diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index 99ae91605..346710958 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -9,16 +9,12 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-20.04]
-        python-version: ["3.8", "3.9"]
+        python-version: ["3.9", "3.10"]
         include:
-          - os: ubuntu-20.04
-            python-version: "3.10"
-          - os: macos-11.0
-            python-version: "3.10"
-          - os: ubuntu-20.04
-            python-version: "3.11"
           - os: ubuntu-22.04
             python-version: "3.11"
+          - os: macos-11.0
+            python-version: "3.10"
           - os: macos-11.0
             python-version: "3.11"
     steps:
@@ -31,7 +27,7 @@ jobs:
           python-version: ${{ matrix.python-version }}
 
       - name: Install poetry
-        run: pip install "poetry~=1.2"
+        run: pip install "poetry~=1.7.1"
 
       - name: Build libraries used by Stan
         run: make -j2
diff --git a/pyproject.toml b/pyproject.toml
index 3a3973a79..a7df6376d 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -30,7 +30,7 @@ include = [
 ]
 
 [tool.poetry.dependencies]
-python = "^3.8"
+python = "^3.9"
 setuptools = ">=48.0"
 aiohttp = "^3.7"
 appdirs = "^1.4"
@@ -46,11 +46,11 @@ autoflake = "^1.4"
 black = "22.3.0"
 isort = "^5.9"
 mypy = "0.981"
-flake8 = "^3.9"
+flake8 = "^7.0.0"
 # documentation
 # NOTE: when changing these, update docs-requirements.txt
-sphinx = "^4.2"
-sphinx-autoapi = "^1.8.4"
+sphinx = "^7.2"
+sphinx-autoapi = "^3.0.0"
 sphinx-rtd-theme = "^1.0.0"
 sphinxcontrib-openapi = "^0.8.1"
 jsonschema = ">=4.10.0,<4.18.0"  # newer versions break sphinxcontrib-openapi