diff --git a/agent/agent_init.py b/agent/agent_init.py
index 32a06259441..495260d2188 100644
--- a/agent/agent_init.py
+++ b/agent/agent_init.py
@@ -1570,6 +1570,16 @@ def init_agent(
     compression_in_place = is_truthy_value(
         _compression_cfg.get("in_place"), default=False
     )
+    codex_app_server_auto_compaction = str(
+        _compression_cfg.get("codex_app_server_auto", "native") or "native"
+    ).lower()
+    if codex_app_server_auto_compaction not in {"native", "hermes", "off"}:
+        _ra().logger.warning(
+            "Invalid compression.codex_app_server_auto=%r; using 'native'. "
+            "Valid values are: native, hermes, off.",
+            codex_app_server_auto_compaction,
+        )
+        codex_app_server_auto_compaction = "native"
 
     # Read optional explicit context_length override for the auxiliary
     # compression model. Custom endpoints often cannot report this via
@@ -1824,6 +1834,7 @@ def init_agent(
             pass
     agent.compression_enabled = compression_enabled
     agent.compression_in_place = compression_in_place
+    agent.codex_app_server_auto_compaction = codex_app_server_auto_compaction
 
     # Reject models whose context window is below the minimum required
     # for reliable tool-calling workflows (64K tokens).
diff --git a/agent/codex_runtime.py b/agent/codex_runtime.py
index 1cf48ec1705..2077d2fddca 100644
--- a/agent/codex_runtime.py
+++ b/agent/codex_runtime.py
@@ -228,6 +228,76 @@ def _record_codex_app_server_usage(agent, turn) -> dict[str, Any]:
     }
 
 
+def _record_codex_app_server_compaction(
+    agent,
+    turn,
+    *,
+    approx_tokens: int | None = None,
+    force: bool = False,
+) -> bool:
+    """Record a Codex-native context compaction boundary in Hermes state.
+
+    The app-server owns the compacted thread context, so Hermes should not
+    rewrite local transcript rows here; state.db records the boundary via the
+    session event/usage counters while preserving the visible transcript.
+    """
+    if not force and not getattr(turn, "compacted", False):
+        return False
+
+    thread_id = getattr(turn, "thread_id", None) or ""
+    turn_id = getattr(turn, "turn_id", None) or ""
+    logger.info(
+        "codex app-server compaction observed: session=%s thread=%s turn=%s force=%s",
+        getattr(agent, "session_id", None) or "none",
+        thread_id,
+        turn_id,
+        force,
+    )
+    if not force:
+        try:
+            from agent.conversation_compression import COMPACTION_STATUS
+
+            agent._emit_status(COMPACTION_STATUS)
+        except Exception:
+            pass
+
+    compressor = getattr(agent, "context_compressor", None)
+    if compressor is not None:
+        compressor.compression_count = getattr(
+            compressor, "compression_count", 0
+        ) + 1
+        compressor.last_compression_rough_tokens = approx_tokens or 0
+        if not getattr(turn, "token_usage_last", None):
+            compressor.last_prompt_tokens = -1
+            compressor.last_completion_tokens = 0
+            compressor.awaiting_real_usage_after_compression = True
+
+    agent._last_compaction_in_place = False
+    try:
+        if getattr(agent, "event_callback", None):
+            agent.event_callback(
+                "session:compress",
+                {
+                    "platform": getattr(agent, "platform", None) or "",
+                    "session_id": getattr(agent, "session_id", None) or "",
+                    "old_session_id": "",
+                    "in_place": False,
+                    "compression_count": getattr(
+                        compressor, "compression_count", 0
+                    )
+                    if compressor is not None
+                    else 0,
+                    "runtime": "codex_app_server",
+                    "thread_id": thread_id,
+                    "turn_id": turn_id,
+                },
+            )
+    except Exception:
+        logger.debug("event_callback error on codex session:compress", exc_info=True)
+
+    return True
+
+
 def run_codex_app_server_turn(
     agent,
     *,
@@ -393,6 +463,7 @@ def run_codex_app_server_turn(
     agent._iters_since_skill = (
         getattr(agent, "_iters_since_skill", 0) + turn.tool_iterations
     )
+    _record_codex_app_server_compaction(agent, turn)
     usage_result = _record_codex_app_server_usage(agent, turn)
     api_calls = 1
 
diff --git a/agent/conversation_compression.py b/agent/conversation_compression.py
index 7e7a26dc2ed..843960cc281 100644
--- a/agent/conversation_compression.py
+++ b/agent/conversation_compression.py
@@ -465,6 +465,21 @@ def compress_context(
         prompt — the session is NOT rotated.  Callers should detect the
         no-op via ``len(returned) == len(input)`` and stop the retry loop.
     """
+    # Codex app-server sessions: the codex agent owns the real thread context;
+    # Hermes' summarizer would only rewrite a local mirror without shrinking
+    # the actual thread (#36801). Route compaction to the app server's own
+    # thread/compact mechanism. Behavior is controlled by
+    # ``compression.codex_app_server_auto`` (native|hermes|off).
+    if getattr(agent, "api_mode", None) == "codex_app_server":
+        return _compress_context_via_codex_app_server(
+            agent,
+            messages,
+            system_message,
+            approx_tokens=approx_tokens,
+            task_id=task_id,
+            force=force,
+        )
+
     # Lazy feasibility check — run the auxiliary-provider probe + context
     # length lookup just-in-time on the first compression attempt instead of
     # at AIAgent.__init__. Saves ~400ms cold off every short session that
@@ -971,6 +986,122 @@ def compress_context(
         _release_lock()
 
 
+def _compress_context_via_codex_app_server(
+    agent: Any,
+    messages: list,
+    system_message: Optional[str],
+    *,
+    approx_tokens: Optional[int] = None,
+    task_id: str = "default",
+    force: bool = False,
+) -> Tuple[list, str]:
+    """Route compaction to Codex app-server for Codex-owned threads.
+
+    Hermes' normal compressor rewrites the local OpenAI-style transcript.
+    That does not shrink the actual Codex app-server thread context. For this
+    runtime, ask Codex to compact its own thread and keep Hermes' transcript
+    unchanged.
+    """
+    auto_mode = str(
+        getattr(agent, "codex_app_server_auto_compaction", "native") or "native"
+    ).lower()
+    if auto_mode not in {"native", "hermes", "off"}:
+        auto_mode = "native"
+    if not force and auto_mode != "hermes":
+        logger.info(
+            "codex app-server compaction skipped: mode=%s force=false "
+            "(session=%s messages=%d tokens=~%s)",
+            auto_mode,
+            getattr(agent, "session_id", None) or "none",
+            len(messages),
+            f"{approx_tokens:,}" if approx_tokens else "unknown",
+        )
+        existing_prompt = getattr(agent, "_cached_system_prompt", None)
+        if not existing_prompt:
+            existing_prompt = agent._build_system_prompt(system_message)
+        return messages, existing_prompt
+
+    codex_session = getattr(agent, "_codex_session", None)
+    if codex_session is None:
+        logger.info(
+            "codex app-server compaction skipped: no active codex thread "
+            "(session=%s messages=%d tokens=~%s)",
+            getattr(agent, "session_id", None) or "none",
+            len(messages),
+            f"{approx_tokens:,}" if approx_tokens else "unknown",
+        )
+        existing_prompt = getattr(agent, "_cached_system_prompt", None)
+        if not existing_prompt:
+            existing_prompt = agent._build_system_prompt(system_message)
+        return messages, existing_prompt
+
+    logger.info(
+        "codex app-server compaction started: session=%s messages=%d tokens=~%s",
+        getattr(agent, "session_id", None) or "none",
+        len(messages),
+        f"{approx_tokens:,}" if approx_tokens else "unknown",
+    )
+    try:
+        agent._emit_status(COMPACTION_STATUS)
+    except Exception:
+        pass
+
+    result = codex_session.compact_thread()
+    if getattr(result, "should_retire", False):
+        try:
+            codex_session.close()
+        except Exception:
+            pass
+        agent._codex_session = None
+
+    if getattr(result, "error", None):
+        try:
+            agent._emit_warning(
+                f"⚠ Codex app-server compaction failed: {result.error}"
+            )
+        except Exception:
+            pass
+        existing_prompt = getattr(agent, "_cached_system_prompt", None)
+        if not existing_prompt:
+            existing_prompt = agent._build_system_prompt(system_message)
+        return messages, existing_prompt
+
+    try:
+        from agent.codex_runtime import (
+            _record_codex_app_server_compaction,
+            _record_codex_app_server_usage,
+        )
+
+        _record_codex_app_server_compaction(
+            agent,
+            result,
+            approx_tokens=approx_tokens,
+            force=True,
+        )
+        if getattr(result, "token_usage_last", None):
+            _record_codex_app_server_usage(agent, result)
+    except Exception:
+        logger.debug("codex compaction bookkeeping failed", exc_info=True)
+
+    try:
+        from tools.file_tools import reset_file_dedup
+
+        reset_file_dedup(task_id)
+    except Exception:
+        pass
+
+    logger.info(
+        "codex app-server compaction done: session=%s thread=%s turn=%s",
+        getattr(agent, "session_id", None) or "none",
+        getattr(result, "thread_id", None) or "",
+        getattr(result, "turn_id", None) or "",
+    )
+    existing_prompt = getattr(agent, "_cached_system_prompt", None)
+    if not existing_prompt:
+        existing_prompt = agent._build_system_prompt(system_message)
+    return messages, existing_prompt
+
+
 def try_shrink_image_parts_in_messages(
     api_messages: list,
     *,
diff --git a/agent/transports/codex_app_server_session.py b/agent/transports/codex_app_server_session.py
index 7292823766e..78af728711d 100644
--- a/agent/transports/codex_app_server_session.py
+++ b/agent/transports/codex_app_server_session.py
@@ -75,6 +75,7 @@ class TurnResult:
     token_usage_last: Optional[dict[str, Any]] = None
     token_usage_total: Optional[dict[str, Any]] = None
     model_context_window: Optional[int] = None
+    compacted: bool = False
     # Hint to the caller that the underlying codex subprocess is likely
     # wedged (turn-level timeout fired, post-tool watchdog tripped, or
     # token-refresh failure killed the child). The caller should retire
@@ -505,6 +506,7 @@ class CodexAppServerSession:
                     if pending is None:
                         break
                     _apply_token_usage_notification(result, pending)
+                    _apply_compaction_notification(result, pending)
                     self._track_pending_file_change(pending)
                     proj = projector.project(pending)
                     if proj.messages:
@@ -541,6 +543,7 @@ class CodexAppServerSession:
                     logger.debug("on_event callback raised", exc_info=True)
 
             _apply_token_usage_notification(result, note)
+            _apply_compaction_notification(result, note)
 
             # Track in-progress fileChange items so the approval bridge
             # can surface a real change summary when codex requests
@@ -632,6 +635,154 @@ class CodexAppServerSession:
 
         return result
 
+    def compact_thread(
+        self,
+        *,
+        turn_timeout: float = 600.0,
+        notification_poll_timeout: float = 0.25,
+    ) -> TurnResult:
+        """Trigger Codex-native history compaction for the current thread.
+
+        `thread/compact/start` returns immediately; the actual compaction
+        progress streams through the same turn/item notifications as a normal
+        turn. We wait for the matching `turn/completed` so callers can treat a
+        successful return as a completed compaction boundary.
+        """
+        result = TurnResult()
+        try:
+            self.ensure_started()
+        except (CodexAppServerError, TimeoutError) as exc:
+            result.error = self._format_error_with_stderr(
+                "codex app-server startup failed", exc
+            )
+            result.should_retire = True
+            return result
+
+        assert self._client is not None and self._thread_id is not None
+        result.thread_id = self._thread_id
+        self._interrupt_event.clear()
+        projector = CodexEventProjector()
+
+        try:
+            self._client.request(
+                "thread/compact/start",
+                {"threadId": self._thread_id},
+                timeout=10,
+            )
+        except CodexAppServerError as exc:
+            stderr_blob = "\n".join(self._client.stderr_tail(40))
+            hint = _classify_oauth_failure(exc.message, stderr_blob)
+            if hint is not None:
+                result.error = hint
+                result.should_retire = True
+            else:
+                result.error = self._format_error_with_stderr(
+                    "thread/compact/start failed", exc
+                )
+            return result
+        except TimeoutError as exc:
+            stderr_blob = "\n".join(self._client.stderr_tail(40))
+            hint = _classify_oauth_failure(stderr_blob)
+            result.error = hint or self._format_error_with_stderr(
+                "thread/compact/start timed out", exc
+            )
+            result.should_retire = True
+            return result
+
+        deadline = time.monotonic() + turn_timeout
+        turn_complete = False
+
+        while time.monotonic() < deadline and not turn_complete:
+            if self._interrupt_event.is_set():
+                self._issue_interrupt(result.turn_id)
+                result.interrupted = True
+                break
+
+            if not self._client.is_alive():
+                stderr_blob = "\n".join(self._client.stderr_tail(60))
+                hint = _classify_oauth_failure(stderr_blob)
+                if hint is not None:
+                    result.error = hint
+                else:
+                    result.error = self._format_error_with_stderr(
+                        "codex app-server subprocess exited unexpectedly",
+                        tail_lines=20,
+                    )
+                result.should_retire = True
+                break
+
+            sreq = self._client.take_server_request(timeout=0)
+            if sreq is not None:
+                self._handle_server_request(sreq)
+                continue
+
+            note = self._client.take_notification(
+                timeout=notification_poll_timeout
+            )
+            if note is None:
+                continue
+
+            method = note.get("method", "")
+            if self._on_event is not None:
+                try:
+                    self._on_event(note)
+                except Exception:  # pragma: no cover - display callback
+                    logger.debug("on_event callback raised", exc_info=True)
+
+            _apply_token_usage_notification(result, note)
+            _apply_compaction_notification(result, note)
+            self._track_pending_file_change(note)
+
+            projection = projector.project(note)
+            if projection.messages:
+                result.projected_messages.extend(projection.messages)
+            if projection.is_tool_iteration:
+                result.tool_iterations += 1
+            if projection.final_text is not None:
+                result.final_text = projection.final_text
+                if _has_turn_aborted_marker(projection.final_text):
+                    turn_complete = True
+                    result.interrupted = True
+                    result.error = (
+                        result.error or "codex reported turn_aborted"
+                    )
+
+            if method == "turn/started":
+                turn_obj = (note.get("params") or {}).get("turn") or {}
+                result.turn_id = turn_obj.get("id") or result.turn_id
+            elif method == "turn/completed":
+                turn_complete = True
+                turn_obj = (note.get("params") or {}).get("turn") or {}
+                result.turn_id = turn_obj.get("id") or result.turn_id
+                turn_status = turn_obj.get("status")
+                if turn_status and turn_status not in {"completed", "interrupted"}:
+                    err_obj = turn_obj.get("error")
+                    if err_obj:
+                        err_msg = _format_responses_error(err_obj, str(turn_status))
+                        stderr_blob = "\n".join(
+                            self._client.stderr_tail(40)
+                        )
+                        hint = _classify_oauth_failure(err_msg, stderr_blob)
+                        if hint is not None:
+                            result.error = hint
+                            result.should_retire = True
+                        else:
+                            result.error = self._format_error_with_stderr(
+                                f"compact turn ended status={turn_status}",
+                                err_msg,
+                            )
+
+        if not turn_complete and not result.interrupted:
+            self._issue_interrupt(result.turn_id)
+            result.interrupted = True
+            if not result.error:
+                result.error = self._format_error_with_stderr(
+                    f"compact turn timed out after {turn_timeout}s"
+                )
+            result.should_retire = True
+
+        return result
+
     # ---------- internals ----------
 
     def _issue_interrupt(self, turn_id: Optional[str]) -> None:
@@ -845,6 +996,38 @@ def _apply_token_usage_notification(result: TurnResult, note: dict) -> None:
         result.model_context_window = window
 
 
+def _apply_compaction_notification(result: TurnResult, note: dict) -> None:
+    """Capture Codex-native context compaction boundaries.
+
+    Recent app-server builds expose compaction as a ContextCompaction item.
+    Older builds also emit the deprecated thread/compacted notification. Both
+    mean the underlying Codex thread history has been compacted.
+    """
+    if not isinstance(note, dict):
+        return
+    method = note.get("method") or ""
+    params = note.get("params") or {}
+    if not isinstance(params, dict):
+        return
+
+    if method == "thread/compacted":
+        result.compacted = True
+        result.thread_id = params.get("threadId") or result.thread_id
+        result.turn_id = params.get("turnId") or result.turn_id
+        return
+
+    if method not in {"item/started", "item/completed"}:
+        return
+
+    item = params.get("item") or {}
+    if not isinstance(item, dict) or item.get("type") != "contextCompaction":
+        return
+
+    result.compacted = True
+    result.thread_id = params.get("threadId") or result.thread_id
+    result.turn_id = params.get("turnId") or result.turn_id
+
+
 def _approval_choice_to_codex_decision(choice: str) -> str:
     """Map Hermes approval choices onto codex's CommandExecutionApprovalDecision
     / FileChangeApprovalDecision wire values.
diff --git a/agent/turn_context.py b/agent/turn_context.py
index 89b00819c2c..4fd6ddff2c3 100644
--- a/agent/turn_context.py
+++ b/agent/turn_context.py
@@ -369,6 +369,20 @@ def build_turn_context(
             lambda _tokens: False,
         )
         _preflight_deferred = _defer_preflight(_preflight_tokens)
+        # Codex app-server threads are compacted by the codex agent itself;
+        # Hermes only initiates compaction in "hermes" mode (#36801).
+        _codex_native_auto = (
+            getattr(agent, "api_mode", None) == "codex_app_server"
+            and str(
+                getattr(
+                    agent,
+                    "codex_app_server_auto_compaction",
+                    "native",
+                )
+                or "native"
+            ).lower()
+            in {"native", "off"}
+        )
 
         if not _preflight_deferred:
             _last = _compressor.last_prompt_tokens
@@ -397,6 +411,12 @@ def build_turn_context(
                 int(_compression_cooldown.get("remaining_seconds", 0.0)),
                 agent.session_id or "none",
             )
+        elif _codex_native_auto:
+            logger.info(
+                "Skipping Hermes preflight compression for codex app-server "
+                "(mode=%s); Hermes will not start thread compaction here.",
+                getattr(agent, "codex_app_server_auto_compaction", "native"),
+            )
         elif _compressor.should_compress(_preflight_tokens):
             logger.info(
                 "Preflight compression: ~%s tokens >= %s threshold (model %s, ctx %s)",
diff --git a/cli-config.yaml.example b/cli-config.yaml.example
index f058705cfe2..8de33b80735 100644
--- a/cli-config.yaml.example
+++ b/cli-config.yaml.example
@@ -410,6 +410,21 @@ compression:
   # Trigger compression at this % of model's context limit (default: 0.50 = 50%)
   # Lower values = more aggressive compression, higher values = compress later
   threshold: 0.50
+
+  # Existing Codex gpt-5.5 behavior: raise Hermes' compaction trigger to 85%
+  # for the ChatGPT Codex OAuth route. Set false to opt back down to threshold.
+  codex_gpt55_autoraise: true
+
+  # Codex-native compaction paths are opt-in (default: false) to preserve
+  # Hermes' existing auxiliary summarizer behavior for existing installs.
+  # When true, Codex OAuth uses Responses API compact and Codex app-server
+  # compaction uses the app-server thread compact API.
+  codex_native_compaction: false
+
+  # Codex OAuth / Responses API compaction trigger (default: 0.85 = 85%).
+  # Used only when codex_native_compaction is true. The recent tail still uses
+  # protect_last_n below.
+  codex_responses_threshold: 0.85
   
   # Fraction of the threshold to preserve as recent tail (default: 0.20 = 20%)
   # e.g. 20% of 50% threshold = 10% of total context kept as recent messages.
@@ -422,6 +437,13 @@ compression:
   # compression of older turns.
   protect_last_n: 20
 
+  # Codex app-server auto-compaction mode:
+  # Used only when codex_native_compaction is true.
+  #   native = let Codex decide when to compact its own thread (default)
+  #   hermes = let Hermes threshold trigger Codex thread/compact/start
+  #   off    = Hermes will not auto-trigger compaction; Codex may still compact natively
+  codex_app_server_auto: native
+
   # Number of non-system messages to protect at the head of the transcript, in
   # ADDITION to the system prompt (which is always implicitly protected).
   # Head messages are NEVER summarized — they survive every compression
diff --git a/hermes_cli/config.py b/hermes_cli/config.py
index 81d66e99eba..7f2945de5f8 100644
--- a/hermes_cli/config.py
+++ b/hermes_cli/config.py
@@ -1377,6 +1377,14 @@ DEFAULT_CONFIG = {
                                       # autoraise banner. Set False to keep the
                                       # 85% threshold autoraise but suppress the
                                       # user-facing notice in CLI/gateway output.
+        "codex_app_server_auto": "native",  # Codex app-server (codex CLI runtime) thread
+                                      # compaction mode. The codex agent owns the real
+                                      # thread context, so Hermes' summarizer cannot
+                                      # shrink it (#36801). native = codex decides when
+                                      # to compact its own thread (default); hermes =
+                                      # Hermes' compression threshold triggers
+                                      # thread/compact/start; off = never auto-trigger
+                                      # (codex may still compact natively).
         "in_place": True,             # When True, compaction rewrites the message
                                       # list and rebuilds the system prompt WITHOUT
                                       # rotating the session id — the conversation
diff --git a/scripts/release.py b/scripts/release.py
index 32f7c577a27..b7895aa051b 100755
--- a/scripts/release.py
+++ b/scripts/release.py
@@ -163,6 +163,7 @@ AUTHOR_MAP = {
     "65363919+coygeek@users.noreply.github.com": "coygeek",  # PR #37951 salvage (fail closed when provider env blocklist import fails; #37950)
     "5261694+djstunami@users.noreply.github.com": "djstunami",  # PR #5316 salvage / co-author (suppress transient check_fn flakes so subagents keep file/terminal tools; #21658 / #5304)
     "jmmaloney4@gmail.com": "jmmaloney4",  # PR #25206 salvage (re-select credential pool on primary runtime restore; #25205)
+    "hmirin@users.noreply.github.com": "hmirin",
     "dale@dalenguyen.me": "dalenguyen",  # PR #53678 salvage (strip VIRTUAL_ENV/CONDA_PREFIX from terminal subprocess env; #23473)
     "liruixinch@outlook.com": "HexLab98",  # PR #53863 salvage (env-only proxy policy for auxiliary OpenAI clients on macOS; #53702)
     "blaryx@gmail.com": "Blaryxoff",  # PR #32602 salvage (deep-merge PUT /api/config to preserve unrelated sections; #13396)
diff --git a/tests/agent/transports/test_codex_app_server_session.py b/tests/agent/transports/test_codex_app_server_session.py
index 0322fb08721..adc3470131e 100644
--- a/tests/agent/transports/test_codex_app_server_session.py
+++ b/tests/agent/transports/test_codex_app_server_session.py
@@ -445,6 +445,107 @@ class TestRunTurn:
         r = s.run_turn("x", turn_timeout=1.0)
         assert r.error and "model error" in r.error
 
+    def test_run_turn_records_native_compaction_item(self):
+        client = FakeClient()
+        client.queue_notification(
+            "item/completed",
+            threadId="thread-fake-001",
+            turnId="turn-fake-001",
+            item={"type": "contextCompaction", "id": "compact-item-1"},
+        )
+        client.queue_notification(
+            "turn/completed", threadId="thread-fake-001",
+            turn={"id": "turn-fake-001", "status": "completed", "error": None},
+        )
+
+        r = make_session(client).run_turn("x", turn_timeout=1.0)
+
+        assert r.compacted is True
+        assert r.thread_id == "thread-fake-001"
+        assert r.turn_id == "turn-fake-001"
+
+    def test_run_turn_records_deprecated_thread_compacted_notification(self):
+        client = FakeClient()
+        client.queue_notification(
+            "thread/compacted",
+            threadId="thread-fake-001",
+            turnId="turn-fake-001",
+        )
+        client.queue_notification(
+            "turn/completed", threadId="thread-fake-001",
+            turn={"id": "turn-fake-001", "status": "completed", "error": None},
+        )
+
+        r = make_session(client).run_turn("x", turn_timeout=1.0)
+
+        assert r.compacted is True
+
+
+class TestCompactThread:
+    def test_compact_thread_sends_rpc_and_waits_for_completion(self):
+        client = FakeClient()
+        client.queue_notification(
+            "turn/started",
+            threadId="thread-fake-001",
+            turn={"id": "compact-turn-1"},
+        )
+        client.queue_notification(
+            "item/completed",
+            threadId="thread-fake-001",
+            turnId="compact-turn-1",
+            item={"type": "contextCompaction", "id": "compact-item-1"},
+        )
+        client.queue_notification(
+            "item/completed",
+            threadId="thread-fake-001",
+            turnId="compact-turn-1",
+            item={"type": "agentMessage", "id": "m1", "text": "compacted"},
+        )
+        client.queue_notification(
+            "thread/tokenUsage/updated",
+            threadId="thread-fake-001",
+            turnId="compact-turn-1",
+            tokenUsage={
+                "last": {"inputTokens": 10, "outputTokens": 2, "totalTokens": 12},
+                "total": {"inputTokens": 100, "outputTokens": 20, "totalTokens": 120},
+                "modelContextWindow": 200000,
+            },
+        )
+        client.queue_notification(
+            "turn/completed",
+            threadId="thread-fake-001",
+            turn={"id": "compact-turn-1", "status": "completed", "error": None},
+        )
+
+        r = make_session(client).compact_thread(turn_timeout=2.0)
+
+        assert ("thread/compact/start", {"threadId": "thread-fake-001"}) in client.requests
+        assert r.error is None
+        assert r.thread_id == "thread-fake-001"
+        assert r.turn_id == "compact-turn-1"
+        assert r.compacted is True
+        assert r.final_text == "compacted"
+        assert r.token_usage_last["totalTokens"] == 12
+        assert r.model_context_window == 200000
+
+    def test_compact_thread_failure_returns_error(self):
+        client = FakeClient()
+        from agent.transports.codex_app_server import CodexAppServerError
+
+        def boom(method, params):
+            if method == "thread/compact/start":
+                raise CodexAppServerError(code=-32603, message="compact unavailable")
+            if method == "thread/start":
+                return {"thread": {"id": "thread-fake-001"}}
+            return {}
+
+        client._request_handler = boom
+        r = make_session(client).compact_thread(turn_timeout=2.0)
+
+        assert r.error is not None
+        assert "compact unavailable" in r.error
+        assert r.should_retire is False
+
 
 # ---- approval bridge ----
 
diff --git a/tests/gateway/test_agent_cache.py b/tests/gateway/test_agent_cache.py
index 73a4941db3f..708b2d3ac71 100644
--- a/tests/gateway/test_agent_cache.py
+++ b/tests/gateway/test_agent_cache.py
@@ -228,16 +228,24 @@ class TestExtractCacheBustingConfig:
                 "compression": {
                     "enabled": False,
                     "threshold": 0.6,
+                    "codex_gpt55_autoraise": False,
+                    "codex_native_compaction": True,
+                    "codex_responses_threshold": 0.85,
                     "target_ratio": 0.3,
                     "protect_last_n": 25,
+                    "codex_app_server_auto": "hermes",
                     "some_other_key": "ignored",
                 }
             }
         )
         assert out["compression.enabled"] is False
         assert out["compression.threshold"] == 0.6
+        assert out["compression.codex_gpt55_autoraise"] is False
+        assert out["compression.codex_native_compaction"] is True
+        assert out["compression.codex_responses_threshold"] == 0.85
         assert out["compression.target_ratio"] == 0.3
         assert out["compression.protect_last_n"] == 25
+        assert out["compression.codex_app_server_auto"] == "hermes"
 
     def test_missing_keys_yield_none(self):
         """Absent config keys must produce None values (still contribute to signature)."""
@@ -2116,4 +2124,3 @@ class TestCrossProcessInvalidationDefersCleanup:
 
         assert release_calls == [old_agent]
         runner._cleanup_agent_resources.assert_not_called()
-
diff --git a/tests/hermes_cli/test_config.py b/tests/hermes_cli/test_config.py
index b777bf393ce..b580ca14471 100644
--- a/tests/hermes_cli/test_config.py
+++ b/tests/hermes_cli/test_config.py
@@ -1780,3 +1780,54 @@ class TestConfigNormalizationDoesNotOverwriteUserValues:
 
     def test_explicit_config_paths_ignore_empty_sections(self):
         assert _explicit_config_paths({"memory": {}, "display": {}}) == set()
+
+
+class TestCodexNativeCompactionConfig:
+    """Codex-native compaction stays opt-in without mutating existing configs."""
+
+    def _write(self, tmp_path, body):
+        (tmp_path / "config.yaml").write_text(body, encoding="utf-8")
+
+    def test_default_config_keeps_codex_native_compaction_opt_in(self):
+        assert DEFAULT_CONFIG["compression"]["codex_native_compaction"] is False
+        assert DEFAULT_CONFIG["compression"]["codex_gpt55_autoraise"] is True
+
+    def test_migration_does_not_write_codex_native_compaction_default(self, tmp_path):
+        with patch.dict(os.environ, {"HERMES_HOME": str(tmp_path)}):
+            self._write(
+                tmp_path,
+                "_config_version: 31\n"
+                "compression:\n"
+                "  threshold: 0.5\n"
+                "  codex_gpt55_autoraise: false\n",
+            )
+
+            result = migrate_config(interactive=False, quiet=True)
+
+            raw = yaml.safe_load((tmp_path / "config.yaml").read_text())
+            assert raw["compression"]["codex_gpt55_autoraise"] is False
+            assert "codex_native_compaction" not in raw["compression"]
+            assert raw["compression"]["threshold"] == 0.5
+            assert raw["_config_version"] == DEFAULT_CONFIG["_config_version"]
+            assert (
+                "compression.codex_native_compaction=false"
+                not in result["config_added"]
+            )
+
+    def test_preserves_existing_codex_native_compaction_value(self, tmp_path):
+        with patch.dict(os.environ, {"HERMES_HOME": str(tmp_path)}):
+            self._write(
+                tmp_path,
+                "_config_version: 31\n"
+                "compression:\n"
+                "  codex_native_compaction: true\n",
+            )
+
+            result = migrate_config(interactive=False, quiet=True)
+
+            raw = yaml.safe_load((tmp_path / "config.yaml").read_text())
+            assert raw["compression"]["codex_native_compaction"] is True
+            assert (
+                "compression.codex_native_compaction=false"
+                not in result["config_added"]
+            )
diff --git a/tests/run_agent/test_codex_app_server_compaction.py b/tests/run_agent/test_codex_app_server_compaction.py
new file mode 100644
index 00000000000..8f9cea51f81
--- /dev/null
+++ b/tests/run_agent/test_codex_app_server_compaction.py
@@ -0,0 +1,196 @@
+from types import SimpleNamespace
+
+from agent.codex_runtime import _record_codex_app_server_compaction
+from agent.conversation_compression import COMPACTION_STATUS, compress_context
+from agent.transports.codex_app_server_session import TurnResult
+
+
+class FakeCodexSession:
+    def __init__(self, result):
+        self.result = result
+        self.calls = 0
+        self.closed = False
+
+    def compact_thread(self):
+        self.calls += 1
+        return self.result
+
+    def close(self):
+        self.closed = True
+
+
+class DummyAgent:
+    def __init__(
+        self,
+        result,
+        *,
+        auto_compaction="native",
+        codex_native_compaction=True,
+    ):
+        self.api_mode = "codex_app_server"
+        self.codex_native_compaction_enabled = codex_native_compaction
+        self.codex_app_server_auto_compaction = auto_compaction
+        self.session_id = "hermes-session-1"
+        self.platform = "cli"
+        self._cached_system_prompt = "cached prompt"
+        self._codex_session = FakeCodexSession(result)
+        self.context_compressor = SimpleNamespace(
+            compression_count=0,
+            last_compression_rough_tokens=0,
+            last_prompt_tokens=123,
+            last_completion_tokens=45,
+            awaiting_real_usage_after_compression=False,
+        )
+        self.statuses = []
+        self.warnings = []
+        self.events = []
+        self.built_prompts = []
+
+    def _emit_status(self, message):
+        self.statuses.append(message)
+
+    def _emit_warning(self, message):
+        self.warnings.append(message)
+
+    def _build_system_prompt(self, system_message):
+        self.built_prompts.append(system_message)
+        return "built prompt"
+
+    def event_callback(self, name, payload):
+        self.events.append((name, payload))
+
+
+def test_codex_app_server_native_auto_mode_leaves_thread_compaction_to_codex():
+    agent = DummyAgent(
+        TurnResult(thread_id="thread-1", turn_id="compact-turn-1")
+    )
+    messages = [{"role": "user", "content": "hi"}]
+
+    returned, prompt = compress_context(
+        agent,
+        messages,
+        "system",
+        approx_tokens=100000,
+        task_id="test",
+    )
+
+    assert returned is messages
+    assert prompt == "cached prompt"
+    assert agent._codex_session.calls == 0
+    assert agent.context_compressor.compression_count == 0
+    assert agent.events == []
+
+
+def test_codex_app_server_manual_compression_routes_to_codex_thread():
+    agent = DummyAgent(
+        TurnResult(thread_id="thread-1", turn_id="compact-turn-1")
+    )
+    messages = [
+        {"role": "user", "content": "hi"},
+        {"role": "assistant", "content": "hello"},
+    ]
+
+    returned, prompt = compress_context(
+        agent,
+        messages,
+        "system",
+        approx_tokens=100000,
+        task_id="test",
+        force=True,
+    )
+
+    assert returned is messages
+    assert prompt == "cached prompt"
+    assert agent._codex_session.calls == 1
+    assert agent.context_compressor.compression_count == 1
+    assert agent.context_compressor.last_compression_rough_tokens == 100000
+    assert agent.context_compressor.last_prompt_tokens == -1
+    assert agent.context_compressor.last_completion_tokens == 0
+    assert agent.context_compressor.awaiting_real_usage_after_compression is True
+    assert agent.events == [
+        (
+            "session:compress",
+            {
+                "platform": "cli",
+                "session_id": "hermes-session-1",
+                "old_session_id": "",
+                "in_place": False,
+                "compression_count": 1,
+                "runtime": "codex_app_server",
+                "thread_id": "thread-1",
+                "turn_id": "compact-turn-1",
+            },
+        )
+    ]
+
+
+def test_codex_app_server_hermes_mode_auto_compression_routes_to_codex_thread():
+    agent = DummyAgent(
+        TurnResult(thread_id="thread-1", turn_id="compact-turn-1"),
+        auto_compaction="hermes",
+    )
+    messages = [{"role": "user", "content": "hi"}]
+
+    returned, prompt = compress_context(
+        agent,
+        messages,
+        "system",
+        approx_tokens=100000,
+    )
+
+    assert returned is messages
+    assert prompt == "cached prompt"
+    assert agent._codex_session.calls == 1
+    assert agent.context_compressor.compression_count == 1
+
+
+def test_codex_app_server_compression_failure_preserves_bookkeeping():
+    agent = DummyAgent(TurnResult(error="compact failed"))
+    messages = [{"role": "user", "content": "hi"}]
+
+    returned, prompt = compress_context(
+        agent,
+        messages,
+        "system",
+        approx_tokens=100000,
+        force=True,
+    )
+
+    assert returned is messages
+    assert prompt == "cached prompt"
+    assert agent._codex_session.calls == 1
+    assert agent.context_compressor.compression_count == 0
+    assert agent.context_compressor.last_prompt_tokens == 123
+    assert agent.warnings
+
+
+def test_codex_app_server_native_compaction_notice_emits_status_and_event():
+    agent = DummyAgent(
+        TurnResult(thread_id="thread-1", turn_id="normal-turn-1")
+    )
+    turn = TurnResult(
+        thread_id="thread-1",
+        turn_id="normal-turn-1",
+        compacted=True,
+    )
+
+    recorded = _record_codex_app_server_compaction(agent, turn)
+
+    assert recorded is True
+    assert agent.context_compressor.compression_count == 1
+    assert agent.statuses == [COMPACTION_STATUS]
+    assert agent.events == [
+        (
+            "session:compress",
+            {
+                "platform": "cli",
+                "session_id": "hermes-session-1",
+                "old_session_id": "",
+                "in_place": False,
+                "compression_count": 1,
+                "runtime": "codex_app_server",
+                "thread_id": "thread-1",
+                "turn_id": "normal-turn-1",
+            },
+        )
+    ]
diff --git a/tests/run_agent/test_codex_app_server_integration.py b/tests/run_agent/test_codex_app_server_integration.py
index f9d2dcf652d..df16807ca84 100644
--- a/tests/run_agent/test_codex_app_server_integration.py
+++ b/tests/run_agent/test_codex_app_server_integration.py
@@ -49,7 +49,7 @@ def fake_session(monkeypatch):
     )
 
 
-def _make_codex_agent():
+def _make_codex_agent(**kwargs):
     """Construct an AIAgent in codex_app_server mode without contacting any
     real provider. We pass api_mode explicitly so the constructor takes the
     fast path for direct credentials."""
@@ -61,6 +61,7 @@ def _make_codex_agent():
         quiet_mode=True,
         skip_context_files=True,
         skip_memory=True,
+        **kwargs,
     )
 
 
@@ -134,6 +135,46 @@ class TestRunConversationCodexPath:
         assert agent.context_compressor.last_total_tokens == 130
         assert agent.context_compressor.context_length == 200000
 
+    def test_native_codex_compaction_updates_bookkeeping(self, monkeypatch):
+        def fake_run_turn(self, user_input: str, **kwargs):
+            return TurnResult(
+                final_text="done",
+                projected_messages=[{"role": "assistant", "content": "done"}],
+                turn_id="turn-compact-1",
+                thread_id="thread-compact-1",
+                compacted=True,
+            )
+
+        monkeypatch.setattr(CodexAppServerSession, "run_turn", fake_run_turn)
+        monkeypatch.setattr(
+            CodexAppServerSession, "ensure_started", lambda self: "thread-compact-1"
+        )
+        events = []
+        agent = _make_codex_agent(event_callback=lambda name, payload: events.append((name, payload)))
+
+        with patch.object(agent, "_spawn_background_review", return_value=None):
+            result = agent.run_conversation("hello")
+
+        assert result["completed"] is True
+        assert agent.context_compressor.compression_count == 1
+        assert agent.context_compressor.last_prompt_tokens == -1
+        assert agent.context_compressor.awaiting_real_usage_after_compression is True
+        assert events == [
+            (
+                "session:compress",
+                {
+                    "platform": "",
+                    "session_id": agent.session_id,
+                    "old_session_id": "",
+                    "in_place": False,
+                    "compression_count": 1,
+                    "runtime": "codex_app_server",
+                    "thread_id": "thread-compact-1",
+                    "turn_id": "turn-compact-1",
+                },
+            )
+        ]
+
     def test_projected_messages_are_spliced(self, fake_session):
         agent = _make_codex_agent()
         with patch.object(agent, "_spawn_background_review", return_value=None):
diff --git a/website/docs/developer-guide/context-compression-and-caching.md b/website/docs/developer-guide/context-compression-and-caching.md
index d9f4f6aac05..aa817190c17 100644
--- a/website/docs/developer-guide/context-compression-and-caching.md
+++ b/website/docs/developer-guide/context-compression-and-caching.md
@@ -86,6 +86,7 @@ compression:
   protect_last_n: 20         # Minimum protected tail messages (default: 20)
   codex_gpt55_autoraise: true  # gpt-5.5 on Codex OAuth: raise trigger to 85% (default: true)
   codex_gpt55_autoraise_notice: true  # Show the one-time autoraise notice (default: true)
+  codex_app_server_auto: native  # native|hermes|off for Codex app-server thread compaction
 
 # Summarization model/provider configured under auxiliary:
 auxiliary:
@@ -105,6 +106,7 @@ auxiliary:
 | `protect_first_n` | `3` | (hardcoded) | System prompt + first exchange always preserved |
 | `codex_gpt55_autoraise` | `true` | bool | Raise the trigger to 85% for gpt-5.5 on the ChatGPT Codex OAuth route (see below). Set `false` to keep the global `threshold` |
 | `codex_gpt55_autoraise_notice` | `true` | bool | Show the one-time Codex gpt-5.5 autoraise notice. Set `false` to keep the 85% autoraise but suppress the banner |
+| `codex_app_server_auto` | `native` | `native`, `hermes`, `off` | Thread-compaction mode for Codex app-server sessions (see below) |
 
 ### Codex gpt-5.5 threshold autoraise
 
@@ -131,6 +133,28 @@ To keep the 85% autoraise but hide only the one-time notice:
 hermes config set compression.codex_gpt55_autoraise_notice false
 ```
 
+### Codex app-server thread compaction
+
+Codex app-server sessions (`api_mode: codex_app_server` — the codex CLI/agent
+runtime) are different from every other route: the codex agent owns the backing
+thread context, so Hermes' auxiliary summarizer cannot shrink it — rewriting the
+local transcript mirror leaves the real thread growing unbounded until a hard
+context reset. For this runtime, compaction goes through the app-server's own
+mechanism instead:
+
+- Manual compaction (`/compress`) asks the app-server to compact the thread
+  (`thread/compact/start`) and waits for the compaction turn to complete.
+- Automatic compaction is controlled by `compression.codex_app_server_auto`:
+  the default `native` lets the app-server decide when to compact and Hermes
+  records the resulting compaction events (compression counters, session
+  events). Set `hermes` to let Hermes' compression threshold initiate
+  app-server compaction, or `off` to disable Hermes-initiated automatic
+  compaction entirely (codex may still compact natively).
+
+Hermes' local transcript is never rewritten on this runtime — state.db records
+the compaction boundary while the visible transcript stays intact. All other
+routes (including Codex OAuth chat sessions) keep Hermes' summary compressor.
+
 ### Computed Values (for a 200K context model at defaults)
 
 ```