diff --git a/fastapi/applications.py b/fastapi/applications.py
index 41d86143e..84f01d7a7 100644
--- a/fastapi/applications.py
+++ b/fastapi/applications.py
@@ -974,6 +974,7 @@ class FastAPI(Starlette):
             include_in_schema=include_in_schema,
             responses=responses,
             generate_unique_id_function=generate_unique_id_function,
+            defer_init=False,
         )
         self.exception_handlers: dict[
             Any, Callable[[Request, Any], Response | Awaitable[Response]]
diff --git a/fastapi/routing.py b/fastapi/routing.py
index ea82ab14a..3a525d9d2 100644
--- a/fastapi/routing.py
+++ b/fastapi/routing.py
@@ -21,6 +21,7 @@ from contextlib import (
     asynccontextmanager,
 )
 from enum import Enum, IntEnum
+from functools import cached_property
 from typing import (
     Annotated,
     Any,
@@ -582,6 +583,7 @@ class APIRoute(routing.Route):
         openapi_extra: dict[str, Any] | None = None,
         generate_unique_id_function: Callable[["APIRoute"], str]
         | DefaultPlaceholder = Default(generate_unique_id),
+        defer_init: bool = True,
     ) -> None:
         self.path = path
         self.endpoint = endpoint
@@ -630,20 +632,32 @@ class APIRoute(routing.Route):
             assert is_body_allowed_for_status_code(status_code), (
                 f"Status code {status_code} must not have a response body"
             )
-            response_name = "Response_" + self.unique_id
-            self.response_field = create_model_field(
-                name=response_name,
-                type_=self.response_model,
-                mode="serialization",
-            )
-        else:
-            self.response_field = None  # type: ignore
+
         self.dependencies = list(dependencies or [])
         self.description = description or inspect.cleandoc(self.endpoint.__doc__ or "")
         # if a "form feed" character (page break) is found in the description text,
         # truncate description text to the content preceding the first "form feed"
         self.description = self.description.split("\f")[0].strip()
-        response_fields = {}
+
+        assert callable(endpoint), "An endpoint must be a callable"
+
+        if not defer_init:
+            self.init_attributes()
+
+    @cached_property
+    def response_field(self) -> ModelField | None:
+        if not self.response_model:
+            return None
+        response_name = "Response_" + self.unique_id
+        return create_model_field(
+            name=response_name,
+            type_=self.response_model,
+            mode="serialization",
+        )
+
+    @cached_property
+    def response_fields(self) -> dict[int | str, ModelField]:
+        response_fields: dict[int | str, ModelField] = {}
         for additional_status_code, response in self.responses.items():
             assert isinstance(response, dict), "An additional response must be a dict"
             model = response.get("model")
@@ -656,30 +670,49 @@ class APIRoute(routing.Route):
                     name=response_name, type_=model, mode="serialization"
                 )
                 response_fields[additional_status_code] = response_field
-        if response_fields:
-            self.response_fields: dict[int | str, ModelField] = response_fields
-        else:
-            self.response_fields = {}
 
-        assert callable(endpoint), "An endpoint must be a callable"
-        self.dependant = get_dependant(
+        return response_fields
+
+    @cached_property
+    def dependant(self) -> Dependant:
+        dependant = get_dependant(
             path=self.path_format, call=self.endpoint, scope="function"
         )
         for depends in self.dependencies[::-1]:
-            self.dependant.dependencies.insert(
+            dependant.dependencies.insert(
                 0,
                 get_parameterless_sub_dependant(depends=depends, path=self.path_format),
             )
-        self._flat_dependant = get_flat_dependant(self.dependant)
-        self._embed_body_fields = _should_embed_body_fields(
-            self._flat_dependant.body_params
-        )
-        self.body_field = get_body_field(
+        return dependant
+
+    @cached_property
+    def _flat_dependant(self) -> Dependant:
+        return get_flat_dependant(self.dependant)
+
+    @cached_property
+    def _embed_body_fields(self) -> bool:
+        return _should_embed_body_fields(self._flat_dependant.body_params)
+
+    @cached_property
+    def body_field(self) -> ModelField | None:
+        return get_body_field(
             flat_dependant=self._flat_dependant,
             name=self.unique_id,
             embed_body_fields=self._embed_body_fields,
         )
-        self.app = request_response(self.get_route_handler())
+
+    @cached_property
+    def app(self) -> ASGIApp:  # type: ignore
+        return request_response(self.get_route_handler())
+
+    def init_attributes(self) -> None:
+        _ = self.app
+        _ = self.dependant
+        _ = self.response_field
+        _ = self.response_fields
+        _ = self.body_field
+        _ = self._flat_dependant
+        _ = self._embed_body_fields
 
     def get_route_handler(self) -> Callable[[Request], Coroutine[Any, Any, Response]]:
         return get_request_handler(
@@ -946,6 +979,16 @@ class APIRouter(routing.Router):
                 """
             ),
         ] = Default(generate_unique_id),
+        defer_init: Annotated[
+            bool,
+            Doc(
+                """
+                By default, every route will defer its initialization until the first call.
+                This flag can be used to deactivate this behavior for the routes defined in this router,
+                causing the routes to initialize immediately when they are defined.
+                """
+            ),
+        ] = True,
     ) -> None:
         # Determine the lifespan context to use
         if lifespan is None:
@@ -992,6 +1035,9 @@ class APIRouter(routing.Router):
         self.route_class = route_class
         self.default_response_class = default_response_class
         self.generate_unique_id_function = generate_unique_id_function
+        self.defer_init = defer_init
+        if not self.defer_init:
+            self.init_routes()
 
     def route(
         self,
@@ -1088,6 +1134,7 @@ class APIRouter(routing.Router):
             callbacks=current_callbacks,
             openapi_extra=openapi_extra,
             generate_unique_id_function=current_generate_unique_id,
+            defer_init=self.defer_init,
         )
         self.routes.append(route)
 
@@ -1250,6 +1297,11 @@ class APIRouter(routing.Router):
 
         return decorator
 
+    def init_routes(self) -> None:
+        for route in self.routes:
+            if isinstance(route, APIRoute):
+                route.init_attributes()
+
     def include_router(
         self,
         router: Annotated["APIRouter", Doc("The `APIRouter` to include.")],
diff --git a/tests/test_route_deferred_init.py b/tests/test_route_deferred_init.py
new file mode 100644
index 000000000..17e927425
--- /dev/null
+++ b/tests/test_route_deferred_init.py
@@ -0,0 +1,113 @@
+from itertools import chain
+
+from fastapi import APIRouter, Depends, FastAPI
+from fastapi.routing import APIRoute
+from fastapi.testclient import TestClient
+from pydantic import BaseModel
+from starlette.routing import BaseRoute
+
+deferred_keys = [
+    "app",
+    "response_fields",
+    "body_field",
+    "response_field",
+    "dependant",
+    "_flat_dependant",
+    "_embed_body_fields",
+]
+
+
+def check_if_initialized(route: APIRoute, should_not: bool = False):
+    for key in deferred_keys:
+        if should_not:
+            assert key not in route.__dict__
+        else:
+            assert key in route.__dict__
+
+
+def create_test_router(routes: list[BaseRoute] | None = None, defer_init: bool = True):
+    router = APIRouter(routes=routes or [], defer_init=defer_init)
+
+    class UserIdBody(BaseModel):
+        user_id: int
+
+    @router.get("/user_id", dependencies=[Depends(lambda: True)])
+    async def get_user_id(user_id: int = Depends(lambda: 1)) -> UserIdBody:
+        return {"user_id": user_id}
+
+    return router
+
+
+def test_route_defers():
+    app = FastAPI()
+    router = create_test_router(routes=app.router.routes)
+
+    for route in router.routes:
+        if not isinstance(route, APIRoute):
+            continue
+        check_if_initialized(route, should_not=True)
+
+    app.router = router
+    client = TestClient(app)
+    response = client.get("/user_id")
+    assert response.status_code == 200
+    response = client.get("/openapi.json")
+    assert response.status_code == 200
+
+    for route in router.routes:
+        if not isinstance(route, APIRoute):
+            continue
+        check_if_initialized(route)
+
+
+def test_route_manual_init():
+    router = create_test_router()
+    for route in router.routes:
+        check_if_initialized(route, should_not=True)
+        route.init_attributes()
+        check_if_initialized(route)
+
+    router = create_test_router()
+    router.init_routes()
+    for route in router.routes:
+        check_if_initialized(route)
+
+
+def test_router_defer_init_flag():
+    route = APIRoute("/test", lambda: {"test": True}, defer_init=False)
+    check_if_initialized(route)
+
+    deferring_router = create_test_router()
+    router = create_test_router(routes=deferring_router.routes, defer_init=False)
+
+    for route in router.routes:
+        check_if_initialized(route)
+
+
+def test_root_router_always_initialized():
+    app = FastAPI()
+
+    @app.get("/test")
+    async def test_get():
+        return {"test": 1}
+
+    router = create_test_router()
+    app.include_router(router)
+    for route in app.router.routes:
+        if not isinstance(route, APIRoute):
+            continue
+        check_if_initialized(route)
+
+    client = TestClient(app)
+    response = client.get("/test")
+    assert response.status_code == 200
+
+
+def test_include_router_no_init():
+    router1 = create_test_router()
+
+    router2 = create_test_router()
+    router2.include_router(router1)
+
+    for route in chain(router1.routes, router2.routes):
+        check_if_initialized(route, should_not=True)