ToClient)
-      return bundleDir == BundleType::Direction::To;
-    return bundleDir == BundleType::Direction::From;
-  }
-
-  /// Construct a port.
-  BundlePort(AppID id, std::map<std::string, ChannelPort &> channels);
-
-  /// Get the ID of the port.
-  AppID getID() const { return _id; }
-
-  /// Get access to the raw byte streams of a channel. Intended for internal
-  /// usage and binding to other languages (e.g. Python) which have their own
-  /// message serialization code.
-  WriteChannelPort &getRawWrite(const std::string &name) const;
-  ReadChannelPort &getRawRead(const std::string &name) const;
-  const std::map<std::string, ChannelPort &> &getChannels() const {
-    return _channels;
-  }
-
-private:
-  AppID _id;
-  std::map<std::string, ChannelPort &> _channels;
-};
-
-class Design {
-public:
-  Design(std::optional<ModuleInfo> info,
-         std::vector<std::unique_ptr<Instance>> children,
-         std::vector<services::Service *> services,
-         std::vector<BundlePort> ports);
-
-  std::optional<ModuleInfo> getInfo() const { return info; }
-  const std::vector<std::unique_ptr<Instance>> &getChildrenOrdered() const {
-    return children;
-  }
-  const std::map<AppID, Instance *> &getChildren() const { return childIndex; }
-  const std::vector<BundlePort> &getPortsOrdered() const { return ports; }
-  const std::map<AppID, const BundlePort &> &getPorts() const {
-    return portIndex;
-  }
-
-protected:
-  const std::optional<ModuleInfo> info;
-  const std::vector<std::unique_ptr<Instance>> children;
-  const std::map<AppID, Instance *> childIndex;
-  const std::vector<services::Service *> services;
-  const std::vector<BundlePort> ports;
-  const std::map<AppID, const BundlePort &> portIndex;
-};
-
-class Instance : public Design {
-public:
-  Instance() = delete;
-  Instance(const Instance &) = delete;
-  ~Instance() = default;
-  Instance(AppID id, std::optional<ModuleInfo> info,
-           std::vector<std::unique_ptr<Instance>> children,
-           std::vector<services::Service *> services,
-           std::vector<BundlePort> ports)
-      : Design(info, std::move(children), services, ports), id(id) {}
-
-  const AppID getID() const { return id; }
-
-protected:
-  const AppID id;
-};
-
-} // namespace esi
-
-#endif // ESI_DESIGN_H
diff --git a/lib/Dialect/ESI/runtime/cpp/include/esi/Manifest.h b/lib/Dialect/ESI/runtime/cpp/include/esi/Manifest.h
index 18b7c35500ba..01b1c723860b 100644
--- a/lib/Dialect/ESI/runtime/cpp/include/esi/Manifest.h
+++ b/lib/Dialect/ESI/runtime/cpp/include/esi/Manifest.h
@@ -6,7 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 //
-//
+// Manifest parsing and API creation.
 //
 // DO NOT EDIT!
 // This file is distributed as part of an ESI package. The source for this file
@@ -18,6 +18,7 @@
 #ifndef ESI_MANIFEST_H
 #define ESI_MANIFEST_H
 
+#include "esi/Common.h"
 #include "esi/Types.h"
 
 #include <any>
@@ -31,69 +32,9 @@
 
 namespace esi {
 
-//===----------------------------------------------------------------------===//
-// Common accelerator description types.
-//===----------------------------------------------------------------------===//
-
-struct AppID {
-  std::string name;
-  std::optional<uint32_t> idx;
-
-  AppID(const AppID &) = default;
-  AppID(std::string name, std::optional<uint32_t> idx = std::nullopt)
-      : name(name), idx(idx) {}
-
-  bool operator==(const AppID &other) const {
-    return name == other.name && idx == other.idx;
-  }
-  bool operator!=(const AppID &other) const { return !(*this == other); }
-};
-bool operator<(const AppID &a, const AppID &b);
-
-class AppIDPath : public std::vector<AppID> {
-public:
-  using std::vector<AppID>::vector;
-
-  AppIDPath operator+(const AppIDPath &b);
-  std::string toStr() const;
-};
-bool operator<(const AppIDPath &a, const AppIDPath &b);
-std::ostream &operator<<(std::ostream &, const esi::AppIDPath &);
-
-struct ModuleInfo {
-  const std::optional<std::string> name;
-  const std::optional<std::string> summary;
-  const std::optional<std::string> version;
-  const std::optional<std::string> repo;
-  const std::optional<std::string> commitHash;
-  const std::map<std::string, std::any> extra;
-};
-
-/// A description of a service port. Used pretty exclusively in setting up the
-/// design.
-struct ServicePortDesc {
-  std::string name;
-  std::string portName;
-};
-
-/// A description of a hardware client. Used pretty exclusively in setting up
-/// the design.
-struct HWClientDetail {
-  AppIDPath relPath;
-  ServicePortDesc port;
-  std::map<std::string, std::any> implOptions;
-};
-using HWClientDetails = std::vector<HWClientDetail>;
-using ServiceImplDetails = std::map<std::string, std::any>;
-
-//===----------------------------------------------------------------------===//
-// Manifest parsing and API creation.
-//===----------------------------------------------------------------------===//
-
 // Forward declarations.
-namespace internal {} // namespace internal
+class AcceleratorConnection;
 class Accelerator;
-class Design;
 
 /// Class to parse a manifest. It also constructs the dynamic API for the
 /// accelerator.
@@ -110,7 +51,8 @@ class Manifest {
   std::vector<ModuleInfo> getModuleInfos() const;
 
   // Build a dynamic design hierarchy from the manifest.
-  std::unique_ptr<Design> buildDesign(Accelerator &acc) const;
+  std::unique_ptr<Accelerator>
+  buildAccelerator(AcceleratorConnection &acc) const;
 
   /// Get a Type from the manifest based on its ID. Types are uniqued here.
   std::optional<std::reference_wrapper<const Type>> getType(Type::ID id) const;
@@ -122,7 +64,7 @@ class Manifest {
   const std::vector<std::reference_wrapper<const Type>> &getTypeTable() const;
 
 private:
-  Impl &impl;
+  std::shared_ptr<Impl> impl;
 };
 
 } // namespace esi
diff --git a/lib/Dialect/ESI/runtime/cpp/include/esi/Ports.h b/lib/Dialect/ESI/runtime/cpp/include/esi/Ports.h
new file mode 100644
index 000000000000..934376438fa3
--- /dev/null
+++ b/lib/Dialect/ESI/runtime/cpp/include/esi/Ports.h
@@ -0,0 +1,103 @@
+//===- Ports.h - ESI communication channels ---------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// DO NOT EDIT!
+// This file is distributed as part of an ESI package. The source for this file
+// should always be modified within CIRCT.
+//
+//===----------------------------------------------------------------------===//
+
+// NOLINTNEXTLINE(llvm-header-guard)
+#ifndef ESI_PORTS_H
+#define ESI_PORTS_H
+
+#include "esi/Common.h"
+#include "esi/Types.h"
+
+namespace esi {
+
+/// Unidirectional channels are the basic communication primitive between the
+/// host and accelerator. A 'ChannelPort' is the host side of a channel. It can
+/// be either read or write but not both. At this level, channels are untyped --
+/// just streams of bytes. They are not intended to be used directly by users
+/// but used by higher level APIs which add types.
+class ChannelPort {
+public:
+  ChannelPort(const Type &type) : type(type) {}
+  virtual ~ChannelPort() = default;
+
+  virtual void connect() {}
+  virtual void disconnect() {}
+
+  const Type &getType() const { return type; }
+
+private:
+  const Type &type;
+};
+
+/// A ChannelPort which sends data to the accelerator.
+class WriteChannelPort : public ChannelPort {
+public:
+  using ChannelPort::ChannelPort;
+
+  /// A very basic write API. Will likely change for performance reasons.
+  virtual void write(const void *data, size_t size) = 0;
+};
+
+/// A ChannelPort which reads data from the accelerator.
+class ReadChannelPort : public ChannelPort {
+public:
+  using ChannelPort::ChannelPort;
+
+  /// Specify a buffer to read into and a maximum size to read. Returns the
+  /// number of bytes read, or -1 on error. Basic API, will likely change for
+  /// performance reasons.
+  virtual std::ptrdiff_t read(void *data, size_t maxSize) = 0;
+};
+
+/// Services provide connections to 'bundles' -- collections of named,
+/// unidirectional communication channels. This class provides access to those
+/// ChannelPorts.
+class BundlePort {
+public:
+  /// Direction of a bundle. This -- combined with the channel direction in the
+  /// bundle -- can be used to determine if a channel should be writing to or
+  /// reading from the accelerator.
+  enum Direction { ToServer, ToClient };
+
+  /// Compute the direction of a channel given the bundle direction and the
+  /// bundle port's direction.
+  static bool isWrite(BundleType::Direction bundleDir, Direction svcDir) {
+    if (svcDir == Direction::ToClient)
+      return bundleDir == BundleType::Direction::To;
+    return bundleDir == BundleType::Direction::From;
+  }
+
+  /// Construct a port.
+  BundlePort(AppID id, std::map<std::string, ChannelPort &> channels);
+
+  /// Get the ID of the port.
+  AppID getID() const { return _id; }
+
+  /// Get access to the raw byte streams of a channel. Intended for internal
+  /// usage and binding to other languages (e.g. Python) which have their own
+  /// message serialization code.
+  WriteChannelPort &getRawWrite(const std::string &name) const;
+  ReadChannelPort &getRawRead(const std::string &name) const;
+  const std::map<std::string, ChannelPort &> &getChannels() const {
+    return _channels;
+  }
+
+private:
+  AppID _id;
+  std::map<std::string, ChannelPort &> _channels;
+};
+
+} // namespace esi
+
+#endif // ESI_PORTS_H
diff --git a/lib/Dialect/ESI/runtime/cpp/include/esi/StdServices.h b/lib/Dialect/ESI/runtime/cpp/include/esi/Services.h
similarity index 62%
rename from lib/Dialect/ESI/runtime/cpp/include/esi/StdServices.h
rename to lib/Dialect/ESI/runtime/cpp/include/esi/Services.h
index 718182984256..fed3091d534e 100644
--- a/lib/Dialect/ESI/runtime/cpp/include/esi/StdServices.h
+++ b/lib/Dialect/ESI/runtime/cpp/include/esi/Services.h
@@ -17,16 +17,52 @@
 //===----------------------------------------------------------------------===//
 
 // NOLINTNEXTLINE(llvm-header-guard)
-#ifndef ESI_RUNTIME_STDSERVICES_H
-#define ESI_RUNTIME_STDSERVICES_H
+#ifndef ESI_RUNTIME_SERVICES_H
+#define ESI_RUNTIME_SERVICES_H
 
-#include "esi/Accelerator.h"
+#include "esi/Common.h"
+#include "esi/Ports.h"
 
 #include <cstdint>
 
 namespace esi {
 namespace services {
 
+/// Parent class of all APIs modeled as 'services'. May or may not map to a
+/// hardware side 'service'.
+class Service {
+public:
+  using Type = const std::type_info &;
+  virtual ~Service() = default;
+
+  virtual std::string getServiceSymbol() const = 0;
+};
+
+/// A service for which there are no standard services registered. Requires
+/// ports be added to the design hierarchy instead of high level interfaces like
+/// the ones in StdServices.h.
+class CustomService : public Service {
+public:
+  CustomService(AppIDPath idPath, const ServiceImplDetails &details,
+                const HWClientDetails &clients);
+  virtual ~CustomService() = default;
+
+  virtual std::string getServiceSymbol() const override {
+    return serviceSymbol;
+  }
+
+  /// Request the host side channel ports for a particular instance (identified
+  /// by the AppID path). For convenience, provide the bundle type and direction
+  /// of the bundle port.
+  virtual std::map<std::string, ChannelPort &>
+  requestChannelsFor(AppIDPath, const BundleType &,
+                     BundlePort::Direction portDir) = 0;
+
+protected:
+  std::string serviceSymbol;
+  AppIDPath id;
+};
+
 /// Information about the Accelerator system.
 class SysInfo : public Service {
 public:
@@ -70,4 +106,4 @@ class MMIOSysInfo final : public SysInfo {
 } // namespace services
 } // namespace esi
 
-#endif // ESI_RUNTIME_STDSERVICES_H
+#endif // ESI_RUNTIME_SERVICES_H
diff --git a/lib/Dialect/ESI/runtime/cpp/include/esi/backends/Cosim.h b/lib/Dialect/ESI/runtime/cpp/include/esi/backends/Cosim.h
index f852ebfaf064..d20b204b088f 100644
--- a/lib/Dialect/ESI/runtime/cpp/include/esi/backends/Cosim.h
+++ b/lib/Dialect/ESI/runtime/cpp/include/esi/backends/Cosim.h
@@ -29,12 +29,13 @@ namespace backends {
 namespace cosim {
 
 /// Connect to an ESI simulation.
-class CosimAccelerator : public esi::Accelerator {
+class CosimAccelerator : public esi::AcceleratorConnection {
 public:
   struct Impl;
 
   CosimAccelerator(std::string hostname, uint16_t port);
-  static std::unique_ptr<Accelerator> connect(std::string connectionString);
+  static std::unique_ptr<AcceleratorConnection>
+  connect(std::string connectionString);
 
 protected:
   virtual Service *createService(Service::Type service, AppIDPath path,
diff --git a/lib/Dialect/ESI/runtime/cpp/include/esi/backends/Trace.h b/lib/Dialect/ESI/runtime/cpp/include/esi/backends/Trace.h
index 8965cd2e88dc..918fba8c05be 100644
--- a/lib/Dialect/ESI/runtime/cpp/include/esi/backends/Trace.h
+++ b/lib/Dialect/ESI/runtime/cpp/include/esi/backends/Trace.h
@@ -32,7 +32,7 @@ namespace backends {
 namespace trace {
 
 /// Connect to an ESI simulation.
-class TraceAccelerator : public esi::Accelerator {
+class TraceAccelerator : public esi::AcceleratorConnection {
 public:
   enum Mode {
     // Write data sent to the accelerator to the trace file. Produce random
@@ -55,7 +55,8 @@ class TraceAccelerator : public esi::Accelerator {
 
   /// Parse the connection string and instantiate the accelerator. Format is:
   /// "<mode>:<manifest path>[:<traceFile>]".
-  static std::unique_ptr<Accelerator> connect(std::string connectionString);
+  static std::unique_ptr<AcceleratorConnection>
+  connect(std::string connectionString);
 
   /// Internal implementation.
   struct Impl;
diff --git a/lib/Dialect/ESI/runtime/cpp/lib/Accelerator.cpp b/lib/Dialect/ESI/runtime/cpp/lib/Accelerator.cpp
index 0589c9f65f05..d32c2c26916a 100644
--- a/lib/Dialect/ESI/runtime/cpp/lib/Accelerator.cpp
+++ b/lib/Dialect/ESI/runtime/cpp/lib/Accelerator.cpp
@@ -22,22 +22,39 @@ using namespace std;
 using namespace esi;
 using namespace esi::services;
 
-CustomService::CustomService(AppIDPath idPath,
-                             const ServiceImplDetails &details,
-                             const HWClientDetails &clients)
-    : id(idPath) {
-  if (auto f = details.find("service"); f != details.end()) {
-    serviceSymbol = any_cast<string>(f->second);
-    // Strip off initial '@'.
-    serviceSymbol = serviceSymbol.substr(1);
-  }
+namespace esi {
+
+/// Build an index of children by AppID.
+static map<AppID, Instance *>
+buildIndex(const vector<unique_ptr<Instance>> &insts) {
+  map<AppID, Instance *> index;
+  for (auto &item : insts)
+    index[item->getID()] = item.get();
+  return index;
 }
 
-namespace esi {
-services::Service *Accelerator::getService(Service::Type svcType, AppIDPath id,
-                                           std::string implName,
-                                           ServiceImplDetails details,
-                                           HWClientDetails clients) {
+/// Build an index of ports by AppID.
+static map<AppID, const BundlePort &>
+buildIndex(const vector<BundlePort> &ports) {
+  map<AppID, const BundlePort &> index;
+  for (auto &item : ports)
+    index.emplace(item.getID(), item);
+  return index;
+}
+
+HWModule::HWModule(std::optional<ModuleInfo> info,
+                   std::vector<std::unique_ptr<Instance>> children,
+                   std::vector<services::Service *> services,
+                   std::vector<BundlePort> ports)
+    : info(info), children(std::move(children)),
+      childIndex(buildIndex(this->children)), services(services), ports(ports),
+      portIndex(buildIndex(this->ports)) {}
+
+services::Service *AcceleratorConnection::getService(Service::Type svcType,
+                                                     AppIDPath id,
+                                                     std::string implName,
+                                                     ServiceImplDetails details,
+                                                     HWClientDetails clients) {
   unique_ptr<Service> &cacheEntry = serviceCache[make_tuple(&svcType, id)];
   if (cacheEntry == nullptr) {
     Service *svc = createService(svcType, id, implName, details, clients);
@@ -59,7 +76,7 @@ void registerBackend(string name, BackendCreate create) {
 }
 } // namespace internal
 
-unique_ptr<Accelerator> connect(string backend, string connection) {
+unique_ptr<AcceleratorConnection> connect(string backend, string connection) {
   auto f = internal::backendRegistry.find(backend);
   if (f == internal::backendRegistry.end())
     throw runtime_error("Backend not found");
diff --git a/lib/Dialect/ESI/runtime/cpp/lib/Manifest.cpp b/lib/Dialect/ESI/runtime/cpp/lib/Manifest.cpp
index 6018490d4261..111c9baacfdf 100644
--- a/lib/Dialect/ESI/runtime/cpp/lib/Manifest.cpp
+++ b/lib/Dialect/ESI/runtime/cpp/lib/Manifest.cpp
@@ -14,8 +14,7 @@
 
 #include "esi/Manifest.h"
 #include "esi/Accelerator.h"
-#include "esi/Design.h"
-#include "esi/StdServices.h"
+#include "esi/Services.h"
 
 #include <nlohmann/json.hpp>
 
@@ -50,13 +49,14 @@ class Manifest::Impl {
 
   /// Get a Service for the service specified in 'json'. Update the
   /// activeServices table.
-  services::Service *getService(AppIDPath idPath, Accelerator &,
+  services::Service *getService(AppIDPath idPath, AcceleratorConnection &,
                                 const nlohmann::json &,
                                 ServiceTable &activeServices) const;
 
   /// Get all the services in the description of an instance. Update the active
   /// services table.
-  vector<services::Service *> getServices(AppIDPath idPath, Accelerator &,
+  vector<services::Service *> getServices(AppIDPath idPath,
+                                          AcceleratorConnection &,
                                           const nlohmann::json &,
                                           ServiceTable &activeServices) const;
 
@@ -69,13 +69,14 @@ class Manifest::Impl {
   /// Build the set of child instances (recursively) for the module instance
   /// description.
   vector<unique_ptr<Instance>>
-  getChildInstances(AppIDPath idPath, Accelerator &acc,
+  getChildInstances(AppIDPath idPath, AcceleratorConnection &acc,
                     const ServiceTable &activeServices,
                     const nlohmann::json &instJson) const;
 
   /// Get a single child instance. Implicitly copy the active services table so
   /// that it can be safely updated for the child's branch of the tree.
-  unique_ptr<Instance> getChildInstance(AppIDPath idPath, Accelerator &acc,
+  unique_ptr<Instance> getChildInstance(AppIDPath idPath,
+                                        AcceleratorConnection &acc,
                                         ServiceTable activeServices,
                                         const nlohmann::json &childJson) const;
 
@@ -96,7 +97,8 @@ class Manifest::Impl {
 
   /// Build a dynamic API for the Accelerator connection 'acc' based on the
   /// manifest stored herein.
-  unique_ptr<Design> buildDesign(Accelerator &acc) const;
+  unique_ptr<Accelerator> buildAccelerator(AcceleratorConnection &acc,
+                                           std::shared_ptr<Impl> me) const;
 
   const Type &parseType(const nlohmann::json &typeJson);
 
@@ -202,7 +204,9 @@ Manifest::Impl::Impl(const string &manifestStr) {
   populateTypes(manifestJson.at("types"));
 }
 
-unique_ptr<Design> Manifest::Impl::buildDesign(Accelerator &acc) const {
+unique_ptr<Accelerator>
+Manifest::Impl::buildAccelerator(AcceleratorConnection &acc,
+                                 std::shared_ptr<Impl> me) const {
   auto designJson = manifestJson.at("design");
 
   // Get the initial active services table. Update it as we descend down.
@@ -210,10 +214,10 @@ unique_ptr<Design> Manifest::Impl::buildDesign(Accelerator &acc) const {
   vector<services::Service *> services =
       getServices({}, acc, designJson, activeSvcs);
 
-  return make_unique<Design>(getModInfo(designJson),
-                             getChildInstances({}, acc, activeSvcs, designJson),
-                             services,
-                             getBundlePorts({}, activeSvcs, designJson));
+  return make_unique<Accelerator>(
+      getModInfo(designJson),
+      getChildInstances({}, acc, activeSvcs, designJson), services,
+      getBundlePorts({}, activeSvcs, designJson), me);
 }
 
 optional<ModuleInfo>
@@ -228,7 +232,7 @@ Manifest::Impl::getModInfo(const nlohmann::json &json) const {
 }
 
 vector<unique_ptr<Instance>>
-Manifest::Impl::getChildInstances(AppIDPath idPath, Accelerator &acc,
+Manifest::Impl::getChildInstances(AppIDPath idPath, AcceleratorConnection &acc,
                                   const ServiceTable &activeServices,
                                   const nlohmann::json &instJson) const {
   vector<unique_ptr<Instance>> ret;
@@ -240,7 +244,7 @@ Manifest::Impl::getChildInstances(AppIDPath idPath, Accelerator &acc,
   return ret;
 }
 unique_ptr<Instance>
-Manifest::Impl::getChildInstance(AppIDPath idPath, Accelerator &acc,
+Manifest::Impl::getChildInstance(AppIDPath idPath, AcceleratorConnection &acc,
                                  ServiceTable activeServices,
                                  const nlohmann::json &child) const {
   AppID childID = parseID(child.at("app_id"));
@@ -256,7 +260,7 @@ Manifest::Impl::getChildInstance(AppIDPath idPath, Accelerator &acc,
 }
 
 services::Service *
-Manifest::Impl::getService(AppIDPath idPath, Accelerator &acc,
+Manifest::Impl::getService(AppIDPath idPath, AcceleratorConnection &acc,
                            const nlohmann::json &svcJson,
                            ServiceTable &activeServices) const {
 
@@ -304,7 +308,7 @@ Manifest::Impl::getService(AppIDPath idPath, Accelerator &acc,
 }
 
 vector<services::Service *>
-Manifest::Impl::getServices(AppIDPath idPath, Accelerator &acc,
+Manifest::Impl::getServices(AppIDPath idPath, AcceleratorConnection &acc,
                             const nlohmann::json &svcsJson,
                             ServiceTable &activeServices) const {
   vector<services::Service *> ret;
@@ -503,33 +507,33 @@ void Manifest::Impl::populateTypes(const nlohmann::json &typesJson) {
 // Manifest class implementation.
 //===----------------------------------------------------------------------===//
 
-Manifest::Manifest(const string &jsonManifest)
-    : impl(*new Impl(jsonManifest)) {}
+Manifest::Manifest(const string &jsonManifest) : impl(new Impl(jsonManifest)) {}
 Manifest::~Manifest() { delete &impl; }
 
 uint32_t Manifest::getApiVersion() const {
-  return impl.at("api_version").get<uint32_t>();
+  return impl->at("api_version").get<uint32_t>();
 }
 
 vector<ModuleInfo> Manifest::getModuleInfos() const {
   vector<ModuleInfo> ret;
-  for (auto &mod : impl.at("symbols"))
+  for (auto &mod : impl->at("symbols"))
     ret.push_back(parseModuleInfo(mod));
   return ret;
 }
 
-unique_ptr<Design> Manifest::buildDesign(Accelerator &acc) const {
-  return impl.buildDesign(acc);
+unique_ptr<Accelerator>
+Manifest::buildAccelerator(AcceleratorConnection &acc) const {
+  return impl->buildAccelerator(acc, impl);
 }
 
 optional<reference_wrapper<const Type>> Manifest::getType(Type::ID id) const {
-  if (auto f = impl._types.find(id); f != impl._types.end())
+  if (auto f = impl->_types.find(id); f != impl->_types.end())
     return *f->second;
   return nullopt;
 }
 
 const vector<reference_wrapper<const Type>> &Manifest::getTypeTable() const {
-  return impl.getTypeTable();
+  return impl->getTypeTable();
 }
 
 //===----------------------------------------------------------------------===//
diff --git a/lib/Dialect/ESI/runtime/cpp/lib/Design.cpp b/lib/Dialect/ESI/runtime/cpp/lib/Ports.cpp
similarity index 58%
rename from lib/Dialect/ESI/runtime/cpp/lib/Design.cpp
rename to lib/Dialect/ESI/runtime/cpp/lib/Ports.cpp
index 9d537325cb04..44f79fadd778 100644
--- a/lib/Dialect/ESI/runtime/cpp/lib/Design.cpp
+++ b/lib/Dialect/ESI/runtime/cpp/lib/Ports.cpp
@@ -1,4 +1,4 @@
-//===- Design.cpp - Implementation of dynamic API -------------------------===//
+//===- Ports.cpp - ESI communication channels  -------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -12,8 +12,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "esi/Design.h"
-#include "esi/Accelerator.h"
+#include "esi/Ports.h"
 
 using namespace std;
 using namespace esi;
@@ -40,29 +39,3 @@ ReadChannelPort &BundlePort::getRawRead(const string &name) const {
     throw runtime_error("Channel '" + name + "' is not a read channel");
   return *read;
 }
-
-/// Build an index of children by AppID.
-static map<AppID, Instance *>
-buildIndex(const vector<unique_ptr<Instance>> &insts) {
-  map<AppID, Instance *> index;
-  for (auto &item : insts)
-    index[item->getID()] = item.get();
-  return index;
-}
-
-/// Build an index of ports by AppID.
-static map<AppID, const BundlePort &>
-buildIndex(const vector<BundlePort> &ports) {
-  map<AppID, const BundlePort &> index;
-  for (auto &item : ports)
-    index.emplace(item.getID(), item);
-  return index;
-}
-
-Design::Design(std::optional<ModuleInfo> info,
-               std::vector<std::unique_ptr<Instance>> children,
-               std::vector<services::Service *> services,
-               std::vector<BundlePort> ports)
-    : info(info), children(std::move(children)),
-      childIndex(buildIndex(this->children)), services(services), ports(ports),
-      portIndex(buildIndex(this->ports)) {}
diff --git a/lib/Dialect/ESI/runtime/cpp/lib/StdServices.cpp b/lib/Dialect/ESI/runtime/cpp/lib/Services.cpp
similarity index 82%
rename from lib/Dialect/ESI/runtime/cpp/lib/StdServices.cpp
rename to lib/Dialect/ESI/runtime/cpp/lib/Services.cpp
index 3c741431ca03..d56b2581d20a 100644
--- a/lib/Dialect/ESI/runtime/cpp/lib/StdServices.cpp
+++ b/lib/Dialect/ESI/runtime/cpp/lib/Services.cpp
@@ -13,7 +13,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "esi/StdServices.h"
+#include "esi/Services.h"
+#include "esi/Accelerator.h"
 
 #include "zlib.h"
 
@@ -57,3 +58,14 @@ vector<uint8_t> MMIOSysInfo::getCompressedManifest() const {
   assert(false && "Not implemented");
   throw runtime_error("Not implemented");
 }
+
+CustomService::CustomService(AppIDPath idPath,
+                             const ServiceImplDetails &details,
+                             const HWClientDetails &clients)
+    : id(idPath) {
+  if (auto f = details.find("service"); f != details.end()) {
+    serviceSymbol = any_cast<string>(f->second);
+    // Strip off initial '@'.
+    serviceSymbol = serviceSymbol.substr(1);
+  }
+}
diff --git a/lib/Dialect/ESI/runtime/cpp/lib/backends/Cosim.cpp b/lib/Dialect/ESI/runtime/cpp/lib/backends/Cosim.cpp
index 9e669a8d1d33..70d876c96a87 100644
--- a/lib/Dialect/ESI/runtime/cpp/lib/backends/Cosim.cpp
+++ b/lib/Dialect/ESI/runtime/cpp/lib/backends/Cosim.cpp
@@ -14,7 +14,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "esi/backends/Cosim.h"
-#include "esi/StdServices.h"
+#include "esi/Services.h"
 
 #include "CosimDpi.capnp.h"
 #include <capnp/ez-rpc.h>
@@ -33,7 +33,8 @@ using namespace esi::backends::cosim;
 /// traditional 'host:port' syntax and a path to 'cosim.cfg' which is output by
 /// the cosimulation when it starts (which is useful when it chooses its own
 /// port).
-unique_ptr<Accelerator> CosimAccelerator::connect(string connectionString) {
+unique_ptr<AcceleratorConnection>
+CosimAccelerator::connect(string connectionString) {
   string portStr;
   string host = "localhost";
 
diff --git a/lib/Dialect/ESI/runtime/cpp/lib/backends/Trace.cpp b/lib/Dialect/ESI/runtime/cpp/lib/backends/Trace.cpp
index b7e7ed891c36..f037b8b84c0e 100644
--- a/lib/Dialect/ESI/runtime/cpp/lib/backends/Trace.cpp
+++ b/lib/Dialect/ESI/runtime/cpp/lib/backends/Trace.cpp
@@ -13,8 +13,9 @@
 //===----------------------------------------------------------------------===//
 
 #include "esi/backends/Trace.h"
-#include "esi/Design.h"
-#include "esi/StdServices.h"
+
+#include "esi/Accelerator.h"
+#include "esi/Services.h"
 #include "esi/Utils.h"
 
 #include <fstream>
@@ -83,7 +84,8 @@ void TraceAccelerator::Impl::write(const AppIDPath &id, const string &portName,
   *traceWrite << "write " << id << '.' << portName << ": " << b64data << endl;
 }
 
-unique_ptr<Accelerator> TraceAccelerator::connect(string connectionString) {
+unique_ptr<AcceleratorConnection>
+TraceAccelerator::connect(string connectionString) {
   string modeStr;
   string manifestPath;
   string traceFile = "trace.json";
diff --git a/lib/Dialect/ESI/runtime/cpp/tools/esiquery.cpp b/lib/Dialect/ESI/runtime/cpp/tools/esiquery.cpp
index f7ea7c0b1a78..d29ac033fb9d 100644
--- a/lib/Dialect/ESI/runtime/cpp/tools/esiquery.cpp
+++ b/lib/Dialect/ESI/runtime/cpp/tools/esiquery.cpp
@@ -15,7 +15,7 @@
 
 #include "esi/Accelerator.h"
 #include "esi/Manifest.h"
-#include "esi/StdServices.h"
+#include "esi/Services.h"
 
 #include <iostream>
 #include <map>
@@ -25,7 +25,7 @@ using namespace std;
 
 using namespace esi;
 
-void printInfo(ostream &os, Accelerator &acc);
+void printInfo(ostream &os, AcceleratorConnection &acc);
 
 int main(int argc, const char *argv[]) {
   // TODO: find a command line parser library rather than doing this by hand.
@@ -42,7 +42,7 @@ int main(int argc, const char *argv[]) {
     cmd = argv[3];
 
   try {
-    unique_ptr<Accelerator> acc = registry::connect(backend, conn);
+    unique_ptr<AcceleratorConnection> acc = registry::connect(backend, conn);
     const auto &info = *acc->getService<services::SysInfo>();
 
     if (cmd == "version")
@@ -66,7 +66,7 @@ int main(int argc, const char *argv[]) {
   }
 }
 
-void printInfo(ostream &os, Accelerator &acc) {
+void printInfo(ostream &os, AcceleratorConnection &acc) {
   string jsonManifest = acc.getService<services::SysInfo>()->getJsonManifest();
   Manifest m(jsonManifest);
   os << "API version: " << m.getApiVersion() << endl << endl;
diff --git a/lib/Dialect/ESI/runtime/python/esi/__init__.py b/lib/Dialect/ESI/runtime/python/esi/__init__.py
index 51f51c517b64..af06e501ef17 100644
--- a/lib/Dialect/ESI/runtime/python/esi/__init__.py
+++ b/lib/Dialect/ESI/runtime/python/esi/__init__.py
@@ -2,12 +2,12 @@
 #  See https://llvm.org/LICENSE.txt for license information.
 #  SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-from .accelerator import Accelerator
+from .accelerator import AcceleratorConnection
 
 from .esiCppAccel import (AppID, Type, BundleType, ChannelType, ArrayType,
                           StructType, BitsType, UIntType, SIntType)
 
 __all__ = [
-    "Accelerator", "AppID", "Type", "BundleType", "ChannelType", "ArrayType",
-    "StructType", "BitsType", "UIntType", "SIntType"
+    "AcceleratorConnection", "AppID", "Type", "BundleType", "ChannelType",
+    "ArrayType", "StructType", "BitsType", "UIntType", "SIntType"
 ]
diff --git a/lib/Dialect/ESI/runtime/python/esi/accelerator.py b/lib/Dialect/ESI/runtime/python/esi/accelerator.py
index e40efd6d5c08..968152400f32 100644
--- a/lib/Dialect/ESI/runtime/python/esi/accelerator.py
+++ b/lib/Dialect/ESI/runtime/python/esi/accelerator.py
@@ -5,9 +5,9 @@
 from . import esiCppAccel as cpp
 
 
-class Accelerator(cpp.Accelerator):
-  """A connection to an ESI accelerator."""
+class AcceleratorConnection(cpp.AcceleratorConnection):
+  """An ESI accelerator."""
 
   def manifest(self) -> cpp.Manifest:
-    """Get and parse the accelerator manifest."""
+    """Returns the accelerator's manifest."""
     return cpp.Manifest(self.sysinfo().json_manifest())
diff --git a/lib/Dialect/ESI/runtime/python/esi/esiCppAccel.cpp b/lib/Dialect/ESI/runtime/python/esi/esiCppAccel.cpp
index 1dee56d6763f..267508129813 100644
--- a/lib/Dialect/ESI/runtime/python/esi/esiCppAccel.cpp
+++ b/lib/Dialect/ESI/runtime/python/esi/esiCppAccel.cpp
@@ -11,8 +11,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "esi/Accelerator.h"
-#include "esi/Design.h"
-#include "esi/StdServices.h"
+#include "esi/Services.h"
 
 #include <sstream>
 
@@ -153,37 +152,41 @@ PYBIND11_MODULE(esiCppAccel, m) {
 
   // Store this variable (not commonly done) as the "children" method needs for
   // "Instance" to be defined first.
-  auto design =
-      py::class_<Design>(m, "Design")
-          .def_property_readonly("info", &Design::getInfo)
-          .def_property_readonly("ports", &Design::getPorts,
+  auto hwmodule =
+      py::class_<HWModule>(m, "HWModule")
+          .def_property_readonly("info", &HWModule::getInfo)
+          .def_property_readonly("ports", &HWModule::getPorts,
                                  py::return_value_policy::reference_internal);
 
   // In order to inherit methods from "Design", it needs to be defined first.
-  py::class_<Instance, Design>(m, "Instance")
+  py::class_<Instance, HWModule>(m, "Instance")
       .def_property_readonly("id", &Instance::getID);
 
+  py::class_<Accelerator, HWModule>(m, "Accelerator");
+
   // Since this returns a vector of Instance*, we need to define Instance first
   // or else pybind11-stubgen complains.
-  design.def_property_readonly("children", &Design::getChildren,
-                               py::return_value_policy::reference_internal);
+  hwmodule.def_property_readonly("children", &HWModule::getChildren,
+                                 py::return_value_policy::reference_internal);
 
-  py::class_<Accelerator>(m, "Accelerator")
+  py::class_<AcceleratorConnection>(m, "AcceleratorConnection")
       .def(py::init(&registry::connect))
       .def(
           "sysinfo",
-          [](Accelerator &acc) {
+          [](AcceleratorConnection &acc) {
             return acc.getService<services::SysInfo>({});
           },
           py::return_value_policy::reference_internal)
       .def(
           "get_service_mmio",
-          [](Accelerator &acc) { return acc.getService<services::MMIO>({}); },
+          [](AcceleratorConnection &acc) {
+            return acc.getService<services::MMIO>({});
+          },
           py::return_value_policy::reference_internal);
 
   py::class_<Manifest>(m, "Manifest")
       .def(py::init<std::string>())
       .def_property_readonly("api_version", &Manifest::getApiVersion)
-      .def("build_design", &Manifest::buildDesign)
+      .def("build_accelerator", &Manifest::buildAccelerator)
       .def_property_readonly("type_table", &Manifest::getTypeTable);
 }
diff --git a/lib/Dialect/ESI/runtime/python/esi/esiCppAccel.pyi b/lib/Dialect/ESI/runtime/python/esi/esiCppAccel.pyi
index 9e046472e476..71d85c62bafa 100644
--- a/lib/Dialect/ESI/runtime/python/esi/esiCppAccel.pyi
+++ b/lib/Dialect/ESI/runtime/python/esi/esiCppAccel.pyi
@@ -7,15 +7,19 @@ from __future__ import annotations
 import typing
 
 __all__ = [
-    'Accelerator', 'AnyType', 'AppID', 'ArrayType', 'BitVectorType', 'BitsType',
-    'BundlePort', 'BundleType', 'ChannelPort', 'ChannelType', 'Design',
-    'Direction', 'From', 'Instance', 'IntegerType', 'MMIO', 'Manifest',
-    'ModuleInfo', 'ReadChannelPort', 'SIntType', 'StructType', 'SysInfo', 'To',
-    'Type', 'UIntType', 'WriteChannelPort'
+    'Accelerator', 'AcceleratorConnection', 'AnyType', 'AppID', 'ArrayType',
+    'BitVectorType', 'BitsType', 'BundlePort', 'BundleType', 'ChannelPort',
+    'ChannelType', 'Direction', 'From', 'HWModule', 'Instance', 'IntegerType',
+    'MMIO', 'Manifest', 'ModuleInfo', 'ReadChannelPort', 'SIntType',
+    'StructType', 'SysInfo', 'To', 'Type', 'UIntType', 'WriteChannelPort'
 ]
 
 
-class Accelerator:
+class Accelerator(HWModule):
+  pass
+
+
+class AcceleratorConnection:
 
   def __init__(self, arg0: str, arg1: str) -> None:
     ...
@@ -117,21 +121,6 @@ class ChannelType(Type):
     ...
 
 
-class Design:
-
-  @property
-  def children(self) -> dict[AppID, Instance]:
-    ...
-
-  @property
-  def info(self) -> ModuleInfo | None:
-    ...
-
-  @property
-  def ports(self) -> dict[AppID, BundlePort]:
-    ...
-
-
 class Direction:
   """
     Members:
@@ -185,7 +174,22 @@ class Direction:
     ...
 
 
-class Instance(Design):
+class HWModule:
+
+  @property
+  def children(self) -> dict[AppID, Instance]:
+    ...
+
+  @property
+  def info(self) -> ModuleInfo | None:
+    ...
+
+  @property
+  def ports(self) -> dict[AppID, BundlePort]:
+    ...
+
+
+class Instance(HWModule):
 
   @property
   def id(self) -> AppID:
@@ -210,7 +214,7 @@ class Manifest:
   def __init__(self, arg0: str) -> None:
     ...
 
-  def build_design(self, arg0: Accelerator) -> Design:
+  def build_accelerator(self, arg0: AcceleratorConnection) -> Accelerator:
     ...
 
   @property