release: 3.19.0 (#325)

* feat(internal): implement indices array format for query and form serialization

* STG-1537 default local-mode sessions to local browser

* release: 3.19.0

---------

Co-authored-by: stainless-app[bot] <142633134+stainless-app[bot]@users.noreply.github.com>
Co-authored-by: monadoid <sam.finton@gmail.com>
Co-authored-by: Sam F <43347795+monadoid@users.noreply.github.com>

Author: stainless-app[bot]

.release-please-manifest.json

@@ -1,3 +1,3 @@
 {
-  ".": "3.18.0"
+  ".": "3.19.0"
 }

CHANGELOG.md

@@ -1,5 +1,13 @@
 # Changelog
 
+## 3.19.0 (2026-03-27)
+
+Full Changelog: [v3.18.0...v3.19.0](https://github.com/browserbase/stagehand-python/compare/v3.18.0...v3.19.0)
+
+### Features
+
+* **internal:** implement indices array format for query and form serialization ([b2cccf5](https://github.com/browserbase/stagehand-python/commit/b2cccf56bc7e99d7869b8ed9339956a9f160348a))
+
 ## 3.18.0 (2026-03-25)
 
 Full Changelog: [v3.7.0...v3.18.0](https://github.com/browserbase/stagehand-python/compare/v3.7.0...v3.18.0)

pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "stagehand"
-version = "3.18.0"
+version = "3.19.0"
 description = "The official Python library for the stagehand API"
 dynamic = ["readme"]
 license = "MIT"

src/stagehand/_qs.py

@@ -101,7 +101,10 @@ def _stringify_item(
                     items.extend(self._stringify_item(key, item, opts))
                 return items
             elif array_format == "indices":
-                raise NotImplementedError("The array indices format is not supported yet")
+                items = []
+                for i, item in enumerate(value):
+                    items.extend(self._stringify_item(f"{key}[{i}]", item, opts))
+                return items
             elif array_format == "brackets":
                 items = []
                 key = key + "[]"

src/stagehand/_version.py

@@ -1,4 +1,4 @@
 # File generated from our OpenAPI spec by Stainless. See CONTRIBUTING.md for details.
 
 __title__ = "stagehand"
-__version__ = "3.18.0"  # x-release-please-version
+__version__ = "3.19.0"  # x-release-please-version

src/stagehand/resources/sessions_helpers.py

@@ -83,6 +83,9 @@ def start(
         extra_body: Body | None = None,
         timeout: float | httpx.Timeout | None | NotGiven = not_given,
     ) -> Session:
+        if browser is omit and getattr(self._client, "_server_mode", None) == "local":
+            browser = {"type": "local"}
+
         start_response = super().start(
             model_name=model_name,
             act_timeout_ms=act_timeout_ms,
@@ -136,6 +139,9 @@ async def start(
         extra_body: Body | None = None,
         timeout: float | httpx.Timeout | None | NotGiven = not_given,
     ) -> AsyncSession:
+        if browser is omit and getattr(self._client, "_server_mode", None) == "local":
+            browser = {"type": "local"}
+
         start_response: SessionStartResponse = await super().start(
             model_name=model_name,
             act_timeout_ms=act_timeout_ms,

tests/test_local_server.py

@@ -1,5 +1,7 @@
 from __future__ import annotations
 
+import json
+
 import httpx
 import pytest
 from respx import MockRouter
@@ -67,6 +69,45 @@ def test_sync_local_mode_starts_before_first_request(respx_mock: MockRouter, mon
     assert dummy.closed == 1
 
 
+@pytest.mark.respx(base_url="http://127.0.0.1:43127")
+def test_sync_local_mode_defaults_browser_type_local_when_omitted(
+    respx_mock: MockRouter, monkeypatch: pytest.MonkeyPatch
+) -> None:
+    _set_required_env(monkeypatch)
+
+    dummy = _DummySeaServer("http://127.0.0.1:43127")
+    request_body: dict[str, object] = {}
+
+    def _capture_start_request(request: httpx.Request) -> httpx.Response:
+        request_body["json"] = json.loads(request.content.decode("utf-8"))
+        return httpx.Response(
+            200,
+            json={
+                "success": True,
+                "data": {
+                    "available": True,
+                    "connectUrl": "ws://example",
+                    "sessionId": "00000000-0000-0000-0000-000000000001",
+                },
+            },
+        )
+
+    respx_mock.post("/v1/sessions/start").mock(side_effect=_capture_start_request)
+
+    client = Stagehand(server="local", _local_stagehand_binary_path="/does/not/matter/in/test")
+    client._sea_server = dummy  # type: ignore[attr-defined]
+
+    resp = client.sessions.start(model_name="openai/gpt-5-nano")
+    assert resp.success is True
+    assert request_body["json"] == {
+        "modelName": "openai/gpt-5-nano",
+        "browser": {"type": "local"},
+    }
+
+    client.close()
+    assert dummy.closed == 1
+
+
 @pytest.mark.respx(base_url="http://127.0.0.1:43124")
 @pytest.mark.asyncio
 async def test_async_local_mode_starts_before_first_request(