diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 0012f58c..67037870 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -17,12 +17,12 @@ env:
   COVERAGE_PYTHON: "3.11"
 
 jobs:
-  test:
+  test:  # standard support: failures block merges
     runs-on: ubuntu-latest
     strategy:
       fail-fast: false
       matrix:
-        python-version: ["3.8", "3.9", "3.10", "3.11"]
+        python-version: ["3.10", "3.11"]
 
     steps:
     - uses: actions/checkout@v6
@@ -65,3 +65,37 @@ jobs:
           pytest.yml
           pr_number.txt
         retention-days: 3
+
+  test-legacy:  # legacy support: failures are visible but do not block merges
+    runs-on: ubuntu-latest
+    continue-on-error: true
+    strategy:
+      fail-fast: false
+      matrix:
+        python-version: ["3.8", "3.9"]
+
+    steps:
+    - uses: actions/checkout@v6
+
+    - name: Set up Python ${{ matrix.python-version }}
+      uses: actions/setup-python@v6
+      with:
+        python-version: ${{ matrix.python-version }}
+        cache: "pip"
+
+    - name: Install dependencies
+      run: |
+        python -m pip install --upgrade pip
+        python -m pip install pytest pytest-cov "pytest-github-actions-annotate-failures!=0.3.0"
+        pip install .[dev]
+      # NOTE: pytest-github-actions-annotate-failures v0.3.0 causes INTERNALERROR in Python 3.8 and 3.9.
+      # c.f. https://github.com/pytest-dev/pytest-github-actions-annotate-failures/issues/106
+
+    # https://stackoverflow.com/questions/985876/tee-and-exit-status
+    - name: Test with pytest
+      run: |
+        (
+          set -o pipefail
+          pytest --junitxml=pytest.yml \
+            --cov-report=term-missing:skip-covered --cov=bdpy tests | tee pytest-coverage.txt
+        )
diff --git a/.github/workflows/test_old.yml b/.github/workflows/test_old.yml
deleted file mode 100644
index be0a5c95..00000000
--- a/.github/workflows/test_old.yml
+++ /dev/null
@@ -1,68 +0,0 @@
-name: test_old
-
-on:
-  push:
-    branches: [ "maintenance/legacy" ]
-
-jobs:
-  test_py36:
-    runs-on: ubuntu-22.04
-
-    # NOTE: Python 3.6 is not supported in Ubuntu 22.04, so we use a container with Python 3.6 installed.
-    container:
-      image: python:3.6-buster
-    steps:
-    - uses: actions/checkout@v6
-
-    - name: Install dependencies
-      run: |
-        python -m pip install --upgrade pip
-        python -m pip install pytest pytest-cov pytest-github-actions-annotate-failures
-        pip install Cython==0.29.36 numpy
-        pip install .[dev]
-
-    - name: Test with pytest
-      shell: bash
-      run: |
-        (
-          set -o pipefail
-          pytest \
-            --ignore=tests/dl/torch \
-            --ignore=tests/recon/torch \
-            --ignore=tests/task \
-            --junitxml=pytest.yml \
-            --cov-report=term-missing:skip-covered --cov=bdpy tests | tee pytest-coverage.txt
-        )
-
-
-  test_py37:
-    runs-on: ubuntu-22.04
-    strategy:
-      fail-fast: false
-      matrix:
-        python-version: ["3.7"]
-
-    steps:
-    - uses: actions/checkout@v6
-
-    - name: Set up Python ${{ matrix.python-version }}
-      uses: actions/setup-python@v6
-      with:
-        python-version: ${{ matrix.python-version }}
-        cache: "pip"
-
-    - name: Install dependencies
-      run: |
-        python -m pip install --upgrade pip
-        python -m pip install pytest pytest-cov pytest-github-actions-annotate-failures
-        pip install Cython==0.29.36 numpy
-        pip install .[dev]
-
-    - name: Test with pytest
-      run: |
-        (
-          set -o pipefail
-          pytest \
-            --junitxml=pytest.yml \
-            --cov-report=term-missing:skip-covered --cov=bdpy tests | tee pytest-coverage.txt
-        )
diff --git a/README.md b/README.md
index e56a7835..0ccdfaaa 100644
--- a/README.md
+++ b/README.md
@@ -58,16 +58,6 @@ To install the latest development version ("master" branch of the repository), p
 $ pip install git+https://github.com/KamitaniLab/bdpy.git
 ```
 
-## Installation (Python 3.6~3.8)
-For Python 3.6, use the following commands:
-
-```shell
-$ pip install "Cython==0.29.36" "numpy"
-$ pip install bdpy
-```
-
-
-
 ## Packages
 
 - bdata: BdPy data format (BData) core package
diff --git a/pyproject.toml b/pyproject.toml
index a3cd00d6..8f153111 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -10,23 +10,20 @@ authors = [
     { name = "Shuntaro C. Aoki", email = "s_aoki@i.kyoto-u.ac.jp" }
 ]
 readme = "README.md"
-requires-python = ">= 3.6, < 3.12"
+requires-python = ">= 3.8, < 3.12"
 license = { file = "LICENSE" }
 keywords = ["neuroscience", "neuroimaging", "brain decoding", "fmri", "machine learning"]
 
 dependencies = [
-    "numpy>=1.19; python_version < '3.7'",
-    "numpy>=1.20; python_version >= '3.7'",
+    "numpy>=1.20",
     "scipy",
     "scikit-learn",
-    "h5py>=3.0; python_version >= '3.7'",
-    "h5py<3.0; python_version < '3.7'",
+    "h5py>=3.0",
     "hdf5storage",
     "pyyaml",
     "pandas",
     "tqdm",
-    "typing-extensions>=4.1.0; python_version < '3.8'",
-    "typing-extensions>=4.5.0; python_version >= '3.8'"
+    "typing-extensions>=4.5.0"
 ]
 
 [project.optional-dependencies]
@@ -45,8 +42,7 @@ fig = [
 mri = [
     "numpy<1.24",
     "nibabel==3.2",
-    "nipy>=0.6.0; python_version >= '3.8'",
-    "nipy<0.6.0; python_version < '3.8'"
+    "nipy>=0.6.0"
 ]
 pipeline = [
     "hydra-core",
@@ -79,9 +75,9 @@ dev = [
     "mypy"
 ]
 docs = [
-    "mkdocs>=1.6; python_version >= '3.8'",
-    "mkdocs-material>=9.5; python_version >= '3.8'",
-    "mkdocstrings[python]>=0.25; python_version >= '3.8'",
+    "mkdocs>=1.6",
+    "mkdocs-material>=9.5",
+    "mkdocstrings[python]>=0.25",
 ]
 
 [tool.uv]