diff --git a/gateway/run.py b/gateway/run.py
index fdd30423e47..abe941fb1cc 100644
--- a/gateway/run.py
+++ b/gateway/run.py
@@ -8969,7 +8969,11 @@ class GatewayRunner(GatewayAuthorizationMixin, GatewayKanbanWatchersMixin, Gatew
                     self._record_telegram_topic_binding(source, session_entry)
                 except Exception:
                     logger.debug("Failed to record Telegram topic binding", exc_info=True)
-        if getattr(session_entry, "was_auto_reset", False):
+        # Capture and immediately consume was_auto_reset so it does not
+        # re-fire on subsequent messages — preventing the cleanup from
+        # wiping model/reasoning overrides set between turns (Closes #48031).
+        _was_auto_reset = getattr(session_entry, "was_auto_reset", False)
+        if _was_auto_reset:
             # Treat auto-reset as a full conversation boundary — drop every
             # session-scoped transient state so the fresh session does not
             # inherit the previous conversation's model/reasoning overrides
@@ -8978,11 +8982,12 @@ class GatewayRunner(GatewayAuthorizationMixin, GatewayKanbanWatchersMixin, Gatew
             self._set_session_reasoning_override(session_key, None)
             if hasattr(self, "_pending_model_notes"):
                 self._pending_model_notes.pop(session_key, None)
+            session_entry.was_auto_reset = False
         
         # Emit session:start for new or auto-reset sessions
         _is_new_session = (
             session_entry.created_at == session_entry.updated_at
-            or getattr(session_entry, "was_auto_reset", False)
+            or _was_auto_reset
             or getattr(session_entry, "is_fresh_reset", False)
         )
         # Consume the is_fresh_reset flag immediately so it doesn't leak
@@ -9018,7 +9023,7 @@ class GatewayRunner(GatewayAuthorizationMixin, GatewayKanbanWatchersMixin, Gatew
         
         # If the previous session expired and was auto-reset, prepend a notice
         # so the agent knows this is a fresh conversation (not an intentional /reset).
-        if getattr(session_entry, 'was_auto_reset', False):
+        if _was_auto_reset:
             reset_reason = getattr(session_entry, 'auto_reset_reason', None) or 'idle'
             if reset_reason == "suspended":
                 context_note = "[System note: The user's previous session was stopped and suspended. This is a fresh conversation with no prior context.]"
@@ -9077,7 +9082,8 @@ class GatewayRunner(GatewayAuthorizationMixin, GatewayKanbanWatchersMixin, Gatew
             except Exception as e:
                 logger.debug("Auto-reset notification failed (non-fatal): %s", e)
 
-            session_entry.was_auto_reset = False
+            # was_auto_reset is already consumed in the cleanup block above
+            # (single source of truth); only the reset reason needs clearing here.
             session_entry.auto_reset_reason = None
 
         # Auto-load skill(s) for topic/channel bindings (Telegram DM Topics,
diff --git a/gateway/slash_commands.py b/gateway/slash_commands.py
index d982cb2d582..9aa5c47060d 100644
--- a/gateway/slash_commands.py
+++ b/gateway/slash_commands.py
@@ -1488,6 +1488,11 @@ class GatewaySlashCommandsMixin:
             if _sess_db is not None:
                 try:
                     _sess_entry = self.session_store.get_or_create_session(source)
+                    # If this session was auto-reset, consume the flag so the
+                    # next regular message's cleanup does not wipe the model
+                    # override just stored below (Closes #48031).
+                    if getattr(_sess_entry, "was_auto_reset", False):
+                        _sess_entry.was_auto_reset = False
                     _sess_db.update_session_model(
                         _sess_entry.session_id, result.new_model
                     )
diff --git a/tests/gateway/test_48031_model_switch_after_auto_reset.py b/tests/gateway/test_48031_model_switch_after_auto_reset.py
new file mode 100644
index 00000000000..14bd08bd332
--- /dev/null
+++ b/tests/gateway/test_48031_model_switch_after_auto_reset.py
@@ -0,0 +1,91 @@
+"""Regression test for #48031 — /model switch lost after session auto-reset.
+
+When `/model X` is the FIRST message after an idle/daily/suspended auto-reset,
+it stores a session model override but the `was_auto_reset` flag is left True
+(the slash-command path doesn't pass through the message handler that consumes
+it). On the NEXT regular message, the auto-reset cleanup block in
+`_handle_message_with_agent` pops the freshly-stored override BEFORE the flag
+is consumed, so the switch is silently lost and resolution falls back to the
+config default — while the session DB still shows the switched model (a
+two-sources-of-truth divergence).
+
+The fix consumes `was_auto_reset` at two sites:
+  1. the cleanup block in gateway/run.py captures it into a local and sets the
+     attribute False immediately (so it can't re-fire next message);
+  2. the slash-command model path in gateway/slash_commands.py consumes it
+     before storing the override (so a /model-first-after-reset isn't wiped).
+
+These are AST invariants — load-bearing pins that fail if either consume is
+removed (mirrors test_35809_auto_reset_clean_context.py's approach).
+"""
+from __future__ import annotations
+
+import ast
+import inspect
+
+from gateway import run as gateway_run
+from gateway import slash_commands as gateway_slash
+
+
+def _assigns_false(node: ast.AST, attr: str) -> bool:
+    """True if `node` contains an assignment `<something>.<attr> = False`."""
+    for sub in ast.walk(node):
+        if isinstance(sub, ast.Assign):
+            for tgt in sub.targets:
+                if (
+                    isinstance(tgt, ast.Attribute)
+                    and tgt.attr == attr
+                    and isinstance(sub.value, ast.Constant)
+                    and sub.value.value is False
+                ):
+                    return True
+    return False
+
+
+def test_run_consumes_was_auto_reset_in_cleanup_block():
+    """The auto-reset cleanup block in gateway/run.py must set
+    `session_entry.was_auto_reset = False` so the cleanup (which pops the
+    session model/reasoning overrides) cannot re-fire on the next message and
+    wipe an override stored between turns (#48031)."""
+    tree = ast.parse(inspect.getsource(gateway_run))
+
+    # Find the cleanup branch: an `if <flag>:` block that pops a model/reasoning
+    # override AND clears the flag. We assert at least one such block sets
+    # was_auto_reset False.
+    found = False
+    for node in ast.walk(tree):
+        if not isinstance(node, ast.If):
+            continue
+        names = {
+            n.attr
+            for n in ast.walk(node)
+            if isinstance(n, ast.Attribute)
+        }
+        calls = {
+            n.func.attr
+            for n in ast.walk(node)
+            if isinstance(n, ast.Call) and isinstance(n.func, ast.Attribute)
+        }
+        # The cleanup block references the reasoning-override setter and pops
+        # pending model notes — fingerprint of the transient-state cleanup.
+        if "_set_session_reasoning_override" in calls and _assigns_false(node, "was_auto_reset"):
+            found = True
+            break
+    assert found, (
+        "gateway/run.py auto-reset cleanup block must consume "
+        "`was_auto_reset` (set it False) so it can't re-fire and wipe a "
+        "model override stored between turns (#48031)."
+    )
+
+
+def test_slash_command_model_path_consumes_was_auto_reset():
+    """The slash-command model path in gateway/slash_commands.py must consume
+    `was_auto_reset` before storing the new model override, so a
+    /model-first-after-auto-reset isn't wiped by the next message's cleanup
+    (#48031)."""
+    src = inspect.getsource(gateway_slash)
+    tree = ast.parse(src)
+    assert _assigns_false(tree, "was_auto_reset"), (
+        "gateway/slash_commands.py model path must set "
+        "`was_auto_reset = False` before storing the model override (#48031)."
+    )