diff --git a/sdk/python/docs/api-reference.md b/sdk/python/docs/api-reference.md
index 46c76f92a8..6442daaf73 100644
--- a/sdk/python/docs/api-reference.md
+++ b/sdk/python/docs/api-reference.md
@@ -67,8 +67,8 @@ Properties/methods:
 - `logout() -> None`
 - `thread_start(*, approval_mode=ApprovalMode.auto_review, base_instructions=None, config=None, cwd=None, developer_instructions=None, ephemeral=None, model=None, model_provider=None, personality=None, sandbox: Sandbox | None = None) -> Thread`
 - `thread_list(*, archived=None, cursor=None, cwd=None, limit=None, model_providers=None, sort_key=None, source_kinds=None) -> ThreadListResponse`
-- `thread_resume(thread_id: str, *, approval_mode=ApprovalMode.auto_review, base_instructions=None, config=None, cwd=None, developer_instructions=None, model=None, model_provider=None, personality=None, sandbox: Sandbox | None = None) -> Thread`
-- `thread_fork(thread_id: str, *, approval_mode=ApprovalMode.auto_review, base_instructions=None, config=None, cwd=None, developer_instructions=None, model=None, model_provider=None, sandbox: Sandbox | None = None) -> Thread`
+- `thread_resume(thread_id: str, *, approval_mode=None, base_instructions=None, config=None, cwd=None, developer_instructions=None, include_turns: bool | None = None, model=None, model_provider=None, personality=None, sandbox: Sandbox | None = None, service_tier=None) -> Thread`
+- `thread_fork(thread_id: str, *, approval_mode=None, base_instructions=None, config=None, cwd=None, developer_instructions=None, ephemeral=None, include_turns: bool | None = None, model=None, model_provider=None, sandbox: Sandbox | None = None, service_tier=None) -> Thread`
 - `thread_archive(thread_id: str) -> ThreadArchiveResponse`
 - `thread_unarchive(thread_id: str) -> Thread`
 - `models(*, include_hidden: bool = False) -> ModelListResponse`
@@ -80,6 +80,13 @@ with Codex() as codex:
     ...
 ```
 
+`thread_resume(...)` and `thread_fork(...)` accept `include_turns` to control
+whether the server loads turn history into its response. `False` skips that
+work; `True` requests it. Omitting the option, or passing `None`, preserves the
+server's default behavior. This does not remove history from the model's
+context. Both methods return a thread handle; use `thread.read(include_turns=True)`
+to retrieve its history.
+
 ## AsyncCodex (async parity)
 
 ```python
@@ -107,8 +114,8 @@ Properties/methods:
 - `logout() -> Awaitable[None]`
 - `thread_start(*, approval_mode=ApprovalMode.auto_review, base_instructions=None, config=None, cwd=None, developer_instructions=None, ephemeral=None, model=None, model_provider=None, personality=None, sandbox: Sandbox | None = None) -> Awaitable[AsyncThread]`
 - `thread_list(*, archived=None, cursor=None, cwd=None, limit=None, model_providers=None, sort_key=None, source_kinds=None) -> Awaitable[ThreadListResponse]`
-- `thread_resume(thread_id: str, *, approval_mode=ApprovalMode.auto_review, base_instructions=None, config=None, cwd=None, developer_instructions=None, model=None, model_provider=None, personality=None, sandbox: Sandbox | None = None) -> Awaitable[AsyncThread]`
-- `thread_fork(thread_id: str, *, approval_mode=ApprovalMode.auto_review, base_instructions=None, config=None, cwd=None, developer_instructions=None, ephemeral=None, model=None, model_provider=None, sandbox: Sandbox | None = None) -> Awaitable[AsyncThread]`
+- `thread_resume(thread_id: str, *, approval_mode=None, base_instructions=None, config=None, cwd=None, developer_instructions=None, include_turns: bool | None = None, model=None, model_provider=None, personality=None, sandbox: Sandbox | None = None, service_tier=None) -> Awaitable[AsyncThread]`
+- `thread_fork(thread_id: str, *, approval_mode=None, base_instructions=None, config=None, cwd=None, developer_instructions=None, ephemeral=None, include_turns: bool | None = None, model=None, model_provider=None, sandbox: Sandbox | None = None, service_tier=None) -> Awaitable[AsyncThread]`
 - `thread_archive(thread_id: str) -> Awaitable[ThreadArchiveResponse]`
 - `thread_unarchive(thread_id: str) -> Awaitable[AsyncThread]`
 - `models(*, include_hidden: bool = False) -> Awaitable[ModelListResponse]`
@@ -150,23 +157,23 @@ attempt. API-key login completes synchronously and does not return a handle.
 
 ### Thread
 
-- `run(input: str | Input, *, approval_mode=None, cwd=None, effort=None, model=None, output_schema=None, personality=None, sandbox: Sandbox | None = None, service_tier=None, summary=None) -> TurnResult`
-- `turn(input: str | Input, *, approval_mode=None, cwd=None, effort=None, model=None, output_schema=None, personality=None, sandbox: Sandbox | None = None, service_tier=None, summary=None) -> TurnHandle`
+- `run(input: RunInput, *, approval_mode=None, cwd=None, effort=None, model=None, output_schema=None, personality=None, sandbox: Sandbox | None = None, service_tier=None, source=None, summary=None, turn_service_tier=None) -> TurnResult`
+- `turn(input: RunInput, *, approval_mode=None, cwd=None, effort=None, model=None, output_schema=None, personality=None, sandbox: Sandbox | None = None, service_tier=None, source=None, summary=None, turn_service_tier=None) -> TurnHandle`
 - `read(*, include_turns: bool = False) -> ThreadReadResponse`
 - `set_name(name: str) -> ThreadSetNameResponse`
 - `compact() -> ThreadCompactStartResponse`
 
 ### AsyncThread
 
-- `run(input: str | Input, *, approval_mode=None, cwd=None, effort=None, model=None, output_schema=None, personality=None, sandbox: Sandbox | None = None, service_tier=None, summary=None) -> Awaitable[TurnResult]`
-- `turn(input: str | Input, *, approval_mode=None, cwd=None, effort=None, model=None, output_schema=None, personality=None, sandbox: Sandbox | None = None, service_tier=None, summary=None) -> Awaitable[AsyncTurnHandle]`
+- `run(input: RunInput, *, approval_mode=None, cwd=None, effort=None, model=None, output_schema=None, personality=None, sandbox: Sandbox | None = None, service_tier=None, source=None, summary=None, turn_service_tier=None) -> Awaitable[TurnResult]`
+- `turn(input: RunInput, *, approval_mode=None, cwd=None, effort=None, model=None, output_schema=None, personality=None, sandbox: Sandbox | None = None, service_tier=None, source=None, summary=None, turn_service_tier=None) -> Awaitable[AsyncTurnHandle]`
 - `read(*, include_turns: bool = False) -> Awaitable[ThreadReadResponse]`
 - `set_name(name: str) -> Awaitable[ThreadSetNameResponse]`
 - `compact() -> Awaitable[ThreadCompactStartResponse]`
 
-`run(...)` is the common-case convenience path. It accepts plain strings, starts
-the turn, consumes notifications until completion, and returns a small result
-object with:
+`run(...)` is the common-case convenience path. It accepts the same input and
+options as `turn(...)`, consumes notifications until completion, and returns a
+small result object with:
 
 - `id: str`
 - `status: TurnStatus`
@@ -184,6 +191,24 @@ phase-less assistant message item.
 Use `turn(...)` when you need low-level turn control (`stream()`, `steer()`,
 `interrupt()`) before collecting the turn result.
 
+### Turn options
+
+These options have the same behavior on sync and async `run(...)` and `turn(...)`:
+
+| Option | Behavior |
+| --- | --- |
+| `service_tier: str | None = None` | Sets the thread's service tier for this and subsequent turns. |
+| `turn_service_tier: str | None = None` | Overrides the tier for a newly started turn only. `None` inherits the thread setting; `"default"` selects standard speed. Does not change the thread default and is ignored when input joins an active turn. |
+| `source: str | None = None` | Labels the caller that initiated a new turn, such as `"review_ui"`. This is metadata; it does not schedule work or grant authority. Ignored when input joins an active turn. |
+
+`turn_service_tier`, `source`, and explicit `include_turns`
+on resume/fork require Codex CLI 0.151.0 or newer. The SDK raises `CodexError`
+before sending these options to an older runtime, which would otherwise ignore
+them. Published SDK releases install a matching runtime automatically; when
+using `CodexConfig.codex_bin`, choose a compatible executable. Unversioned local
+builds are checked lazily against their experimental schema before these options
+are sent. A custom `launch_args_override` must report a supported version.
+
 ## Sandbox
 
 Use `sandbox=` consistently on thread lifecycle methods and turns:
diff --git a/sdk/python/docs/faq.md b/sdk/python/docs/faq.md
index b633ea420a..7886e335e8 100644
--- a/sdk/python/docs/faq.md
+++ b/sdk/python/docs/faq.md
@@ -37,6 +37,22 @@ Choose `run()` for most apps. Choose `stream()` for progress UIs, custom timeout
 
 If your app is not already async, stay with `Codex`.
 
+## Does `include_turns=False` remove the conversation's context?
+
+No. On `thread_resume(...)` and `thread_fork(...)`, it only skips loading turn
+history into the server's response. Omitting it preserves the server's
+existing default. Retrieve saved history with `thread.read(include_turns=True)`.
+
+## How do I change the service tier for just one turn?
+
+Pass `turn_service_tier=` to `thread.run(...)` or `thread.turn(...)`.
+`None` inherits the thread setting, and `"default"` selects standard speed.
+The override applies only when starting a new turn. Use `service_tier=` when
+you want to change the thread's setting for subsequent turns too.
+
+`source=` on those methods only labels what initiated the turn. It does not
+schedule work or grant authority, and it is ignored when joining an active turn.
+
 ## How do I log in?
 
 - `login_api_key(...)` authenticates immediately with an API key.
diff --git a/sdk/python/pyproject.toml b/sdk/python/pyproject.toml
index e7f88396f0..1e08cd3ce6 100644
--- a/sdk/python/pyproject.toml
+++ b/sdk/python/pyproject.toml
@@ -16,7 +16,7 @@ classifiers = [
   "Intended Audience :: Developers",
   "Topic :: Software Development :: Libraries :: Python Modules",
 ]
-dependencies = ["pydantic>=2.12", "openai-codex-cli-bin==0.147.0"]
+dependencies = ["pydantic>=2.12", "packaging>=26.2", "openai-codex-cli-bin==0.153.4"]
 
 [project.urls]
 Homepage = "https://github.com/openai/codex"
@@ -68,10 +68,10 @@ combine-as-imports = true
 
 [tool.uv]
 exclude-newer = "7 days"
-exclude-newer-package = { openai-codex-cli-bin = "2026-08-19T00:00:00Z" }
+exclude-newer-package = { openai-codex-cli-bin = "2026-09-09T06:06:45Z" }
 index-strategy = "first-index"
 
 [tool.uv.pip]
 exclude-newer = "7 days"
-exclude-newer-package = { openai-codex-cli-bin = "2026-08-19T00:00:00Z" }
+exclude-newer-package = { openai-codex-cli-bin = "2026-09-09T06:06:45Z" }
 index-strategy = "first-index"
diff --git a/sdk/python/scripts/update_sdk_artifacts.py b/sdk/python/scripts/update_sdk_artifacts.py
index 1b022177d9..2b26e8e900 100755
--- a/sdk/python/scripts/update_sdk_artifacts.py
+++ b/sdk/python/scripts/update_sdk_artifacts.py
@@ -5,6 +5,7 @@ import importlib.util
 import json
 import platform
 import re
+import runpy
 import shutil
 import subprocess
 import sys
@@ -175,6 +176,11 @@ def stage_python_sdk_package(
     )
     if len(runtime_versions) != 1:
         raise RuntimeError("Expected exactly one pinned Codex runtime dependency")
+    requirements = runpy.run_path(sdk_root() / "src/openai_codex/_runtime_requirements.py")
+    try:
+        requirements["require_runtime_version"](runtime_versions[0])
+    except ValueError as exc:
+        raise RuntimeError(f"Cannot package the Python SDK: {exc}") from exc
     pyproject_path.write_text(pyproject_text)
     return staging_dir
 
@@ -834,7 +840,10 @@ FIELD_ANNOTATION_OVERRIDES: dict[str, str] = {
 }
 
 PUBLIC_FIELD_NAMES = {
+    "exclude_turns": "include_turns",
     "sandbox_policy": "sandbox",
+    "service_tier_for_turn": "turn_service_tier",
+    "turn_trigger": "source",
 }
 
 # Adding a protocol field must not silently add a public SDK parameter. These
@@ -873,6 +882,7 @@ PUBLIC_METHOD_FIELDS = {
         "config",
         "cwd",
         "developer_instructions",
+        "exclude_turns",
         "model",
         "model_provider",
         "personality",
@@ -885,6 +895,7 @@ PUBLIC_METHOD_FIELDS = {
         "cwd",
         "developer_instructions",
         "ephemeral",
+        "exclude_turns",
         "model",
         "model_provider",
         "sandbox",
@@ -899,7 +910,9 @@ PUBLIC_METHOD_FIELDS = {
         "personality",
         "sandbox_policy",
         "service_tier",
+        "service_tier_for_turn",
         "summary",
+        "turn_trigger",
     ),
 }
 
@@ -1033,6 +1046,8 @@ def _model_arg_lines(fields: list[PublicFieldSpec], *, indent: str = "
             arg = "_sandbox_mode(sandbox)"
         elif field.wire_name == "sandbox_policy":
             arg = "_sandbox_policy(sandbox)"
+        elif field.wire_name == "exclude_turns":
+            arg = "None if include_turns is None else not include_turns"
         lines.append(f"{indent}{field.wire_name}={arg},")
     return lines
 
@@ -1088,7 +1103,11 @@ def _render_codex_block(
         *_approval_mode_override_signature_lines(),
         *_kw_signature_lines(resume_fields),
         "    ) -> Thread:",
-        '        """Resume an existing conversation thread by ID."""',
+        '        """Resume an existing conversation thread by ID.',
+        "",
+        "        include_turns controls the runtime response history, not model context.",
+        "        Omit it to preserve the runtime default. Use thread.read() for history.",
+        '        """',
         _approval_mode_assignment_line("_approval_mode_override_settings"),
         "        params = ThreadResumeParams(",
         "            thread_id=thread_id,",
@@ -1105,7 +1124,11 @@ def _render_codex_block(
         *_approval_mode_override_signature_lines(),
         *_kw_signature_lines(fork_fields),
         "    ) -> Thread:",
-        '        """Create a new thread from an existing thread."""',
+        '        """Create a new thread from an existing thread.',
+        "",
+        "        include_turns controls the runtime response history, not model context.",
+        "        Omit it to preserve the runtime default. Use thread.read() for history.",
+        '        """',
         _approval_mode_assignment_line("_approval_mode_override_settings"),
         "        params = ThreadForkParams(",
         "            thread_id=thread_id,",
@@ -1169,7 +1192,11 @@ def _render_async_codex_block(
         *_approval_mode_override_signature_lines(),
         *_kw_signature_lines(resume_fields),
         "    ) -> AsyncThread:",
-        '        """Resume an existing conversation thread by ID."""',
+        '        """Resume an existing conversation thread by ID.',
+        "",
+        "        include_turns controls the runtime response history, not model context.",
+        "        Omit it to preserve the runtime default. Use thread.read() for history.",
+        '        """',
         "        await self._ensure_initialized()",
         _approval_mode_assignment_line("_approval_mode_override_settings"),
         "        params = ThreadResumeParams(",
@@ -1187,7 +1214,11 @@ def _render_async_codex_block(
         *_approval_mode_override_signature_lines(),
         *_kw_signature_lines(fork_fields),
         "    ) -> AsyncThread:",
-        '        """Create a new thread from an existing thread."""',
+        '        """Create a new thread from an existing thread.',
+        "",
+        "        include_turns controls the runtime response history, not model context.",
+        "        Omit it to preserve the runtime default. Use thread.read() for history.",
+        '        """',
         "        await self._ensure_initialized()",
         _approval_mode_assignment_line("_approval_mode_override_settings"),
         "        params = ThreadForkParams(",
@@ -1212,19 +1243,46 @@ def _render_async_codex_block(
     return "\n".join(lines)
 
 
-def _render_thread_block(
-    turn_fields: list[PublicFieldSpec],
-) -> str:
+def _render_thread_block(turn_fields: list[PublicFieldSpec], *, is_async: bool = False) -> str:
+    async_prefix = "async " if is_async else ""
+    await_prefix = "await " if is_async else ""
+    client = "self._codex._client" if is_async else "self._client"
+    handle_type = "AsyncTurnHandle" if is_async else "TurnHandle"
+    handle_owner = "self._codex" if is_async else "self._client"
     lines = [
-        "    def turn(",
+        f"    {async_prefix}def run(",
         "        self,",
         "        input: RunInput,",
         "        *,",
         *_approval_mode_override_signature_lines(),
         *_kw_signature_lines(turn_fields),
-        "    ) -> TurnHandle:",
-        '        """Start a turn and return a handle for streaming or control."""',
+        "    ) -> TurnResult:",
+        '        """Run a complete turn and collect its final result.',
+        "",
+        "        Accepts the same input and options as turn().",
+        '        """',
+        f"        turn = {await_prefix}self.turn(",
+        "            input,",
+        "            approval_mode=approval_mode,",
+        *[f"            {field.py_name}={field.py_name}," for field in turn_fields],
+        "        )",
+        f"        return {await_prefix}turn.run()",
+        "",
+        f"    {async_prefix}def turn(",
+        "        self,",
+        "        input: RunInput,",
+        "        *,",
+        *_approval_mode_override_signature_lines(),
+        *_kw_signature_lines(turn_fields),
+        f"    ) -> {handle_type}:",
+        '        """Start a turn and return a handle for streaming or control.',
+        "",
+        "        turn_service_tier applies only to this new turn; service_tier updates",
+        "        the thread default. source labels what initiated a new turn and grants",
+        "        no authority. Both turn_service_tier and source are ignored when joining.",
+        '        """',
         "        wire_input = _to_wire_input(_normalize_run_input(input))",
+        *(["        await self._codex._ensure_initialized()"] if is_async else []),
         _approval_mode_assignment_line("_approval_mode_override_settings"),
         "        params = TurnStartParams(",
         "            thread_id=self.id,",
@@ -1232,39 +1290,8 @@ def _render_thread_block(
         *_approval_mode_model_arg_lines(),
         *_model_arg_lines(turn_fields),
         "        )",
-        "        turn = self._client.turn_start(self.id, wire_input, params=params)",
-        "        return TurnHandle(self._client, self.id, turn.turn.id)",
-    ]
-    return "\n".join(lines)
-
-
-def _render_async_thread_block(
-    turn_fields: list[PublicFieldSpec],
-) -> str:
-    lines = [
-        "    async def turn(",
-        "        self,",
-        "        input: RunInput,",
-        "        *,",
-        *_approval_mode_override_signature_lines(),
-        *_kw_signature_lines(turn_fields),
-        "    ) -> AsyncTurnHandle:",
-        '        """Start a turn and return a handle for streaming or control."""',
-        "        await self._codex._ensure_initialized()",
-        "        wire_input = _to_wire_input(_normalize_run_input(input))",
-        _approval_mode_assignment_line("_approval_mode_override_settings"),
-        "        params = TurnStartParams(",
-        "            thread_id=self.id,",
-        "            input=wire_input,",
-        *_approval_mode_model_arg_lines(),
-        *_model_arg_lines(turn_fields),
-        "        )",
-        "        turn = await self._codex._client.turn_start(",
-        "            self.id,",
-        "            wire_input,",
-        "            params=params,",
-        "        )",
-        "        return AsyncTurnHandle(self._codex, self.id, turn.turn.id)",
+        f"        turn = {await_prefix}{client}.turn_start(self.id, wire_input, params=params)",
+        f"        return {handle_type}({handle_owner}, self.id, turn.turn.id)",
     ]
     return "\n".join(lines)
 
@@ -1315,7 +1342,7 @@ def generate_public_api_flat_methods() -> None:
     source = _replace_generated_block(
         source,
         "AsyncThread.flat_methods",
-        _render_async_thread_block(turn_start_fields),
+        _render_thread_block(turn_start_fields, is_async=True),
     )
     public_api_path.write_text(source)
     run_python_module("ruff", ["format", str(public_api_path)], cwd=sdk_root())
diff --git a/sdk/python/src/openai_codex/_runtime_requirements.py b/sdk/python/src/openai_codex/_runtime_requirements.py
new file mode 100644
index 0000000000..ccc89ce360
--- /dev/null
+++ b/sdk/python/src/openai_codex/_runtime_requirements.py
@@ -0,0 +1,64 @@
+"""Runtime version and checkout-schema requirements for newer SDK options."""
+
+import json
+import re
+import subprocess
+from dataclasses import dataclass
+from functools import cached_property
+from pathlib import Path
+from tempfile import TemporaryDirectory
+
+from packaging.version import InvalidVersion, Version
+
+MINIMUM_RUNTIME_VERSION = "0.151.0"
+
+
+def require_runtime_version(version: str | None) -> None:
+    """Reject unknown or unsupported versions, including prereleases at the minimum."""
+    # CLI alpha hotfixes use 0.154.0-alpha.1.2; PEP 440 spells that a1.post2.
+    normalized = re.sub(r"-alpha\.(\d+)\.(\d+)$", r"a\1.post\2", version or "")
+    try:
+        if Version(normalized) >= Version(MINIMUM_RUNTIME_VERSION):
+            return
+    except InvalidVersion:
+        pass
+    raise ValueError(
+        f"Codex CLI {MINIMUM_RUNTIME_VERSION} or newer is required; "
+        f"reported version is {version or 'unknown'!r}"
+    )
+
+
+@dataclass
+class CheckoutCapabilities:
+    """Lazily inspect the same executable and configuration as a running checkout."""
+
+    command: tuple[str, ...]
+    cwd: str | None
+    env: dict[str, str]
+
+    @cached_property
+    def fields(self) -> dict[str, frozenset[str]]:
+        try:
+            with TemporaryDirectory(prefix="codex-sdk-schema-") as directory:
+                subprocess.run(
+                    [*self.command, "generate-json-schema", "--experimental", "--out", directory],
+                    cwd=self.cwd,
+                    env=self.env,
+                    capture_output=True,
+                    check=True,
+                    timeout=30,
+                )
+                result = {}
+                for method, name in (
+                    ("turn/start", "TurnStartParams"),
+                    ("thread/resume", "ThreadResumeParams"),
+                    ("thread/fork", "ThreadForkParams"),
+                ):
+                    schema = json.loads((Path(directory) / "v2" / f"{name}.json").read_text())
+                    properties = schema.get("properties") if isinstance(schema, dict) else None
+                    if not isinstance(properties, dict):
+                        raise ValueError(f"Missing properties in {name} schema")
+                    result[method] = frozenset(properties)
+                return result
+        except (OSError, subprocess.SubprocessError, ValueError) as exc:
+            raise ValueError("Could not inspect the unversioned CLI's experimental schema") from exc
diff --git a/sdk/python/src/openai_codex/api.py b/sdk/python/src/openai_codex/api.py
index 00a3d364fa..d68d2c8771 100644
--- a/sdk/python/src/openai_codex/api.py
+++ b/sdk/python/src/openai_codex/api.py
@@ -209,13 +209,18 @@ class Codex:
         config: JsonObject | None = None,
         cwd: str | None = None,
         developer_instructions: str | None = None,
+        include_turns: bool | None = None,
         model: str | None = None,
         model_provider: str | None = None,
         personality: Personality | None = None,
         sandbox: Sandbox | None = None,
         service_tier: str | None = None,
     ) -> Thread:
-        """Resume an existing conversation thread by ID."""
+        """Resume an existing conversation thread by ID.
+
+        include_turns controls the runtime response history, not model context.
+        Omit it to preserve the runtime default. Use thread.read() for history.
+        """
         approval_policy, approvals_reviewer = _approval_mode_override_settings(approval_mode)
         params = ThreadResumeParams(
             thread_id=thread_id,
@@ -225,6 +230,7 @@ class Codex:
             config=config,
             cwd=cwd,
             developer_instructions=developer_instructions,
+            exclude_turns=None if include_turns is None else not include_turns,
             model=model,
             model_provider=model_provider,
             personality=personality,
@@ -244,13 +250,18 @@ class Codex:
         cwd: str | None = None,
         developer_instructions: str | None = None,
         ephemeral: bool | None = None,
+        include_turns: bool | None = None,
         model: str | None = None,
         model_provider: str | None = None,
         sandbox: Sandbox | None = None,
         service_tier: str | None = None,
         thread_source: ThreadSource | None = None,
     ) -> Thread:
-        """Create a new thread from an existing thread."""
+        """Create a new thread from an existing thread.
+
+        include_turns controls the runtime response history, not model context.
+        Omit it to preserve the runtime default. Use thread.read() for history.
+        """
         approval_policy, approvals_reviewer = _approval_mode_override_settings(approval_mode)
         params = ThreadForkParams(
             thread_id=thread_id,
@@ -261,6 +272,7 @@ class Codex:
             cwd=cwd,
             developer_instructions=developer_instructions,
             ephemeral=ephemeral,
+            exclude_turns=None if include_turns is None else not include_turns,
             model=model,
             model_provider=model_provider,
             sandbox=_sandbox_mode(sandbox),
@@ -453,13 +465,18 @@ class AsyncCodex:
         config: JsonObject | None = None,
         cwd: str | None = None,
         developer_instructions: str | None = None,
+        include_turns: bool | None = None,
         model: str | None = None,
         model_provider: str | None = None,
         personality: Personality | None = None,
         sandbox: Sandbox | None = None,
         service_tier: str | None = None,
     ) -> AsyncThread:
-        """Resume an existing conversation thread by ID."""
+        """Resume an existing conversation thread by ID.
+
+        include_turns controls the runtime response history, not model context.
+        Omit it to preserve the runtime default. Use thread.read() for history.
+        """
         await self._ensure_initialized()
         approval_policy, approvals_reviewer = _approval_mode_override_settings(approval_mode)
         params = ThreadResumeParams(
@@ -470,6 +487,7 @@ class AsyncCodex:
             config=config,
             cwd=cwd,
             developer_instructions=developer_instructions,
+            exclude_turns=None if include_turns is None else not include_turns,
             model=model,
             model_provider=model_provider,
             personality=personality,
@@ -489,13 +507,18 @@ class AsyncCodex:
         cwd: str | None = None,
         developer_instructions: str | None = None,
         ephemeral: bool | None = None,
+        include_turns: bool | None = None,
         model: str | None = None,
         model_provider: str | None = None,
         sandbox: Sandbox | None = None,
         service_tier: str | None = None,
         thread_source: ThreadSource | None = None,
     ) -> AsyncThread:
-        """Create a new thread from an existing thread."""
+        """Create a new thread from an existing thread.
+
+        include_turns controls the runtime response history, not model context.
+        Omit it to preserve the runtime default. Use thread.read() for history.
+        """
         await self._ensure_initialized()
         approval_policy, approvals_reviewer = _approval_mode_override_settings(approval_mode)
         params = ThreadForkParams(
@@ -507,6 +530,7 @@ class AsyncCodex:
             cwd=cwd,
             developer_instructions=developer_instructions,
             ephemeral=ephemeral,
+            exclude_turns=None if include_turns is None else not include_turns,
             model=model,
             model_provider=model_provider,
             sandbox=_sandbox_mode(sandbox),
@@ -541,6 +565,7 @@ class Thread:
     _client: CodexClient
     id: str
 
+    # BEGIN GENERATED: Thread.flat_methods
     def run(
         self,
         input: RunInput,
@@ -553,9 +578,14 @@ class Thread:
         personality: Personality | None = None,
         sandbox: Sandbox | None = None,
         service_tier: str | None = None,
+        source: str | None = None,
         summary: ReasoningSummary | None = None,
+        turn_service_tier: str | None = None,
     ) -> TurnResult:
-        """Run a complete turn and collect its final result."""
+        """Run a complete turn and collect its final result.
+
+        Accepts the same input and options as turn().
+        """
         turn = self.turn(
             input,
             approval_mode=approval_mode,
@@ -566,15 +596,12 @@ class Thread:
             personality=personality,
             sandbox=sandbox,
             service_tier=service_tier,
+            source=source,
             summary=summary,
+            turn_service_tier=turn_service_tier,
         )
-        stream = turn.stream()
-        try:
-            return _collect_turn_result(stream, turn_id=turn.id)
-        finally:
-            stream.close()
+        return turn.run()
 
-    # BEGIN GENERATED: Thread.flat_methods
     def turn(
         self,
         input: RunInput,
@@ -587,9 +614,16 @@ class Thread:
         personality: Personality | None = None,
         sandbox: Sandbox | None = None,
         service_tier: str | None = None,
+        source: str | None = None,
         summary: ReasoningSummary | None = None,
+        turn_service_tier: str | None = None,
     ) -> TurnHandle:
-        """Start a turn and return a handle for streaming or control."""
+        """Start a turn and return a handle for streaming or control.
+
+        turn_service_tier applies only to this new turn; service_tier updates
+        the thread default. source labels what initiated a new turn and grants
+        no authority. Both turn_service_tier and source are ignored when joining.
+        """
         wire_input = _to_wire_input(_normalize_run_input(input))
         approval_policy, approvals_reviewer = _approval_mode_override_settings(approval_mode)
         params = TurnStartParams(
@@ -604,7 +638,9 @@ class Thread:
             personality=personality,
             sandbox_policy=_sandbox_policy(sandbox),
             service_tier=service_tier,
+            turn_trigger=source,
             summary=summary,
+            service_tier_for_turn=turn_service_tier,
         )
         turn = self._client.turn_start(self.id, wire_input, params=params)
         return TurnHandle(self._client, self.id, turn.turn.id)
@@ -629,6 +665,7 @@ class AsyncThread:
     _codex: AsyncCodex
     id: str
 
+    # BEGIN GENERATED: AsyncThread.flat_methods
     async def run(
         self,
         input: RunInput,
@@ -641,9 +678,14 @@ class AsyncThread:
         personality: Personality | None = None,
         sandbox: Sandbox | None = None,
         service_tier: str | None = None,
+        source: str | None = None,
         summary: ReasoningSummary | None = None,
+        turn_service_tier: str | None = None,
     ) -> TurnResult:
-        """Run a complete turn asynchronously and collect its final result."""
+        """Run a complete turn and collect its final result.
+
+        Accepts the same input and options as turn().
+        """
         turn = await self.turn(
             input,
             approval_mode=approval_mode,
@@ -654,15 +696,12 @@ class AsyncThread:
             personality=personality,
             sandbox=sandbox,
             service_tier=service_tier,
+            source=source,
             summary=summary,
+            turn_service_tier=turn_service_tier,
         )
-        stream = turn.stream()
-        try:
-            return await _collect_async_turn_result(stream, turn_id=turn.id)
-        finally:
-            await stream.aclose()
+        return await turn.run()
 
-    # BEGIN GENERATED: AsyncThread.flat_methods
     async def turn(
         self,
         input: RunInput,
@@ -675,11 +714,18 @@ class AsyncThread:
         personality: Personality | None = None,
         sandbox: Sandbox | None = None,
         service_tier: str | None = None,
+        source: str | None = None,
         summary: ReasoningSummary | None = None,
+        turn_service_tier: str | None = None,
     ) -> AsyncTurnHandle:
-        """Start a turn and return a handle for streaming or control."""
-        await self._codex._ensure_initialized()
+        """Start a turn and return a handle for streaming or control.
+
+        turn_service_tier applies only to this new turn; service_tier updates
+        the thread default. source labels what initiated a new turn and grants
+        no authority. Both turn_service_tier and source are ignored when joining.
+        """
         wire_input = _to_wire_input(_normalize_run_input(input))
+        await self._codex._ensure_initialized()
         approval_policy, approvals_reviewer = _approval_mode_override_settings(approval_mode)
         params = TurnStartParams(
             thread_id=self.id,
@@ -693,13 +739,11 @@ class AsyncThread:
             personality=personality,
             sandbox_policy=_sandbox_policy(sandbox),
             service_tier=service_tier,
+            turn_trigger=source,
             summary=summary,
+            service_tier_for_turn=turn_service_tier,
         )
-        turn = await self._codex._client.turn_start(
-            self.id,
-            wire_input,
-            params=params,
-        )
+        turn = await self._codex._client.turn_start(self.id, wire_input, params=params)
         return AsyncTurnHandle(self._codex, self.id, turn.turn.id)
 
     # END GENERATED: AsyncThread.flat_methods
diff --git a/sdk/python/src/openai_codex/client.py b/sdk/python/src/openai_codex/client.py
index ab5390ae52..b8513a5caa 100644
--- a/sdk/python/src/openai_codex/client.py
+++ b/sdk/python/src/openai_codex/client.py
@@ -14,7 +14,9 @@ from typing import Callable, Iterator, TypeVar
 from pydantic import BaseModel
 
 from ._goal import _GoalOperationState
+from ._initialize_metadata import _split_user_agent
 from ._message_router import MessageRouter
+from ._runtime_requirements import CheckoutCapabilities, require_runtime_version
 from ._version import __version__ as SDK_VERSION
 from .errors import CodexError, InvalidRequestError, TransportClosedError
 from .generated.notification_registry import NOTIFICATION_MODELS
@@ -227,6 +229,8 @@ class CodexClient:
         self._stderr_lines: deque[str] = deque(maxlen=400)
         self._stderr_thread: threading.Thread | None = None
         self._reader_thread: threading.Thread | None = None
+        self._runtime_version: str | None = None
+        self._checkout_capabilities: CheckoutCapabilities | None = None
 
     def __enter__(self) -> "CodexClient":
         self.start()
@@ -256,6 +260,11 @@ class CodexClient:
             env.update(self.config.env)
         _prepend_path_dirs(env, path_dirs)
 
+        if self.config.launch_args_override is None:
+            self._checkout_capabilities = CheckoutCapabilities(
+                command=tuple(args[:-2]), cwd=self.config.cwd, env=env.copy()
+            )
+
         self._proc = subprocess.Popen(
             args,
             stdin=subprocess.PIPE,
@@ -272,6 +281,8 @@ class CodexClient:
         self._start_reader_thread()
 
     def close(self) -> None:
+        self._runtime_version = None
+        self._checkout_capabilities = None
         if self._proc is None:
             return
         proc = self._proc
@@ -291,6 +302,7 @@ class CodexClient:
             self._reader_thread.join(timeout=0.5)
 
     def initialize(self) -> InitializeResponse:
+        self._runtime_version = None
         result = self.request(
             "initialize",
             {
@@ -305,6 +317,10 @@ class CodexClient:
             },
             response_model=InitializeResponse,
         )
+        version = result.serverInfo.version if result.serverInfo is not None else None
+        if not version or not version.strip():
+            _, version = _split_user_agent(result.userAgent or "")
+        self._runtime_version = version.split()[0] if version and version.strip() else None
         self.notify("initialized", None)
         return result
 
@@ -315,6 +331,35 @@ class CodexClient:
         *,
         response_model: type[ModelT],
     ) -> ModelT:
+        runtime_fields = {
+            "turn/start": ("turnTrigger", "serviceTierForTurn"),
+            "thread/resume": ("excludeTurns",),
+            "thread/fork": ("excludeTurns",),
+        }
+        supplied_fields = [
+            field
+            for field in runtime_fields.get(method, ())
+            if (params or {}).get(field) is not None
+        ]
+        if supplied_fields:
+            try:
+                if self._runtime_version == "0.0.0":
+                    if self._checkout_capabilities is None:
+                        raise ValueError(
+                            "Cannot verify an unversioned CLI with a custom launch command"
+                        )
+                    supported = self._checkout_capabilities.fields[method]
+                    if missing := set(supplied_fields) - supported:
+                        raise ValueError(
+                            f"The checkout does not support {', '.join(sorted(missing))}"
+                        )
+                else:
+                    require_runtime_version(self._runtime_version)
+            except ValueError as exc:
+                raise CodexError(
+                    f"{method} with {', '.join(supplied_fields)}: {exc}. "
+                    "Configure CodexConfig.codex_bin with a supported CLI."
+                ) from exc
         result = self._request_raw(method, params)
         if not isinstance(result, dict):
             raise CodexError(f"{method} response must be a JSON object")
diff --git a/sdk/python/tests/installed_sdk_smoke.py b/sdk/python/tests/installed_sdk_smoke.py
index 352a047a10..cf662bd5b7 100644
--- a/sdk/python/tests/installed_sdk_smoke.py
+++ b/sdk/python/tests/installed_sdk_smoke.py
@@ -21,7 +21,12 @@ def main() -> None:
         harness.responses.enqueue_assistant_message("Installed SDK works")
         config = replace(harness.app_server_config(), codex_bin=None)
         with Codex(config=config) as codex:
-            result = codex.thread_start().run("Check the installed SDK")
+            thread = codex.thread_start()
+            result = thread.run(
+                "Check the installed SDK", turn_service_tier="default", source="automation"
+            )
+            codex.thread_resume(thread.id, include_turns=False)
+            codex.thread_fork(thread.id, include_turns=True)
         assert result.final_response == "Installed SDK works"
         assert harness.responses.single_request().message_input_texts("user")[-1:] == [
             "Check the installed SDK"
diff --git a/sdk/python/tests/test_app_server_run.py b/sdk/python/tests/test_app_server_run.py
index 4e453bf66e..bda8a68dc7 100644
--- a/sdk/python/tests/test_app_server_run.py
+++ b/sdk/python/tests/test_app_server_run.py
@@ -52,6 +52,20 @@ def test_sync_thread_run_uses_mock_responses(
     }
 
 
+def test_checkout_supports_new_options_and_history_selection(tmp_path) -> None:
+    with AppServerHarness(tmp_path) as harness:
+        harness.responses.enqueue_assistant_message("Options supported")
+        with Codex(config=harness.app_server_config()) as codex:
+            thread = codex.thread_start()
+            result = thread.run("hello", turn_service_tier="default", source="automation")
+            resumed = codex.thread_resume(thread.id, include_turns=False)
+            forked = codex.thread_fork(thread.id, include_turns=True)
+        assert result.final_response == "Options supported"
+        assert resumed.id == thread.id
+        assert forked.id != thread.id
+        assert harness.responses.single_request().message_input_texts("user")[-1:] == ["hello"]
+
+
 def test_run_params_and_usage_cross_app_server_boundary(tmp_path) -> None:
     """Thread.run should pass overrides and collect app-server token usage."""
     with AppServerHarness(tmp_path) as harness:
diff --git a/sdk/python/tests/test_artifact_workflow_and_binaries.py b/sdk/python/tests/test_artifact_workflow_and_binaries.py
index 80a5da37ca..c89f75d1a1 100644
--- a/sdk/python/tests/test_artifact_workflow_and_binaries.py
+++ b/sdk/python/tests/test_artifact_workflow_and_binaries.py
@@ -637,7 +637,7 @@ def test_runtime_setup_reads_independent_runtime_pin_and_release_tags() -> None:
     } == {
         "package_name": "openai-codex-cli-bin",
         "sdk_template_version": "0.0.0-dev",
-        "runtime_pin": "0.147.0",
+        "runtime_pin": "0.153.4",
         "normalized_release_version": "0.116.0a1",
         "normalized_alpha_hotfix_version": "0.116.0a1.post2",
         "release_tag": "rust-v0.116.0-alpha.1",
@@ -955,17 +955,24 @@ def test_stage_sdk_release_packages_reviewed_artifacts(
     assert not any((staged / "src" / "openai_codex").glob("bin/**"))
 
 
+@pytest.mark.parametrize("source_runtime", ["0.147.0", "0.153.0"])
 @pytest.mark.parametrize("sdk_version", ["0.154.0", "0.2.0b1"])
 def test_built_sdk_uses_explicit_release_versions(
-    tmp_path: Path, monkeypatch: pytest.MonkeyPatch, sdk_release_source: Path, sdk_version: str
+    tmp_path: Path,
+    monkeypatch: pytest.MonkeyPatch,
+    sdk_release_source: Path,
+    sdk_version: str,
+    source_runtime: str,
 ) -> None:
     script = _load_update_script_module()
     monkeypatch.setattr(script, "sdk_root", lambda: sdk_release_source)
-    source_project = (sdk_release_source / "pyproject.toml").read_bytes()
+    project_path = sdk_release_source / "pyproject.toml"
+    project_path.write_text(project_path.read_text().replace("==0.153.0", f"=={source_runtime}"))
+    source_project = project_path.read_bytes()
     expected_dependencies = {
         *tomllib.loads(source_project.decode())["project"]["dependencies"],
         "openai-codex-cli-bin==0.154.0",
-    } - {"openai-codex-cli-bin==0.153.0"}
+    } - {f"openai-codex-cli-bin=={source_runtime}"}
     reviewed_files = {
         path: (sdk_release_source / path).read_bytes()
         for path in (
@@ -1058,11 +1065,52 @@ def test_sdk_release_matches_stable_runtime(
         "runtime_version": "0.153.0",
         "sdk_dependencies": [
             "pydantic>=2.12",
+            "packaging>=26.2",
             "openai-codex-cli-bin==0.153.0",
         ],
     }
 
 
+@pytest.mark.parametrize("runtime_version", ["0.149.0", "0.151.0a1", "0.0.0", "unknown"])
+def test_sdk_release_rejects_unsupported_runtime_even_for_beta(
+    tmp_path: Path,
+    monkeypatch: pytest.MonkeyPatch,
+    sdk_release_source: Path,
+    runtime_version: str,
+) -> None:
+    script = _load_update_script_module()
+    monkeypatch.setattr(script, "sdk_root", lambda: sdk_release_source)
+    project = sdk_release_source / "pyproject.toml"
+    project.write_text(project.read_text().replace("==0.153.0", f"=={runtime_version}"))
+
+    with pytest.raises(RuntimeError, match=r"Cannot package.*Codex CLI 0\.151\.0 or newer"):
+        script.stage_python_sdk_package(tmp_path / "sdk-stage", "0.1.0b1")
+
+
+def test_sdk_runtime_override_is_checked_after_stamping(
+    tmp_path: Path, monkeypatch: pytest.MonkeyPatch, sdk_release_source: Path
+) -> None:
+    script = _load_update_script_module()
+    monkeypatch.setattr(script, "sdk_root", lambda: sdk_release_source)
+    with pytest.raises(RuntimeError, match=r"Cannot package.*Codex CLI 0\.151\.0 or newer"):
+        script.stage_python_sdk_package(tmp_path / "sdk-stage", "0.1.0b1", "0.149.0")
+
+
+def test_sdk_beta_can_use_a_supported_runtime(
+    tmp_path: Path, monkeypatch: pytest.MonkeyPatch, sdk_release_source: Path
+) -> None:
+    script = _load_update_script_module()
+    monkeypatch.setattr(script, "sdk_root", lambda: sdk_release_source)
+
+    staged = script.stage_python_sdk_package(tmp_path / "sdk-stage", "0.1.0b1")
+
+    project = tomllib.loads((staged / "pyproject.toml").read_text())["project"]
+    assert (project["version"], project["dependencies"]) == (
+        "0.1.0b1",
+        ["pydantic>=2.12", "packaging>=26.2", "openai-codex-cli-bin==0.153.0"],
+    )
+
+
 def test_stage_runtime_stages_package_without_type_generation(tmp_path: Path) -> None:
     script = _load_update_script_module()
     package_archive = _write_fake_codex_package_archive(tmp_path, script)
@@ -1255,7 +1303,7 @@ def test_sdk_beta_can_pin_an_independent_runtime(tmp_path: Path) -> None:
     project = tomllib.loads((staged / "pyproject.toml").read_text())["project"]
     assert (project["version"], project["dependencies"]) == (
         "0.1.0b1",
-        ["pydantic>=2.12", "openai-codex-cli-bin==0.153.0"],
+        ["pydantic>=2.12", "packaging>=26.2", "openai-codex-cli-bin==0.153.0"],
     )
 
 
@@ -1297,6 +1345,7 @@ def test_sdk_release_matches_runtime(
         "runtime_version": package_version,
         "sdk_dependencies": [
             "pydantic>=2.12",
+            "packaging>=26.2",
             f"openai-codex-cli-bin=={package_version}",
         ],
     }
diff --git a/sdk/python/tests/test_client_rpc_methods.py b/sdk/python/tests/test_client_rpc_methods.py
index e055e551c4..3f9035ee30 100644
--- a/sdk/python/tests/test_client_rpc_methods.py
+++ b/sdk/python/tests/test_client_rpc_methods.py
@@ -1,11 +1,14 @@
 from __future__ import annotations
 
+import json
 from pathlib import Path
 from typing import get_type_hints
 
 import pytest
 
+from openai_codex._runtime_requirements import CheckoutCapabilities
 from openai_codex.client import CodexClient, _params_dict
+from openai_codex.errors import CodexError
 from openai_codex.generated.notification_registry import notification_turn_id
 from openai_codex.generated.v2_all import (
     AbsolutePathBuf,
@@ -30,7 +33,7 @@ from openai_codex.generated.v2_all import (
     TurnStartParams,
     WarningNotification,
 )
-from openai_codex.models import Notification, UnknownNotification
+from openai_codex.models import InitializeResponse, JsonObject, Notification, UnknownNotification
 from openai_codex.types import ThreadSource
 
 ROOT = Path(__file__).resolve().parents[1]
@@ -61,6 +64,160 @@ def test_approval_review_paths_preserve_existing_wrappers(model, fields) -> None
     assert isinstance(action.cwd, AbsolutePathBuf)
 
 
+def _initialized_client(
+    monkeypatch: pytest.MonkeyPatch, metadata: JsonObject
+) -> tuple[CodexClient, list[tuple[str, JsonObject | None]]]:
+    client = CodexClient()
+    requests: list[tuple[str, JsonObject | None]] = []
+
+    def request_raw(method: str, params: JsonObject | None) -> JsonObject:
+        requests.append((method, params))
+        return metadata if method == "initialize" else {}
+
+    monkeypatch.setattr(client, "_request_raw", request_raw)
+    monkeypatch.setattr(client, "notify", lambda *_args: None)
+    client.initialize()
+    requests.clear()
+    return client, requests
+
+
+@pytest.mark.parametrize(
+    ("method", "params"),
+    [
+        ("turn/start", {"input": [], "turnTrigger": "automation"}),
+        ("turn/start", {"input": [], "serviceTierForTurn": "default"}),
+        ("thread/resume", {"threadId": "thread-1", "excludeTurns": False}),
+        ("thread/fork", {"threadId": "thread-1", "excludeTurns": True}),
+    ],
+)
+@pytest.mark.parametrize("version", ["0.147.0", "0.149.0", "0.151.0-alpha.6", "unknown", ""])
+def test_new_options_reject_unsupported_runtime_before_sending(
+    monkeypatch: pytest.MonkeyPatch, method: str, params: JsonObject, version: str
+) -> None:
+    client, requests = _initialized_client(monkeypatch, {"userAgent": f"codex-cli/{version}"})
+
+    with pytest.raises(CodexError, match=r"Codex CLI 0\.151\.0 or newer"):
+        client.request(method, params, response_model=InitializeResponse)
+
+    assert requests == []
+
+
+@pytest.mark.parametrize(
+    "metadata",
+    [
+        {"userAgent": "codex-cli/0.151.0 (Linux)"},
+        {"userAgent": "codex-cli 0.153.0"},
+        {"userAgent": "codex-cli/0.154.0-alpha.1"},
+        {"userAgent": "codex-cli/0.154.0-alpha.1.2"},
+        {"userAgent": "codex-cli/0.151.0.post1"},
+        {"userAgent": "unknown", "serverInfo": {"name": "codex", "version": "0.153.0"}},
+    ],
+)
+def test_new_options_accept_supported_runtime_metadata(
+    monkeypatch: pytest.MonkeyPatch, metadata: JsonObject
+) -> None:
+    client, requests = _initialized_client(monkeypatch, metadata)
+    params = {"input": [], "turnTrigger": "automation"}
+
+    client.request("turn/start", params, response_model=InitializeResponse)
+
+    assert requests == [("turn/start", params)]
+
+
+@pytest.mark.parametrize("supports_options", [True, False])
+def test_unversioned_checkout_probes_and_caches_its_own_schema(
+    monkeypatch: pytest.MonkeyPatch, tmp_path: Path, supports_options: bool
+) -> None:
+    client, requests = _initialized_client(monkeypatch, {"userAgent": "codex-cli/0.0.0"})
+    command = ("checkout-codex", "--config", "key=value", "app-server")
+    client._checkout_capabilities = CheckoutCapabilities(
+        command, str(tmp_path), {"CUSTOM": "value"}
+    )
+    probes = []
+
+    def generate_schema(args, **kwargs):
+        probes.append((args[:-1], kwargs))
+        output = Path(args[-1]) / "v2"
+        output.mkdir()
+        for name, fields in (
+            ("TurnStartParams", ["turnTrigger", "serviceTierForTurn"]),
+            ("ThreadResumeParams", ["excludeTurns"]),
+            ("ThreadForkParams", ["excludeTurns"]),
+        ):
+            (output / f"{name}.json").write_text(
+                json.dumps(
+                    {"properties": {field: {} for field in fields} if supports_options else {}}
+                )
+            )
+
+    monkeypatch.setattr("openai_codex._runtime_requirements.subprocess.run", generate_schema)
+    for method, params in (
+        ("turn/start", {"input": [], "turnTrigger": "automation"}),
+        ("thread/resume", {"threadId": "thread-1", "excludeTurns": False}),
+    ):
+        if supports_options:
+            client.request(method, params, response_model=InitializeResponse)
+        else:
+            with pytest.raises(CodexError, match="checkout does not support"):
+                client.request(method, params, response_model=InitializeResponse)
+    assert len(requests) == (2 if supports_options else 0)
+    assert probes == [
+        (
+            [*command, "generate-json-schema", "--experimental", "--out"],
+            {
+                "cwd": str(tmp_path),
+                "env": {"CUSTOM": "value"},
+                "capture_output": True,
+                "check": True,
+                "timeout": 30,
+            },
+        )
+    ]
+    client.close()
+    assert client._checkout_capabilities is None
+
+
+def test_unversioned_custom_launch_requires_verifiable_capabilities(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    client, requests = _initialized_client(monkeypatch, {"userAgent": "codex-cli/0.0.0"})
+    with pytest.raises(CodexError, match="Cannot verify an unversioned CLI"):
+        client.request(
+            "turn/start", {"turnTrigger": "automation"}, response_model=InitializeResponse
+        )
+    assert requests == []
+
+
+@pytest.mark.parametrize("metadata", [{}, {"userAgent": "codex-cli/0.147.0"}])
+def test_ordinary_requests_keep_working_on_old_or_unknown_runtime(
+    monkeypatch: pytest.MonkeyPatch, metadata: JsonObject
+) -> None:
+    client, requests = _initialized_client(monkeypatch, metadata)
+    params = {"input": [{"type": "text", "text": "Hello"}], "serviceTier": "default"}
+
+    client.request("turn/start", params, response_model=InitializeResponse)
+    client.request("thread/resume", {"threadId": "thread-1"}, response_model=InitializeResponse)
+    client.request("thread/fork", {"threadId": "thread-1"}, response_model=InitializeResponse)
+
+    assert requests == [
+        ("turn/start", params),
+        ("thread/resume", {"threadId": "thread-1"}),
+        ("thread/fork", {"threadId": "thread-1"}),
+    ]
+
+
+def test_new_options_require_fresh_initialize_metadata_after_close(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    client, requests = _initialized_client(monkeypatch, {"userAgent": "codex-cli/0.153.0"})
+    client.close()
+
+    with pytest.raises(CodexError, match="reported version is 'unknown'"):
+        client.request("thread/resume", {"excludeTurns": True}, response_model=InitializeResponse)
+
+    assert requests == []
+
+
 def test_generated_params_models_are_snake_case_and_dump_by_alias() -> None:
     params = ThreadListParams(search_term="needle", limit=5)
 
diff --git a/sdk/python/tests/test_public_api_runtime_behavior.py b/sdk/python/tests/test_public_api_runtime_behavior.py
index 4cee695fee..a948a86178 100644
--- a/sdk/python/tests/test_public_api_runtime_behavior.py
+++ b/sdk/python/tests/test_public_api_runtime_behavior.py
@@ -2,7 +2,9 @@ from __future__ import annotations
 
 import asyncio
 from pathlib import Path
+from types import SimpleNamespace
 from typing import Any
+from unittest.mock import AsyncMock, Mock
 
 import pytest
 
@@ -13,8 +15,9 @@ from openai_codex.api import (
     Codex,
     Sandbox,
 )
-from openai_codex.generated.v2_all import TurnStartParams
-from openai_codex.models import InitializeResponse
+from openai_codex.client import _params_dict
+from openai_codex.generated.v2_all import TurnCompletedNotification, TurnStartParams
+from openai_codex.models import InitializeResponse, Notification
 
 ROOT = Path(__file__).resolve().parents[1]
 
@@ -128,6 +131,97 @@ def test_async_codex_initializes_only_once_under_concurrency() -> None:
     asyncio.run(scenario())
 
 
+@pytest.mark.parametrize("api_type", [Codex, AsyncCodex])
+@pytest.mark.parametrize(
+    ("options", "expected"),
+    [
+        ({}, {}),
+        ({"include_turns": None}, {}),
+        ({"include_turns": True}, {"excludeTurns": False}),
+        ({"include_turns": False}, {"excludeTurns": True}),
+    ],
+)
+def test_include_turns_preserves_omission_and_inverts_explicit_values(
+    api_type, options, expected
+) -> None:
+    async def scenario() -> None:
+        async_api = api_type is AsyncCodex
+        rpc = AsyncMock if async_api else Mock
+        thread_response = SimpleNamespace(thread=SimpleNamespace(id="thread-2"))
+        client = SimpleNamespace(
+            thread_resume=rpc(return_value=thread_response),
+            thread_fork=rpc(return_value=thread_response),
+        )
+        codex = api_type.__new__(api_type)
+        codex._client = client
+        codex._initialized = True
+
+        for method in ("thread_resume", "thread_fork"):
+            thread = getattr(codex, method)("thread-1", **options)
+            if async_api:
+                thread = await thread
+            assert thread.id == "thread-2"
+            assert _params_dict(getattr(client, method).call_args.args[1]) == {
+                "threadId": "thread-1",
+                **expected,
+            }
+
+    asyncio.run(scenario())
+
+
+@pytest.mark.parametrize("api_type", [Codex, AsyncCodex])
+@pytest.mark.parametrize("method", ["run", "turn"])
+def test_turn_inputs_and_options_reach_the_client(api_type, method) -> None:
+    """Turn options reach the client through both sync and async entry points."""
+
+    async def scenario() -> None:
+        async_api = api_type is AsyncCodex
+        rpc = AsyncMock if async_api else Mock
+        completed = Notification(
+            method="turn/completed",
+            payload=TurnCompletedNotification.model_validate(
+                {
+                    "threadId": "thread-1",
+                    "turn": {"id": "turn-1", "items": [], "status": "completed"},
+                }
+            ),
+        )
+        client = SimpleNamespace(
+            turn_start=rpc(return_value=SimpleNamespace(turn=SimpleNamespace(id="turn-1"))),
+            register_turn_notifications=Mock(),
+            unregister_turn_notifications=Mock(),
+            next_turn_notification=rpc(return_value=completed),
+        )
+        codex = api_type.__new__(api_type)
+        codex._client = client
+        codex._initialized = True
+        thread = (
+            public_api_module.AsyncThread(codex, "thread-1")
+            if async_api
+            else public_api_module.Thread(client, "thread-1")
+        )
+        input = "Continue."
+        turn = getattr(thread, method)(
+            input,
+            service_tier="priority",
+            turn_service_tier="default",
+            source="automation",
+        )
+        if async_api:
+            turn = await turn
+        assert turn.id == "turn-1"
+        expected_input = [{"type": "text", "text": "Continue.", "text_elements": []}]
+        assert _params_dict(client.turn_start.call_args.kwargs["params"]) == {
+            "threadId": "thread-1",
+            "input": expected_input,
+            "serviceTier": "priority",
+            "serviceTierForTurn": "default",
+            "turnTrigger": "automation",
+        }
+
+    asyncio.run(scenario())
+
+
 def _approval_mode_turn_params(approval_mode: ApprovalMode) -> TurnStartParams:
     """Build real generated turn params from one public approval mode."""
     approval_policy, approvals_reviewer = public_api_module._approval_mode_settings(approval_mode)
diff --git a/sdk/python/tests/test_public_api_signatures.py b/sdk/python/tests/test_public_api_signatures.py
index 9a67073b52..f9349196da 100644
--- a/sdk/python/tests/test_public_api_signatures.py
+++ b/sdk/python/tests/test_public_api_signatures.py
@@ -5,8 +5,6 @@ import inspect
 from pathlib import Path
 from typing import Any
 
-import tomllib
-
 import openai_codex
 import openai_codex.types as public_types
 from openai_codex import (
@@ -24,6 +22,11 @@ from openai_codex import (
 from openai_codex._initialize_metadata import validate_initialize_metadata
 from openai_codex.types import InitializeResponse
 
+try:
+    import tomllib
+except ModuleNotFoundError:
+    import tomli as tomllib
+
 EXPECTED_ROOT_EXPORTS = [
     "__version__",
     "CodexConfig",
@@ -176,13 +179,15 @@ def test_turn_input_methods_accept_string_shortcut() -> None:
         Thread.turn,
         AsyncThread.run,
         AsyncThread.turn,
-        TurnHandle.steer,
-        AsyncTurnHandle.steer,
     ]
 
     assert {fn: inspect.signature(fn).parameters["input"].annotation for fn in funcs} == (
         dict.fromkeys(funcs, "RunInput")
     )
+    assert {
+        fn: inspect.signature(fn).parameters["input"].annotation
+        for fn in (TurnHandle.steer, AsyncTurnHandle.steer)
+    } == dict.fromkeys((TurnHandle.steer, AsyncTurnHandle.steer), "RunInput")
 
 
 def test_root_exports_approval_mode() -> None:
@@ -351,6 +356,7 @@ def test_generated_public_signatures_are_snake_case_and_typed() -> None:
             "config",
             "cwd",
             "developer_instructions",
+            "include_turns",
             "model",
             "model_provider",
             "personality",
@@ -364,6 +370,7 @@ def test_generated_public_signatures_are_snake_case_and_typed() -> None:
             "cwd",
             "developer_instructions",
             "ephemeral",
+            "include_turns",
             "model",
             "model_provider",
             "sandbox",
@@ -379,7 +386,9 @@ def test_generated_public_signatures_are_snake_case_and_typed() -> None:
             "personality",
             "sandbox",
             "service_tier",
+            "source",
             "summary",
+            "turn_service_tier",
         ],
         Thread.run: [
             "approval_mode",
@@ -390,7 +399,9 @@ def test_generated_public_signatures_are_snake_case_and_typed() -> None:
             "personality",
             "sandbox",
             "service_tier",
+            "source",
             "summary",
+            "turn_service_tier",
         ],
         AsyncCodex.thread_start: [
             "approval_mode",
@@ -427,6 +438,7 @@ def test_generated_public_signatures_are_snake_case_and_typed() -> None:
             "config",
             "cwd",
             "developer_instructions",
+            "include_turns",
             "model",
             "model_provider",
             "personality",
@@ -440,6 +452,7 @@ def test_generated_public_signatures_are_snake_case_and_typed() -> None:
             "cwd",
             "developer_instructions",
             "ephemeral",
+            "include_turns",
             "model",
             "model_provider",
             "sandbox",
@@ -455,7 +468,9 @@ def test_generated_public_signatures_are_snake_case_and_typed() -> None:
             "personality",
             "sandbox",
             "service_tier",
+            "source",
             "summary",
+            "turn_service_tier",
         ],
         AsyncThread.run: [
             "approval_mode",
@@ -466,7 +481,9 @@ def test_generated_public_signatures_are_snake_case_and_typed() -> None:
             "personality",
             "sandbox",
             "service_tier",
+            "source",
             "summary",
+            "turn_service_tier",
         ],
     }
 
diff --git a/sdk/python/uv.lock b/sdk/python/uv.lock
index 6f6f867ede..f2727dc162 100644
--- a/sdk/python/uv.lock
+++ b/sdk/python/uv.lock
@@ -7,7 +7,7 @@ exclude-newer = "0001-01-01T00:00:00Z" # This has no effect and is included for
 exclude-newer-span = "P7D"
 
 [options.exclude-newer-package]
-openai-codex-cli-bin = "2026-08-19T00:00:00Z"
+openai-codex-cli-bin = "2026-09-09T06:06:45Z"
 
 [[package]]
 name = "annotated-types"
@@ -286,6 +286,7 @@ version = "0.0.0.dev0"
 source = { editable = "." }
 dependencies = [
     { name = "openai-codex-cli-bin" },
+    { name = "packaging" },
     { name = "pydantic" },
 ]
 
@@ -306,7 +307,8 @@ test = [
 
 [package.metadata]
 requires-dist = [
-    { name = "openai-codex-cli-bin", specifier = "==0.147.0" },
+    { name = "openai-codex-cli-bin", specifier = "==0.153.4" },
+    { name = "packaging", specifier = ">=26.2" },
     { name = "pydantic", specifier = ">=2.12" },
 ]
 
@@ -325,17 +327,17 @@ test = [
 
 [[package]]
 name = "openai-codex-cli-bin"
-version = "0.147.0"
+version = "0.153.4"
 source = { registry = "https://pypi.org/simple" }
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 [[package]]