diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index d3d8d2e76..d4135fb2c 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -45,7 +45,7 @@ jobs:
       python: ${{ steps.filter.outputs.python }}
       extensions: ${{ steps.filter.outputs.llvm }}
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v5
       - uses: ./.github/actions/check-changes
         id: filter
 
@@ -58,7 +58,7 @@ jobs:
       # Fail on rust compiler warnings.
       RUSTFLAGS: -D warnings
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v5
       - uses: mozilla-actions/sccache-action@v0.0.9
       - name: Install stable toolchain
         uses: dtolnay/rust-toolchain@stable
@@ -89,7 +89,7 @@ jobs:
     if: ${{ needs.changes.outputs.python == 'true' }}
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v5
       - uses: mozilla-actions/sccache-action@v0.0.9
       - name: Set up uv
         uses: astral-sh/setup-uv@v6
@@ -115,7 +115,7 @@ jobs:
     permissions:
       checks: write
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v5
       - uses: mozilla-actions/sccache-action@v0.0.9
       - name: Install stable toolchain
         uses: dtolnay/rust-toolchain@stable
@@ -139,7 +139,7 @@ jobs:
     runs-on: ubuntu-latest
     name: tests (Rust stable, no features)
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v5
       - uses: mozilla-actions/sccache-action@v0.0.9
       - id: toolchain
         uses: dtolnay/rust-toolchain@master
@@ -159,7 +159,7 @@ jobs:
     runs-on: ubuntu-latest
     name: tests (Rust stable, all features)
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v5
       - uses: mozilla-actions/sccache-action@v0.0.9
       - id: toolchain
         uses: dtolnay/rust-toolchain@master
@@ -195,7 +195,7 @@ jobs:
         rust: ['1.85', beta]
     name: tests (Rust ${{ matrix.rust }})
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v5
       - uses: mozilla-actions/sccache-action@v0.0.9
       - id: toolchain
         uses: dtolnay/rust-toolchain@master
@@ -229,7 +229,7 @@ jobs:
     runs-on: ubuntu-latest
     name: tests (Rust nightly, coverage)
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v5
       - uses: mozilla-actions/sccache-action@v0.0.9
       - uses: dtolnay/rust-toolchain@master
         with:
@@ -271,7 +271,7 @@ jobs:
     runs-on: ubuntu-latest
     name: tests (Python, coverage)
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v5
       - uses: mozilla-actions/sccache-action@v0.0.9
       - name: Install stable toolchain
         uses: dtolnay/rust-toolchain@stable
@@ -305,7 +305,7 @@ jobs:
     name: Check standard extensions
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v5
       - uses: mozilla-actions/sccache-action@v0.0.9
       - name: Install stable toolchain
         uses: dtolnay/rust-toolchain@stable
@@ -328,7 +328,7 @@ jobs:
     if: ${{ needs.changes.outputs.extensions == 'true' }}
     name: Check extension versions
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v5
         with:
           fetch-depth: 0  # Need full history to compare with main
 
diff --git a/.github/workflows/python-pure-wheels.yml b/.github/workflows/python-pure-wheels.yml
index 53b43993d..d1798dc9d 100644
--- a/.github/workflows/python-pure-wheels.yml
+++ b/.github/workflows/python-pure-wheels.yml
@@ -46,7 +46,7 @@ jobs:
         env:
           SHOULD_RUN: ${{ github.event_name != 'release' || ( github.ref_type == 'tag' && startsWith(github.ref, format('refs/tags/{0}-v', matrix.target.dir)) ) }}
 
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v5
         if: ${{ steps.check-tag.outputs.run == 'true' }}
       - name: Run sccache-cache
         if: ${{ steps.check-tag.outputs.run == 'true' }}
diff --git a/.github/workflows/python-wheels.yml b/.github/workflows/python-wheels.yml
index bc1ebb379..4b764ef2d 100644
--- a/.github/workflows/python-wheels.yml
+++ b/.github/workflows/python-wheels.yml
@@ -59,7 +59,7 @@ jobs:
           - runner: ubuntu-latest
             target: ppc64le
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v5
       - uses: actions/setup-python@v5
         with:
           python-version: 3.x
@@ -93,7 +93,7 @@ jobs:
           - runner: ubuntu-latest
             target: armv7
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v5
       - uses: actions/setup-python@v5
         with:
           python-version: 3.x
@@ -123,7 +123,7 @@ jobs:
           - runner: windows-latest
             target: x86
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v5
       - uses: actions/setup-python@v5
         with:
           python-version: 3.x
@@ -153,7 +153,7 @@ jobs:
           - runner: macos-14
             target: aarch64
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v5
       - uses: actions/setup-python@v5
         with:
           python-version: 3.x
@@ -175,7 +175,7 @@ jobs:
     if: ${{ needs.check-tag.outputs.run == 'true' }}
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v5
       - name: Build sdist
         uses: PyO3/maturin-action@v1
         with:
diff --git a/.github/workflows/release-checks.yml b/.github/workflows/release-checks.yml
index 0659d1881..95ed498c0 100644
--- a/.github/workflows/release-checks.yml
+++ b/.github/workflows/release-checks.yml
@@ -28,7 +28,7 @@ jobs:
     # release-please always uses this branch name.
     if: ${{ github.ref == 'refs/heads/release-please--branches--main--components--tket-py' }}
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v5
       - uses: mozilla-actions/sccache-action@v0.0.9
       - name: Set up uv
         uses: astral-sh/setup-uv@v6
diff --git a/.github/workflows/release-plz.yml b/.github/workflows/release-plz.yml
index 397659e50..d4a2230ac 100644
--- a/.github/workflows/release-plz.yml
+++ b/.github/workflows/release-plz.yml
@@ -21,7 +21,7 @@ jobs:
 
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v4
+        uses: actions/checkout@v5
         with:
           fetch-depth: 0
           token: ${{ secrets.HUGRBOT_PAT }}
@@ -48,7 +48,7 @@ jobs:
       id-token: write     # Required for OIDC token exchange
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v4
+        uses: actions/checkout@v5
         with:
           fetch-depth: 0
           token: ${{ secrets.HUGRBOT_PAT }}
diff --git a/.github/workflows/semver-checks.yml b/.github/workflows/semver-checks.yml
index 2b2bf49de..cd648cf6b 100644
--- a/.github/workflows/semver-checks.yml
+++ b/.github/workflows/semver-checks.yml
@@ -16,7 +16,7 @@ jobs:
       rust: ${{ steps.filter.outputs.rust }}
       python: ${{ steps.filter.outputs.python }}
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v5
       - uses: ./.github/actions/check-changes
         id: filter
 
@@ -29,7 +29,7 @@ jobs:
       LD_LIBRARY_PATH: ${{ github.workspace }}/tket-c-api/lib
     steps:
       - name: Checkout tket
-        uses: actions/checkout@v4
+        uses: actions/checkout@v5
       - name: Install tket-c-api library
         uses: ./.github/actions/tket-c-api
         with:
diff --git a/.github/workflows/unsoundness.yml b/.github/workflows/unsoundness.yml
index dcc222336..af196bbc7 100644
--- a/.github/workflows/unsoundness.yml
+++ b/.github/workflows/unsoundness.yml
@@ -27,7 +27,7 @@ jobs:
     name: "Miri"
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v5
       - name: Install Miri
         run: |
           rustup toolchain install nightly --component miri