diff --git a/docs/provider/configuration.md b/docs/provider/configuration.md
index d2695fd9..20668e60 100644
--- a/docs/provider/configuration.md
+++ b/docs/provider/configuration.md
@@ -65,7 +65,7 @@ in `routstr/upstream/deepseek.py`, not from litellm or OpenRouter:
   does not price shows up disabled in the Admin Dashboard. Enable it with a
   manual price, or add it to the table.
 - **Cache hits** bill at DeepSeek's cache-hit rate (about 2% of the input
-  rate).
+  rate on flash, about 3% on pro).
 
 Thinking-mode `reasoning_content` is returned to clients unchanged in
 responses, and forwarded unchanged when it appears in conversation history.
diff --git a/pyproject.toml b/pyproject.toml
index 296fab3f..da1c339a 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -22,6 +22,7 @@ dependencies = [
     "pillow>=10",
     "openai>=1.98.0",
     "litellm>=1.101.2,<1.102",
+    "backoff>=2.2",  # litellm's native Anthropic-messages streaming (e.g. deepseek/) imports litellm.proxy, which needs it
     "orjson>=3.10",
 ]
 
diff --git a/routstr/upstream/deepseek.py b/routstr/upstream/deepseek.py
index 01e5e334..a4eed7b3 100644
--- a/routstr/upstream/deepseek.py
+++ b/routstr/upstream/deepseek.py
@@ -1,9 +1,10 @@
 """First-class upstream for the DeepSeek API.
 
 Pricing comes from ``_PEAK_RATES`` below, not from litellm or OpenRouter:
-litellm's bundled ``deepseek-v4-flash`` entry is stale, the OpenRouter feed
-carries resale prices below DeepSeek's own peak rate, and neither knows the
-current ``deepseek-flash`` id. A model DeepSeek lists that the table does not
+litellm's bundled ``deepseek-v4-flash`` entry is stale (input, output and cache
+rates alike), the OpenRouter feed carries resale prices below DeepSeek's own
+peak rate, and neither the bundled map nor OpenRouter knows the current
+``deepseek-flash`` id. A model DeepSeek lists that the table does not
 cover is imported disabled rather than priced from those sources.
 
 DeepSeek bills peak hours at twice the off-peak rate. The node has one flat
diff --git a/tests/unit/test_upstream_deepseek.py b/tests/unit/test_upstream_deepseek.py
index f310f7ac..96ab14f9 100644
--- a/tests/unit/test_upstream_deepseek.py
+++ b/tests/unit/test_upstream_deepseek.py
@@ -12,9 +12,13 @@ with ``tools`` answers 400 when it is stripped.
 from __future__ import annotations
 
 import json
+import threading
+from collections.abc import Iterator
+from http.server import BaseHTTPRequestHandler, ThreadingHTTPServer
 from typing import Any
 from unittest.mock import AsyncMock, Mock, patch
 
+import litellm
 import pytest
 
 from routstr.upstream import upstream_provider_classes
@@ -230,3 +234,64 @@ async def test_reasoning_content_in_history_reaches_upstream() -> None:
     sent = json.loads(out)
     assert sent["model"] == "deepseek-flash"
     assert sent["messages"] == messages
+
+
+_ANTHROPIC_SSE = (
+    b"event: message_start\n"
+    b'data: {"type":"message_start","message":{"id":"msg_1","type":"message",'
+    b'"role":"assistant","model":"deepseek-flash","content":[],'
+    b'"stop_reason":null,"usage":{"input_tokens":3,"output_tokens":0}}}\n\n'
+    b"event: message_stop\n"
+    b'data: {"type":"message_stop"}\n\n'
+)
+
+
+@pytest.fixture
+def anthropic_stub() -> Iterator[tuple[str, list[tuple[str, dict[str, Any]]]]]:
+    """Loopback stand-in for DeepSeek's Anthropic-format endpoint."""
+    seen: list[tuple[str, dict[str, Any]]] = []
+
+    class Handler(BaseHTTPRequestHandler):
+        def do_POST(self) -> None:
+            length = int(self.headers["Content-Length"])
+            seen.append((self.path, json.loads(self.rfile.read(length))))
+            self.send_response(200)
+            self.send_header("Content-Type", "text/event-stream")
+            self.send_header("Content-Length", str(len(_ANTHROPIC_SSE)))
+            self.end_headers()
+            self.wfile.write(_ANTHROPIC_SSE)
+
+        def log_message(self, *args: Any) -> None:
+            return None
+
+    server = ThreadingHTTPServer(("127.0.0.1", 0), Handler)
+    thread = threading.Thread(target=server.serve_forever, daemon=True)
+    thread.start()
+    try:
+        yield f"http://127.0.0.1:{server.server_address[1]}", seen
+    finally:
+        server.shutdown()
+        server.server_close()
+
+
+@pytest.mark.asyncio
+async def test_messages_stream_reaches_deepseek_anthropic_endpoint(
+    anthropic_stub: tuple[str, list[tuple[str, dict[str, Any]]]],
+) -> None:
+    # litellm sends deepseek/ Messages calls to DeepSeek's /anthropic endpoint;
+    # its stream iterator imports litellm.proxy, which needs ``backoff``.
+    api_base, seen = anthropic_stub
+    stream = await litellm.anthropic.messages.acreate(
+        model=DeepSeekUpstreamProvider.litellm_provider_prefix + "deepseek-flash",
+        messages=[{"role": "user", "content": "hi"}],
+        max_tokens=8,
+        stream=True,
+        api_key="sk-test",
+        api_base=api_base,
+    )
+    chunks = [chunk async for chunk in stream]  # type: ignore[union-attr]
+
+    assert b"message_stop" in b"".join(chunks)
+    assert len(seen) == 1
+    assert seen[0][0] == "/anthropic/v1/messages"
+    assert seen[0][1]["model"] == "deepseek-flash"
diff --git a/uv.lock b/uv.lock
index 86d2be5d..ee38717c 100644
--- a/uv.lock
+++ b/uv.lock
@@ -282,6 +282,15 @@ wheels = [
     { url = "https://files.pythonhosted.org/packages/77/06/bb80f5f86020c4551da315d78b3ab75e8228f89f0162f2c3a819e407941a/attrs-25.3.0-py3-none-any.whl", hash = "sha256:427318ce031701fea540783410126f03899a97ffc6f61596ad581ac2e40e3bc3", size = 63815, upload-time = "2025-03-13T11:10:21.14Z" },
 ]
 
+[[package]]
+name = "backoff"
+version = "2.2.1"
+source = { registry = "https://pypi.org/simple" }
+sdist = { url = "https://files.pythonhosted.org/packages/47/d7/5bbeb12c44d7c4f2fb5b56abce497eb5ed9f34d85701de869acedd602619/backoff-2.2.1.tar.gz", hash = "sha256:03f829f5bb1923180821643f8753b0502c3b682293992485b0eef2807afa5cba", size = 17001, upload-time = "2022-10-05T19:19:32.061Z" }
+wheels = [
+    { url = "https://files.pythonhosted.org/packages/df/73/b6e24bd22e6720ca8ee9a85a0c4a2971af8497d8f3193fa05390cbd46e09/backoff-2.2.1-py3-none-any.whl", hash = "sha256:63579f9a0628e06278f7e47b7d7d5b6ce20dc65c5e96a6f3ca99a6adca0396e8", size = 15148, upload-time = "2022-10-05T19:19:30.546Z" },
+]
+
 [[package]]
 name = "base58"
 version = "2.1.1"
@@ -2711,6 +2720,7 @@ source = { editable = "." }
 dependencies = [
     { name = "aiosqlite" },
     { name = "alembic" },
+    { name = "backoff" },
     { name = "cashu" },
     { name = "fastapi", extra = ["standard-no-fastapi-cloud-cli"] },
     { name = "greenlet" },
@@ -2747,6 +2757,7 @@ dev = [
 requires-dist = [
     { name = "aiosqlite", specifier = ">=0.20" },
     { name = "alembic", specifier = ">=1.13" },
+    { name = "backoff", specifier = ">=2.2" },
     { name = "cashu", specifier = ">=0.20" },
     { name = "fastapi", extras = ["standard-no-fastapi-cloud-cli"], specifier = ">=0.141" },
     { name = "greenlet", specifier = ">=3.2.1" },