diff --git a/reflex/compiler/templates.py b/reflex/compiler/templates.py
index 2abcb6dd533..a8a7dbe4ec2 100644
--- a/reflex/compiler/templates.py
+++ b/reflex/compiler/templates.py
@@ -502,6 +502,7 @@ def vite_config_template(
     force_full_reload: bool,
     experimental_hmr: bool,
     sourcemap: bool | Literal["inline", "hidden"],
+    allowed_hosts: bool | list[str] = False,
 ):
     """Template for vite.config.js.
 
@@ -511,10 +512,17 @@ def vite_config_template(
         force_full_reload: Whether to force a full reload on changes.
         experimental_hmr: Whether to enable experimental HMR features.
         sourcemap: The sourcemap configuration.
+        allowed_hosts: Allow all hosts (True), specific hosts (list of strings), or only localhost (False).
 
     Returns:
         Rendered vite.config.js content as string.
     """
+    if allowed_hosts is True:
+        allowed_hosts_line = "\n    allowedHosts: true,"
+    elif isinstance(allowed_hosts, list) and allowed_hosts:
+        allowed_hosts_line = f"\n    allowedHosts: {json.dumps(allowed_hosts)},"
+    else:
+        allowed_hosts_line = ""
     return rf"""import {{ fileURLToPath, URL }} from "url";
 import {{ reactRouter }} from "@react-router/dev/vite";
 import {{ defineConfig }} from "vite";
@@ -586,7 +594,7 @@ def vite_config_template(
     hmr: {"true" if experimental_hmr else "false"},
   }},
   server: {{
-    port: process.env.PORT,
+    port: process.env.PORT,{allowed_hosts_line}
     hmr: {"true" if hmr else "false"},
     watch: {{
       ignored: [
diff --git a/reflex/config.py b/reflex/config.py
index 6977d745631..225fe5bf2be 100644
--- a/reflex/config.py
+++ b/reflex/config.py
@@ -213,6 +213,11 @@ class BaseConfig:
         dataclasses.field(default=("*",))
     )
 
+    # Allowed hosts for the Vite dev server. Set to True to allow all hosts,
+    # or provide a list of hostnames (e.g. ["myservice.local"]) to allow specific ones.
+    # Prevents 403 errors in Docker, Codespaces, reverse proxies, etc.
+    vite_allowed_hosts: bool | list[str] = False
+
     # Whether to use React strict mode.
     react_strict_mode: bool = True
 
diff --git a/reflex/environment.py b/reflex/environment.py
index 279fc5f60c1..ec8f08c5401 100644
--- a/reflex/environment.py
+++ b/reflex/environment.py
@@ -243,8 +243,14 @@ def interpret_env_var_value(
     field_type = value_inside_optional(field_type)
 
     if is_union(field_type):
-        msg = f"Union types are not supported for environment variables: {field_name}."
-        raise ValueError(msg)
+        errors = []
+        for arg in (union_types := get_args(field_type)):
+            try:
+                return interpret_env_var_value(value, arg, field_name)
+            except (ValueError, EnvironmentVarValueError) as e:  # noqa: PERF203
+                errors.append(e)
+        msg = f"Could not interpret {value!r} for {field_name} as any of {union_types}: {errors}"
+        raise EnvironmentVarValueError(msg)
 
     value = value.strip()
 
diff --git a/reflex/utils/frontend_skeleton.py b/reflex/utils/frontend_skeleton.py
index 96ced280fe2..6084219df03 100644
--- a/reflex/utils/frontend_skeleton.py
+++ b/reflex/utils/frontend_skeleton.py
@@ -197,6 +197,7 @@ def _compile_vite_config(config: Config):
         force_full_reload=environment.VITE_FORCE_FULL_RELOAD.get(),
         experimental_hmr=environment.VITE_EXPERIMENTAL_HMR.get(),
         sourcemap=environment.VITE_SOURCEMAP.get(),
+        allowed_hosts=config.vite_allowed_hosts,
     )
 
 
diff --git a/tests/units/test_environment.py b/tests/units/test_environment.py
index 839fea4545a..0665c6f5f0d 100644
--- a/tests/units/test_environment.py
+++ b/tests/units/test_environment.py
@@ -190,10 +190,19 @@ def test_interpret_enum(self):
         result = interpret_env_var_value("value1", _TestEnum, "TEST_FIELD")
         assert result == _TestEnum.VALUE1
 
-    def test_interpret_union_error(self):
-        """Test that union types raise an error."""
-        with pytest.raises(ValueError, match="Union types are not supported"):
-            interpret_env_var_value("test", int | str, "TEST_FIELD")
+    def test_interpret_union_tries_each_type(self):
+        """Test that union types try each type in order."""
+        # str matches first
+        assert interpret_env_var_value("hello", int | str, "TEST_FIELD") == "hello"
+        # int matches first
+        assert interpret_env_var_value("42", int | str, "TEST_FIELD") == 42
+        # bool matches before str
+        assert interpret_env_var_value("true", bool | str, "TEST_FIELD") is True
+
+    def test_interpret_union_no_match(self):
+        """Test that union types raise an error if no type matches."""
+        with pytest.raises(EnvironmentVarValueError, match="Could not interpret"):
+            interpret_env_var_value("not_a_number", int | bool, "TEST_FIELD")
 
     def test_interpret_unsupported_type(self):
         """Test unsupported type raises an error."""