diff --git a/.github/workflows/ci.yaml b/.github/workflows/ci.yaml
index 60f1a175e..c3f5a729e 100644
--- a/.github/workflows/ci.yaml
+++ b/.github/workflows/ci.yaml
@@ -3,8 +3,8 @@ on:
   push:
     branches: [master]
   pull_request:
-jobs:
 
+jobs:
   lint:
     name: Lint
     runs-on: ubuntu-latest
@@ -23,18 +23,25 @@ jobs:
       fail-fast: false # Set on "false" to get the results of ALL builds
       matrix:
         os: ["ubuntu-latest"]
-        python-version: ["3.10", "3.12"]
-        sphinx-version: ["7.0", "8.0"]
+        python-version: ["3.9", "3.12", "3.13"]
+        sphinx-version: ["7.4", "8.2"]
         include:
-          - os: "ubuntu-latest"
-            python-version: "3.9"
-            sphinx-version: "7.0"
+          # corner cases for Windows
           - os: "windows-latest"
             python-version: "3.9"
-            sphinx-version: "7.0"
+            sphinx-version: "7.4"
           - os: "windows-latest"
             python-version: "3.12"
-            sphinx-version: "8.0"
+            sphinx-version: "8.2"
+          - os: "windows-latest"
+            python-version: "3.13"
+            sphinx-version: "8.2"
+        exclude:
+          # Sphinx 8.2 only supports py3.11+
+          - os: "ubuntu-latest"
+            python-version: "3.9"
+            sphinx-version: "8.2"
+
     steps:
       - uses: actions/checkout@v4
       - name: Install graphviz (linux)
@@ -75,10 +82,10 @@ jobs:
         include:
           - os: "ubuntu-latest"
             python-version: "3.9"
-            sphinx-version: "7.0"
+            sphinx-version: "7.4"
           - os: "ubuntu-latest"
-            python-version: "3.12"
-            sphinx-version: "8.0"
+            python-version: "3.13"
+            sphinx-version: "8.2"
     steps:
       - uses: actions/checkout@v4
       - name: Use Node.js
diff --git a/docs/directives/needimport.rst b/docs/directives/needimport.rst
index e7dd78b42..afcfa6acb 100644
--- a/docs/directives/needimport.rst
+++ b/docs/directives/needimport.rst
@@ -26,26 +26,34 @@ The directive argument can be one of the following formats:
 - A remote URL from which to download the ``needs.json``:
 
   .. code-block:: rst
-   
+
      .. needimport:: https://my_company.com/docs/remote-needs.json
 
 - A local path relative to the containing document:
 
   .. code-block:: rst
-   
+
      .. needimport:: needs.json
 
 - A local path starting with ``/`` is relative to the Sphinx source directory:
 
   .. code-block:: rst
-   
+
      .. needimport:: /path/to/needs.json
 
-- For an absolute path, make sure to start with two ``//`` (on Linux/OSX):
+- For an absolute path on Linux/OSX, make sure to start with two ``//``:
 
   .. code-block:: rst
-   
-     .. needimport:: //absoulte/path/to/needs.json
+
+     .. needimport:: //absolute/path/to/needs.json
+
+- For an absolute path on Windows, just use the normal drive letters with either forward or backward slashes:
+
+  .. code-block:: rst
+
+     .. needimport:: c:/absolute/path/to/needs.json
+
+     .. needimport:: c:\absolute\path\to\needs.json
 
 Options
 -------
diff --git a/pyproject.toml b/pyproject.toml
index baf01189d..c9f4635b7 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -21,13 +21,14 @@ classifiers = [
   'Programming Language :: Python :: 3.10',
   'Programming Language :: Python :: 3.11',
   'Programming Language :: Python :: 3.12',
+  'Programming Language :: Python :: 3.13',
   'Topic :: Documentation',
   'Topic :: Utilities',
   'Framework :: Sphinx :: Extension',
 ]
 requires-python = ">=3.9,<4"
 dependencies = [
-  "sphinx>=7.0,<9",
+  "sphinx>=7.4,<9",
   "requests-file~=2.1",             # external links
   "requests~=2.32",                 # external links
   "jsonschema>=3.2.0",              # needsimport schema validation
diff --git a/sphinx_needs/directives/needimport.py b/sphinx_needs/directives/needimport.py
index 66454e2c0..39f5ac70d 100644
--- a/sphinx_needs/directives/needimport.py
+++ b/sphinx_needs/directives/needimport.py
@@ -81,34 +81,9 @@ def run(self) -> Sequence[nodes.Node]:
         else:
             logger.info(f"Importing needs from {need_import_path}")
 
-            if not os.path.isabs(need_import_path):
-                # Relative path should start from current rst file directory
-                curr_dir = os.path.dirname(self.docname)
-                new_need_import_path = os.path.join(
-                    self.env.app.srcdir, curr_dir, need_import_path
-                )
-
-                correct_need_import_path = new_need_import_path
-                if not os.path.exists(new_need_import_path):
-                    # Check the old way that calculates relative path starting from conf.py directory
-                    old_need_import_path = os.path.join(
-                        self.env.app.srcdir, need_import_path
-                    )
-                    if os.path.exists(old_need_import_path):
-                        correct_need_import_path = old_need_import_path
-                        log_warning(
-                            logger,
-                            "Deprecation warning: Relative path must be relative to the current document in future, "
-                            "not to the conf.py location. Use a starting '/', like '/needs.json', to make the path "
-                            "relative to conf.py.",
-                            "deprecated",
-                            location=(self.env.docname, self.lineno),
-                        )
-            else:
-                # Absolute path starts with /, based on the source directory. The / need to be striped
-                correct_need_import_path = os.path.join(
-                    self.env.app.srcdir, need_import_path[1:]
-                )
+            correct_need_import_path = self.env.relfn2path(
+                need_import_path, self.env.docname
+            )[1]
 
             if not os.path.exists(correct_need_import_path):
                 raise ReferenceError(
diff --git a/sphinx_needs/directives/needuml.py b/sphinx_needs/directives/needuml.py
index 92e15ebf1..dfb2282b5 100644
--- a/sphinx_needs/directives/needuml.py
+++ b/sphinx_needs/directives/needuml.py
@@ -4,6 +4,7 @@
 import os
 import time
 from collections.abc import Sequence
+from pathlib import PurePosixPath
 from typing import TYPE_CHECKING, Any, TypedDict
 
 from docutils import nodes
@@ -107,9 +108,9 @@ def run(self) -> Sequence[nodes.Node]:
         save_path = self.options.get("save")
         plantuml_code_out_path = None
         if save_path:
-            if os.path.isabs(save_path):
+            if PurePosixPath(save_path).is_absolute():
                 raise NeedumlException(
-                    f"Given save path: {save_path}, is not a relative path."
+                    f"Given save path: {save_path}, is not a relative posix path."
                 )
             else:
                 plantuml_code_out_path = save_path
diff --git a/sphinx_needs/needs.py b/sphinx_needs/needs.py
index c684738fa..d88737775 100644
--- a/sphinx_needs/needs.py
+++ b/sphinx_needs/needs.py
@@ -8,12 +8,14 @@
 from docutils import nodes
 from docutils.parsers.rst import directives
 from sphinx.application import Sphinx
+from sphinx.builders import Builder
 from sphinx.config import Config
 from sphinx.environment import BuildEnvironment
 from sphinx.errors import SphinxError
 
 import sphinx_needs.debug as debug  # Need to set global var in it for timeing measurements
 from sphinx_needs import __version__
+from sphinx_needs.api import get_needs_view
 from sphinx_needs.api.need import _split_list_with_dyn_funcs
 from sphinx_needs.builder import (
     NeedsBuilder,
@@ -305,6 +307,8 @@ def setup(app: Sphinx) -> dict[str, Any]:
     app.connect("doctree-resolved", process_need_nodes)
     app.connect("doctree-resolved", process_creator(NODE_TYPES))
 
+    app.connect("write-started", ensure_post_process_needs_data)
+
     app.connect("build-finished", process_warnings)
     app.connect("build-finished", build_needs_json)
     app.connect("build-finished", build_needs_id_json)
@@ -324,6 +328,15 @@ def setup(app: Sphinx) -> dict[str, Any]:
     }
 
 
+def ensure_post_process_needs_data(app: Sphinx, builder: Builder) -> None:
+    """
+    Make sure post_process_needs_data is called at least once.
+
+    Warnings are emitted in that step, even when no docs are updated.
+    """
+    get_needs_view(app)
+
+
 def process_creator(
     node_list: _NODE_TYPES_T, doc_category: str = "all"
 ) -> Callable[[Sphinx, nodes.document, str], None]:
diff --git a/tests/__snapshots__/test_needimport.ambr b/tests/__snapshots__/test_needimport.ambr
index b73fb2dde..c990d4448 100644
--- a/tests/__snapshots__/test_needimport.ambr
+++ b/tests/__snapshots__/test_needimport.ambr
@@ -78,7 +78,7 @@
             'external_css': 'external_link',
             'id': 'REQ_1',
             'layout': '',
-            'lineno': 48,
+            'lineno': 47,
             'section_name': 'FILTERED',
             'sections': list([
               'FILTERED',
@@ -193,7 +193,7 @@
             'external_css': 'external_link',
             'id': 'SPEC_1',
             'layout': '',
-            'lineno': 51,
+            'lineno': 50,
             'section_name': 'FILTERED',
             'sections': list([
               'FILTERED',
@@ -1250,21 +1250,6 @@
             'type': 'req',
             'type_name': 'Requirement',
           }),
-          'small_depr_rel_path_TEST_01': dict({
-            'content': 'small_depr_rel_path_TEST_01',
-            'docname': 'subdoc/deprecated_rel_path_import',
-            'external_css': 'external_link',
-            'id': 'small_depr_rel_path_TEST_01',
-            'is_import': True,
-            'lineno': 6,
-            'section_name': 'Deprecated Relative path import test',
-            'sections': list([
-              'Deprecated Relative path import test',
-            ]),
-            'title': 'TEST_01 DESCRIPTION',
-            'type': 'impl',
-            'type_name': 'Implementation',
-          }),
           'small_rel_path_TEST_01': dict({
             'content': 'small_rel_path_TEST_01',
             'docname': 'subdoc/rel_path_import',
@@ -1635,7 +1620,7 @@
             'type_name': 'Test Case',
           }),
         }),
-        'needs_amount': 66,
+        'needs_amount': 65,
         'needs_defaults_removed': True,
         'needs_schema': dict({
           '$schema': 'http://json-schema.org/draft-07/schema#',
diff --git a/tests/conftest.py b/tests/conftest.py
index c3c93af8d..a3108410a 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -54,6 +54,19 @@ def copy_srcdir_to_tmpdir(srcdir: path, tmp: path) -> path:
     return tmproot
 
 
+def create_src_files_in_tmpdir(files: list[tuple[Path, str]], tmp: path) -> path:
+    """Create source files in a temporary directory under the subdir src."""
+    subdir = path("src")
+    tmproot = tmp.joinpath(generate_random_string()) / subdir
+    tmproot.makedirs(exist_ok=True)
+    for file in files:
+        file_path, content = file
+        file_abs = tmproot.joinpath(str(file_path))
+        file_abs.parent.makedirs(exist_ok=True)
+        file_abs.write_text(content)
+    return tmproot
+
+
 def get_abspath(relpath: str) -> str:
     """
     Get the absolute path from a relative path.
@@ -264,9 +277,18 @@ def test_app(make_app, sphinx_test_tempdir, request):
         )
         sphinx_conf_overrides.update(plantuml=plantuml)
 
-    # copy test srcdir to test temporary directory sphinx_test_tempdir
     srcdir = builder_params.get("srcdir")
-    src_dir = copy_srcdir_to_tmpdir(srcdir, sphinx_test_tempdir)
+    files = builder_params.get("files")
+    if (srcdir is None) == (files is None):
+        raise ValueError("Exactly one of srcdir, files must not be None")
+
+    if srcdir is not None:
+        # copy test srcdir to test temporary directory sphinx_test_tempdir
+        src_dir = copy_srcdir_to_tmpdir(srcdir, sphinx_test_tempdir)
+    else:
+        # create given files in tmpdir
+        src_dir = create_src_files_in_tmpdir(files, sphinx_test_tempdir)
+
     parent_path = Path(str(src_dir.parent.abspath()))
 
     if version_info >= (7, 2):
diff --git a/tests/doc_test/import_doc/index.rst b/tests/doc_test/import_doc/index.rst
index 6c2e2f108..0f9bb2122 100644
--- a/tests/doc_test/import_doc/index.rst
+++ b/tests/doc_test/import_doc/index.rst
@@ -43,7 +43,6 @@ FILTERED
    subdoc/filter
    subdoc/abs_path_import
    subdoc/rel_path_import
-   subdoc/deprecated_rel_path_import
 
 .. req:: Test requirement 1
    :id: REQ_1
diff --git a/tests/doc_test/import_doc/subdoc/deprecated_rel_path_import.rst b/tests/doc_test/import_doc/subdoc/deprecated_rel_path_import.rst
deleted file mode 100644
index 4de3fc026..000000000
--- a/tests/doc_test/import_doc/subdoc/deprecated_rel_path_import.rst
+++ /dev/null
@@ -1,8 +0,0 @@
-Deprecated Relative path import test
-====================================
-
-Test import file with relative path, which based on directory of conf.py.
-
-.. needimport:: subdoc/needs_test_small.json
-   :id_prefix: small_depr_rel_path_
-   :filter: "impl" in type
diff --git a/tests/test_needimport.py b/tests/test_needimport.py
index ca76932cc..14cb018e7 100644
--- a/tests/test_needimport.py
+++ b/tests/test_needimport.py
@@ -1,5 +1,6 @@
 import json
 import os
+import sys
 from pathlib import Path
 
 import pytest
@@ -20,17 +21,8 @@
 def test_import_json(test_app):
     app = test_app
     app.build()
-    warnings = app._warning.getvalue()
-    warnings_list = strip_colors(
-        warnings.replace(str(app.srcdir) + os.sep + "subdoc" + os.sep, "srcdir/subdoc/")
-    ).splitlines()
-
-    if os.name != "nt":
-        assert warnings_list == [
-            "srcdir/subdoc/deprecated_rel_path_import.rst:6: WARNING: Deprecation warning: Relative path must be relative to the current document in future, not to the conf.py location. Use a starting '/', like '/needs.json', to make the path relative to conf.py. [needs.deprecated]"
-        ]
-    else:
-        assert "Deprecation" in warnings
+    assert app.statuscode == 0
+    assert not app.warning_list
 
     html = Path(app.outdir, "index.html").read_text()
     assert "TEST IMPORT TITLE" in html
@@ -61,11 +53,130 @@ def test_import_json(test_app):
     rel_path_import_html = Path(app.outdir, "subdoc/rel_path_import.html").read_text()
     assert "small_rel_path_TEST_01" in rel_path_import_html
 
-    # Check deprecated relative path import based on conf.py
-    deprec_rel_path_import_html = Path(
-        app.outdir, "subdoc/deprecated_rel_path_import.html"
-    ).read_text()
-    assert "small_depr_rel_path_TEST_01" in deprec_rel_path_import_html
+
+needs_json = """
+{
+    "current_version": "1",
+    "versions": {
+        "1": {
+            "needs": {
+                "TEST_01": {
+                    "id": "TEST_01",
+                    "title": "TEST IMPORT TITLE",
+                    "type": "impl"
+                }
+            },
+            "needs_amount": 1
+        }
+    }
+}
+"""
+
+
+@pytest.mark.parametrize(
+    "index_content",
+    [
+        ".. needimport:: needs.json",
+        ".. needimport:: nested/needs.json",
+        ".. needimport:: /needs.json",
+        ".. needimport:: /nested/needs.json",
+    ],
+)
+@pytest.mark.parametrize(
+    "test_app",
+    [
+        {
+            "buildername": "html",
+            "files": [
+                ("conf.py", 'extensions = ["sphinx_needs"]'),
+                ("needs.json", needs_json),
+                ("nested/needs.json", needs_json),
+            ],
+            "no_plantuml": True,
+        }
+    ],
+    indirect=True,
+)
+def test_import_rel_abs_sphinx_paths(test_app, index_content):
+    """Test various relative and absolute import file paths."""
+    # write the parametrized index.rst content
+    index_path = Path(test_app.srcdir, "index.rst")
+    index_path.write_text(index_content)
+
+    app = test_app
+    app.build()
+    assert app.statuscode == 0
+    assert not app.warning_list
+
+    html = Path(app.outdir, "index.html").read_text()
+    assert "TEST IMPORT TITLE" in html
+    assert "TEST_01" in html
+
+
+@pytest.mark.parametrize("path_sep", ["/", "\\", "\\\\"])
+@pytest.mark.parametrize(
+    "test_app",
+    [
+        {
+            "buildername": "html",
+            "files": [
+                ("conf.py", 'extensions = ["sphinx_needs"]'),
+                ("needs.json", needs_json),
+            ],
+            "no_plantuml": True,
+        }
+    ],
+    indirect=True,
+)
+@pytest.mark.skipif(sys.platform != "win32", reason="Test only runs on Windows")
+def test_import_abs_paths_win(test_app, path_sep):
+    """Test various relative and absolute import file paths."""
+    # write the parametrized index.rst content
+    index_path = Path(test_app.srcdir, "index.rst")
+    json_abs_path = str((Path(test_app.srcdir).resolve() / "needs.json").absolute())
+    json_abs_path = json_abs_path.replace(os.path.sep, path_sep)
+    index_path.write_text(f".. needimport:: {json_abs_path}")
+
+    app = test_app
+    app.build()
+    assert app.statuscode == 0
+    assert not app.warning_list
+
+    html = Path(app.outdir, "index.html").read_text()
+    assert "TEST IMPORT TITLE" in html
+    assert "TEST_01" in html
+
+
+@pytest.mark.parametrize(
+    "test_app",
+    [
+        {
+            "buildername": "html",
+            "files": [
+                ("conf.py", 'extensions = ["sphinx_needs"]'),
+                ("needs.json", needs_json),
+            ],
+            "no_plantuml": True,
+        }
+    ],
+    indirect=True,
+)
+@pytest.mark.skipif(sys.platform == "win32", reason="Test only runs on Linux and MacOS")
+def test_import_abs_paths_lin_mac(test_app):
+    """Test various relative and absolute import file paths."""
+    # write the parametrized index.rst content
+    index_path = Path(test_app.srcdir, "index.rst")
+    json_abs_path = str((Path(test_app.srcdir).resolve() / "needs.json").absolute())
+    index_path.write_text(f".. needimport:: /{json_abs_path}")
+
+    app = test_app
+    app.build()
+    assert app.statuscode == 0
+    assert not app.warning_list
+
+    html = Path(app.outdir, "index.html").read_text()
+    assert "TEST IMPORT TITLE" in html
+    assert "TEST_01" in html
 
 
 @pytest.mark.parametrize(
diff --git a/tests/test_needs_external_needs_build.py b/tests/test_needs_external_needs_build.py
index 408f21d72..45a95dddf 100644
--- a/tests/test_needs_external_needs_build.py
+++ b/tests/test_needs_external_needs_build.py
@@ -5,6 +5,8 @@
 import pytest
 import responses
 from docutils import __version__ as doc_ver
+from sphinx import version_info
+from sphinx.testing.util import SphinxTestApp
 from sphinx.util.console import strip_colors
 
 
@@ -13,13 +15,11 @@
     [{"buildername": "html", "srcdir": "doc_test/doc_needs_external_needs"}],
     indirect=True,
 )
-def test_doc_build_html(test_app, sphinx_test_tempdir):
+def test_doc_build_html(test_app: SphinxTestApp, sphinx_test_tempdir):
     import subprocess
 
-    app = test_app
-
-    src_dir = Path(app.srcdir)
-    out_dir = Path(app.outdir)
+    src_dir = Path(test_app.srcdir)
+    out_dir = Path(test_app.outdir)
     plantuml = r"java -Djava.awt.headless=true -jar {}".format(
         os.path.join(sphinx_test_tempdir, "utils", "plantuml.jar")
     )
@@ -27,17 +27,27 @@ def test_doc_build_html(test_app, sphinx_test_tempdir):
         ["sphinx-build", "-b", "html", "-D", rf"plantuml={plantuml}", src_dir, out_dir],
         capture_output=True,
     )
-    assert strip_colors(output.stderr.decode("utf-8")).splitlines() == [
+    expected_warnings = [
         "WARNING: http://my_company.com/docs/v1/index.html#TEST_01: Need 'EXT_TEST_01' has unknown outgoing link 'SPEC_1' in field 'links' [needs.external_link_outgoing]",
         "WARNING: ../../_build/html/index.html#TEST_01: Need 'EXT_REL_PATH_TEST_01' has unknown outgoing link 'SPEC_1' in field 'links' [needs.external_link_outgoing]",
     ]
+    assert strip_colors(output.stderr.decode("utf-8")).splitlines() == expected_warnings
 
     # run second time and check
     output_second = subprocess.run(
         ["sphinx-build", "-b", "html", "-D", rf"plantuml={plantuml}", src_dir, out_dir],
         capture_output=True,
     )
-    assert not output_second.stderr
+
+    # Sphinx 8.2 removed an early return in case no documents were updated in
+    # https://github.com/sphinx-doc/sphinx/pull/13236
+    # which leads to some SN warnings not being emitted for incremental builds
+    if version_info < (8, 2):
+        expected_warnings = []
+    assert (
+        strip_colors(output_second.stderr.decode("utf-8")).splitlines()
+        == expected_warnings
+    )
 
     # check if incremental build used
     # first build output
@@ -46,6 +56,7 @@ def test_doc_build_html(test_app, sphinx_test_tempdir):
         in strip_colors(output.stdout.decode("utf-8"))
     )
     # second build output
+    # TODO(Marco) check why 3 added configs are expected, should be 0 for incremental builds without changes
     assert "loading pickled environment" in output_second.stdout.decode("utf-8")
     assert (
         "updating environment: [new config] 3 added, 0 changed, 0 removed"
diff --git a/tests/test_needuml.py b/tests/test_needuml.py
index 04b6c5ea3..801281992 100644
--- a/tests/test_needuml.py
+++ b/tests/test_needuml.py
@@ -126,6 +126,7 @@ def test_needuml_save_with_abs_path(test_app):
     srcdir = Path(app.srcdir)
     out_dir = srcdir / "_build"
 
+    # this fails before plantuml is required, so the plantuml path is not provided
     out = subprocess.run(
         ["sphinx-build", "-M", "html", srcdir, out_dir], capture_output=True
     )
@@ -133,7 +134,7 @@ def test_needuml_save_with_abs_path(test_app):
 
     assert (
         "sphinx_needs.directives.needuml.NeedumlException: "
-        "Given save path: /_out/my_needuml.puml, is not a relative path."
+        "Given save path: /_out/my_needuml.puml, is not a relative posix path."
         in out.stderr.decode("utf-8")
     )