diff --git a/agent/anthropic_adapter.py b/agent/anthropic_adapter.py
index f5dea26121..0ecd5110d7 100644
--- a/agent/anthropic_adapter.py
+++ b/agent/anthropic_adapter.py
@@ -1282,12 +1282,21 @@ def create_anthropic_message(
                     for _event in stream:
                         try:
                             on_stream_event(_event)
+                        except TimeoutError:
+                            # The callback is the caller's deadline seam
+                            # (#99692: the host waiting on this summary has
+                            # already given up). Abandon the stream — the
+                            # ``with`` closes it — instead of streaming an
+                            # answer nobody will read.
+                            raise
                         except Exception:
                             logger.debug(
                                 "%son_stream_event callback failed",
                                 log_prefix, exc_info=True,
                             )
                 return stream.get_final_message()
+        except TimeoutError:
+            raise
         except Exception as exc:
             if not _is_stream_unavailable_error(exc):
                 raise
diff --git a/agent/auxiliary_client.py b/agent/auxiliary_client.py
index 923d9906f1..47c682fde6 100644
--- a/agent/auxiliary_client.py
+++ b/agent/auxiliary_client.py
@@ -535,6 +535,37 @@ def _anthropic_event_has_content(event: Any) -> bool:
     return False
 
 
+def _anthropic_aux_stream_event_hook() -> Callable[[Any], None]:
+    """Per-event callback for the Anthropic auxiliary wire.
+
+    Records provider-response timing for every frame, ticks the forward-progress
+    hook only for substantive payloads (keepalive pings must not keep a stalled
+    summary alive), and — #99692 — stops the stream at the waiting host's
+    absolute deadline (``aux_stream_deadline``) or on an explicit hard cancel,
+    the same two stop conditions the chat.completions and Codex wires honour.
+    The ``TimeoutError`` is phrased with "timed out" so ``_is_timeout_error``
+    classifies it like any other request timeout.
+    """
+    host_deadline = _current_aux_stream_deadline()
+    started = time.monotonic()
+
+    def _on_event(event: Any) -> None:
+        if _anthropic_event_has_content(event):
+            _notify_aux_provider_response()
+        else:
+            _notify_aux_timing_response()
+        if _aux_interrupt_cancel_requested():
+            raise AuxiliaryExplicitCancellation()
+        if host_deadline is not None and time.monotonic() >= host_deadline:
+            raise TimeoutError(
+                "Anthropic auxiliary stream timed out at the host compression "
+                f"deadline after {time.monotonic() - started:.0f}s "
+                "(the caller already stopped waiting)"
+            )
+
+    return _on_event
+
+
 _CODEX_PROGRESS_DELTA_TYPES = frozenset(
     {
         "response.output_text.delta",
@@ -1937,6 +1968,15 @@ class _CodexCompletionsAdapter:
         if total_timeout is not None:
             no_progress_timeout = min(no_progress_timeout, float(total_timeout))
         hard_deadline = _start_monotonic + _aux_stream_total_ceiling(total_timeout)
+        # #99692: the waiting host's absolute deadline (compress_context
+        # publishes its commit-fence ceiling via aux_stream_deadline) clamps
+        # the hard ceiling so the re-armable watchdog Timer wakes and severs
+        # the socket at the instant the host stops waiting — a live Codex
+        # stream cannot otherwise be stopped by a per-event cancel check
+        # while it is blocked between events.
+        _host_deadline = _current_aux_stream_deadline()
+        if isinstance(_host_deadline, (int, float)) and _host_deadline < hard_deadline:
+            hard_deadline = float(_host_deadline)
         deadline_lock = threading.Lock()
         progress_deadline = [_start_monotonic + no_progress_timeout]
         saw_content = threading.Event()
@@ -2552,13 +2592,7 @@ class _AnthropicCompletionsAdapter:
             # stalled summary open. No-op when no hook is installed (None
             # keeps the fast get_final_message path).
             on_stream_event=(
-                (
-                    lambda event: (
-                        _notify_aux_provider_response()
-                        if _anthropic_event_has_content(event)
-                        else _notify_aux_timing_response()
-                    )
-                )
+                _anthropic_aux_stream_event_hook()
                 if _aux_progress_active()
                 else None
             ),
diff --git a/tests/agent/test_aux_stream_host_deadline_sibling_wires.py b/tests/agent/test_aux_stream_host_deadline_sibling_wires.py
new file mode 100644
index 0000000000..250b5ac132
--- /dev/null
+++ b/tests/agent/test_aux_stream_host_deadline_sibling_wires.py
@@ -0,0 +1,189 @@
+"""#99692 sibling wires — the host compression deadline must stop EVERY aux
+stream consumer, not only the chat.completions accumulator.
+
+``aux_stream_deadline`` (salvaged from PR #99779 by @JoaoMarcos44) publishes
+the ``CompressionCommitFence`` ceiling to the streamed chat.completions path.
+Two other auxiliary wires consume their streams internally and were left with
+their own, always-larger budgets:
+
+* the Codex Responses adapter (``_CodexCompletionsAdapter.create``) — its
+  re-armable watchdog only knew ``_aux_stream_total_ceiling`` (>= 600s);
+* the Anthropic Messages adapter — its ``on_stream_event`` hook only ticked
+  progress and never stopped the stream at all (nor honoured a hard cancel).
+
+Both now stop at the host's absolute deadline, so an abandoned summary is not
+billed to completion on a socket nobody is waiting for.
+"""
+
+from __future__ import annotations
+
+import time
+from types import SimpleNamespace
+from unittest.mock import patch
+
+import pytest
+
+from agent import auxiliary_client as aux
+from agent.anthropic_adapter import create_anthropic_message
+
+
+# ── Codex Responses wire ─────────────────────────────────────────────────
+
+
+def _codex_content_event(text="tok"):
+    return SimpleNamespace(type="response.output_text.delta", delta=text)
+
+
+def _consume_codex(stream, *, model, on_event):
+    del model
+    for event in stream:
+        on_event(event)
+    return SimpleNamespace(
+        output=[SimpleNamespace(
+            type="message",
+            content=[SimpleNamespace(type="output_text", text="summary")],
+        )],
+        usage=None,
+    )
+
+
+def _make_codex_adapter(event_iter):
+    real_client = SimpleNamespace(
+        base_url="https://chatgpt.com/backend-api/codex",
+        responses=SimpleNamespace(create=lambda **_kwargs: event_iter),
+        close=lambda: None,
+    )
+    return aux._CodexCompletionsAdapter(real_client, "gpt-5.6-sol")
+
+
+def test_codex_stream_stops_at_the_host_deadline_not_its_own_ceiling():
+    """A live (re-arming) Codex stream must die at the host's deadline even
+    though its own hard ceiling is >= 600s and every token re-arms the
+    no-progress window."""
+    yielded = [0]
+
+    def _live_forever():
+        while True:
+            time.sleep(0.02)
+            yielded[0] += 1
+            yield _codex_content_event()
+
+    adapter = _make_codex_adapter(_live_forever())
+    start = time.monotonic()
+    with (
+        patch("agent.codex_runtime._consume_codex_event_stream", _consume_codex),
+        aux.aux_stream_deadline(time.monotonic() + 0.4),
+        pytest.raises(TimeoutError, match="hard ceiling"),
+    ):
+        adapter.create(
+            messages=[{"role": "user", "content": "summarize"}],
+            timeout=300,
+        )
+    elapsed = time.monotonic() - start
+    assert elapsed < 5.0, f"stream outlived the host deadline by {elapsed:.1f}s"
+    assert yielded[0] < 100
+
+
+def test_codex_stream_without_host_deadline_keeps_its_ceiling():
+    def _short():
+        for _ in range(3):
+            yield _codex_content_event()
+
+    adapter = _make_codex_adapter(_short())
+    with patch("agent.codex_runtime._consume_codex_event_stream", _consume_codex):
+        response = adapter.create(
+            messages=[{"role": "user", "content": "summarize"}], timeout=300,
+        )
+    assert response.choices[0].message.content == "summary"
+
+
+# ── Anthropic Messages wire ──────────────────────────────────────────────
+
+
+class _AnthropicStream:
+    def __init__(self, count=10_000, delay=0.01):
+        self._count, self._delay = count, delay
+        self.yielded = 0
+        self.exited = False
+        self.response = None
+
+    def __enter__(self):
+        return self
+
+    def __exit__(self, *exc):
+        self.exited = True
+        return False
+
+    def __iter__(self):
+        for _ in range(self._count):
+            time.sleep(self._delay)
+            self.yielded += 1
+            yield SimpleNamespace(
+                type="content_block_delta", delta=SimpleNamespace(text="tok"),
+            )
+
+    def get_final_message(self):
+        return SimpleNamespace(content=[SimpleNamespace(type="text", text="summary")])
+
+
+def _anthropic_client(stream):
+    return SimpleNamespace(
+        messages=SimpleNamespace(
+            stream=lambda **_kw: stream,
+            create=lambda **_kw: pytest.fail("must not fall back to create()"),
+        )
+    )
+
+
+def test_anthropic_stream_stops_at_the_host_deadline():
+    stream = _AnthropicStream()
+    ticks = []
+    with (
+        aux.aux_progress_hook(lambda: ticks.append(1)),
+        aux.aux_stream_deadline(time.monotonic() + 0.3),
+    ):
+        hook = aux._anthropic_aux_stream_event_hook()
+        start = time.monotonic()
+        with pytest.raises(TimeoutError, match="timed out at the host compression deadline"):
+            create_anthropic_message(
+                _anthropic_client(stream), {"model": "m", "messages": []},
+                on_stream_event=hook,
+            )
+    assert time.monotonic() - start < 5.0
+    assert stream.exited, "stream context must be closed on the deadline"
+    assert ticks, "substantive deltas must still tick the progress hook"
+    assert stream.yielded < 1000
+
+
+def test_anthropic_stream_honours_an_explicit_hard_cancel():
+    stream = _AnthropicStream()
+    cancelled = {"v": False}
+    with (
+        aux.aux_progress_hook(lambda: None),
+        aux.aux_interrupt_protection(cancel_check=lambda: cancelled["v"]),
+    ):
+        hook = aux._anthropic_aux_stream_event_hook()
+
+        def _flip_after_first(event, _inner=hook):
+            cancelled["v"] = True
+            _inner(event)
+
+        with pytest.raises(aux.AuxiliaryExplicitCancellation):
+            create_anthropic_message(
+                _anthropic_client(stream), {"model": "m", "messages": []},
+                on_stream_event=_flip_after_first,
+            )
+    assert stream.yielded == 1
+    assert stream.exited
+
+
+def test_anthropic_stream_without_host_deadline_runs_to_completion():
+    stream = _AnthropicStream(count=5, delay=0)
+    with aux.aux_progress_hook(lambda: None):
+        hook = aux._anthropic_aux_stream_event_hook()
+        message = create_anthropic_message(
+            _anthropic_client(stream), {"model": "m", "messages": []},
+            on_stream_event=hook,
+        )
+    assert message.content[0].text == "summary"
+    assert stream.yielded == 5