diff --git a/stabilityai/client.py b/stabilityai/client.py
index 97fe164..8fd1282 100644
--- a/stabilityai/client.py
+++ b/stabilityai/client.py
@@ -1,11 +1,10 @@
-import json
 import os
+import textwrap
 from typing import Optional
 
 import aiohttp
-from pydantic import (
-    validate_arguments,
-)
+from pydantic import validate_arguments
+
 from stabilityai.constants import (
     DEFAULT_GENERATION_ENGINE,
     DEFAULT_STABILITY_API_HOST,
@@ -13,7 +12,10 @@ from stabilityai.constants import (
     DEFAULT_STABILITY_CLIENT_VERSION,
     DEFAULT_UPSCALE_ENGINE,
 )
-from stabilityai.exceptions import ThisFunctionRequiresAPrompt, YouNeedToUseAContextManager
+from stabilityai.exceptions import (
+    ThisFunctionRequiresAPrompt,
+    YouNeedToUseAContextManager,
+)
 from stabilityai.models import (
     AccountResponseBody,
     BalanceResponseBody,
@@ -44,8 +46,6 @@ from stabilityai.models import (
     UpscaleImageHeight,
     UpscaleImageWidth,
 )
-from stabilityai.utils import omit_none
-import textwrap
 
 
 class AsyncStabilityClient:
@@ -69,7 +69,6 @@ class AsyncStabilityClient:
         self.session = await aiohttp.ClientSession(
             base_url=self.api_host,
             headers={
-                "Content-Type": "application/json",
                 "Accept": "application/json",
                 "Authorization": f"Bearer {self.api_key}",
                 "Stability-Client-ID": self.client_id,
@@ -122,9 +121,7 @@ class AsyncStabilityClient:
             )
 
     def _normalize_text_prompts(
-        self,
-        text_prompts: Optional[TextPrompts],
-        text_prompt: Optional[SingleTextPrompt]
+        self, text_prompts: Optional[TextPrompts], text_prompt: Optional[SingleTextPrompt]
     ):
         if not bool(text_prompt) ^ bool(text_prompts):
             raise ThisFunctionRequiresAPrompt(
@@ -147,14 +144,10 @@ class AsyncStabilityClient:
                                 TextPrompt(text="A beautiful sunrise", weight=1.0)
                             ],
                         )
-                    """ 
+                    """
                 )
             )
 
-        if text_prompt:
-            text_prompts = [TextPrompt(text=text_prompt)]
-
-        # After this moment text_prompts can't be None.
         assert text_prompts is not None
         return text_prompts
 
@@ -197,7 +190,8 @@ class AsyncStabilityClient:
 
         res = await self.session.post(
             f"/v1/generation/{engine_id}/text-to-image",
-            data=json.dumps(omit_none(json.loads(request_body.json()))),
+            headers={"Content-Type": "application/json"},
+            data=request_body.json(exclude_defaults=True, exclude_none=True, exclude_unset=True),
         )
         Sampler.K_DPMPP_2M
 
@@ -224,7 +218,7 @@ class AsyncStabilityClient:
             height=dim,
         )
 
-    @validate_arguments
+    @validate_arguments(config={"arbitrary_types_allowed": True})
     async def image_to_image(
         self,
         text_prompts: TextPrompts,
@@ -265,11 +259,12 @@ class AsyncStabilityClient:
 
         res = await self.session.post(
             f"/v1/generation/{engine_id}/text-to-image",
-            data=json.dumps(omit_none(json.loads(request_body.json()))),
+            data=request_body.json(exclude_none=True, exclude_defaults=True, exclude_unset=True),
         )
 
         return ImageToImageResponseBody.parse_obj(await res.json())
 
+    @validate_arguments(config={"arbitrary_types_allowed": True})
     async def image_to_image_upscale(
         self,
         image: InitImage,
@@ -284,9 +279,13 @@ class AsyncStabilityClient:
 
         request_body = ImageToImageUpscaleRequestBody(image=image, width=width, height=height)
 
+        form = aiohttp.FormData()
+        form.add_field("width", "1024")
+        form.add_field("image", request_body.image)
+
         res = await self.session.post(
             f"/v1/generation/{engine_id}/image-to-image/upscale",
-            data=json.dumps(omit_none(json.loads(request_body.json()))),
+            data=form,
         )
 
         return ImageToImageUpscaleResponseBody.parse_obj(await res.json())
diff --git a/stabilityai/constants.py b/stabilityai/constants.py
index 84963dc..8083cff 100644
--- a/stabilityai/constants.py
+++ b/stabilityai/constants.py
@@ -1,6 +1,5 @@
 from typing import Final
 
-
 DEFAULT_STABILITY_API_HOST: Final[str] = "https://api.stability.ai"
 DEFAULT_STABILITY_CLIENT_ID: Final[str] = "Stability Python SDK"
 DEFAULT_STABILITY_CLIENT_VERSION: Final[str] = "1.0.0"
diff --git a/stabilityai/models.py b/stabilityai/models.py
index 695a06e..5e90e3a 100644
--- a/stabilityai/models.py
+++ b/stabilityai/models.py
@@ -3,15 +3,8 @@ import io
 from enum import StrEnum
 from typing import Annotated, List, Optional
 
-from pydantic import (
-    AnyUrl,
-    BaseModel,
-    EmailStr,
-    confloat,
-    conint,
-    constr,
-    validator,
-)
+from pydantic import AnyUrl, BaseModel, EmailStr, confloat, conint, constr, validator
+
 
 class Type(StrEnum):
     AUDIO = "AUDIO"
@@ -103,11 +96,12 @@ class TextPrompt(BaseModel):
     text: Annotated[str, constr(max_length=2000)]
     weight: Optional[float] = None
 
+
 SingleTextPrompt = str
 
 TextPrompts = List[TextPrompt]
 
-InitImage = bytes
+InitImage = io.IOBase
 
 InitImageStrength = Annotated[float, confloat(ge=0.0, le=1.0)]
 
@@ -146,6 +140,9 @@ class LatentUpscalerUpscaleRequestBody(BaseModel):
     steps: Optional[Steps] = None
     cfg_scale: Optional[CfgScale] = None
 
+    class Config:
+        arbitrary_types_allowed = True
+
 
 class ImageToImageRequestBody(BaseModel):
     text_prompts: TextPrompts
@@ -163,6 +160,9 @@ class ImageToImageRequestBody(BaseModel):
     style_preset: Optional[StylePreset] = None
     extras: Optional[Extras] = None
 
+    class Config:
+        arbitrary_types_allowed = True
+
 
 class MaskingRequestBody(BaseModel):
     init_image: InitImage
@@ -178,6 +178,9 @@ class MaskingRequestBody(BaseModel):
     style_preset: Optional[StylePreset] = None
     extras: Optional[Extras] = None
 
+    class Config:
+        arbitrary_types_allowed = True
+
 
 class TextToImageRequestBody(GenerationRequestOptionalParams):
     height: Optional[DiffuseImageHeight] = None
@@ -196,6 +199,9 @@ class ImageToImageUpscaleRequestBody(BaseModel):
             raise ValueError("You can only specify one of width and height.")
         return v
 
+    class Config:
+        arbitrary_types_allowed = True
+
 
 class BalanceResponseBody(BaseModel):
     credits: float
diff --git a/stabilityai/utils.py b/stabilityai/utils.py
deleted file mode 100644
index ae49f21..0000000
--- a/stabilityai/utils.py
+++ /dev/null
@@ -1,6 +0,0 @@
-from typing import Dict, Mapping, TypeVar
-
-T, U = TypeVar("T"), TypeVar("U")
-
-def omit_none(m: Mapping[T, U]) -> Dict[T, U]:
-    return {k: v for k, v in m.items() if v is not None}