🔖 Release version 0.140.12 (#16095)

Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

.github/workflows/latest-changes.yml

@@ -40,11 +40,7 @@ jobs:
         if: ${{ github.event_name == 'workflow_dispatch' && github.event.inputs.debug_enabled == 'true' }}
         with:
           limit-access-to-actor: true
-      - uses: tiangolo/latest-changes@c9b73efbc8992ef1a401e4235ea307a8ca8a724b # 0.6.1
+      - uses: tiangolo/latest-changes@8a940392f4c65274539453a5d5a76d9550203ac1 # 0.7.1
         with:
           token: ${{ secrets.GITHUB_TOKEN }}
-          latest_changes_file: docs/en/docs/release-notes.md
-          latest_changes_header: '## Latest Changes'
-          end_regex: '^## '
           debug_logs: true
-          label_header_prefix: '### '

.github/workflows/test.yml

@@ -201,6 +201,78 @@ jobs:
           mode: memory
           run: uv run --no-sync pytest tests/memory_benchmarks --codspeed
 
+  regression-test:
+    runs-on: ubuntu-latest
+    timeout-minutes: 10
+    steps:
+      - name: Check out the pull request
+        if: github.event_name == 'pull_request'
+        uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
+        with:
+          ref: ${{ github.sha }}
+          path: pr
+          persist-credentials: false
+          fetch-depth: 0
+      - name: Find changed tests
+        if: github.event_name == 'pull_request'
+        id: changed-tests
+        working-directory: pr
+        env:
+          BASE_SHA: ${{ github.event.pull_request.base.sha }}
+          HEAD_SHA: ${{ github.event.pull_request.head.sha }}
+        run: |
+          git diff --name-only --diff-filter=AM -z "$BASE_SHA" "$HEAD_SHA" -- tests \
+            | while IFS= read -r -d '' file; do
+                case "$(basename "$file")" in
+                  test_*.py) printf '%s\0' "$file" ;;
+                esac
+              done > "$RUNNER_TEMP/changed-tests"
+          if [ -s "$RUNNER_TEMP/changed-tests" ]; then
+            echo "found=true" >> "$GITHUB_OUTPUT"
+            git diff --binary "$BASE_SHA" "$HEAD_SHA" -- tests \
+              > "$RUNNER_TEMP/tests.patch"
+          else
+            echo "found=false" >> "$GITHUB_OUTPUT"
+            echo "No added or modified test files; regression proof is not applicable."
+          fi
+      - name: Check out the base revision
+        if: steps.changed-tests.outputs.found == 'true'
+        uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
+        with:
+          ref: ${{ github.event.pull_request.base.sha }}
+          path: base
+          persist-credentials: false
+      - name: Set up Python
+        if: steps.changed-tests.outputs.found == 'true'
+        uses: actions/setup-python@ece7cb06caefa5fff74198d8649806c4678c61a1 # v6.3.0
+        with:
+          python-version-file: "base/.python-version"
+      - name: Setup uv
+        if: steps.changed-tests.outputs.found == 'true'
+        uses: astral-sh/setup-uv@d31148d669074a8d0a63714ba94f3201e7020bc3 # v8.3.0
+        with:
+          # Before upgrading uv version, make sure astral-sh/setup-uv knows its checksum.
+          # See: https://github.com/astral-sh/setup-uv/issues/851#issuecomment-4282017837
+          version: "0.11.18"
+          enable-cache: true
+      - name: Run the changed tests against the base code
+        if: steps.changed-tests.outputs.found == 'true'
+        working-directory: base
+        run: |
+          git apply "$RUNNER_TEMP/tests.patch"
+          uv sync --locked --no-dev --group tests --extra all
+          set +e
+          xargs -0 uv run --no-sync pytest -- < "$RUNNER_TEMP/changed-tests"
+          status=$?
+          set -e
+          if [ "$status" -eq 0 ]; then
+            echo "::warning::The changed tests already pass on the base revision. Check whether the fix is still needed."
+            echo "### Regression proof: base already passes :warning:" >> "$GITHUB_STEP_SUMMARY"
+            echo "The changed tests pass without the pull request's code changes." >> "$GITHUB_STEP_SUMMARY"
+          else
+            echo "The changed tests fail on the base revision as expected (pytest exit code $status)."
+            echo "### Regression proof: base fails as expected :white_check_mark:" >> "$GITHUB_STEP_SUMMARY"
+          fi
   coverage-combine:
     needs:
       - test
@@ -253,6 +325,7 @@ jobs:
       - test
       - coverage-combine
       - benchmark
+      - regression-test
     runs-on: ubuntu-latest
     timeout-minutes: 5
     steps:

docs/en/docs/release-notes.md

@@ -7,6 +7,83 @@ hide:
 
 ## Latest Changes
 
+## 0.140.12 (2026-07-28)
+
+### Fixes
+
+* 🐛 Fix line splitting in `format_sse_event` to comply with SSE spec. PR [#15515](https://github.com/fastapi/fastapi/pull/15515) by [@Zawwarsami16](https://github.com/Zawwarsami16).
+
+## 0.140.11 (2026-07-28)
+
+### Fixes
+
+* 🐛 Fix `response_model_*` params ignored for non-generator endpoints with `Iterable[..]` return type. PR [#15093](https://github.com/fastapi/fastapi/pull/15093) by [@YuriiMotov](https://github.com/YuriiMotov).
+
+## 0.140.10 (2026-07-28)
+
+### Fixes
+
+* 🐛 Fix handling sequences with nested Annotated types. PR [#14874](https://github.com/fastapi/fastapi/pull/14874) by [@YuriiMotov](https://github.com/YuriiMotov).
+
+### Internal
+
+* 🐛 Accept any base test failure as regression. PR [#16092](https://github.com/fastapi/fastapi/pull/16092) by [@tiangolo](https://github.com/tiangolo).
+* 🐛 Preserve pytest exit code in regression check. PR [#16091](https://github.com/fastapi/fastapi/pull/16091) by [@tiangolo](https://github.com/tiangolo).
+* ✅ Test PR regressions against base code. PR [#16090](https://github.com/fastapi/fastapi/pull/16090) by [@tiangolo](https://github.com/tiangolo).
+
+## 0.140.9 (2026-07-28)
+
+### Fixes
+
+* 🐛 Fix `exclude_defaults` not propagated to dict keys and values in `jsonable_encoder`. PR [#16043](https://github.com/fastapi/fastapi/pull/16043) by [@MBGrao](https://github.com/MBGrao).
+
+### Internal
+
+* ⬆ Bump gitpython from 3.1.50 to 3.1.54. PR [#16047](https://github.com/fastapi/fastapi/pull/16047) by [@dependabot[bot]](https://github.com/apps/dependabot).
+* ⬆ Bump pymdown-extensions from 10.21.3 to 11.0. PR [#16048](https://github.com/fastapi/fastapi/pull/16048) by [@dependabot[bot]](https://github.com/apps/dependabot).
+* ⬆ Bump pyasn1 from 0.6.3 to 0.6.4. PR [#16045](https://github.com/fastapi/fastapi/pull/16045) by [@dependabot[bot]](https://github.com/apps/dependabot).
+
+## 0.140.8 (2026-07-28)
+
+### Fixes
+
+* 🐛 Fix stream item type lost when using `include_router()`. PR [#15077](https://github.com/fastapi/fastapi/pull/15077) by [@alex-raw](https://github.com/alex-raw).
+
+## 0.140.7 (2026-07-27)
+
+### Refactors
+
+* ⚡️ Avoid flattening dependencies for OpenAPI. PR [#16076](https://github.com/fastapi/fastapi/pull/16076) by [@tiangolo](https://github.com/tiangolo).
+
+### Internal
+
+* ⬆️ Upgrade latest-changes to 0.7.1. PR [#16077](https://github.com/fastapi/fastapi/pull/16077) by [@tiangolo](https://github.com/tiangolo).
+* 👷 Add OpenAPI dependency benchmarks. PR [#16075](https://github.com/fastapi/fastapi/pull/16075) by [@tiangolo](https://github.com/tiangolo).
+
+## 0.140.6 (2026-07-27)
+
+### Refactors
+
+* ⚡️ Avoid flattening dependencies for request parameters, mainly for OpenAPI. PR [#16073](https://github.com/fastapi/fastapi/pull/16073) by [@tiangolo](https://github.com/tiangolo).
+
+## 0.140.5 (2026-07-27)
+
+### Refactors
+
+* ⚡️ Avoid flattening dependencies for body fields. PR [#16071](https://github.com/fastapi/fastapi/pull/16071) by [@tiangolo](https://github.com/tiangolo).
+
+## 0.140.4 (2026-07-27)
+
+### Refactors
+
+* ⚡️ Skip unused dependency repeat bookkeeping. PR [#16069](https://github.com/fastapi/fastapi/pull/16069) by [@tiangolo](https://github.com/tiangolo).
+
+## 0.140.3 (2026-07-27)
+
+### Refactors
+
+* ⚡️ Avoid repeated dependency flattening in OpenAPI. PR [#16067](https://github.com/fastapi/fastapi/pull/16067) by [@tiangolo](https://github.com/tiangolo).
+
 ## 0.140.2 (2026-07-27)
 
 ### Refactors

fastapi/__init__.py

@@ -1,6 +1,6 @@
 """FastAPI framework, high performance, easy to learn, fast to code, ready for production"""
 
-__version__ = "0.140.2"
+__version__ = "0.140.12"
 
 from starlette import status as status
 

fastapi/_compat/shared.py

@@ -63,6 +63,10 @@ def _annotation_is_sequence(annotation: type[Any] | None) -> bool:
 
 def field_annotation_is_sequence(annotation: type[Any] | None) -> bool:
     origin = get_origin(annotation)
+
+    if origin is Annotated:
+        return field_annotation_is_sequence(get_args(annotation)[0])
+
     if origin is Union or origin is UnionType:
         for arg in get_args(annotation):
             if field_annotation_is_sequence(arg):
@@ -108,6 +112,10 @@ def field_annotation_is_scalar(annotation: Any) -> bool:
 
 def field_annotation_is_scalar_sequence(annotation: type[Any] | None) -> bool:
     origin = get_origin(annotation)
+
+    if origin is Annotated:
+        return field_annotation_is_scalar_sequence(get_args(annotation)[0])
+
     if origin is Union or origin is UnionType:
         at_least_one_scalar_sequence = False
         for arg in get_args(annotation):

fastapi/dependencies/models.py

@@ -134,10 +134,6 @@ def _get_security_scheme(*, dependant: Dependant) -> SecurityBase:
     return unwrapped
 
 
-def _get_security_dependencies(*, dependant: Dependant) -> list[Dependant]:
-    return [dep for dep in dependant.dependencies if _is_security_scheme(dependant=dep)]
-
-
 @lru_cache(maxsize=_CALLABLE_CLASSIFICATION_CACHE_SIZE)
 def _is_gen_callable_cached(call_identity: _CallIdentity) -> bool:
     call = call_identity.call

fastapi/dependencies/utils.py

@@ -144,74 +144,14 @@ def get_parameterless_sub_dependant(*, depends: params.Depends, path: str) -> De
     )
 
 
-def get_flat_dependant(
-    dependant: Dependant,
-    *,
-    skip_repeats: bool = False,
-    visited: list[DependencyCacheKey] | None = None,
-    parent_oauth_scopes: list[str] | None = None,
-    _uses_scopes_cache: _UsesScopesCache | None = None,
-) -> Dependant:
-    if visited is None:
-        visited = []
-    if _uses_scopes_cache is None:
-        _uses_scopes_cache = {}
-    visited.append(
-        _get_cache_key(
-            dependant=dependant,
-            uses_scopes_cache=_uses_scopes_cache,
-        )
-    )
-    use_parent_oauth_scopes = (parent_oauth_scopes or []) + (
-        _get_oauth_scopes(dependant=dependant)
-    )
-
-    flat_dependant = Dependant(
-        path_params=dependant.path_params.copy(),
-        query_params=dependant.query_params.copy(),
-        header_params=dependant.header_params.copy(),
-        cookie_params=dependant.cookie_params.copy(),
-        body_params=dependant.body_params.copy(),
-        name=dependant.name,
-        call=dependant.call,
-        request_param_name=dependant.request_param_name,
-        websocket_param_name=dependant.websocket_param_name,
-        http_connection_param_name=dependant.http_connection_param_name,
-        response_param_name=dependant.response_param_name,
-        background_tasks_param_name=dependant.background_tasks_param_name,
-        security_scopes_param_name=dependant.security_scopes_param_name,
-        own_oauth_scopes=dependant.own_oauth_scopes,
-        parent_oauth_scopes=use_parent_oauth_scopes,
-        use_cache=dependant.use_cache,
-        path=dependant.path,
-        scope=dependant.scope,
-    )
-    for sub_dependant in dependant.dependencies:
-        if (
-            skip_repeats
-            and _get_cache_key(
-                dependant=sub_dependant,
-                uses_scopes_cache=_uses_scopes_cache,
-            )
-            in visited
-        ):
-            continue
-        flat_sub = get_flat_dependant(
-            sub_dependant,
-            skip_repeats=skip_repeats,
-            visited=visited,
-            parent_oauth_scopes=_get_oauth_scopes(dependant=flat_dependant),
-            _uses_scopes_cache=_uses_scopes_cache,
-        )
-        flat_dependant.dependencies.append(flat_sub)
-        flat_dependant.path_params.extend(flat_sub.path_params)
-        flat_dependant.query_params.extend(flat_sub.query_params)
-        flat_dependant.header_params.extend(flat_sub.header_params)
-        flat_dependant.cookie_params.extend(flat_sub.cookie_params)
-        flat_dependant.body_params.extend(flat_sub.body_params)
-        flat_dependant.dependencies.extend(flat_sub.dependencies)
-
-    return flat_dependant
+def _get_flat_body_params(dependant: Dependant) -> list[ModelField]:
+    body_params: list[ModelField] = []
+    dependants = [dependant]
+    while dependants:
+        current_dependant = dependants.pop()
+        body_params.extend(current_dependant.body_params)
+        dependants.extend(reversed(current_dependant.dependencies))
+    return body_params
 
 
 def _get_flat_fields_from_params(fields: list[ModelField]) -> list[ModelField]:
@@ -227,11 +167,31 @@ def _get_flat_fields_from_params(fields: list[ModelField]) -> list[ModelField]:
 
 
 def get_flat_params(dependant: Dependant) -> list[ModelField]:
-    flat_dependant = get_flat_dependant(dependant, skip_repeats=True)
-    path_params = _get_flat_fields_from_params(flat_dependant.path_params)
-    query_params = _get_flat_fields_from_params(flat_dependant.query_params)
-    header_params = _get_flat_fields_from_params(flat_dependant.header_params)
-    cookie_params = _get_flat_fields_from_params(flat_dependant.cookie_params)
+    path_params: list[ModelField] = []
+    query_params: list[ModelField] = []
+    header_params: list[ModelField] = []
+    cookie_params: list[ModelField] = []
+    visited: list[DependencyCacheKey] = []
+    uses_scopes_cache: _UsesScopesCache = {}
+    dependants = [dependant]
+    while dependants:
+        current_dependant = dependants.pop()
+        cache_key = _get_cache_key(
+            dependant=current_dependant,
+            uses_scopes_cache=uses_scopes_cache,
+        )
+        if cache_key in visited:
+            continue
+        visited.append(cache_key)
+        path_params.extend(current_dependant.path_params)
+        query_params.extend(current_dependant.query_params)
+        header_params.extend(current_dependant.header_params)
+        cookie_params.extend(current_dependant.cookie_params)
+        dependants.extend(reversed(current_dependant.dependencies))
+    path_params = _get_flat_fields_from_params(path_params)
+    query_params = _get_flat_fields_from_params(query_params)
+    header_params = _get_flat_fields_from_params(header_params)
+    cookie_params = _get_flat_fields_from_params(cookie_params)
     return path_params + query_params + header_params + cookie_params
 
 
@@ -1038,8 +998,8 @@ async def request_body_to_args(
     return values, errors
 
 
-def get_body_field(
-    *, flat_dependant: Dependant, name: str, embed_body_fields: bool
+def _get_body_field(
+    *, body_params: list[ModelField], name: str, embed_body_fields: bool
 ) -> ModelField | None:
     """
     Get a ModelField representing the request body for a path operation, combining
@@ -1051,34 +1011,30 @@ def get_body_field(
     This is **not** used to validate/parse the request body, that's done with each
     individual body parameter.
     """
-    if not flat_dependant.body_params:
+    if not body_params:
         return None
-    first_param = flat_dependant.body_params[0]
+    first_param = body_params[0]
     if not embed_body_fields:
         return first_param
     model_name = "Body_" + name
-    BodyModel = create_body_model(
-        fields=flat_dependant.body_params, model_name=model_name
-    )
-    required = any(
-        True for f in flat_dependant.body_params if f.field_info.is_required()
-    )
+    BodyModel = create_body_model(fields=body_params, model_name=model_name)
+    required = any(True for f in body_params if f.field_info.is_required())
     BodyFieldInfo_kwargs: dict[str, Any] = {
         "annotation": BodyModel,
         "alias": "body",
     }
     if not required:
         BodyFieldInfo_kwargs["default"] = None
-    if any(isinstance(f.field_info, params.File) for f in flat_dependant.body_params):
+    if any(isinstance(f.field_info, params.File) for f in body_params):
         BodyFieldInfo: type[params.Body] = params.File
-    elif any(isinstance(f.field_info, params.Form) for f in flat_dependant.body_params):
+    elif any(isinstance(f.field_info, params.Form) for f in body_params):
         BodyFieldInfo = params.Form
     else:
         BodyFieldInfo = params.Body
 
         body_param_media_types = [
             f.field_info.media_type
-            for f in flat_dependant.body_params
+            for f in body_params
             if isinstance(f.field_info, params.Body)
         ]
         if len(set(body_param_media_types)) == 1:

fastapi/encoders.py

@@ -299,6 +299,7 @@ def jsonable_encoder(
                     key,
                     by_alias=by_alias,
                     exclude_unset=exclude_unset,
+                    exclude_defaults=exclude_defaults,
                     exclude_none=exclude_none,
                     custom_encoder=custom_encoder,
                     sqlalchemy_safe=sqlalchemy_safe,
@@ -307,6 +308,7 @@ def jsonable_encoder(
                     value,
                     by_alias=by_alias,
                     exclude_unset=exclude_unset,
+                    exclude_defaults=exclude_defaults,
                     exclude_none=exclude_none,
                     custom_encoder=custom_encoder,
                     sqlalchemy_safe=sqlalchemy_safe,

fastapi/openapi/utils.py

@@ -3,6 +3,7 @@ import http.client
 import inspect
 import warnings
 from collections.abc import Sequence
+from dataclasses import dataclass, field
 from typing import Any, Literal, cast
 
 from fastapi import routing
@@ -17,13 +18,14 @@ from fastapi._compat import (
 from fastapi.datastructures import DefaultPlaceholder, _Unset
 from fastapi.dependencies.models import (
     Dependant,
+    _get_cache_key,
     _get_oauth_scopes,
-    _get_security_dependencies,
     _get_security_scheme,
+    _is_security_scheme,
+    _UsesScopesCache,
 )
 from fastapi.dependencies.utils import (
     _get_flat_fields_from_params,
-    get_flat_dependant,
     get_flat_params,
     get_validation_alias,
 )
@@ -34,7 +36,7 @@ from fastapi.openapi.models import OpenAPI
 from fastapi.params import Body, ParamTypes
 from fastapi.responses import Response
 from fastapi.sse import _SSE_EVENT_SCHEMA
-from fastapi.types import ModelNameMap
+from fastapi.types import DependencyCacheKey, ModelNameMap
 from fastapi.utils import (
     deep_dict_update,
     generate_operation_id_for_path,
@@ -83,13 +85,57 @@ status_code_ranges: dict[str, str] = {
 }
 
 
-def get_openapi_security_definitions(
-    flat_dependant: Dependant,
+@dataclass
+class _OpenAPIDependencyData:
+    path_params: list[ModelField] = field(default_factory=list)
+    query_params: list[ModelField] = field(default_factory=list)
+    header_params: list[ModelField] = field(default_factory=list)
+    cookie_params: list[ModelField] = field(default_factory=list)
+    security_dependencies: list[tuple[Dependant, list[str]]] = field(
+        default_factory=list
+    )
+
+
+def _get_openapi_dependency_data(dependant: Dependant) -> _OpenAPIDependencyData:
+    dependency_data = _OpenAPIDependencyData()
+    visited: list[DependencyCacheKey] = []
+    uses_scopes_cache: _UsesScopesCache = {}
+    dependants: list[tuple[Dependant, list[str], bool]] = [(dependant, [], True)]
+    while dependants:
+        current_dependant, parent_oauth_scopes, is_root = dependants.pop()
+        cache_key = _get_cache_key(
+            dependant=current_dependant,
+            uses_scopes_cache=uses_scopes_cache,
+        )
+        if cache_key in visited:
+            continue
+        visited.append(cache_key)
+        dependency_data.path_params.extend(current_dependant.path_params)
+        dependency_data.query_params.extend(current_dependant.query_params)
+        dependency_data.header_params.extend(current_dependant.header_params)
+        dependency_data.cookie_params.extend(current_dependant.cookie_params)
+        oauth_scopes = parent_oauth_scopes.copy()
+        for scope in _get_oauth_scopes(dependant=current_dependant):
+            if scope not in oauth_scopes:
+                oauth_scopes.append(scope)
+        if not is_root and _is_security_scheme(dependant=current_dependant):
+            dependency_data.security_dependencies.append(
+                (current_dependant, oauth_scopes)
+            )
+        dependants.extend(
+            (sub_dependant, oauth_scopes, False)
+            for sub_dependant in reversed(current_dependant.dependencies)
+        )
+    return dependency_data
+
+
+def _get_openapi_security_definitions(
+    security_dependencies: list[tuple[Dependant, list[str]]],
 ) -> tuple[dict[str, Any], list[dict[str, Any]]]:
     security_definitions = {}
     # Use a dict to merge scopes for same security scheme
     operation_security_dict: dict[str, list[str]] = {}
-    for security_dependency in _get_security_dependencies(dependant=flat_dependant):
+    for security_dependency, oauth_scopes in security_dependencies:
         security_scheme = _get_security_scheme(dependant=security_dependency)
         security_definition = jsonable_encoder(
             security_scheme.model,
@@ -101,7 +147,7 @@ def get_openapi_security_definitions(
         # Merge scopes for the same security scheme
         if security_name not in operation_security_dict:
             operation_security_dict[security_name] = []
-        for scope in _get_oauth_scopes(dependant=security_dependency):
+        for scope in oauth_scopes:
             if scope not in operation_security_dict[security_name]:
                 operation_security_dict[security_name].append(scope)
     operation_security = [
@@ -112,7 +158,7 @@ def get_openapi_security_definitions(
 
 def _get_openapi_operation_parameters(
     *,
-    dependant: Dependant,
+    dependency_data: _OpenAPIDependencyData,
     model_name_map: ModelNameMap,
     field_mapping: dict[
         tuple[ModelField, Literal["validation", "serialization"]], dict[str, Any]
@@ -120,11 +166,10 @@ def _get_openapi_operation_parameters(
     separate_input_output_schemas: bool = True,
 ) -> list[dict[str, Any]]:
     parameters = []
-    flat_dependant = get_flat_dependant(dependant, skip_repeats=True)
-    path_params = _get_flat_fields_from_params(flat_dependant.path_params)
-    query_params = _get_flat_fields_from_params(flat_dependant.query_params)
-    header_params = _get_flat_fields_from_params(flat_dependant.header_params)
-    cookie_params = _get_flat_fields_from_params(flat_dependant.cookie_params)
+    path_params = _get_flat_fields_from_params(dependency_data.path_params)
+    query_params = _get_flat_fields_from_params(dependency_data.query_params)
+    header_params = _get_flat_fields_from_params(dependency_data.header_params)
+    cookie_params = _get_flat_fields_from_params(dependency_data.cookie_params)
     parameter_groups = [
         (ParamTypes.path, path_params),
         (ParamTypes.query, query_params),
@@ -132,8 +177,8 @@ def _get_openapi_operation_parameters(
         (ParamTypes.cookie, cookie_params),
     ]
     default_convert_underscores = True
-    if len(flat_dependant.header_params) == 1:
-        first_field = flat_dependant.header_params[0]
+    if len(dependency_data.header_params) == 1:
+        first_field = dependency_data.header_params[0]
         if lenient_issubclass(first_field.field_info.annotation, BaseModel):
             default_convert_underscores = getattr(
                 first_field.field_info, "convert_underscores", True
@@ -284,21 +329,33 @@ def get_openapi_path(
     assert current_response_class, "A response class is needed to generate OpenAPI"
     route_response_media_type: str | None = current_response_class.media_type
     if route.include_in_schema:
+        dependency_data = _get_openapi_dependency_data(route.dependant)
+        all_route_params = [
+            field
+            for fields in (
+                dependency_data.path_params,
+                dependency_data.query_params,
+                dependency_data.header_params,
+                dependency_data.cookie_params,
+            )
+            for field in _get_flat_fields_from_params(fields)
+        ]
         for method in route.methods:
             operation = get_openapi_operation_metadata(
                 route=route, method=method, operation_ids=operation_ids
             )
             parameters: list[dict[str, Any]] = []
-            flat_dependant = get_flat_dependant(route.dependant, skip_repeats=True)
-            security_definitions, operation_security = get_openapi_security_definitions(
-                flat_dependant=flat_dependant
+            security_definitions, operation_security = (
+                _get_openapi_security_definitions(
+                    security_dependencies=dependency_data.security_dependencies
+                )
             )
             if operation_security:
                 operation.setdefault("security", []).extend(operation_security)
             if security_definitions:
                 security_schemes.update(security_definitions)
             operation_parameters = _get_openapi_operation_parameters(
-                dependant=route.dependant,
+                dependency_data=dependency_data,
                 model_name_map=model_name_map,
                 field_mapping=field_mapping,
                 separate_input_output_schemas=separate_input_output_schemas,
@@ -458,7 +515,6 @@ def get_openapi_path(
                     deep_dict_update(openapi_response, process_response)
                     openapi_response["description"] = description
             http422 = "422"
-            all_route_params = get_flat_params(route.dependant)
             if (all_route_params or route.body_field) and not any(
                 status in operation["responses"]
                 for status in [http422, "4XX", "default"]

fastapi/routing.py

@@ -55,10 +55,10 @@ from fastapi.dependencies.models import (
     _is_gen_callable,
 )
 from fastapi.dependencies.utils import (
+    _get_body_field,
+    _get_flat_body_params,
     _should_embed_body_fields,
-    get_body_field,
     get_dependant,
-    get_flat_dependant,
     get_parameterless_sub_dependant,
     get_stream_item_type,
     get_typed_return_annotation,
@@ -849,16 +849,16 @@ def _build_dependant_with_parameterless_dependencies(
     path: str,
     call: Callable[..., Any],
     dependencies: Sequence[params.Depends],
-) -> tuple[Dependant, Dependant, bool]:
+) -> tuple[Dependant, list[ModelField], bool]:
     dependant = get_dependant(path=path, call=call, scope="function")
     for depends in dependencies[::-1]:
         dependant.dependencies.insert(
             0,
             get_parameterless_sub_dependant(depends=depends, path=path),
         )
-    flat_dependant = get_flat_dependant(dependant)
-    embed_body_fields = _should_embed_body_fields(flat_dependant.body_params)
-    return dependant, flat_dependant, embed_body_fields
+    body_params = _get_flat_body_params(dependant)
+    embed_body_fields = _should_embed_body_fields(body_params)
+    return dependant, body_params, embed_body_fields
 
 
 class _RouteWithPath(Protocol):
@@ -982,32 +982,11 @@ def _populate_api_route_state(
         generate_unique_id
     ),
     strict_content_type: bool | DefaultPlaceholder = Default(True),
+    stream_item_type: Any | None = None,
 ) -> None:
     route.path = path
     route.endpoint = endpoint
-    route.stream_item_type = None
-    if isinstance(response_model, DefaultPlaceholder):
-        return_annotation = get_typed_return_annotation(endpoint)
-        if lenient_issubclass(return_annotation, Response):
-            response_model = None
-        else:
-            stream_item = get_stream_item_type(return_annotation)
-            if stream_item is not None:
-                # Extract item type for JSONL or SSE streaming when
-                # response_class is DefaultPlaceholder (JSONL) or
-                # EventSourceResponse (SSE).
-                # ServerSentEvent is excluded: it's a transport
-                # wrapper, not a data model, so it shouldn't feed
-                # into validation or OpenAPI schema generation.
-                if (
-                    isinstance(response_class, DefaultPlaceholder)
-                    or lenient_issubclass(response_class, EventSourceResponse)
-                ) and not lenient_issubclass(stream_item, ServerSentEvent):
-                    route.stream_item_type = stream_item
-                response_model = None
-            else:
-                response_model = return_annotation
-    route.response_model = response_model
+    route.stream_item_type = stream_item_type
     route.summary = summary
     route.response_description = response_description
     route.deprecated = deprecated
@@ -1043,27 +1022,6 @@ def _populate_api_route_state(
     if isinstance(status_code, IntEnum):
         status_code = int(status_code)
     route.status_code = status_code
-    if route.response_model:
-        assert is_body_allowed_for_status_code(status_code), (
-            f"Status code {status_code} must not have a response body"
-        )
-        response_name = "Response_" + route.unique_id
-        route.response_field = create_model_field(
-            name=response_name,
-            type_=route.response_model,
-            mode="serialization",
-        )
-    else:
-        route.response_field = None
-    if route.stream_item_type:
-        stream_item_name = "StreamItem_" + route.unique_id
-        route.stream_item_field = create_model_field(
-            name=stream_item_name,
-            type_=route.stream_item_type,
-            mode="serialization",
-        )
-    else:
-        route.stream_item_field = None
     route.dependencies = list(dependencies or [])
     route.description = description or inspect.cleandoc(route.endpoint.__doc__ or "")
     # if a "form feed" character (page break) is found in the description text,
@@ -1090,15 +1048,15 @@ def _populate_api_route_state(
     assert callable(endpoint), "An endpoint must be a callable"
     (
         route.dependant,
-        flat_dependant,
+        body_params,
         route._embed_body_fields,
     ) = _build_dependant_with_parameterless_dependencies(
         path=route.path_format,
         call=route.endpoint,
         dependencies=route.dependencies,
     )
-    route.body_field = get_body_field(
-        flat_dependant=flat_dependant,
+    route.body_field = _get_body_field(
+        body_params=body_params,
         name=route.unique_id,
         embed_body_fields=route._embed_body_fields,
     )
@@ -1112,6 +1070,49 @@ def _populate_api_route_state(
     route.is_json_stream = is_generator and isinstance(
         response_class, DefaultPlaceholder
     )
+    if isinstance(response_model, DefaultPlaceholder):
+        return_annotation = get_typed_return_annotation(endpoint)
+        if lenient_issubclass(return_annotation, Response):
+            response_model = None
+        else:
+            stream_item = get_stream_item_type(return_annotation)
+            if stream_item is not None and is_generator:
+                # Extract item type for JSONL or SSE streaming for
+                # generator endpoints when response_class is
+                # DefaultPlaceholder (JSONL) or EventSourceResponse (SSE).
+                # ServerSentEvent is excluded: it's a transport
+                # wrapper, not a data model, so it shouldn't feed
+                # into validation or OpenAPI schema generation.
+                if (
+                    isinstance(response_class, DefaultPlaceholder)
+                    or lenient_issubclass(response_class, EventSourceResponse)
+                ) and not lenient_issubclass(stream_item, ServerSentEvent):
+                    route.stream_item_type = stream_item
+                response_model = None
+            else:
+                response_model = return_annotation
+    route.response_model = response_model
+    if route.response_model:
+        assert is_body_allowed_for_status_code(status_code), (
+            f"Status code {status_code} must not have a response body"
+        )
+        response_name = "Response_" + route.unique_id
+        route.response_field = create_model_field(
+            name=response_name,
+            type_=route.response_model,
+            mode="serialization",
+        )
+    else:
+        route.response_field = None
+    if route.stream_item_type:
+        stream_item_name = "StreamItem_" + route.unique_id
+        route.stream_item_field = create_model_field(
+            name=stream_item_name,
+            type_=route.stream_item_type,
+            mode="serialization",
+        )
+    else:
+        route.stream_item_field = None
 
 
 class APIRoute(routing.Route):
@@ -1464,6 +1465,7 @@ class _EffectiveRouteContext:
                 include_context.included_router.strict_content_type,
                 include_context.strict_content_type,
             ),
+            stream_item_type=route.stream_item_type,
         )
         return context
 

fastapi/sse.py

@@ -156,6 +156,12 @@ class ServerSentEvent(BaseModel):
         return self
 
 
+def _split_sse_lines(value: str) -> list[str]:
+    # Split on SSE-spec line terminators only (\n, \r\n, \r), preserving
+    # trailing empty strings.
+    return value.replace("\r\n", "\n").replace("\r", "\n").split("\n")
+
+
 def format_sse_event(
     *,
     data_str: Annotated[
@@ -206,14 +212,14 @@ def format_sse_event(
     lines: list[str] = []
 
     if comment is not None:
-        for line in comment.splitlines():
+        for line in _split_sse_lines(comment):
             lines.append(f": {line}")
 
     if event is not None:
         lines.append(f"event: {event}")
 
     if data_str is not None:
-        for line in data_str.splitlines():
+        for line in _split_sse_lines(data_str):
             lines.append(f"data: {line}")
 
     if id is not None:

tests/benchmarks/test_openapi.py

@@ -0,0 +1,33 @@
+import sys
+
+import pytest
+
+from tests.benchmarks.utils import (
+    ROUTE_COUNT,
+    ROUTE_PATH_PREFIX,
+    create_openapi_app,
+    generate_openapi,
+)
+
+if "--codspeed" not in sys.argv:
+    pytest.skip(
+        "Benchmark tests are skipped by default; run with --codspeed.",
+        allow_module_level=True,
+    )
+
+
+@pytest.mark.timeout(60)
+def test_openapi_dependency_graph(benchmark) -> None:
+    app = create_openapi_app()
+    schema = benchmark(generate_openapi, app)
+    dynamic_paths = [
+        path for path in schema["paths"] if path.startswith(ROUTE_PATH_PREFIX)
+    ]
+    assert len(dynamic_paths) == ROUTE_COUNT
+    assert all(
+        any(
+            parameter["in"] == "query" and parameter["name"] == "query_value"
+            for parameter in schema["paths"][path]["get"]["parameters"]
+        )
+        for path in dynamic_paths
+    )

tests/benchmarks/utils.py

@@ -0,0 +1,51 @@
+from collections.abc import Callable
+from typing import Annotated, Any
+
+from fastapi import Depends, FastAPI
+
+LAST_DEPENDENCY_INDEX = 100
+ROUTE_COUNT = 20
+ROUTE_PATH_PREFIX = "/openapi-route-"
+
+
+def create_openapi_app() -> FastAPI:
+    app = FastAPI()
+    dependencies: dict[int, Callable[..., Any]] = {}
+
+    def create_dependency(index: int) -> Callable[..., Any]:
+        if index == LAST_DEPENDENCY_INDEX:
+
+            def dependency(query_value: int = index) -> str:
+                return str(query_value)
+
+            dependency.__name__ = f"dependency_{index}"
+            return dependency
+
+        next_dependency = dependencies[index + 1]
+
+        async def dependency(
+            sub_dependency: Annotated[str, Depends(next_dependency)],
+            query_value: int = index,
+        ) -> str:
+            return f"{query_value} -> {sub_dependency}"
+
+        dependency.__name__ = f"dependency_{index}"
+        return dependency
+
+    for index in reversed(range(LAST_DEPENDENCY_INDEX + 1)):
+        dependencies[index] = create_dependency(index)
+
+    async def endpoint(
+        value: Annotated[str, Depends(dependencies[0])],
+    ) -> dict[str, str]:
+        return {"value": value}
+
+    for index in range(ROUTE_COUNT):
+        app.add_api_route(f"{ROUTE_PATH_PREFIX}{index}", endpoint, methods=["GET"])
+
+    return app
+
+
+def generate_openapi(app: FastAPI) -> dict[str, Any]:
+    app.openapi_schema = None
+    return app.openapi()

tests/memory_benchmarks/test_openapi.py

@@ -0,0 +1,33 @@
+import sys
+
+import pytest
+
+from tests.benchmarks.utils import (
+    ROUTE_COUNT,
+    ROUTE_PATH_PREFIX,
+    create_openapi_app,
+    generate_openapi,
+)
+
+if "--codspeed" not in sys.argv:
+    pytest.skip(
+        "Benchmark tests are skipped by default; run with --codspeed.",
+        allow_module_level=True,
+    )
+
+
+@pytest.mark.timeout(60)
+def test_openapi_dependency_graph(benchmark) -> None:
+    app = create_openapi_app()
+    schema = benchmark(generate_openapi, app)
+    dynamic_paths = [
+        path for path in schema["paths"] if path.startswith(ROUTE_PATH_PREFIX)
+    ]
+    assert len(dynamic_paths) == ROUTE_COUNT
+    assert all(
+        any(
+            parameter["in"] == "query" and parameter["name"] == "query_value"
+            for parameter in schema["paths"][path]["get"]["parameters"]
+        )
+        for path in dynamic_paths
+    )

tests/test_dependency_models.py

@@ -6,7 +6,6 @@ from fastapi.dependencies.models import (
     _get_cache_key,
     _get_computed_scope,
     _get_oauth_scopes,
-    _get_security_dependencies,
     _get_security_scheme,
     _is_async_gen_callable,
     _is_async_gen_callable_cached,
@@ -146,7 +145,6 @@ def test_derived_values_are_not_stored_on_dependant() -> None:
     assert _get_oauth_scopes(dependant=dependant) == []
     assert not _uses_scopes(dependant=dependant, cache=uses_scopes_cache)
     assert not _uses_scopes(dependant=dependant, cache=uses_scopes_cache)
-    assert _get_security_dependencies(dependant=dependant) == []
     assert _get_computed_scope(dependant=dependant) is None
     assert _get_cache_key(dependant=dependant) == (async_dependency, (), "")
 
@@ -160,7 +158,6 @@ def test_security_scheme_helpers() -> None:
 
     assert _is_security_scheme(dependant=security_dependant)
     assert _get_security_scheme(dependant=security_dependant) is security_scheme
-    assert _get_security_dependencies(dependant=dependant) == [security_dependant]
     assert _uses_scopes(dependant=dependant)
 
 

tests/test_jsonable_encoder.py

@@ -202,6 +202,20 @@ def test_encode_model_with_default():
     }
 
 
+def test_encode_model_with_default_in_dict_and_list():
+    model = ModelWithDefault(foo="foo", bar="bar")
+    assert jsonable_encoder([model], exclude_defaults=True) == [{"foo": "foo"}]
+    assert jsonable_encoder({"key": model}, exclude_defaults=True) == {
+        "key": {"foo": "foo"}
+    }
+    assert jsonable_encoder({"key": [model]}, exclude_defaults=True) == {
+        "key": [{"foo": "foo"}]
+    }
+    assert jsonable_encoder({"key": model}) == {
+        "key": {"foo": "foo", "bar": "bar", "bla": "bla"}
+    }
+
+
 def test_custom_encoders():
     class safe_datetime(datetime):
         pass

tests/test_nested_annotated_in_sequence.py

@@ -0,0 +1,143 @@
+from typing import Annotated
+
+from dirty_equals import IsList
+from fastapi import FastAPI, Query
+from fastapi.testclient import TestClient
+from inline_snapshot import snapshot
+from pydantic import Field
+
+MaxSizedSet = Annotated[set[str], Field(max_length=3)]
+
+app = FastAPI()
+
+
+@app.get("/")
+def read_root(foo: Annotated[MaxSizedSet | None, Query()] = None):
+    return {"foo": foo}
+
+
+client = TestClient(app)
+
+
+def test_endpoint_none():
+    response = client.get("/")
+    assert response.status_code == 200
+    assert response.json() == {"foo": None}
+
+
+def test_endpoint_valid():
+    response = client.get("/", params={"foo": ["a", "b"]})
+    assert response.status_code == 200
+    assert response.json() == {"foo": IsList("a", "b", check_order=False)}
+
+
+def test_endpoint_too_long():
+    response = client.get("/", params={"foo": ["a", "b", "c", "d"]})
+    assert response.status_code == 422
+    assert response.json() == snapshot(
+        {
+            "detail": [
+                {
+                    "type": "too_long",
+                    "loc": ["query", "foo"],
+                    "msg": "Set should have at most 3 items after validation, not more",
+                    "input": IsList("a", "b", "c", "d", check_order=False),
+                    "ctx": {
+                        "actual_length": None,
+                        "field_type": "Set",
+                        "max_length": 3,
+                    },
+                }
+            ]
+        }
+    )
+
+
+def test_openapi():
+    assert app.openapi() == snapshot(
+        {
+            "components": {
+                "schemas": {
+                    "HTTPValidationError": {
+                        "properties": {
+                            "detail": {
+                                "items": {
+                                    "$ref": "#/components/schemas/ValidationError"
+                                },
+                                "title": "Detail",
+                                "type": "array",
+                            },
+                        },
+                        "title": "HTTPValidationError",
+                        "type": "object",
+                    },
+                    "ValidationError": {
+                        "properties": {
+                            "ctx": {"title": "Context", "type": "object"},
+                            "input": {"title": "Input"},
+                            "loc": {
+                                "items": {
+                                    "anyOf": [{"type": "string"}, {"type": "integer"}],
+                                },
+                                "title": "Location",
+                                "type": "array",
+                            },
+                            "msg": {"title": "Message", "type": "string"},
+                            "type": {"title": "Error Type", "type": "string"},
+                        },
+                        "required": ["loc", "msg", "type"],
+                        "title": "ValidationError",
+                        "type": "object",
+                    },
+                },
+            },
+            "info": {
+                "title": "FastAPI",
+                "version": "0.1.0",
+            },
+            "openapi": "3.1.0",
+            "paths": {
+                "/": {
+                    "get": {
+                        "operationId": "read_root__get",
+                        "parameters": [
+                            {
+                                "in": "query",
+                                "name": "foo",
+                                "required": False,
+                                "schema": {
+                                    "anyOf": [
+                                        {
+                                            "items": {"type": "string"},
+                                            "maxItems": 3,
+                                            "type": "array",
+                                            "uniqueItems": True,
+                                        },
+                                        {"type": "null"},
+                                    ],
+                                    "title": "Foo",
+                                },
+                            },
+                        ],
+                        "responses": {
+                            "200": {
+                                "content": {"application/json": {"schema": {}}},
+                                "description": "Successful Response",
+                            },
+                            "422": {
+                                "content": {
+                                    "application/json": {
+                                        "schema": {
+                                            "$ref": "#/components/schemas/HTTPValidationError",
+                                        },
+                                    },
+                                },
+                                "description": "Validation Error",
+                            },
+                        },
+                        "summary": "Read Root",
+                    },
+                },
+            },
+        }
+    )

tests/test_skip_defaults.py

@@ -1,3 +1,5 @@
+from collections.abc import Iterable
+
 from fastapi import FastAPI
 from fastapi.testclient import TestClient
 from pydantic import BaseModel
@@ -65,6 +67,21 @@ def get_exclude_unset_none() -> ModelDefaults:
     return ModelDefaults(x=None, y="y")
 
 
+@app.get("/iterable_exclude_unset", response_model_exclude_unset=True)
+def get_iterable_exclude_unset() -> Iterable[ModelDefaults]:
+    return [ModelDefaults(x=None, y="y")]
+
+
+@app.get("/iterable_exclude_defaults", response_model_exclude_defaults=True)
+def get_iterable_exclude_defaults() -> Iterable[ModelDefaults]:
+    return [ModelDefaults(x=None, y="y")]
+
+
+@app.get("/iterable_exclude_none", response_model_exclude_none=True)
+def get_iterable_exclude_none() -> Iterable[ModelDefaults]:
+    return [ModelDefaults(x=None, y="y")]
+
+
 client = TestClient(app)
 
 
@@ -91,3 +108,18 @@ def test_return_exclude_none():
 def test_return_exclude_unset_none():
     response = client.get("/exclude_unset_none")
     assert response.json() == {"y": "y"}
+
+
+def test_return_iterable_exclude_unset():
+    response = client.get("/iterable_exclude_unset")
+    assert response.json() == [{"x": None, "y": "y"}]
+
+
+def test_return_iterable_exclude_defaults():
+    response = client.get("/iterable_exclude_defaults")
+    assert response.json() == [{}]
+
+
+def test_return_iterable_exclude_none():
+    response = client.get("/iterable_exclude_none")
+    assert response.json() == [{"y": "y", "z": "z"}]

tests/test_sse.py

@@ -6,7 +6,7 @@ import fastapi.routing
 import pytest
 from fastapi import APIRouter, FastAPI
 from fastapi.responses import EventSourceResponse
-from fastapi.sse import ServerSentEvent
+from fastapi.sse import ServerSentEvent, format_sse_event
 from fastapi.testclient import TestClient
 from pydantic import BaseModel
 
@@ -64,7 +64,8 @@ async def sse_items_event():
 
 @app.get("/items/stream-mixed", response_class=EventSourceResponse)
 async def sse_items_mixed() -> AsyncIterable[Item]:
-    yield items[0]
+    for item in items:
+        yield item
     yield ServerSentEvent(data="custom-event", event="special")
     yield items[1]
 
@@ -96,6 +97,12 @@ async def stream_events():
     yield {"msg": "world"}
 
 
+@router.get("/events-typed", response_class=EventSourceResponse)
+async def stream_events_typed() -> AsyncIterable[Item]:
+    for item in items:
+        yield item
+
+
 app.include_router(router, prefix="/api")
 
 
@@ -274,6 +281,45 @@ def test_sse_on_router_included_in_app(client: TestClient):
     assert len(data_lines) == 2
 
 
+def test_sse_router_typed_stream(client: TestClient):
+    response = client.get("/api/events-typed")
+    assert response.status_code == 200
+    assert response.headers["content-type"] == "text/event-stream; charset=utf-8"
+    data_lines = [
+        line for line in response.text.strip().split("\n") if line.startswith("data: ")
+    ]
+    assert len(data_lines) == 3
+
+
+def test_sse_router_typed_openapi_schema(client: TestClient):
+    """Typed SSE endpoint on a router should preserve itemSchema with contentSchema."""
+    response = client.get("/openapi.json")
+    assert response.status_code == 200
+    paths = response.json()["paths"]
+    sse_response = paths["/api/events-typed"]["get"]["responses"]["200"]
+    assert sse_response == {
+        "description": "Successful Response",
+        "content": {
+            "text/event-stream": {
+                "itemSchema": {
+                    "type": "object",
+                    "properties": {
+                        "data": {
+                            "type": "string",
+                            "contentMediaType": "application/json",
+                            "contentSchema": {"$ref": "#/components/schemas/Item"},
+                        },
+                        "event": {"type": "string"},
+                        "id": {"type": "string"},
+                        "retry": {"type": "integer", "minimum": 0},
+                    },
+                    "required": ["data"],
+                }
+            }
+        },
+    }
+
+
 # Keepalive ping tests
 
 
@@ -325,3 +371,120 @@ def test_no_keepalive_when_fast(client: TestClient):
     assert response.status_code == 200
     # KEEPALIVE_COMMENT is ": ping\n\n".
     assert ": ping\n" not in response.text
+
+
+@pytest.mark.parametrize(
+    ("data", "expected_result"),
+    [
+        ("Hello\n", b"data: Hello\ndata: \n\n"),
+        ("Hello\n\n", b"data: Hello\ndata: \ndata: \n\n"),
+        ("\n", b"data: \ndata: \n\n"),
+        ("Hello\r\nWorld", b"data: Hello\ndata: World\n\n"),
+        ("Hello\rWorld", b"data: Hello\ndata: World\n\n"),
+        ("A\u2028B", "data: A\u2028B\n\n".encode()),
+        ("A\vB", b"data: A\x0bB\n\n"),
+        ("", b"data: \n\n"),
+    ],
+)
+def test_format_sse_event_splitlines_behavior_in_data(
+    data: str, expected_result: bytes
+) -> None:
+    assert format_sse_event(data_str=data) == expected_result
+
+
+def test_format_sse_event_splitlines_behavior_in_comment():
+    assert format_sse_event(comment="hi\n") == b": hi\n: \n\n"
+
+
+# default_response_class tests
+
+
+sse_schema_response = {
+    "description": "Successful Response",
+    "content": {
+        "text/event-stream": {
+            "itemSchema": {
+                "type": "object",
+                "properties": {
+                    "data": {
+                        "type": "string",
+                        "contentMediaType": "application/json",
+                        "contentSchema": {"$ref": "#/components/schemas/Item"},
+                    },
+                    "event": {"type": "string"},
+                    "id": {"type": "string"},
+                    "retry": {"type": "integer", "minimum": 0},
+                },
+                "required": ["data"],
+            }
+        }
+    },
+}
+
+
+# default_response_class on app
+
+default_app_app = FastAPI(default_response_class=EventSourceResponse)
+default_app_router = APIRouter()
+
+
+@default_app_router.get("/stream")
+async def default_app_stream() -> AsyncIterable[Item]:
+    for item in items:
+        yield item
+
+
+default_app_app.include_router(default_app_router, prefix="/api")
+
+
+def test_default_response_class_on_app_stream():
+    with TestClient(default_app_app) as client:
+        response = client.get("/api/stream")
+    assert response.status_code == 200
+    assert response.headers["content-type"] == "text/event-stream; charset=utf-8"
+    data_lines = [
+        line for line in response.text.strip().split("\n") if line.startswith("data: ")
+    ]
+    assert len(data_lines) == 3
+
+
+def test_default_response_class_on_app_openapi_schema():
+    assert (
+        default_app_app.openapi()["paths"]["/api/stream"]["get"]["responses"]["200"]
+        == sse_schema_response
+    )
+
+
+# default_response_class on parent router
+
+default_parent_app = FastAPI()
+parent_router = APIRouter(default_response_class=EventSourceResponse)
+child_router = APIRouter()
+
+
+@child_router.get("/stream")
+async def default_parent_stream() -> AsyncIterable[Item]:
+    for item in items:
+        yield item
+
+
+parent_router.include_router(child_router)
+default_parent_app.include_router(parent_router, prefix="/api")
+
+
+def test_default_response_class_on_parent_router_stream():
+    with TestClient(default_parent_app) as client:
+        response = client.get("/api/stream")
+    assert response.status_code == 200
+    assert response.headers["content-type"] == "text/event-stream; charset=utf-8"
+    data_lines = [
+        line for line in response.text.strip().split("\n") if line.startswith("data: ")
+    ]
+    assert len(data_lines) == 3
+
+
+def test_default_response_class_on_parent_router_openapi_schema():
+    assert (
+        default_parent_app.openapi()["paths"]["/api/stream"]["get"]["responses"]["200"]
+        == sse_schema_response
+    )

tests/test_stream_bare_type.py

@@ -1,13 +1,14 @@
 import json
 from typing import AsyncIterable, Iterable  # noqa: UP035 to test coverage
 
-from fastapi import FastAPI
+from fastapi import APIRouter, FastAPI
 from fastapi.testclient import TestClient
 from pydantic import BaseModel
 
 
 class Item(BaseModel):
     name: str
+    optional: str | None = None
 
 
 app = FastAPI()
@@ -23,6 +24,16 @@ def stream_bare_sync() -> Iterable:
     yield {"name": "bar"}
 
 
+router = APIRouter()
+
+
+@router.get("/events-jsonl", response_model_exclude_none=True)
+async def stream_events_jsonl() -> AsyncIterable[Item]:
+    yield Item(name="foo")
+
+
+app.include_router(router, prefix="/api")
+
 client = TestClient(app)
 
 
@@ -40,3 +51,24 @@ def test_stream_bare_sync_iterable():
     assert response.headers["content-type"] == "application/jsonl"
     lines = [json.loads(line) for line in response.text.strip().splitlines()]
     assert lines == [{"name": "bar"}]
+
+
+def test_jsonl_router_typed_stream():
+    response = client.get("/api/events-jsonl")
+    assert response.status_code == 200
+    assert response.headers["content-type"] == "application/jsonl"
+    lines = [json.loads(line) for line in response.text.strip().splitlines()]
+    assert lines == [{"name": "foo"}]
+
+
+def test_jsonl_router_typed_openapi_schema():
+    response = client.get("/openapi.json")
+    assert response.status_code == 200
+    paths = response.json()["paths"]
+    jsonl_response = paths["/api/events-jsonl"]["get"]["responses"]["200"]
+    assert jsonl_response == {
+        "description": "Successful Response",
+        "content": {
+            "application/jsonl": {"itemSchema": {"$ref": "#/components/schemas/Item"}}
+        },
+    }

uv.lock

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+    { url = "https://files.pythonhosted.org/packages/d1/b9/876f442a28df5c068ca69b0122d5c35e65fd2d2fa9992ea5cb5944ea00a6/gitpython-3.1.54-py3-none-any.whl", hash = "sha256:b90d7b3d9bc0238681d24369130826f0dcdb0ceaa45db67cf1d4ffa4c302dedf", size = 216575, upload-time = "2026-07-22T04:08:50.05Z" },
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 [[package]]
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+version = "0.6.4"
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+    { url = "https://files.pythonhosted.org/packages/9a/3b/6163796d69c3977d1e4287bea4a6979161cbbdd170ebb430511e8e1999ce/pyasn1-0.6.4-py3-none-any.whl", hash = "sha256:deda9277cfd454080ec40b207fb6df82206a3a2688735233cdcd8d3d565f088b", size = 84410, upload-time = "2026-07-09T01:12:32.92Z" },
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 [[package]]
@@ -3166,15 +3166,15 @@ crypto = [
 
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+version = "11.0"
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+    { url = "https://files.pythonhosted.org/packages/af/b6/1ae53367e28b9cffa3be7574e13fbe4589694272fd47710fbdbafd3d63c6/pymdown_extensions-11.0-py3-none-any.whl", hash = "sha256:fbc4acb641814fa9d17521bbd21a5240ef739a662f11c06330c4b78c93e954d6", size = 269415, upload-time = "2026-06-23T02:27:43.826Z" },
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