diff --git a/internal/proto/BUILD b/internal/proto/BUILD
index e765eec7..dfa6642f 100644
--- a/internal/proto/BUILD
+++ b/internal/proto/BUILD
@@ -42,3 +42,22 @@ cc_proto_library(
     ],
     deps = [":metadata_proto"],
 )
+
+proto_library(
+    name = "tachyon_proto",
+    srcs = [
+        "duration.proto",
+        "ice.proto",
+        "tachyon.proto",
+        "tachyon_common.proto",
+        "tachyon_enums.proto",
+    ],
+    compatible_with = ["//buildenv/target:non_prod"],
+)
+
+cc_proto_library(
+    name = "tachyon_cc_proto",
+    compatible_with = ["//buildenv/target:non_prod"],
+    visibility = ["//visibility:public"],
+    deps = [":tachyon_proto"],
+)
diff --git a/internal/proto/duration.proto b/internal/proto/duration.proto
new file mode 100644
index 00000000..ab1d6b5c
--- /dev/null
+++ b/internal/proto/duration.proto
@@ -0,0 +1,24 @@
+// Copyright 2021 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+syntax = "proto3";
+
+package nearby.internal.tachyon_proto;
+
+option optimize_for = LITE_RUNTIME;
+
+message Duration {
+  int64 seconds = 1;
+  int32 nanos = 2;
+}
diff --git a/internal/proto/ice.proto b/internal/proto/ice.proto
new file mode 100644
index 00000000..954d7e43
--- /dev/null
+++ b/internal/proto/ice.proto
@@ -0,0 +1,46 @@
+// Copyright 2021 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+syntax = "proto3";
+
+package nearby.internal.tachyon_proto;
+
+import "internal/proto/duration.proto";
+
+option optimize_for = LITE_RUNTIME;
+
+message ICEConfiguration {
+  // Duration the config is valid for.
+  Duration lifetime_duration = 1;
+
+  // ICE servers to be used by the client to establish a connection.
+  // E.g.:
+  // [ { "urls": "stun:stun1.example.net" }, { "urls": "turn:turn.example.org",
+  // "username": "user", "credential": "myPassword" } ]
+  repeated ICEServerList ice_servers = 2;
+}
+
+message ICEServerList {
+  // STUN or TURN URI(s) as defined in [rfc7064] and [rfc7065] or other URI
+  // types.
+  repeated string urls = 1;
+
+  // If this IceServer object represents a TURN server, then this attribute
+  // specifies the credential to use with that TURN server.
+  string username = 2;
+
+  // If this IceServer object represents a TURN server, then this attribute
+  // specifies the credential to use with that TURN server.
+  string credential = 3;
+}
diff --git a/internal/proto/tachyon.proto b/internal/proto/tachyon.proto
new file mode 100644
index 00000000..42427e6a
--- /dev/null
+++ b/internal/proto/tachyon.proto
@@ -0,0 +1,55 @@
+// Copyright 2021 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+syntax = "proto3";
+
+package nearby.internal.tachyon_proto;
+
+import "internal/proto/ice.proto";
+import "internal/proto/tachyon_common.proto";
+
+option optimize_for = LITE_RUNTIME;
+
+message GetICEServerRequest {
+  // header is the request header
+  RequestHeader header = 1;
+  // ICE config preference.
+  string ice_config_preference = 3;
+}
+
+message GetICEServerResponse {
+  // The ice server configuration to use.
+  ICEConfiguration ice_config = 4;
+}
+
+message SendMessageExpressRequest {
+  RequestHeader header = 1;
+  Id dest_id = 3;
+  InboxMessage message = 4;
+}
+
+message ReceiveMessagesExpressRequest {
+  RequestHeader header = 1;
+}
+
+message ReceiveMessagesResponse {
+  message Header {}
+  Header header = 1;
+  message FastPathReady {}
+
+  oneof body {
+    InboxMessage inbox_message = 2;
+    FastPathReady fast_path_ready = 7;
+  }
+}
diff --git a/internal/proto/tachyon_common.proto b/internal/proto/tachyon_common.proto
new file mode 100644
index 00000000..bc155c33
--- /dev/null
+++ b/internal/proto/tachyon_common.proto
@@ -0,0 +1,119 @@
+// Copyright 2021 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+syntax = "proto3";
+
+package nearby.internal.tachyon_proto;
+
+import "internal/proto/tachyon_enums.proto";
+
+option optimize_for = LITE_RUNTIME;
+
+message Id {
+  // type defines what the id field contains, e.g. phone number, Fi-number, Gaia
+  // ID etc.
+  IdType.Type type = 1;
+  // id is a unique (for this type and app) identifier of a message source or
+  // recipient.
+  string id = 2;
+
+  // app is the tachyon client application that generated or is to receive a
+  // message.
+  string app = 3;
+
+  // location_hint is used as a hint for the user's region.
+  LocationHint location_hint = 5;
+}
+
+// LocationHint is used to specify a location as well as format.
+message LocationHint {
+  // Location is the location, provided in the format specified by format.
+  string location = 1;
+
+  // the format of location.
+  LocationStandard.Format format = 2;
+}
+
+// RequestHeader must be included in all request messages with the field name
+// `header`.
+// This will make the generated Go types of requests have GetHeader and
+// SetHeader funcs, which makes it simple to create a common interface to access
+// the header values.
+message RequestHeader {
+  // request_id identifies this request and its responses, must be unique, and
+  // is generated by the request creator.
+  // This does not need to be set if request_id_binary is set.
+  string request_id = 1;
+
+  // app identifies the application; this is used to isolate different
+  // applications in the backend.
+  string app = 3;
+
+  // client_info holds information about the calling client application.
+  ClientInfo client_info = 7;
+
+  // requester_id is the user ID of the requester.
+  Id requester_id = 10;
+}
+
+message ClientInfo {
+  // major, minor, point and details carry version information from client.
+  int32 major = 3;
+  int32 minor = 4;
+  int32 point = 5;
+
+  // api_version identifies what api_version the client was built against.
+  // This is used by server to:
+  // - push warning messages to clients during bind
+  // - fail RPCs if client is using a too old version
+  // - add backwards compatible code
+  ApiVersion.Value api_version = 7;
+
+  // platform_type is the type of platform, used to construct user agent string
+  // and to determine client node type in logging.
+  Platform.Type platform_type = 9;
+
+  // The APK version name (e.g. "4.0.006_RC2").
+  // Fireball Android sends down the version code in the above major field and
+  // leaves minor and point empty. The code results in a version that is tough
+  // to decipher like "20011296.0.0". The version name here is formatted to make
+  // versioning easier and safer on the server. Currently, this field is only
+  // populated by Fireball Android. See go/fireball-gbot-version.
+  string app_version = 10;
+}
+
+message InboxMessage {
+  string message_id = 1;
+
+  enum MessageType {
+    UNKNOWN = 0;
+    BASIC = 4;
+  }
+  MessageType message_type = 2;
+
+  bytes message = 12;
+
+  enum MessageClass {
+    USER = 0;
+    EPHEMERAL = 2;
+  }
+  MessageClass message_class = 5;
+}
+
+// Matches StreamBody definition from the server:
+// google3/google/rpc/stream_body.proto
+message StreamBody {
+  repeated bytes messages = 1;
+  repeated bytes noop = 15;
+}
diff --git a/internal/proto/tachyon_enums.proto b/internal/proto/tachyon_enums.proto
new file mode 100644
index 00000000..3f72a6ab
--- /dev/null
+++ b/internal/proto/tachyon_enums.proto
@@ -0,0 +1,86 @@
+// Copyright 2021 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+syntax = "proto3";
+
+package nearby.internal.tachyon_proto;
+
+option optimize_for = LITE_RUNTIME;
+
+message ApiVersion {
+  enum Value {
+    UNKNOWN = 0;
+
+    // Initial version.
+    V1 = 1;
+
+    // RequestHeaders and AuthToken only.
+    V2 = 2;
+
+    // Block leaked playstore APKs.
+    V3 = 3;
+
+    // InboxMessage.message bytes are used.
+    V4 = 4;
+  }
+}
+
+message Platform {
+  enum Type {
+    UNKNOWN = 0;
+    TEST = 4;
+    DESKTOP = 6;
+  }
+}
+
+message LocationStandard {
+  enum Format {
+    UNKNOWN = 0;
+    // E164 country codes:
+    // https://en.wikipedia.org/wiki/List_of_country_calling_codes
+    // e.g. +1 for USA
+    E164_CALLING = 1;
+
+    // ISO 3166-1 alpha-2 country codes:
+    // https://en.wikipedia.org/wiki/ISO_3166-1_alpha-2
+    ISO_3166_1_ALPHA_2 = 2;
+  }
+}
+
+message IdType {
+  enum Type {
+    UNSET = 0;
+    NOT_KNOWN = 25;  // client does not know the id type.
+    NEARBY_ID = 27;  // Used by Nearby devices. go/tachyon-express-nearby.
+  }
+}
+
+// Connectivity status from the client network to ice_servers.
+//
+// This message is intended to be binary compatible and should be kept up to
+// date with BlockStatus in
+// google3/google/communications/networktraversal/v1alpha/networktraversal.proto
+message ConnectivityStatus {
+  // Status enumerations.
+  enum Type {
+    // Unspecified.
+    UNKNOWN = 0;
+
+    // ICE connectivity is not blocked.
+    ICE_UNBLOCKED = 1;
+
+    // ICE connectivity is possibly blocked.
+    ICE_POSSIBLY_BLOCKED = 2;
+  }
+}