diff --git a/conformance/client_config.yaml b/conformance/client_config.yaml
index 796997a..b34a092 100644
--- a/conformance/client_config.yaml
+++ b/conformance/client_config.yaml
@@ -8,6 +8,7 @@ features:
     - PROTOCOL_GRPC_WEB
   codecs:
     - CODEC_PROTO
+    - CODEC_JSON
   compressions:
     - COMPRESSION_IDENTITY
     - COMPRESSION_GZIP
diff --git a/conformance/client_runner.py b/conformance/client_runner.py
index 52d878e..95a72c5 100755
--- a/conformance/client_runner.py
+++ b/conformance/client_runner.py
@@ -310,6 +310,7 @@ async def handle_message(msg: client_compat_pb2.ClientCompatRequest) -> client_c
         payloads = []
         try:
             options = ClientOptions()
+
             if msg.protocol == config_pb2.PROTOCOL_GRPC:
                 options.protocol = "grpc"
             if msg.protocol == config_pb2.PROTOCOL_GRPC_WEB:
@@ -318,6 +319,9 @@ async def handle_message(msg: client_compat_pb2.ClientCompatRequest) -> client_c
             if msg.compression == config_pb2.COMPRESSION_GZIP:
                 options.request_compression_name = "gzip"
 
+            if msg.codec == config_pb2.CODEC_JSON:
+                options.use_binary_format = False
+
             client = service_connect.ConformanceServiceClient(base_url=url, session=session, options=options)
             if msg.stream_type == config_pb2.STREAM_TYPE_UNARY:
                 if msg.request_delay_ms > 0:
diff --git a/src/connect/client.py b/src/connect/client.py
index b773e9c..e74fbb2 100644
--- a/src/connect/client.py
+++ b/src/connect/client.py
@@ -11,7 +11,7 @@
 from yarl import URL
 
 from connect.code import Code
-from connect.codec import Codec, ProtoBinaryCodec
+from connect.codec import Codec, CodecNameType, ProtoBinaryCodec, ProtoJSONCodec
 from connect.compression import COMPRESSION_IDENTITY, Compression, GZipCompression, get_compresion_from_name
 from connect.connect import (
     Spec,
@@ -120,7 +120,12 @@ def __init__(self, raw_url: str, options: ClientOptions):
         elif options.protocol == "grpc-web":
             self.protocol = ProtocolGRPC(web=True)
         self.procedure = proto_path
-        self.codec = ProtoBinaryCodec()
+
+        if options.use_binary_format:
+            self.codec = ProtoBinaryCodec()
+        else:
+            self.codec = ProtoJSONCodec(CodecNameType.JSON)
+
         self.request_compression_name = options.request_compression_name
         self.compressions = [GZipCompression()]
         if self.request_compression_name and self.request_compression_name != COMPRESSION_IDENTITY:
diff --git a/src/connect/codec.py b/src/connect/codec.py
index faebd0a..84d2932 100644
--- a/src/connect/codec.py
+++ b/src/connect/codec.py
@@ -249,7 +249,7 @@ def marshal(self, message: Any) -> bytes:
 
         json_str = json_format.MessageToJson(message)
 
-        return json_str.encode("utf-8")
+        return json_str.encode()
 
     def unmarshal(self, data: bytes, message: Any) -> Any:
         """Unmarshal the given byte data into a protobuf message.
@@ -269,7 +269,7 @@ def unmarshal(self, data: bytes, message: Any) -> Any:
         if not isinstance(obj, google.protobuf.message.Message):
             raise ValueError("Data is not a protobuf message")
 
-        return json_format.Parse(data.decode("utf-8"), obj, ignore_unknown_fields=True)
+        return json_format.Parse(data.decode(), obj, ignore_unknown_fields=True)
 
     def marshal_stable(self, message: Any) -> bytes:
         """Serialize a protobuf message to a JSON string encoded as UTF-8 bytes in a deterministic way.
@@ -298,7 +298,7 @@ def marshal_stable(self, message: Any) -> bytes:
         parsed = json.loads(json_str)
         compacted_json = json.dumps(parsed, separators=(",", ":"))
 
-        return compacted_json.encode("utf-8")
+        return compacted_json.encode()
 
     def is_binary(self) -> bool:
         """Determine if the codec is binary.
diff --git a/src/connect/options.py b/src/connect/options.py
index ef7eba6..e614f21 100644
--- a/src/connect/options.py
+++ b/src/connect/options.py
@@ -87,6 +87,9 @@ class ClientOptions(BaseModel):
     protocol: Literal["connect", "grpc", "grpc-web"] = Field(default="connect")
     """The protocol to use for the request."""
 
+    use_binary_format: bool = Field(default=True)
+    """A boolean indicating whether to use binary format for the request."""
+
     def merge(self, override_options: "ClientOptions | None" = None) -> "ClientOptions":
         """Merge this options object with an override options object.