diff --git a/docs/html/topics/local-project-installs.md b/docs/html/topics/local-project-installs.md
index 331afadb8..151035b00 100644
--- a/docs/html/topics/local-project-installs.md
+++ b/docs/html/topics/local-project-installs.md
@@ -51,15 +51,17 @@ There are two advantages over using `setup.py develop` directly:
 ## Build artifacts
 
 ```{versionchanged} 21.3
-The project being installed is no longer copied to a temporary directory before invoking the build system.
+The project being installed is no longer copied to a temporary directory before invoking the build system, by default. A `--use-deprecated=out-of-tree-build` option is provided as a temporary fallback to aid user migrations.
 ```
 
-This behaviour change has several consequences:
+```{versionchanged} 22.1
+The `--use-deprecated=out-of-tree-build` option has been removed.
+```
+
+When provided with a project that's in a local directory, pip will invoke the build system "in place". This behaviour has several consequences:
 
 - Local project builds will now be significantly faster, for certain kinds of projects and on systems with slow I/O (eg: via network attached storage or overly aggressive antivirus software).
 - Certain build backends (eg: `setuptools`) will litter the project directory with secondary build artifacts (eg: `.egg-info` directories).
 - Certain build backends (eg: `setuptools`) may not be able to perform with parallel builds anymore, since they previously relied on the fact that pip invoked them in a separate directory for each build.
 
-A `--use-deprecated=out-of-tree-build` option is available, until pip 22.1, as a mechanism to aid users with transitioning to the newer model of in-tree-builds.
-
 [^1]: Specifically, the current machine's filesystem.
diff --git a/news/11001.removal.rst b/news/11001.removal.rst
new file mode 100644
index 000000000..a0dac9018
--- /dev/null
+++ b/news/11001.removal.rst
@@ -0,0 +1 @@
+Drop ``--use-deprecated=out-of-tree-build``, according to deprecation message.
diff --git a/src/pip/_internal/cli/cmdoptions.py b/src/pip/_internal/cli/cmdoptions.py
index dcfbd9bb2..3612dc456 100644
--- a/src/pip/_internal/cli/cmdoptions.py
+++ b/src/pip/_internal/cli/cmdoptions.py
@@ -957,7 +957,7 @@ use_new_feature: Callable[..., Option] = partial(
     metavar="feature",
     action="append",
     default=[],
-    choices=["2020-resolver", "fast-deps", "in-tree-build"],
+    choices=["2020-resolver", "fast-deps"],
     help="Enable new functionality, that may be backward incompatible.",
 )
 
@@ -970,7 +970,6 @@ use_deprecated_feature: Callable[..., Option] = partial(
     default=[],
     choices=[
         "legacy-resolver",
-        "out-of-tree-build",
         "backtrack-on-build-failures",
         "html5lib",
     ],
diff --git a/src/pip/_internal/cli/req_command.py b/src/pip/_internal/cli/req_command.py
index cbb17c5f0..2c2db00de 100644
--- a/src/pip/_internal/cli/req_command.py
+++ b/src/pip/_internal/cli/req_command.py
@@ -288,20 +288,6 @@ class RequirementCommand(IndexGroupCommand):
                     "fast-deps has no effect when used with the legacy resolver."
                 )
 
-        in_tree_build = "out-of-tree-build" not in options.deprecated_features_enabled
-        if "in-tree-build" in options.features_enabled:
-            deprecated(
-                reason="In-tree builds are now the default.",
-                replacement="to remove the --use-feature=in-tree-build flag",
-                gone_in="22.1",
-            )
-        if "out-of-tree-build" in options.deprecated_features_enabled:
-            deprecated(
-                reason="Out-of-tree builds are deprecated.",
-                replacement=None,
-                gone_in="22.1",
-            )
-
         return RequirementPreparer(
             build_dir=temp_build_dir_path,
             src_dir=options.src_dir,
@@ -315,7 +301,6 @@ class RequirementCommand(IndexGroupCommand):
             use_user_site=use_user_site,
             lazy_wheel=lazy_wheel,
             verbosity=verbosity,
-            in_tree_build=in_tree_build,
         )
 
     @classmethod
diff --git a/src/pip/_internal/operations/prepare.py b/src/pip/_internal/operations/prepare.py
index 46252816d..7550d3a90 100644
--- a/src/pip/_internal/operations/prepare.py
+++ b/src/pip/_internal/operations/prepare.py
@@ -35,10 +35,9 @@ from pip._internal.network.lazy_wheel import (
 from pip._internal.network.session import PipSession
 from pip._internal.operations.build.build_tracker import BuildTracker
 from pip._internal.req.req_install import InstallRequirement
-from pip._internal.utils.filesystem import copy2_fixed
 from pip._internal.utils.hashes import Hashes, MissingHashes
 from pip._internal.utils.logging import indent_log
-from pip._internal.utils.misc import display_path, hide_url, is_installable_dir, rmtree
+from pip._internal.utils.misc import display_path, hide_url, is_installable_dir
 from pip._internal.utils.temp_dir import TempDirectory
 from pip._internal.utils.unpacking import unpack_file
 from pip._internal.vcs import vcs
@@ -98,55 +97,6 @@ def get_http_url(
     return File(from_path, content_type)
 
 
-def _copy2_ignoring_special_files(src: str, dest: str) -> None:
-    """Copying special files is not supported, but as a convenience to users
-    we skip errors copying them. This supports tools that may create e.g.
-    socket files in the project source directory.
-    """
-    try:
-        copy2_fixed(src, dest)
-    except shutil.SpecialFileError as e:
-        # SpecialFileError may be raised due to either the source or
-        # destination. If the destination was the cause then we would actually
-        # care, but since the destination directory is deleted prior to
-        # copy we ignore all of them assuming it is caused by the source.
-        logger.warning(
-            "Ignoring special file error '%s' encountered copying %s to %s.",
-            str(e),
-            src,
-            dest,
-        )
-
-
-def _copy_source_tree(source: str, target: str) -> None:
-    target_abspath = os.path.abspath(target)
-    target_basename = os.path.basename(target_abspath)
-    target_dirname = os.path.dirname(target_abspath)
-
-    def ignore(d: str, names: List[str]) -> List[str]:
-        skipped: List[str] = []
-        if d == source:
-            # Pulling in those directories can potentially be very slow,
-            # exclude the following directories if they appear in the top
-            # level dir (and only it).
-            # See discussion at https://github.com/pypa/pip/pull/6770
-            skipped += [".tox", ".nox"]
-        if os.path.abspath(d) == target_dirname:
-            # Prevent an infinite recursion if the target is in source.
-            # This can happen when TMPDIR is set to ${PWD}/...
-            # and we copy PWD to TMPDIR.
-            skipped += [target_basename]
-        return skipped
-
-    shutil.copytree(
-        source,
-        target,
-        ignore=ignore,
-        symlinks=True,
-        copy_function=_copy2_ignoring_special_files,
-    )
-
-
 def get_file_url(
     link: Link, download_dir: Optional[str] = None, hashes: Optional[Hashes] = None
 ) -> File:
@@ -191,19 +141,7 @@ def unpack_url(
         unpack_vcs_link(link, location, verbosity=verbosity)
         return None
 
-    # Once out-of-tree-builds are no longer supported, could potentially
-    # replace the below condition with `assert not link.is_existing_dir`
-    # - unpack_url does not need to be called for in-tree-builds.
-    #
-    # As further cleanup, _copy_source_tree and accompanying tests can
-    # be removed.
-    #
-    # TODO when use-deprecated=out-of-tree-build is removed
-    if link.is_existing_dir():
-        if os.path.isdir(location):
-            rmtree(location)
-        _copy_source_tree(link.file_path, location)
-        return None
+    assert not link.is_existing_dir()
 
     # file urls
     if link.is_file:
@@ -269,7 +207,6 @@ class RequirementPreparer:
         use_user_site: bool,
         lazy_wheel: bool,
         verbosity: int,
-        in_tree_build: bool,
     ) -> None:
         super().__init__()
 
@@ -300,9 +237,6 @@ class RequirementPreparer:
         # How verbose should underlying tooling be?
         self.verbosity = verbosity
 
-        # Should in-tree builds be used for local paths?
-        self.in_tree_build = in_tree_build
-
         # Memoized downloaded files, as mapping of url: path.
         self._downloaded: Dict[str, str] = {}
 
@@ -336,7 +270,7 @@ class RequirementPreparer:
             # directory.
             return
         assert req.source_dir is None
-        if req.link.is_existing_dir() and self.in_tree_build:
+        if req.link.is_existing_dir():
             # build local directories in-tree
             req.source_dir = req.link.file_path
             return
@@ -525,7 +459,7 @@ class RequirementPreparer:
         self._ensure_link_req_src_dir(req, parallel_builds)
         hashes = self._get_linked_req_hashes(req)
 
-        if link.is_existing_dir() and self.in_tree_build:
+        if link.is_existing_dir():
             local_file = None
         elif link.url not in self._downloaded:
             try:
diff --git a/src/pip/_internal/utils/filesystem.py b/src/pip/_internal/utils/filesystem.py
index b7e6191ab..ccf298d0e 100644
--- a/src/pip/_internal/utils/filesystem.py
+++ b/src/pip/_internal/utils/filesystem.py
@@ -2,8 +2,6 @@ import fnmatch
 import os
 import os.path
 import random
-import shutil
-import stat
 import sys
 from contextlib import contextmanager
 from tempfile import NamedTemporaryFile
@@ -42,33 +40,6 @@ def check_path_owner(path: str) -> bool:
     return False  # assume we don't own the path
 
 
-def copy2_fixed(src: str, dest: str) -> None:
-    """Wrap shutil.copy2() but map errors copying socket files to
-    SpecialFileError as expected.
-
-    See also https://bugs.python.org/issue37700.
-    """
-    try:
-        shutil.copy2(src, dest)
-    except OSError:
-        for f in [src, dest]:
-            try:
-                is_socket_file = is_socket(f)
-            except OSError:
-                # An error has already occurred. Another error here is not
-                # a problem and we can ignore it.
-                pass
-            else:
-                if is_socket_file:
-                    raise shutil.SpecialFileError(f"`{f}` is a socket")
-
-        raise
-
-
-def is_socket(path: str) -> bool:
-    return stat.S_ISSOCK(os.lstat(path).st_mode)
-
-
 @contextmanager
 def adjacent_tmp_file(path: str, **kwargs: Any) -> Iterator[BinaryIO]:
     """Return a file-like object pointing to a tmp file next to path.
diff --git a/tests/functional/test_install.py b/tests/functional/test_install.py
index e089a8f69..bec8b72fc 100644
--- a/tests/functional/test_install.py
+++ b/tests/functional/test_install.py
@@ -2,7 +2,6 @@ import distutils
 import glob
 import os
 import re
-import shutil
 import ssl
 import sys
 import textwrap
@@ -30,7 +29,6 @@ from tests.lib import (
     pyversion,
     requirements_file,
 )
-from tests.lib.filesystem import make_socket_file
 from tests.lib.local_repos import local_checkout
 from tests.lib.path import Path
 from tests.lib.server import (
@@ -648,26 +646,6 @@ def test_hashed_install_failure_later_flag(
     )
 
 
-@pytest.mark.usefixtures("with_wheel")
-def test_install_from_local_directory_with_symlinks_to_directories(
-    script: PipTestEnvironment, data: TestData
-) -> None:
-    """
-    Test installing from a local directory containing symlinks to directories.
-    """
-    to_install = data.packages.joinpath("symlinks")
-    result = script.pip(
-        "install",
-        "--use-deprecated=out-of-tree-build",
-        to_install,
-        allow_stderr_warning=True,  # TODO: set to False when removing out-of-tree-build
-    )
-    pkg_folder = script.site_packages / "symlinks"
-    dist_info_folder = script.site_packages / "symlinks-0.1.dev0.dist-info"
-    result.did_create(pkg_folder)
-    result.did_create(dist_info_folder)
-
-
 @pytest.mark.usefixtures("with_wheel")
 def test_install_from_local_directory_with_in_tree_build(
     script: PipTestEnvironment, data: TestData
@@ -688,38 +666,6 @@ def test_install_from_local_directory_with_in_tree_build(
     assert in_tree_build_dir.exists()
 
 
-@pytest.mark.skipif("sys.platform == 'win32'")
-@pytest.mark.usefixtures("with_wheel")
-def test_install_from_local_directory_with_socket_file(
-    script: PipTestEnvironment, data: TestData, tmpdir: Path
-) -> None:
-    """
-    Test installing from a local directory containing a socket file.
-    """
-    # TODO: remove this test when removing out-of-tree-build support,
-    # it is only meant to test the copy of socket files
-    dist_info_folder = script.site_packages / "FSPkg-0.1.dev0.dist-info"
-    package_folder = script.site_packages / "fspkg"
-    to_copy = data.packages.joinpath("FSPkg")
-    to_install = tmpdir.joinpath("src")
-
-    shutil.copytree(to_copy, to_install)
-    # Socket file, should be ignored.
-    socket_file_path = os.path.join(to_install, "example")
-    make_socket_file(socket_file_path)
-
-    result = script.pip(
-        "install",
-        "--use-deprecated=out-of-tree-build",
-        "--verbose",
-        to_install,
-        allow_stderr_warning=True,  # because of the out-of-tree deprecation warning
-    )
-    result.did_create(package_folder)
-    result.did_create(dist_info_folder)
-    assert str(socket_file_path) in result.stderr
-
-
 def test_install_from_local_directory_with_no_setup_py(
     script: PipTestEnvironment, data: TestData
 ) -> None:
diff --git a/tests/lib/filesystem.py b/tests/lib/filesystem.py
index 8563783e7..5f8fe519d 100644
--- a/tests/lib/filesystem.py
+++ b/tests/lib/filesystem.py
@@ -1,38 +1,10 @@
 """Helpers for filesystem-dependent tests.
 """
 import os
-import socket
-import subprocess
-import sys
 from functools import partial
 from itertools import chain
 from typing import Iterator, List, Set
 
-from .path import Path
-
-
-def make_socket_file(path: str) -> None:
-    # Socket paths are limited to 108 characters (sometimes less) so we
-    # chdir before creating it and use a relative path name.
-    cwd = os.getcwd()
-    os.chdir(os.path.dirname(path))
-    try:
-        sock = socket.socket(socket.AF_UNIX)
-        sock.bind(os.path.basename(path))
-    finally:
-        os.chdir(cwd)
-
-
-def make_unreadable_file(path: str) -> None:
-    Path(path).touch()
-    os.chmod(path, 0o000)
-    if sys.platform == "win32":
-        username = os.getlogin()
-        # Remove "Read Data/List Directory" permission for current user, but
-        # leave everything else.
-        args = ["icacls", path, "/deny", username + ":(RD)"]
-        subprocess.check_call(args)
-
 
 def get_filelist(base: str) -> Set[str]:
     def join(dirpath: str, dirnames: List[str], filenames: List[str]) -> Iterator[str]:
diff --git a/tests/unit/test_operations_prepare.py b/tests/unit/test_operations_prepare.py
index a2ee87870..8838fa9ce 100644
--- a/tests/unit/test_operations_prepare.py
+++ b/tests/unit/test_operations_prepare.py
@@ -11,11 +11,10 @@ from pip._internal.exceptions import HashMismatch
 from pip._internal.models.link import Link
 from pip._internal.network.download import Downloader
 from pip._internal.network.session import PipSession
-from pip._internal.operations.prepare import _copy_source_tree, unpack_url
+from pip._internal.operations.prepare import unpack_url
 from pip._internal.utils.hashes import Hashes
 from pip._internal.utils.urls import path_to_url
 from tests.lib import TestData
-from tests.lib.filesystem import get_filelist, make_socket_file, make_unreadable_file
 from tests.lib.path import Path
 from tests.lib.requests_mocks import MockResponse
 
@@ -99,80 +98,6 @@ def clean_project(tmpdir_factory: pytest.TempdirFactory, data: TestData) -> Path
     return new_project_dir
 
 
-def test_copy_source_tree(clean_project: Path, tmpdir: Path) -> None:
-    target = tmpdir.joinpath("target")
-    expected_files = get_filelist(clean_project)
-    assert len(expected_files) == 3
-
-    _copy_source_tree(clean_project, target)
-
-    copied_files = get_filelist(target)
-    assert expected_files == copied_files
-
-
-@pytest.mark.skipif("sys.platform == 'win32'")
-def test_copy_source_tree_with_socket(
-    clean_project: Path, tmpdir: Path, caplog: pytest.LogCaptureFixture
-) -> None:
-    target = tmpdir.joinpath("target")
-    expected_files = get_filelist(clean_project)
-    socket_path = str(clean_project.joinpath("aaa"))
-    make_socket_file(socket_path)
-
-    _copy_source_tree(clean_project, target)
-
-    copied_files = get_filelist(target)
-    assert expected_files == copied_files
-
-    # Warning should have been logged.
-    assert len(caplog.records) == 1
-    record = caplog.records[0]
-    assert record.levelname == "WARNING"
-    assert socket_path in record.message
-
-
-@pytest.mark.skipif("sys.platform == 'win32'")
-def test_copy_source_tree_with_socket_fails_with_no_socket_error(
-    clean_project: Path, tmpdir: Path
-) -> None:
-    target = tmpdir.joinpath("target")
-    expected_files = get_filelist(clean_project)
-    make_socket_file(clean_project.joinpath("aaa"))
-    unreadable_file = clean_project.joinpath("bbb")
-    make_unreadable_file(unreadable_file)
-
-    with pytest.raises(shutil.Error) as e:
-        _copy_source_tree(clean_project, target)
-
-    errored_files = [err[0] for err in e.value.args[0]]
-    assert len(errored_files) == 1
-    assert unreadable_file in errored_files
-
-    copied_files = get_filelist(target)
-    # All files without errors should have been copied.
-    assert expected_files == copied_files
-
-
-def test_copy_source_tree_with_unreadable_dir_fails(
-    clean_project: Path, tmpdir: Path
-) -> None:
-    target = tmpdir.joinpath("target")
-    expected_files = get_filelist(clean_project)
-    unreadable_file = clean_project.joinpath("bbb")
-    make_unreadable_file(unreadable_file)
-
-    with pytest.raises(shutil.Error) as e:
-        _copy_source_tree(clean_project, target)
-
-    errored_files = [err[0] for err in e.value.args[0]]
-    assert len(errored_files) == 1
-    assert unreadable_file in errored_files
-
-    copied_files = get_filelist(target)
-    # All files without errors should have been copied.
-    assert expected_files == copied_files
-
-
 class Test_unpack_url:
     def prep(self, tmpdir: Path, data: TestData) -> None:
         self.build_dir = tmpdir.joinpath("build")
@@ -208,50 +133,3 @@ class Test_unpack_url:
                 hashes=Hashes({"md5": ["bogus"]}),
                 verbosity=0,
             )
-
-    def test_unpack_url_thats_a_dir(self, tmpdir: Path, data: TestData) -> None:
-        self.prep(tmpdir, data)
-        dist_path = data.packages.joinpath("FSPkg")
-        dist_url = Link(path_to_url(dist_path))
-        unpack_url(
-            dist_url,
-            self.build_dir,
-            download=self.no_download,
-            download_dir=self.download_dir,
-            verbosity=0,
-        )
-        assert os.path.isdir(os.path.join(self.build_dir, "fspkg"))
-
-
-@pytest.mark.parametrize("exclude_dir", [".nox", ".tox"])
-def test_unpack_url_excludes_expected_dirs(tmpdir: Path, exclude_dir: str) -> None:
-    src_dir = tmpdir / "src"
-    dst_dir = tmpdir / "dst"
-    src_included_file = src_dir.joinpath("file.txt")
-    src_excluded_dir = src_dir.joinpath(exclude_dir)
-    src_excluded_file = src_dir.joinpath(exclude_dir, "file.txt")
-    src_included_dir = src_dir.joinpath("subdir", exclude_dir)
-
-    # set up source directory
-    src_excluded_dir.mkdir(parents=True)
-    src_included_dir.mkdir(parents=True)
-    src_included_file.touch()
-    src_excluded_file.touch()
-
-    dst_included_file = dst_dir.joinpath("file.txt")
-    dst_excluded_dir = dst_dir.joinpath(exclude_dir)
-    dst_excluded_file = dst_dir.joinpath(exclude_dir, "file.txt")
-    dst_included_dir = dst_dir.joinpath("subdir", exclude_dir)
-
-    src_link = Link(path_to_url(src_dir))
-    unpack_url(
-        src_link,
-        dst_dir,
-        Mock(side_effect=AssertionError),
-        download_dir=None,
-        verbosity=0,
-    )
-    assert not os.path.isdir(dst_excluded_dir)
-    assert not os.path.isfile(dst_excluded_file)
-    assert os.path.isfile(dst_included_file)
-    assert os.path.isdir(dst_included_dir)
diff --git a/tests/unit/test_req.py b/tests/unit/test_req.py
index 4a339e4e2..075d12688 100644
--- a/tests/unit/test_req.py
+++ b/tests/unit/test_req.py
@@ -99,7 +99,6 @@ class TestRequirementSet:
                 use_user_site=False,
                 lazy_wheel=False,
                 verbosity=0,
-                in_tree_build=False,
             )
             yield Resolver(
                 preparer=preparer,
diff --git a/tests/unit/test_utils_filesystem.py b/tests/unit/test_utils_filesystem.py
index b15c3141a..1b730f8b8 100644
--- a/tests/unit/test_utils_filesystem.py
+++ b/tests/unit/test_utils_filesystem.py
@@ -1,11 +1,5 @@
 import os
-import shutil
-from typing import Callable, Type
 
-import pytest
-
-from pip._internal.utils.filesystem import copy2_fixed, is_socket
-from tests.lib.filesystem import make_socket_file, make_unreadable_file
 from tests.lib.path import Path
 
 
@@ -25,44 +19,3 @@ def make_broken_symlink(path: str) -> None:
 
 def make_dir(path: str) -> None:
     os.mkdir(path)
-
-
-skip_on_windows = pytest.mark.skipif("sys.platform == 'win32'")
-
-
-@skip_on_windows
-@pytest.mark.parametrize(
-    "create,result",
-    [
-        (make_socket_file, True),
-        (make_file, False),
-        (make_valid_symlink, False),
-        (make_broken_symlink, False),
-        (make_dir, False),
-    ],
-)
-def test_is_socket(create: Callable[[str], None], result: bool, tmpdir: Path) -> None:
-    target = tmpdir.joinpath("target")
-    create(target)
-    assert os.path.lexists(target)
-    assert is_socket(target) == result
-
-
-@pytest.mark.parametrize(
-    "create,error_type",
-    [
-        pytest.param(make_socket_file, shutil.SpecialFileError, marks=skip_on_windows),
-        (make_unreadable_file, OSError),
-    ],
-)
-def test_copy2_fixed_raises_appropriate_errors(
-    create: Callable[[str], None], error_type: Type[Exception], tmpdir: Path
-) -> None:
-    src = tmpdir.joinpath("src")
-    create(src)
-    dest = tmpdir.joinpath("dest")
-
-    with pytest.raises(error_type):
-        copy2_fixed(src, dest)
-
-    assert not dest.exists()