diff --git a/inngest/_internal/const.py b/inngest/_internal/const.py
index 8b866e92..d71937a9 100644
--- a/inngest/_internal/const.py
+++ b/inngest/_internal/const.py
@@ -21,7 +21,6 @@ class ErrorCode(enum.Enum):
     INVALID_BODY = "invalid_body"
     INVALID_FUNCTION_CONFIG = "invalid_function_config"
     INVALID_REQUEST_SIGNATURE = "invalid_request_signature"
-    INVALID_TRANSFORM = "invalid_transform"
     MISMATCHED_SYNC = "mismatched_sync"
     MISSING_EVENT_KEY = "missing_event_key"
     MISSING_FUNCTION = "missing_function"
diff --git a/inngest/_internal/env.py b/inngest/_internal/env.py
index 73ceee2f..04fa7aa0 100644
--- a/inngest/_internal/env.py
+++ b/inngest/_internal/env.py
@@ -23,10 +23,6 @@ def _equals(key: EnvKey, value: str) -> _EnvCheck:
     return _EnvCheck(expected=value, key=key, operator="equals")
 
 
-def _is_truthy(key: EnvKey) -> _EnvCheck:
-    return _EnvCheck(expected=None, key=key, operator="is_truthy")
-
-
 def _starts_with(key: EnvKey, value: str) -> _EnvCheck:
     return _EnvCheck(expected=value, key=key, operator="starts_with")
 
diff --git a/inngest/_internal/errors.py b/inngest/_internal/errors.py
index 95591c48..264e973e 100644
--- a/inngest/_internal/errors.py
+++ b/inngest/_internal/errors.py
@@ -110,16 +110,6 @@ def __init__(self, message: str | None = None) -> None:
         )
 
 
-class InvalidTransformError(InternalError):
-    status_code: int = http.HTTPStatus.INTERNAL_SERVER_ERROR
-
-    def __init__(self, message: str | None = None) -> None:
-        super().__init__(
-            code=const.ErrorCode.INVALID_TRANSFORM,
-            message=message,
-        )
-
-
 class MissingEventKeyError(InternalError):
     status_code: int = http.HTTPStatus.INTERNAL_SERVER_ERROR
 
diff --git a/inngest/_internal/function.py b/inngest/_internal/function.py
index 115e2ded..fd2b5300 100644
--- a/inngest/_internal/function.py
+++ b/inngest/_internal/function.py
@@ -30,7 +30,7 @@ class _Config:
 
 
 @typing.runtime_checkable
-class FunctionHandlerAsync(typing.Protocol):
+class _FunctionHandlerAsync(typing.Protocol):
     def __call__(
         self,
         *,
@@ -45,7 +45,7 @@ def __call__(
 
 
 @typing.runtime_checkable
-class FunctionHandlerSync(typing.Protocol):
+class _FunctionHandlerSync(typing.Protocol):
     def __call__(
         self,
         *,
@@ -60,18 +60,18 @@ def __call__(
 
 
 def _is_function_handler_async(
-    value: FunctionHandlerAsync | FunctionHandlerSync,
-) -> typing.TypeGuard[FunctionHandlerAsync]:
+    value: _FunctionHandlerAsync | _FunctionHandlerSync,
+) -> typing.TypeGuard[_FunctionHandlerAsync]:
     return inspect.iscoroutinefunction(value)
 
 
 def _is_function_handler_sync(
-    value: FunctionHandlerAsync | FunctionHandlerSync,
-) -> typing.TypeGuard[FunctionHandlerSync]:
+    value: _FunctionHandlerAsync | _FunctionHandlerSync,
+) -> typing.TypeGuard[_FunctionHandlerSync]:
     return not inspect.iscoroutinefunction(value)
 
 
-class FunctionOpts(types.BaseModel):
+class _FunctionOpts(types.BaseModel):
     model_config = pydantic.ConfigDict(arbitrary_types_allowed=True)
 
     batch_events: function_config.Batch | None = None
@@ -79,7 +79,7 @@ class FunctionOpts(types.BaseModel):
     debounce: function_config.Debounce | None = None
     id: str
     name: str | None = None
-    on_failure: FunctionHandlerAsync | FunctionHandlerSync | None = None
+    on_failure: _FunctionHandlerAsync | _FunctionHandlerSync | None = None
     rate_limit: function_config.RateLimit | None = None
     retries: int | None = None
     throttle: function_config.Throttle | None = None
@@ -102,12 +102,12 @@ def create_function(
     ]
     | None = None,
     name: str | None = None,
-    on_failure: FunctionHandlerAsync | FunctionHandlerSync | None = None,
+    on_failure: _FunctionHandlerAsync | _FunctionHandlerSync | None = None,
     rate_limit: function_config.RateLimit | None = None,
     retries: int | None = None,
     throttle: function_config.Throttle | None = None,
     trigger: function_config.TriggerCron | function_config.TriggerEvent,
-) -> typing.Callable[[FunctionHandlerAsync | FunctionHandlerSync], Function]:
+) -> typing.Callable[[_FunctionHandlerAsync | _FunctionHandlerSync], Function]:
     """
     Create an Inngest function.
 
@@ -127,9 +127,11 @@ def create_function(
         trigger: What should trigger runs of this function.
     """
 
-    def decorator(func: FunctionHandlerAsync | FunctionHandlerSync) -> Function:
+    def decorator(
+        func: _FunctionHandlerAsync | _FunctionHandlerSync
+    ) -> Function:
         return Function(
-            FunctionOpts(
+            _FunctionOpts(
                 batch_events=batch_events,
                 cancel=cancel,
                 debounce=debounce,
@@ -149,9 +151,9 @@ def decorator(func: FunctionHandlerAsync | FunctionHandlerSync) -> Function:
 
 
 class Function:
-    _handler: FunctionHandlerAsync | FunctionHandlerSync
+    _handler: _FunctionHandlerAsync | _FunctionHandlerSync
     _on_failure_fn_id: str | None = None
-    _opts: FunctionOpts
+    _opts: _FunctionOpts
     _trigger: function_config.TriggerCron | function_config.TriggerEvent
 
     @property
@@ -179,9 +181,9 @@ def on_failure_fn_id(self) -> str | None:
 
     def __init__(
         self,
-        opts: FunctionOpts,
+        opts: _FunctionOpts,
         trigger: function_config.TriggerCron | function_config.TriggerEvent,
-        handler: FunctionHandlerAsync | FunctionHandlerSync,
+        handler: _FunctionHandlerAsync | _FunctionHandlerSync,
         middleware: list[
             type[middleware_lib.Middleware | middleware_lib.MiddlewareSync]
         ]
@@ -229,7 +231,7 @@ async def call(
                 return execution.CallError.from_error(err)
 
         try:
-            handler: FunctionHandlerAsync | FunctionHandlerSync
+            handler: _FunctionHandlerAsync | _FunctionHandlerSync
             if self.id == fn_id:
                 handler = self._handler
             elif self.on_failure_fn_id == fn_id:
@@ -277,7 +279,8 @@ async def call(
                     ),
                 )
             else:
-                # Should be unreachable.
+                # Should be unreachable but Python's custom type guards don't
+                # support negative checks :(
                 return execution.CallError.from_error(
                     errors.UnknownError(
                         "unable to determine function handler type"
@@ -342,7 +345,7 @@ def call_sync(
             middleware.before_execution_sync()
 
         try:
-            handler: FunctionHandlerAsync | FunctionHandlerSync
+            handler: _FunctionHandlerAsync | _FunctionHandlerSync
             if self.id == fn_id:
                 handler = self._handler
             elif self.on_failure_fn_id == fn_id:
diff --git a/inngest/_internal/types.py b/inngest/_internal/types.py
index 13bf0660..09faaff0 100644
--- a/inngest/_internal/types.py
+++ b/inngest/_internal/types.py
@@ -1,6 +1,5 @@
 from __future__ import annotations
 
-import json
 import logging
 import typing
 
@@ -23,14 +22,6 @@
 SerializableT = typing.TypeVar("SerializableT", bound=Serializable)
 
 
-def is_serializable(obj: object) -> typing.TypeGuard[Serializable]:
-    try:
-        json.dumps(obj)
-        return True
-    except Exception:
-        return False
-
-
 class BaseModel(pydantic.BaseModel):
     model_config = pydantic.ConfigDict(strict=True)