diff --git a/.lint_baselines/falsey_clobber.json b/.lint_baselines/falsey_clobber.json
index b734209..e08f9f7 100644
--- a/.lint_baselines/falsey_clobber.json
+++ b/.lint_baselines/falsey_clobber.json
@@ -22,24 +22,24 @@
     "axonflow/adapters/tool_wrapper.py:190:20",
     "axonflow/adapters/tool_wrapper.py:208:20",
     "axonflow/adapters/tool_wrapper.py:220:20",
-    "axonflow/client.py:1059:16",
-    "axonflow/client.py:1136:16",
-    "axonflow/client.py:1608:37",
-    "axonflow/client.py:1649:18",
-    "axonflow/client.py:1707:37",
-    "axonflow/client.py:2225:24",
-    "axonflow/client.py:2246:33",
-    "axonflow/client.py:2247:31",
-    "axonflow/client.py:2259:25",
-    "axonflow/client.py:2320:28",
-    "axonflow/client.py:2361:69",
+    "axonflow/client.py:1065:16",
+    "axonflow/client.py:1142:16",
+    "axonflow/client.py:1614:37",
+    "axonflow/client.py:1655:18",
+    "axonflow/client.py:1713:37",
+    "axonflow/client.py:2231:24",
+    "axonflow/client.py:2252:33",
+    "axonflow/client.py:2253:31",
+    "axonflow/client.py:2265:25",
+    "axonflow/client.py:2326:28",
+    "axonflow/client.py:2367:69",
     "axonflow/client.py:286:14",
     "axonflow/client.py:291:24",
     "axonflow/client.py:292:20",
     "axonflow/client.py:488:44",
-    "axonflow/client.py:6068:25",
-    "axonflow/client.py:793:20",
-    "axonflow/client.py:879:20",
+    "axonflow/client.py:6074:25",
+    "axonflow/client.py:799:20",
+    "axonflow/client.py:885:20",
     "axonflow/execution.py:205:19",
     "axonflow/interceptors/anthropic.py:134:43",
     "axonflow/interceptors/anthropic.py:161:43",
diff --git a/axonflow/client.py b/axonflow/client.py
index cb79050..a14e380 100644
--- a/axonflow/client.py
+++ b/axonflow/client.py
@@ -509,10 +509,16 @@ def __init__(
         # Configure SSL verification
         verify_ssl: bool = not insecure_skip_verify
 
-        # Build headers
+        # Build headers.
+        # ADR-050 §4: every governed request to the agent carries
+        # X-Axonflow-Client so the agent can derive request scope (sdk) and
+        # validate it against the token's aud.scope via HasScope(). Sourced
+        # from the bundled _SDK_VERSION constant; no env override (the
+        # consumer doesn't get to spoof its own client identity to the agent).
         headers: dict[str, str] = {
             "Content-Type": "application/json",
             "User-Agent": f"axonflow-sdk-python/{_SDK_VERSION}",
+            "X-Axonflow-Client": f"sdk-python/{_SDK_VERSION}",
         }
         # Always send Basic auth — server derives tenant from clientId.
         # Uses effective client_id ("community" default when not configured).
diff --git a/tests/test_client_header.py b/tests/test_client_header.py
new file mode 100644
index 0000000..3ed27db
--- /dev/null
+++ b/tests/test_client_header.py
@@ -0,0 +1,56 @@
+"""X-Axonflow-Client header injection — ADR-050 §4.
+
+Asserts every governed HTTP request forwards
+``X-Axonflow-Client: sdk-python/<__version__>`` so the agent can derive
+request scope (sdk) and validate against the token's aud.scope via
+HasScope().
+
+Header is sourced from the bundled __version__ constant; the consumer
+cannot spoof its own client identity through config (intentional —
+honest-99% header injection per ADR-050 §4).
+"""
+
+import pytest
+
+from axonflow import AxonFlow
+from axonflow._version import __version__
+
+EXPECTED_CLIENT = f"sdk-python/{__version__}"
+
+
+@pytest.mark.asyncio
+async def test_client_header_present_on_proxy_call(httpx_mock):
+    """Every governed request includes X-Axonflow-Client."""
+    httpx_mock.add_response(
+        url="http://localhost:8080/api/request",
+        json={"success": True, "data": {"answer": "ok"}, "blocked": False},
+    )
+
+    client = AxonFlow(
+        endpoint="http://localhost:8080",
+        client_id="test-client",
+        client_secret="test-secret",
+    )
+    async with client:
+        await client.proxy_llm_call(user_token="", query="ping", request_type="chat")
+
+    requests = httpx_mock.get_requests()
+    assert len(requests) == 1
+    headers = dict(requests[0].headers)
+    # httpx normalizes header keys to lowercase
+    assert headers.get("x-axonflow-client") == EXPECTED_CLIENT
+
+
+@pytest.mark.asyncio
+async def test_client_header_format_is_id_slash_semver():
+    """Sanity: the value matches sdk-python/<semver>.
+
+    The agent's deriveScopeFromClientHeader splits on '/' and maps
+    "sdk-*" prefixes to scope=sdk. If we ever ship a different shape
+    this fails loudly so we don't regress agent-side parsing.
+    """
+    import re
+
+    assert EXPECTED_CLIENT.startswith("sdk-python/")
+    assert re.match(r"^sdk-python/\d+\.\d+\.\d+", EXPECTED_CLIENT)
+    assert EXPECTED_CLIENT.count("/") == 1