diff --git a/studio/backend/run.py b/studio/backend/run.py
index b83198626a..a416f07b9d 100644
--- a/studio/backend/run.py
+++ b/studio/backend/run.py
@@ -867,7 +867,7 @@ def _pid_is_studio_backend(pid: int, created_times: "Sequence[float | None]" = (
     the command line rejected real servers.
     """
     known = [c for c in created_times if c is not None]
-    if not known or len(known) < len(created_times):
+    if not known:
         return True
     actual = _process_create_time(pid)
     if actual is None:
@@ -1027,7 +1027,12 @@ def _write_pid_file(port: int, host: str = ""):
     # independently of the per-port record: if that one failed, this is the only
     # thing keeping the server stoppable at all.
     try:
-        _PID_FILE.write_text(str(os.getpid()), encoding = "utf-8")
+        # Never take it from a server that is still running. A pre-upgrade server
+        # is recorded here and nowhere else, so overwriting its entry is exactly
+        # what strands it -- the orphan this file exists to prevent.
+        prior = _read_pid_record(_PID_FILE) if _PID_FILE.is_file() else None
+        if prior is None or prior[0] == os.getpid() or not _pid_alive(prior[0]):
+            _PID_FILE.write_text(str(os.getpid()), encoding = "utf-8")
     except OSError:
         pass
 
@@ -1659,6 +1664,7 @@ def run_server(
     enable_tools: "Optional[bool]" = None,
     password: "Optional[str]" = None,
     emit_tauri_port: bool = True,
+    abort_if_own_studio: "Optional[bool]" = None,
 ):
     """
     Start the FastAPI server.
@@ -1793,11 +1799,13 @@ def run_server(
 
     # Auto-find a free port if the requested one is in use.
     original_port = port
-    # api-only callers read the bound port back (TAURI_PORT for the desktop app,
-    # app.state.server_port for `studio run`), so a fallback there is harmless and
-    # is what the desktop app's 8888-8908 range expects. The interactive path
-    # prints the requested port, so falling back is what strands a server.
-    port = _resolve_port(host, port, avoid_own_studio = not api_only)
+    # Refusing rather than falling back is for callers that cannot follow us to
+    # the new port. `studio run` reads app.state.server_port back and the desktop
+    # app reads TAURI_PORT, so both should keep the plain fallback; only the
+    # bare launch, which has nothing but the banner, benefits from the refusal.
+    if abort_if_own_studio is None:
+        abort_if_own_studio = not api_only
+    port = _resolve_port(host, port, avoid_own_studio = abort_if_own_studio)
     if port != original_port:
         blocker = _get_pid_on_port(original_port)
         if not silent:
diff --git a/studio/backend/tests/test_studio_pid_files.py b/studio/backend/tests/test_studio_pid_files.py
index a5d8d1257c..2f759a19e6 100644
--- a/studio/backend/tests/test_studio_pid_files.py
+++ b/studio/backend/tests/test_studio_pid_files.py
@@ -286,7 +286,17 @@ def test_an_untimed_legacy_record_is_trusted(monkeypatch):
 
     assert run._pid_is_studio_backend(8550) is True
     assert run._pid_is_studio_backend(8550, [None]) is True
-    assert run._pid_is_studio_backend(8550, [111.5, None]) is True
+
+
+def test_the_untimed_legacy_record_does_not_cancel_a_timed_one(monkeypatch):
+    # Mirrors _pid_is_studio_server in the CLI. An untimed record carries no
+    # information, so it must not overrule a start time that says "not ours" --
+    # every current server writes one of each, which made the check inert.
+    monkeypatch.setattr(run, "_pid_is_studio_backend", _REAL_IS_STUDIO_BACKEND)
+    monkeypatch.setattr(run, "_process_create_time", lambda pid: 999.0)
+
+    assert run._pid_is_studio_backend(8550, [111.5, None]) is False
+    assert run._pid_is_studio_backend(8550, [111.5, 999.0]) is True
 
 
 def test_a_legacy_server_on_the_port_is_recognised(tmp_path, monkeypatch):
@@ -510,3 +520,26 @@ def test_a_record_whose_pid_is_not_ascii_digits_is_discarded(tmp_path):
     (tmp_path / "r.pid").write_text("²", encoding = "utf-8")
 
     assert run._read_pid_record(tmp_path / "r.pid") is None
+
+
+def test_the_legacy_file_is_not_taken_from_a_live_server(tmp_path):
+    # A pre-upgrade server is recorded in studio.pid and nowhere else, so a
+    # second launch overwriting it is exactly what strands it. That is the
+    # orphan this file exists to prevent, reached from the other direction.
+    (tmp_path / "studio.pid").write_text("8550", encoding = "utf-8")
+
+    run._write_pid_file(8902, "127.0.0.1")
+
+    assert (tmp_path / "studio.pid").read_text(encoding = "utf-8") == "8550"
+    assert (tmp_path / f"studio-8902-{os.getpid()}.pid").exists()
+
+
+def test_the_legacy_file_is_taken_over_from_a_dead_server(tmp_path, monkeypatch):
+    # A stale record must not keep the pointer forever, or an older CLI could
+    # never stop anything again.
+    monkeypatch.setattr(run, "_pid_alive", lambda pid: False)
+    (tmp_path / "studio.pid").write_text("8550", encoding = "utf-8")
+
+    run._write_pid_file(8902, "127.0.0.1")
+
+    assert (tmp_path / "studio.pid").read_text(encoding = "utf-8") == str(os.getpid())
diff --git a/tests/studio/test_studio_pid_file_contract.py b/tests/studio/test_studio_pid_file_contract.py
index fbc981e485..23ace706b5 100644
--- a/tests/studio/test_studio_pid_file_contract.py
+++ b/tests/studio/test_studio_pid_file_contract.py
@@ -62,6 +62,9 @@ def test_the_legacy_file_stays_a_bare_pid_an_older_cli_can_parse(tmp_path, monke
         "_pid_file_for_port": lambda port: _backend_pid_path(tmp_path, port),
         "_process_create_time": lambda pid: None,
         "_bind_addresses": lambda host, port: {host},
+        # _write_pid_file consults these before taking over studio.pid.
+        "_read_pid_record": lambda path: None,
+        "_pid_alive": lambda pid: False,
         "_OWN_PID_FILE": None,
     }
     exec(_func_source(_RUN_SRC, "_write_pid_file"), ns)
diff --git a/unsloth_cli/commands/studio.py b/unsloth_cli/commands/studio.py
index 34d6c420b0..329e1317d7 100644
--- a/unsloth_cli/commands/studio.py
+++ b/unsloth_cli/commands/studio.py
@@ -2237,6 +2237,9 @@ def run(
         # Headless serving prints its own URL/API-key banner; the Tauri-only
         # TAURI_PORT line would corrupt that machine-parseable output.
         emit_tauri_port = False,
+        # We read the bound port back below, so a fallback past another Studio is
+        # safe here and keeps side-by-side model runs working.
+        abort_if_own_studio = False,
     )
     # Forward the frontend validated before the gate (in-venv path).
     if resolved_frontend is not None: