diff --git a/CHANGES.md b/CHANGES.md
index 56963c2d1..70085b5fd 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -1,5 +1,11 @@
 # Release Notes
 
+## 2.91.5
+
+This release fixes Pex PEX scie behavior to match Pex.
+
+* Make ephemeral exec, venv repl and scie compatible (#3129)
+
 ## 2.91.4
 
 This release brings 2 performance fixes from @tobni:
diff --git a/pex/bin/pex.py b/pex/bin/pex.py
index fd05b1d11..a7dd5c254 100644
--- a/pex/bin/pex.py
+++ b/pex/bin/pex.py
@@ -1289,6 +1289,11 @@ def main(args=None):
 
     try:
         with global_environment(options) as env:
+            # These are set if we're running from within a Pex PEX scie and already installed.
+            # We clear them to allow recursive use of Pex / PEX.
+            env.pop("__PEX_EXE__", None)
+            env.pop("__PEX_ENTRY_POINT__", None)
+
             try:
                 resolver_configuration = resolver_options.configure(
                     options,
diff --git a/pex/pex_boot.py b/pex/pex_boot.py
index 11ed684dc..c69b1b1d1 100644
--- a/pex/pex_boot.py
+++ b/pex/pex_boot.py
@@ -229,12 +229,11 @@ def boot(
             if os.path.isfile(pex_exe):
                 sys.argv[0] = pex_exe
 
-    overridden_entry_point = os.environ.get("__PEX_ENTRY_POINT__", None)
+    overridden_pex = os.environ.get("__PEX_EXE__", None)
     sys.path[0] = os.path.abspath(sys.path[0])
-    sys.path.insert(
-        0, os.path.abspath(os.path.join(overridden_entry_point or entry_point, bootstrap_dir))
-    )
+    sys.path.insert(0, os.path.abspath(os.path.join(overridden_pex or entry_point, bootstrap_dir)))
 
+    overridden_entry_point = os.environ.get("__PEX_ENTRY_POINT__", None)
     if overridden_entry_point and overridden_entry_point != entry_point:
         # This PEX has already been installed out of band; so we short-circuit to execute the
         # pre-installed PEX.
diff --git a/pex/version.py b/pex/version.py
index 10c259b40..9047d3f61 100644
--- a/pex/version.py
+++ b/pex/version.py
@@ -1,4 +1,4 @@
 # Copyright 2015 Pex project contributors.
 # Licensed under the Apache License, Version 2.0 (see LICENSE).
 
-__version__ = "2.91.4"
+__version__ = "2.91.5"
diff --git a/tests/integration/cli/commands/test_lock_subset.py b/tests/integration/cli/commands/test_lock_subset.py
index 2b40fb73b..87a9a266b 100644
--- a/tests/integration/cli/commands/test_lock_subset.py
+++ b/tests/integration/cli/commands/test_lock_subset.py
@@ -139,7 +139,7 @@ def test_lock_subset_miss(lock):
     # type: (str) -> None
 
     _, original_locked_reqs = index(lock)
-    requests_version = original_locked_reqs[ProjectName("requests")].pin.version
+    requests_version = original_locked_reqs[ProjectName("requests")].pin.version.raw
     run_pex3(
         "lock", "subset", "--lock", lock, "requests!={version}".format(version=requests_version)
     ).assert_failure(
diff --git a/tests/integration/scie/test_scie_ephemeral_run.py b/tests/integration/scie/test_scie_ephemeral_run.py
new file mode 100644
index 000000000..505f0ad51
--- /dev/null
+++ b/tests/integration/scie/test_scie_ephemeral_run.py
@@ -0,0 +1,68 @@
+# Copyright 2026 Pex project contributors.
+# Licensed under the Apache License, Version 2.0 (see LICENSE).
+
+from __future__ import absolute_import
+
+import subprocess
+import sys
+
+import pytest
+
+from pex.typing import TYPE_CHECKING
+from testing import IS_PYPY, make_env, run_pex_command
+from testing.pytest_utils.tmp import Tempdir
+from testing.scie import skip_if_no_provider
+
+if TYPE_CHECKING:
+    from typing import List
+
+
+@pytest.mark.parametrize(
+    "execution_mode_args",
+    [
+        pytest.param([], id="ZIPAPP"),
+        pytest.param(["--venv"], id="VENV"),
+    ],
+)
+@skip_if_no_provider
+def test_scie_ephemeral_run(
+    tmpdir,  # type: Tempdir
+    pex_wheel,  # type: str
+    execution_mode_args,  # type: List[str]
+):
+    # type: (...) -> None
+
+    pex_scie = tmpdir.join("pex")
+    run_pex_command(
+        args=[pex_wheel, "-c", "pex", "-o", pex_scie, "--scie", "eager"] + execution_mode_args
+    ).assert_success()
+
+    ic = "{impl}=={major}.{minor}.*".format(
+        impl="PyPy" if IS_PYPY else "CPython", major=sys.version_info[0], minor=sys.version_info[1]
+    )
+
+    # Verify the scie can perform an ephemeral run with `-- -c`.
+    output = subprocess.check_output(
+        args=[
+            pex_scie,
+            "--interpreter-constraint",
+            ic,
+            "--",
+            "-c",
+            "import sys; print(sys.executable)",
+        ],
+        env=make_env(PATH=None),
+    )
+    assert output.decode("utf-8").strip()
+
+    # Verify the scie can drop into a REPL via ephemeral run.
+    process = subprocess.Popen(
+        args=[pex_scie, "--interpreter-constraint", ic, "--"],
+        stdin=subprocess.PIPE,
+        stdout=subprocess.PIPE,
+        stderr=subprocess.PIPE,
+        env=make_env(PATH=None),
+    )
+    stdout, stderr = process.communicate(input=b"import sys; print(sys.executable)\nquit()\n")
+    assert process.returncode == 0, stderr.decode("utf-8")
+    assert b">>>" in stdout or b">>>" in stderr