diff --git a/tests/integration/routing/test_silent_model_shadow_wire.py b/tests/integration/routing/test_silent_model_shadow_wire.py
new file mode 100644
index 00000000000..b00fbca645e
--- /dev/null
+++ b/tests/integration/routing/test_silent_model_shadow_wire.py
@@ -0,0 +1,195 @@
+from __future__ import annotations
+
+import json
+import re
+import uuid
+from collections.abc import Iterator, Mapping
+from dataclasses import dataclass
+from itertools import chain
+from types import MappingProxyType
+from typing import Final, Literal
+from urllib.parse import unquote
+
+import httpx
+import pytest
+from integration._support.anthropic_sse import parse_sse
+from integration._support.client import Gateway, eventually, gateway_from_environment
+from integration._support.openai_wire import chat_reply
+from integration._support.wire import Reply, Request, Wire, wire_server
+from pydantic import JsonValue, TypeAdapter
+
+Shape = Literal["single", "pair"]
+
+_MODEL: Final = "gpt-5.6"
+_API_KEY: Final = "synthetic-shadow-key"
+_ROUTER_ONLY_KEYS: Final = ("silent_model", "include_fallback_errors")
+_ANSWER: Final = "answered by"
+_NONCE: Final = re.compile(r"nonce=([0-9a-f]{32})")
+_JSON: Final = TypeAdapter(dict[str, JsonValue])
+_CHOICES: Final = TypeAdapter(list[dict[str, JsonValue]])
+_FRESH_CONNECTION: Final = MappingProxyType({"Connection": "close"})
+_SPEND_ROW_SECONDS: Final = 70
+_TARGETS: Final[Mapping[Shape, tuple[str, ...]]] = MappingProxyType(
+    {"single": ("shadow-a",), "pair": ("shadow-a", "shadow-b")}
+)
+_CASES: Final = (
+    pytest.param("single", False, id="non-stream-single"),
+    pytest.param("single", True, id="stream-single"),
+    pytest.param("pair", True, id="stream-pair"),
+)
+
+
+def _prompt(nonce: str) -> str:
+    return f"which deployment answers this? nonce={nonce}"
+
+
+def _nonce_of(raw: str) -> str:
+    found: Final = _NONCE.search(raw)
+    assert found is not None, raw
+    return found.group(1)
+
+
+def _identity(segment: str, nonce: str) -> str:
+    return f"chatcmpl-{segment}-{nonce}"
+
+
+def _request(model: str, nonce: str, *, stream: bool) -> dict[str, JsonValue]:
+    body: Final[dict[str, JsonValue]] = {
+        "model": model,
+        "stream": stream,
+        "messages": [{"role": "user", "content": _prompt(nonce)}],
+    }
+    return {**body, "stream_options": {"include_usage": True}} if stream else body
+
+
+def _segment_of(request: Request) -> str:
+    return unquote(request.target).lstrip("/").partition("/")[0]
+
+
+def _peer(request: Request) -> Reply:
+    if request.method == "GET":
+        return Reply(body=json.dumps({"object": "list", "data": []}).encode())
+    segment: Final = _segment_of(request)
+    body: Final = _JSON.validate_json(request.body)
+    return chat_reply(
+        _identity(segment, _nonce_of(request.body.decode())),
+        _MODEL,
+        f"{_ANSWER} {segment}",
+        stream=body.get("stream") is True,
+    )
+
+
+@dataclass(frozen=True, slots=True)
+class _Posted:
+    segment: str
+    streamed: bool
+    leaked: tuple[str, ...]
+
+
+def _posted(wire: Wire, nonce: str) -> tuple[_Posted, ...]:
+    return tuple(
+        _Posted(
+            _segment_of(request),
+            _JSON.validate_json(request.body).get("stream") is True,
+            tuple(key for key in _ROUTER_ONLY_KEYS if key in request.body.decode()),
+        )
+        for request in wire.drain()
+        if request.method == "POST" and nonce in request.body.decode()
+    )
+
+
+def _delta_text(data: Mapping[str, JsonValue]) -> str:
+    deltas: Final = (
+        _JSON.validate_python(choice.get("delta") or {}) for choice in _CHOICES.validate_python(data["choices"])
+    )
+    return "".join(str(delta.get("content") or "") for delta in deltas)
+
+
+def _served(response: httpx.Response, *, stream: bool) -> tuple[frozenset[str], str]:
+    if not stream:
+        body: Final = _JSON.validate_json(response.content)
+        message: Final = _JSON.validate_python(_CHOICES.validate_python(body["choices"])[0]["message"])
+        return frozenset({str(body["id"])}), str(message["content"])
+    events: Final = tuple(event.data for event in parse_sse(response.text))
+    return frozenset(str(data["id"]) for data in events), "".join(_delta_text(data) for data in events)
+
+
+@dataclass(frozen=True, slots=True)
+class _SpendRow:
+    request_id: str
+    model_group: str
+    spend: float
+
+
+def _spend_row(gateway: Gateway, request_id: str) -> tuple[_SpendRow, ...]:
+    rows: Final = gateway.rows(
+        'SELECT model_group, spend FROM "LiteLLM_SpendLogs" WHERE request_id = %s', (request_id,)
+    )
+    return tuple(_SpendRow(request_id, str(row["model_group"]), float(str(row["spend"]))) for row in rows)
+
+
+def _spend_rows(gateway: Gateway, request_ids: tuple[str, ...]) -> tuple[_SpendRow, ...]:
+    return tuple(chain.from_iterable(_spend_row(gateway, request_id) for request_id in request_ids))
+
+
+@dataclass(frozen=True, slots=True)
+class _Mirrors:
+    gateway: Gateway
+    wire: Wire
+    groups: Mapping[str, str]
+
+
+@pytest.fixture(scope="module")
+def mirrors() -> Iterator[_Mirrors]:
+    with gateway_from_environment() as gateway, wire_server(_peer) as wire, gateway.scenario() as scenario:
+
+        def register(segment: str, silent_model: JsonValue) -> str:
+            return scenario.model(
+                model=f"openai/{_MODEL}", api_key=_API_KEY, api_base=f"{wire.url}/{segment}", silent_model=silent_model
+            )
+
+        shadow_a: Final = register("shadow-a", None)
+        shadow_b: Final = register("shadow-b", None)
+        groups: Final = MappingProxyType(
+            {
+                "shadow-a": shadow_a,
+                "shadow-b": shadow_b,
+                "primary-single": register("primary-single", shadow_a),
+                "primary-pair": register("primary-pair", [shadow_a, shadow_b]),
+            }
+        )
+        wire.drain()
+        yield _Mirrors(gateway, wire, groups)
+
+
+@pytest.mark.parametrize(("shape", "stream"), _CASES)
+def test_each_shadow_target_gets_one_request_in_the_callers_stream_mode(
+    mirrors: _Mirrors, shape: Shape, stream: bool
+) -> None:
+    nonce: Final = uuid.uuid4().hex
+    primary: Final = f"primary-{shape}"
+    targets: Final = _TARGETS[shape]
+    response: Final = mirrors.gateway.request(
+        "POST",
+        "/v1/chat/completions",
+        _request(mirrors.groups[primary], nonce, stream=stream),
+        headers=_FRESH_CONNECTION,
+    )
+    assert response.status_code == 200, response.text
+    assert _served(response, stream=stream) == (frozenset({_identity(primary, nonce)}), f"{_ANSWER} {primary}")
+
+    expected_groups: Final = MappingProxyType(
+        {_identity(segment, nonce): mirrors.groups[segment] for segment in (primary, *targets)}
+    )
+    rows: Final = eventually(
+        lambda: _spend_rows(mirrors.gateway, tuple(expected_groups)),
+        lambda found: len(found) == len(expected_groups),
+        seconds=_SPEND_ROW_SECONDS,
+    )
+    assert {row.request_id: row.model_group for row in rows} == expected_groups, rows
+    assert all(row.spend > 0 for row in rows), rows
+
+    posted: Final = _posted(mirrors.wire, nonce)
+    assert sorted(item.segment for item in posted) == sorted((primary, *targets)), posted
+    assert all(item.streamed is stream for item in posted), posted
+    assert all(item.leaked == () for item in posted), posted
diff --git a/tests/integration/sdk/test_router_silent_model_shadow_sdk.py b/tests/integration/sdk/test_router_silent_model_shadow_sdk.py
new file mode 100644
index 00000000000..821e4ddd0b7
--- /dev/null
+++ b/tests/integration/sdk/test_router_silent_model_shadow_sdk.py
@@ -0,0 +1,129 @@
+from __future__ import annotations
+
+import re
+import uuid
+from collections.abc import Mapping
+from dataclasses import dataclass
+from queue import SimpleQueue
+from typing import Final
+
+import pytest
+from integration._support.client import eventually
+from integration._support.openai_wire import chat_reply
+from integration._support.wire import Reply, Request, Wire, wire_server
+from pydantic import JsonValue, TypeAdapter
+
+import litellm
+from litellm import CustomStreamWrapper, Router
+from litellm.integrations.custom_logger import CustomLogger
+from litellm.types.utils import ModelResponseStream
+
+_MODEL: Final = "gpt-5.6"
+_API_KEY: Final = "synthetic-shadow-key"
+_ANSWER: Final = "answered by"
+_NONCE: Final = re.compile(r"nonce=([0-9a-f]{32})")
+_JSON: Final = TypeAdapter(dict[str, JsonValue])
+_OBJECT: Final = TypeAdapter(dict[str, object])
+_SHADOW_SECONDS: Final = 20
+_TARGETS: Final = (
+    pytest.param(("shadow-a",), id="single"),
+    pytest.param(("shadow-a", "shadow-b"), id="pair"),
+)
+
+
+def _prompt(nonce: str) -> str:
+    return f"which deployment answers this? nonce={nonce}"
+
+
+def _peer(request: Request) -> Reply:
+    deployment: Final = request.target.lstrip("/").partition("/")[0]
+    raw: Final = request.body.decode()
+    found: Final = _NONCE.search(raw)
+    assert found is not None, raw
+    return chat_reply(
+        f"chatcmpl-{deployment}-{found.group(1)}",
+        _MODEL,
+        f"{_ANSWER} {deployment}",
+        stream=_JSON.validate_json(request.body).get("stream") is True,
+    )
+
+
+def _deployment(name: str, wire: Wire, **extra: JsonValue) -> dict[str, JsonValue]:
+    return {
+        "model_name": name,
+        "litellm_params": {"model": f"openai/{_MODEL}", "api_base": f"{wire.url}/{name}", "api_key": _API_KEY, **extra},
+    }
+
+
+@dataclass(frozen=True, slots=True)
+class _Posted:
+    deployment: str
+    streamed: bool
+    leaked: bool
+
+
+def _posted(wire: Wire) -> tuple[_Posted, ...]:
+    return tuple(
+        _Posted(
+            request.target.lstrip("/").partition("/")[0],
+            _JSON.validate_json(request.body).get("stream") is True,
+            "silent_model" in request.body.decode(),
+        )
+        for request in wire.drain()
+        if request.method == "POST"
+    )
+
+
+class _ShadowRecorder(CustomLogger):
+    def __init__(self) -> None:
+        super().__init__()
+        self.shadow_groups: SimpleQueue[str] = SimpleQueue()
+
+    async def async_log_success_event(
+        self, kwargs: Mapping[str, object], response_obj: object, start_time: object, end_time: object
+    ) -> None:
+        metadata: Final = _OBJECT.validate_python(_OBJECT.validate_python(kwargs["litellm_params"])["metadata"] or {})
+        if metadata.get("is_silent_experiment") is True:
+            self.shadow_groups.put(str(metadata.get("model_group")))
+
+    def drained(self) -> tuple[str, ...]:
+        return tuple(self.shadow_groups.get_nowait() for _ in range(self.shadow_groups.qsize()))
+
+
+def _delta(chunk: object) -> str:
+    assert isinstance(chunk, ModelResponseStream), chunk
+    return "".join(str(choice.delta.content or "") for choice in chunk.choices)
+
+
+@pytest.mark.parametrize("targets", _TARGETS)
+def test_sync_streamed_completion_streams_and_logs_each_shadow_target(
+    targets: tuple[str, ...], monkeypatch: pytest.MonkeyPatch
+) -> None:
+    recorder: Final = _ShadowRecorder()
+    monkeypatch.setattr(litellm, "callbacks", [recorder])
+    with wire_server(_peer) as wire:
+        silent_model: Final[JsonValue] = targets[0] if len(targets) == 1 else [*targets]
+        router: Final = Router(
+            model_list=[
+                _deployment("mirrored", wire, silent_model=silent_model),
+                *(_deployment(target, wire) for target in targets),
+            ],
+            num_retries=0,
+            disable_cooldowns=True,
+        )
+        response: Final = router.completion(
+            model="mirrored",
+            messages=[{"role": "user", "content": _prompt(uuid.uuid4().hex)}],
+            stream=True,
+        )
+        assert isinstance(response, CustomStreamWrapper), response
+        text: Final = "".join(_delta(chunk) for chunk in response)
+        eventually(wire.received.qsize, lambda count: count >= 1 + len(targets), seconds=_SHADOW_SECONDS)
+        posted: Final = _posted(wire)
+        eventually(recorder.shadow_groups.qsize, lambda count: count >= len(targets), seconds=_SHADOW_SECONDS)
+        logged: Final = recorder.drained()
+    assert text == f"{_ANSWER} mirrored"
+    assert sorted(item.deployment for item in posted) == sorted(("mirrored", *targets)), posted
+    assert all(item.streamed for item in posted), posted
+    assert not any(item.leaked for item in posted), posted
+    assert sorted(logged) == sorted(targets), logged