diff --git a/.bazelrc.deleted_packages b/.bazelrc.deleted_packages
index fb5d2ef0bb..3a0500a2f7 100644
--- a/.bazelrc.deleted_packages
+++ b/.bazelrc.deleted_packages
@@ -35,6 +35,7 @@ common --deleted_packages=tests/integration/custom_commands
 common --deleted_packages=tests/integration/local_toolchains
 common --deleted_packages=tests/integration/pip_parse
 common --deleted_packages=tests/integration/pip_parse/empty
+common --deleted_packages=tests/integration/pip_parse_isolated
 common --deleted_packages=tests/integration/py_cc_toolchain_registered
 common --deleted_packages=tests/modules/another_module
 common --deleted_packages=tests/modules/other
diff --git a/MODULE.bazel b/MODULE.bazel
index 95d6b9e3a9..072f8c1f5c 100644
--- a/MODULE.bazel
+++ b/MODULE.bazel
@@ -64,141 +64,6 @@ register_toolchains("@pythons_hub//:all")
 # Install twine for our own runfiles wheel publishing and allow bzlmod users to use it.
 
 pip = use_extension("//python/extensions:pip.bzl", "pip")
-
-# NOTE @aignas 2025-07-06: we define these platforms to keep backwards compatibility. Whilst we
-# stabilize the API this list may be updated with a mention in the CHANGELOG.
-[
-    pip.default(
-        arch_name = cpu,
-        config_settings = [
-            "@platforms//cpu:{}".format(cpu),
-            "@platforms//os:linux",
-            "//python/config_settings:_is_py_freethreaded_{}".format(
-                "yes" if freethreaded else "no",
-            ),
-        ],
-        env = {"platform_version": "0"},
-        marker = "python_version >= '3.13'" if freethreaded else "",
-        os_name = "linux",
-        platform = "linux_{}{}".format(cpu, freethreaded),
-        whl_abi_tags = ["cp{major}{minor}t"] if freethreaded else [
-            "abi3",
-            "cp{major}{minor}",
-        ],
-        whl_platform_tags = [
-            "linux_{}".format(cpu),
-            "manylinux_*_{}".format(cpu),
-        ],
-    )
-    for cpu in [
-        "x86_64",
-        "aarch64",
-    ]
-    for freethreaded in [
-        "",
-        "_freethreaded",
-    ]
-]
-
-[
-    pip.default(
-        arch_name = cpu,
-        config_settings = [
-            "@platforms//cpu:{}".format(cpu),
-            "@platforms//os:osx",
-            "//python/config_settings:_is_py_freethreaded_{}".format(
-                "yes" if freethreaded else "no",
-            ),
-        ],
-        # We choose the oldest non-EOL version at the time when we release `rules_python`.
-        # See https://endoflife.date/macos
-        env = {"platform_version": "14.0"},
-        marker = "python_version >= '3.13'" if freethreaded else "",
-        os_name = "osx",
-        platform = "osx_{}{}".format(cpu, freethreaded),
-        whl_abi_tags = ["cp{major}{minor}t"] if freethreaded else [
-            "abi3",
-            "cp{major}{minor}",
-        ],
-        whl_platform_tags = [
-            "macosx_*_{}".format(suffix)
-            for suffix in platform_tag_cpus
-        ],
-    )
-    for cpu, platform_tag_cpus in {
-        "aarch64": [
-            "universal2",
-            "arm64",
-        ],
-        "x86_64": [
-            "universal2",
-            "x86_64",
-        ],
-    }.items()
-    for freethreaded in [
-        "",
-        "_freethreaded",
-    ]
-]
-
-[
-    pip.default(
-        arch_name = cpu,
-        config_settings = [
-            "@platforms//cpu:{}".format(cpu),
-            "@platforms//os:windows",
-            "//python/config_settings:_is_py_freethreaded_{}".format(
-                "yes" if freethreaded else "no",
-            ),
-        ],
-        env = {"platform_version": "0"},
-        marker = "python_version >= '3.13'" if freethreaded else "",
-        os_name = "windows",
-        platform = "windows_{}{}".format(cpu, freethreaded),
-        whl_abi_tags = ["cp{major}{minor}t"] if freethreaded else [
-            "abi3",
-            "cp{major}{minor}",
-        ],
-        whl_platform_tags = whl_platform_tags,
-    )
-    for cpu, whl_platform_tags in {
-        "x86_64": ["win_amd64"],
-    }.items()
-    for freethreaded in [
-        "",
-        "_freethreaded",
-    ]
-]
-
-[
-    pip.default(
-        arch_name = cpu,
-        config_settings = [
-            "@platforms//cpu:{}".format(cpu),
-            "@platforms//os:windows",
-            "//python/config_settings:_is_py_freethreaded_{}".format(
-                "yes" if freethreaded else "no",
-            ),
-        ],
-        env = {"platform_version": "0"},
-        marker = "python_version >= '3.13'" if freethreaded else "python_version >= '3.11'",
-        os_name = "windows",
-        platform = "windows_{}{}".format(cpu, freethreaded),
-        whl_abi_tags = ["cp{major}{minor}t"] if freethreaded else [
-            "abi3",
-            "cp{major}{minor}",
-        ],
-        whl_platform_tags = whl_platform_tags,
-    )
-    for cpu, whl_platform_tags in {
-        "aarch64": ["win_arm64"],
-    }.items()
-    for freethreaded in [
-        "",
-        "_freethreaded",
-    ]
-]
-
 pip.parse(
     hub_name = "rules_python_publish_deps",
     python_version = "3.11",
diff --git a/python/private/pypi/extension.bzl b/python/private/pypi/extension.bzl
index a55cf53fb1..b9d522b33a 100644
--- a/python/private/pypi/extension.bzl
+++ b/python/private/pypi/extension.bzl
@@ -56,6 +56,128 @@ def _whl_mods_impl(whl_mods_dict):
             whl_mods = whl_mods,
         )
 
+def default_platforms():
+    """Return the built-in default platform definitions.
+
+    These provide the platform metadata needed for pip wheel resolution
+    (whl_abi_tags, whl_platform_tags, config_settings, etc.) across all
+    common OS/arch combinations. They are always used as the starting point
+    for build_config; root modules can override individual platforms via
+    pip.default tags.
+
+    Returns:
+        A dict of platform name to platform config dicts.
+    """
+    # NOTE @aignas 2025-07-06: we define these platforms to keep backwards compatibility. Whilst we
+    # stabilize the API this list may be updated with a mention in the CHANGELOG.
+
+    platforms = {}
+
+    # Linux platforms
+    for cpu in ["x86_64", "aarch64"]:
+        for freethreaded in ["", "_freethreaded"]:
+            platform_name = "linux_{}{}".format(cpu, freethreaded)
+            platforms[platform_name] = {
+                "arch_name": cpu,
+                "config_settings": [
+                    "@platforms//cpu:{}".format(cpu),
+                    "@platforms//os:linux",
+                    "//python/config_settings:_is_py_freethreaded_{}".format(
+                        "yes" if freethreaded else "no",
+                    ),
+                ],
+                "env": {"platform_version": "0"},
+                "marker": "python_version >= '3.13'" if freethreaded else "",
+                "name": platform_name,
+                "os_name": "linux",
+                "whl_abi_tags": ["cp{major}{minor}t"] if freethreaded else [
+                    "abi3",
+                    "cp{major}{minor}",
+                ],
+                "whl_platform_tags": [
+                    "linux_{}".format(cpu),
+                    "manylinux_*_{}".format(cpu),
+                ],
+            }
+
+    # macOS platforms
+    for cpu, platform_tag_cpus in {
+        "aarch64": ["universal2", "arm64"],
+        "x86_64": ["universal2", "x86_64"],
+    }.items():
+        for freethreaded in ["", "_freethreaded"]:
+            platform_name = "osx_{}{}".format(cpu, freethreaded)
+            platforms[platform_name] = {
+                "arch_name": cpu,
+                "config_settings": [
+                    "@platforms//cpu:{}".format(cpu),
+                    "@platforms//os:osx",
+                    "//python/config_settings:_is_py_freethreaded_{}".format(
+                        "yes" if freethreaded else "no",
+                    ),
+                ],
+                "env": {"platform_version": "14.0"},
+                "marker": "python_version >= '3.13'" if freethreaded else "",
+                "name": platform_name,
+                "os_name": "osx",
+                "whl_abi_tags": ["cp{major}{minor}t"] if freethreaded else [
+                    "abi3",
+                    "cp{major}{minor}",
+                ],
+                "whl_platform_tags": [
+                    "macosx_*_{}".format(suffix)
+                    for suffix in platform_tag_cpus
+                ],
+            }
+
+    # Windows x86_64 platforms
+    for freethreaded in ["", "_freethreaded"]:
+        platform_name = "windows_x86_64{}".format(freethreaded)
+        platforms[platform_name] = {
+            "arch_name": "x86_64",
+            "config_settings": [
+                "@platforms//cpu:x86_64",
+                "@platforms//os:windows",
+                "//python/config_settings:_is_py_freethreaded_{}".format(
+                    "yes" if freethreaded else "no",
+                ),
+            ],
+            "env": {"platform_version": "0"},
+            "marker": "python_version >= '3.13'" if freethreaded else "",
+            "name": platform_name,
+            "os_name": "windows",
+            "whl_abi_tags": ["cp{major}{minor}t"] if freethreaded else [
+                "abi3",
+                "cp{major}{minor}",
+            ],
+            "whl_platform_tags": ["win_amd64"],
+        }
+
+    # Windows aarch64 platforms
+    for freethreaded in ["", "_freethreaded"]:
+        platform_name = "windows_aarch64{}".format(freethreaded)
+        platforms[platform_name] = {
+            "arch_name": "aarch64",
+            "config_settings": [
+                "@platforms//cpu:aarch64",
+                "@platforms//os:windows",
+                "//python/config_settings:_is_py_freethreaded_{}".format(
+                    "yes" if freethreaded else "no",
+                ),
+            ],
+            "env": {"platform_version": "0"},
+            "marker": "python_version >= '3.13'" if freethreaded else "python_version >= '3.11'",
+            "name": platform_name,
+            "os_name": "windows",
+            "whl_abi_tags": ["cp{major}{minor}t"] if freethreaded else [
+                "abi3",
+                "cp{major}{minor}",
+            ],
+            "whl_platform_tags": ["win_arm64"],
+        }
+
+    return platforms
+
 def _configure(config, *, override = False, **kwargs):
     """Set the value in the config if the value is provided"""
     env = kwargs.get("env")
@@ -86,7 +208,7 @@ def build_config(
         A struct with the configuration.
     """
     defaults = {
-        "platforms": {},
+        "platforms": default_platforms(),
     }
     for mod in module_ctx.modules:
         if not (mod.is_root or mod.name == "rules_python"):
diff --git a/tests/integration/BUILD.bazel b/tests/integration/BUILD.bazel
index f0f58daa3a..1807a30902 100644
--- a/tests/integration/BUILD.bazel
+++ b/tests/integration/BUILD.bazel
@@ -67,6 +67,10 @@ rules_python_integration_test(
     name = "pip_parse_test",
 )
 
+rules_python_integration_test(
+    name = "pip_parse_isolated_test",
+)
+
 rules_python_integration_test(
     name = "pip_parse_workspace_test",
     bzlmod = False,
diff --git a/tests/integration/pip_parse_isolated/.bazelrc b/tests/integration/pip_parse_isolated/.bazelrc
new file mode 100644
index 0000000000..227ce5a4cd
--- /dev/null
+++ b/tests/integration/pip_parse_isolated/.bazelrc
@@ -0,0 +1,8 @@
+# Bazel configuration flags
+
+build --enable_runfiles
+
+common --experimental_isolated_extension_usages
+
+# https://docs.bazel.build/versions/main/best-practices.html#using-the-bazelrc-file
+try-import %workspace%/user.bazelrc
diff --git a/tests/integration/pip_parse_isolated/BUILD.bazel b/tests/integration/pip_parse_isolated/BUILD.bazel
new file mode 100644
index 0000000000..2f825107f1
--- /dev/null
+++ b/tests/integration/pip_parse_isolated/BUILD.bazel
@@ -0,0 +1,7 @@
+load("@rules_python//python:py_test.bzl", "py_test")
+
+py_test(
+    name = "test_isolated",
+    srcs = ["test_isolated.py"],
+    deps = ["@pypi//six"],
+)
diff --git a/tests/integration/pip_parse_isolated/MODULE.bazel b/tests/integration/pip_parse_isolated/MODULE.bazel
new file mode 100644
index 0000000000..6c44257acb
--- /dev/null
+++ b/tests/integration/pip_parse_isolated/MODULE.bazel
@@ -0,0 +1,19 @@
+module(name = "pip_parse_isolated")
+
+bazel_dep(name = "rules_python")
+local_path_override(
+    module_name = "rules_python",
+    path = "../../..",
+)
+
+python = use_extension("@rules_python//python/extensions:python.bzl", "python")
+python.toolchain(python_version = "3.13")
+
+# This test module verifies that dependencies can be used with `isolate = True`.
+pip = use_extension("@rules_python//python/extensions:pip.bzl", "pip", isolate = True)
+pip.parse(
+    hub_name = "pypi",
+    python_version = "3.13",
+    requirements_lock = "//:requirements_lock.txt",
+)
+use_repo(pip, "pypi")
diff --git a/tests/integration/pip_parse_isolated/WORKSPACE b/tests/integration/pip_parse_isolated/WORKSPACE
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/tests/integration/pip_parse_isolated/requirements_lock.txt b/tests/integration/pip_parse_isolated/requirements_lock.txt
new file mode 100644
index 0000000000..b1445a37ae
--- /dev/null
+++ b/tests/integration/pip_parse_isolated/requirements_lock.txt
@@ -0,0 +1,2 @@
+six==1.17.0 \
+    --hash=sha256:4721f391ed90541fddacab5acf947aa0d3dc7d27b2e1e8eda2be8970586c3274
diff --git a/tests/integration/pip_parse_isolated/test_isolated.py b/tests/integration/pip_parse_isolated/test_isolated.py
new file mode 100644
index 0000000000..f889f071fb
--- /dev/null
+++ b/tests/integration/pip_parse_isolated/test_isolated.py
@@ -0,0 +1,16 @@
+"""
+Verify that a dependency added using an isolated extension can be imported.
+See MODULE.bazel.
+"""
+
+import six
+import unittest
+
+
+class TestIsolated(unittest.TestCase):
+    def test_import(self):
+        self.assertTrue(hasattr(six, "PY3"))
+
+
+if __name__ == "__main__":
+    unittest.main()
diff --git a/tests/pypi/extension/extension_tests.bzl b/tests/pypi/extension/extension_tests.bzl
index 7999e42a7b..52abffda88 100644
--- a/tests/pypi/extension/extension_tests.bzl
+++ b/tests/pypi/extension/extension_tests.bzl
@@ -16,7 +16,8 @@
 
 load("@rules_testing//lib:test_suite.bzl", "test_suite")
 load("@rules_testing//lib:truth.bzl", "subjects")
-load("//python/private/pypi:extension.bzl", "build_config", "parse_modules")  # buildifier: disable=bzl-visibility
+load("//python/private/pypi:extension.bzl", "build_config", "default_platforms", "parse_modules")  # buildifier: disable=bzl-visibility
+load("//python/private/pypi:platform.bzl", _plat = "platform")  # buildifier: disable=bzl-visibility
 load("//python/private/pypi:whl_config_setting.bzl", "whl_config_setting")  # buildifier: disable=bzl-visibility
 load(":pip_parse.bzl", _parse = "pip_parse")
 
@@ -49,33 +50,63 @@ simple==0.0.1 \
         ],
     )
 
-def _mod(*, name, default = [], parse = [], override = [], whl_mods = [], is_root = True):
+def _default(
+        *,
+        arch_name = None,
+        auth_patterns = None,
+        config_settings = None,
+        env = None,
+        index_url = None,
+        marker = None,
+        netrc = None,
+        os_name = None,
+        platform = None,
+        whl_platform_tags = None,
+        whl_abi_tags = None):
+    return struct(
+        arch_name = arch_name,
+        auth_patterns = auth_patterns or {},
+        config_settings = config_settings,
+        env = env or {},
+        index_url = index_url or "",
+        marker = marker or "",
+        netrc = netrc,
+        os_name = os_name,
+        platform = platform,
+        whl_abi_tags = whl_abi_tags or [],
+        whl_platform_tags = whl_platform_tags or [],
+    )
+
+# The default value for the default platforms tags use in `_mod`.
+_default_tags_default = [
+    _default(
+        platform = "{}_{}{}".format(os, cpu, freethreaded),
+        os_name = os,
+        arch_name = cpu,
+        config_settings = [
+            "@platforms//os:{}".format(os),
+            "@platforms//cpu:{}".format(cpu),
+        ],
+        whl_abi_tags = ["cp{major}{minor}t"] if freethreaded else ["abi3", "cp{major}{minor}"],
+        whl_platform_tags = whl_platform_tags,
+    )
+    for (os, cpu, freethreaded), whl_platform_tags in {
+        ("linux", "x86_64", ""): ["linux_x86_64", "manylinux_*_x86_64"],
+        ("linux", "x86_64", "_freethreaded"): ["linux_x86_64", "manylinux_*_x86_64"],
+        ("linux", "aarch64", ""): ["linux_aarch64", "manylinux_*_aarch64"],
+        ("osx", "aarch64", ""): ["macosx_*_arm64"],
+        ("windows", "aarch64", ""): ["win_arm64"],
+    }.items()
+]
+
+def _mod(*, name, default = _default_tags_default, parse = [], override = [], whl_mods = [], is_root = True):
     return struct(
         name = name,
         tags = struct(
             parse = parse,
             override = override,
             whl_mods = whl_mods,
-            default = default or [
-                _default(
-                    platform = "{}_{}{}".format(os, cpu, freethreaded),
-                    os_name = os,
-                    arch_name = cpu,
-                    config_settings = [
-                        "@platforms//os:{}".format(os),
-                        "@platforms//cpu:{}".format(cpu),
-                    ],
-                    whl_abi_tags = ["cp{major}{minor}t"] if freethreaded else ["abi3", "cp{major}{minor}"],
-                    whl_platform_tags = whl_platform_tags,
-                )
-                for (os, cpu, freethreaded), whl_platform_tags in {
-                    ("linux", "x86_64", ""): ["linux_x86_64", "manylinux_*_x86_64"],
-                    ("linux", "x86_64", "_freethreaded"): ["linux_x86_64", "manylinux_*_x86_64"],
-                    ("linux", "aarch64", ""): ["linux_aarch64", "manylinux_*_aarch64"],
-                    ("osx", "aarch64", ""): ["macosx_*_arm64"],
-                    ("windows", "aarch64", ""): ["win_arm64"],
-                }.items()
-            ],
+            default = default,
         ),
         is_root = is_root,
     )
@@ -110,33 +141,6 @@ def _build_config(env, enable_pipstar = 0, **kwargs):
         ),
     )
 
-def _default(
-        *,
-        arch_name = None,
-        auth_patterns = None,
-        config_settings = None,
-        env = None,
-        index_url = None,
-        marker = None,
-        netrc = None,
-        os_name = None,
-        platform = None,
-        whl_platform_tags = None,
-        whl_abi_tags = None):
-    return struct(
-        arch_name = arch_name,
-        auth_patterns = auth_patterns or {},
-        config_settings = config_settings,
-        env = env or {},
-        index_url = index_url or "",
-        marker = marker or "",
-        netrc = netrc,
-        os_name = os_name,
-        platform = platform,
-        whl_abi_tags = whl_abi_tags or [],
-        whl_platform_tags = whl_platform_tags or [],
-    )
-
 def _test_simple(env):
     pypi = _parse_modules(
         env,
@@ -184,6 +188,59 @@ def _test_simple(env):
 
 _tests.append(_test_simple)
 
+def _test_simple_isolated(env):
+    """Simulate `isolate = True` with parse_modules.
+
+    No pip.default tags, but requirements parsing still produces the expected
+    hub output.
+    """
+    pypi = _parse_modules(
+        env,
+        module_ctx = _mock_mctx(
+            _mod(
+                name = "my_module",
+                default = [],  # no platform tags
+                parse = [
+                    _parse(
+                        hub_name = "pypi",
+                        python_version = "3.15",
+                        simpleapi_skip = ["simple"],
+                        requirements_lock = "requirements.txt",
+                    ),
+                ],
+            ),
+            os_name = "linux",
+            arch_name = "x86_64",
+        ),
+        available_interpreters = {
+            "python_3_15_host": "unit_test_interpreter_target",
+        },
+        minor_mapping = {"3.15": "3.15.19"},
+    )
+
+    pypi.exposed_packages().contains_exactly({"pypi": ["simple"]})
+    pypi.hub_group_map().contains_exactly({"pypi": {}})
+    pypi.hub_whl_map().contains_exactly({"pypi": {
+        "simple": {
+            "pypi_315_simple": [
+                whl_config_setting(
+                    version = "3.15",
+                ),
+            ],
+        },
+    }})
+    pypi.whl_libraries().contains_exactly({
+        "pypi_315_simple": {
+            "config_load": "@pypi//:config.bzl",
+            "dep_template": "@pypi//{name}:{target}",
+            "python_interpreter_target": "unit_test_interpreter_target",
+            "requirement": "simple==0.0.1 --hash=sha256:deadbeef --hash=sha256:deadbaaf",
+        },
+    })
+    pypi.whl_mods().contains_exactly({})
+
+_tests.append(_test_simple_isolated)
+
 def _test_build_pipstar_platform(env):
     config = _build_config(
         env,
@@ -237,6 +294,9 @@ def _test_build_pipstar_platform(env):
             whl_abi_tags = ["none", "abi3", "cp{major}{minor}"],
             whl_platform_tags = ["any"],
         ),
+    } | {
+        name: _plat(**values)
+        for name, values in default_platforms().items()
     })
 
 _tests.append(_test_build_pipstar_platform)