diff --git a/tests/agent/test_compression_concurrent_fork.py b/tests/agent/test_compression_concurrent_fork.py
index d9647dc9ee1..617ded2e0e0 100644
--- a/tests/agent/test_compression_concurrent_fork.py
+++ b/tests/agent/test_compression_concurrent_fork.py
@@ -77,6 +77,10 @@ def _build_agent_with_db(db: SessionDB, session_id: str):
     compressor._last_aux_model_failure_model = None
     compressor._last_aux_model_failure_error = None
     agent.context_compressor = compressor
+    # These tests cover the ROTATION fallback path (forking, child sessions,
+    # lock contention) — pin in_place=False so they keep exercising it
+    # regardless of the global default (which flipped to True in #38763).
+    agent.compression_in_place = False
     return agent
 
 
diff --git a/tests/agent/test_compression_logging_session_context.py b/tests/agent/test_compression_logging_session_context.py
index c67ffc1fde2..85cd4132074 100644
--- a/tests/agent/test_compression_logging_session_context.py
+++ b/tests/agent/test_compression_logging_session_context.py
@@ -50,6 +50,10 @@ def _build_agent_with_db(db: SessionDB, session_id: str):
     compressor._last_aux_model_failure_model = None
     compressor._last_aux_model_failure_error = None
     agent.context_compressor = compressor
+    # This test covers the ROTATION fallback (logging session-context follows
+    # the id rotation) — pin in_place=False so it keeps exercising rotation
+    # regardless of the global default (flipped to True in #38763).
+    agent.compression_in_place = False
     return agent
 
 
diff --git a/tests/agent/test_compression_rotation_state.py b/tests/agent/test_compression_rotation_state.py
index 510c485182a..83ab63e2a69 100644
--- a/tests/agent/test_compression_rotation_state.py
+++ b/tests/agent/test_compression_rotation_state.py
@@ -54,6 +54,9 @@ def _build_agent_with_db(db: SessionDB, session_id: str, platform: str = "telegr
     compressor._last_aux_model_failure_model = None
     compressor._last_aux_model_failure_error = None
     agent.context_compressor = compressor
+    # ROTATION fallback path — pin in_place=False so these keep covering fork
+    # rotation regardless of the global default (flipped to True in #38763).
+    agent.compression_in_place = False
     return agent
 
 
diff --git a/tests/gateway/test_compression_concurrent_sessions.py b/tests/gateway/test_compression_concurrent_sessions.py
index d6fd26deb35..529e694a8f1 100644
--- a/tests/gateway/test_compression_concurrent_sessions.py
+++ b/tests/gateway/test_compression_concurrent_sessions.py
@@ -71,6 +71,10 @@ def _build_agent_with_db(db: SessionDB, session_id: str):
     compressor._last_aux_model_failure_model = None
     compressor._last_aux_model_failure_error = None
     agent.context_compressor = compressor
+    # ROTATION fallback path — pin in_place=False so these keep covering the
+    # concurrent-rotation lock contract regardless of the global default
+    # (flipped to True in #38763).
+    agent.compression_in_place = False
     return agent
 
 
diff --git a/tests/run_agent/test_compression_boundary_hook.py b/tests/run_agent/test_compression_boundary_hook.py
index cf43a50ccf7..db9bb7f4962 100644
--- a/tests/run_agent/test_compression_boundary_hook.py
+++ b/tests/run_agent/test_compression_boundary_hook.py
@@ -22,7 +22,7 @@ class TestCompressionBoundaryHook:
     def _make_agent(self, session_db):
         with patch.dict(os.environ, {"OPENROUTER_API_KEY": "test-key"}):
             from run_agent import AIAgent
-            return AIAgent(
+            agent = AIAgent(
                 api_key="test-key",
                 base_url="https://openrouter.ai/api/v1",
                 model="test/model",
@@ -32,6 +32,9 @@ class TestCompressionBoundaryHook:
                 skip_context_files=True,
                 skip_memory=True,
             )
+            # ROTATION fallback — pin in_place=False regardless of default (#38763).
+            agent.compression_in_place = False
+            return agent
 
     def test_on_session_start_called_with_compression_boundary(self):
         from hermes_state import SessionDB
@@ -167,7 +170,7 @@ class TestSessionCompressEvent:
     def _make_agent(self, session_db, event_callback=None):
         with patch.dict(os.environ, {"OPENROUTER_API_KEY": "test-key"}):
             from run_agent import AIAgent
-            return AIAgent(
+            agent = AIAgent(
                 api_key="test-key",
                 base_url="https://openrouter.ai/api/v1",
                 model="test/model",
@@ -178,6 +181,9 @@ class TestSessionCompressEvent:
                 skip_memory=True,
                 event_callback=event_callback,
             )
+            # ROTATION fallback — pin in_place=False regardless of default (#38763).
+            agent.compression_in_place = False
+            return agent
 
     def _stub_compressor(self):
         compressor = MagicMock()
diff --git a/tests/run_agent/test_in_place_compaction.py b/tests/run_agent/test_in_place_compaction.py
index 999eec343ab..2d19021af13 100644
--- a/tests/run_agent/test_in_place_compaction.py
+++ b/tests/run_agent/test_in_place_compaction.py
@@ -184,9 +184,11 @@ class TestInPlaceCompaction:
             assert calls["n"] == 1
 
 
-class TestRotationStillDefault:
+class TestRotationFallbackWhenFlagOff:
     def test_rotation_when_flag_off(self):
-        """Regression guard: flag off => legacy rotation is unchanged."""
+        """Rotation is now the OPT-OUT fallback (default flipped to in-place in
+        #38763). With in_place=False explicitly set, legacy rotation is
+        unchanged — forks a renamed continuation session."""
         from hermes_state import SessionDB
         from agent.conversation_compression import compress_context
 
@@ -247,10 +249,12 @@ class TestInPlaceSignalForGateway:
 
 
 class TestInPlaceConfigDefault:
-    def test_flag_defaults_off(self):
+    def test_flag_defaults_on(self):
+        """In-place is the default as of #38763 (rotation is now opt-out via
+        compression.in_place: false)."""
         from hermes_cli.config import DEFAULT_CONFIG
 
-        assert DEFAULT_CONFIG["compression"].get("in_place") is False
+        assert DEFAULT_CONFIG["compression"].get("in_place") is True
 
 
 class TestCompactedTurnsStaySearchable: