diff --git a/.github/workflows/format.yml b/.github/workflows/format.yml
index 29e9129..7ecba5c 100644
--- a/.github/workflows/format.yml
+++ b/.github/workflows/format.yml
@@ -1,28 +1,17 @@
 name: format
 
 on:
-  pull_request:
   push:
     branches:
       - main
+  pull_request:
 
 jobs:
   format:
     name: format
-    strategy:
-      matrix:
-        ocaml-compiler:
-            - '5.3'
     runs-on: 'ubuntu-latest'
+    container: ghcr.io/c-cube/c-cube-commmon/ci-doc-5.3:latest
     steps:
-      - uses: actions/checkout@main
-      - name: Use OCaml ${{ matrix.ocaml-compiler }}
-        uses: ocaml/setup-ocaml@v3
-        with:
-          ocaml-compiler: ${{ matrix.ocaml-compiler }}
-          dune-cache: true
-          allow-prerelease-opam: true
-
-      - run: opam install ocamlformat.0.27.0
+      - uses: actions/checkout@v6
       - run: opam exec -- make format-check
 
diff --git a/.github/workflows/gh-pages.yml b/.github/workflows/gh-pages.yml
index 1df1d1e..6a87d09 100644
--- a/.github/workflows/gh-pages.yml
+++ b/.github/workflows/gh-pages.yml
@@ -11,20 +11,12 @@ jobs:
     runs-on: ubuntu-latest
     permissions:
       contents: write
+    container: ghcr.io/c-cube/c-cube-commmon/ci-doc-5.3:latest
     steps:
-      - uses: actions/checkout@main
+      - uses: actions/checkout@v6
 
-      - name: Use OCaml
-        uses: ocaml/setup-ocaml@v3
-        with:
-          ocaml-compiler: '5.1.x'
-          allow-prerelease-opam: true
-          dune-cache: true
-
-      - run: opam pin odoc 3.1.0 -y -n
-        # crash with 2.4, see https://github.com/ocaml/odoc/issues/1066
       - name: Deps
-        run: opam install odig thread-local-storage trace trace-tef trace-fuchsia ppx_trace
+        run: opam install thread-local-storage trace trace-tef trace-fuchsia ppx_trace
 
       - name: Build
         run: opam exec -- odig odoc --cache-dir=_doc/ trace trace-tef trace-fuchsia ppx_trace
diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index cc2d7e4..5d3e76d 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -1,4 +1,4 @@
-name: Build and Test
+name: build
 
 on:
   push:
@@ -8,28 +8,21 @@ on:
 
 jobs:
   run:
-    name: build
+    name: build  # build+test on various versions of OCaml, on linux
+    timeout-minutes: 15
     strategy:
       fail-fast: true
       matrix:
-        os:
-            - ubuntu-latest
-              #- macos-latest
-              #- windows-latest
-        ocaml-compiler:
-            - '4.08.x'
-            - '4.14.x'
-            - '5.3.x'
+        container:
+          - ghcr.io/c-cube/c-cube-commmon/ci-4.08:latest
+          - ghcr.io/c-cube/c-cube-commmon/ci-4.14:latest
+          - ghcr.io/c-cube/c-cube-commmon/ci-5.0:latest
+          - ghcr.io/c-cube/c-cube-commmon/ci-5.4:latest
 
-    runs-on: ${{ matrix.os }}
+    runs-on: ubuntu-latest
+    container: ${{ matrix.container }}
     steps:
-      - uses: actions/checkout@main
-      - name: Use OCaml ${{ matrix.ocaml-compiler }}
-        uses: ocaml/setup-ocaml@v3
-        with:
-          ocaml-compiler: ${{ matrix.ocaml-compiler }}
-          dune-cache: true
-          allow-prerelease-opam: true
+      - uses: actions/checkout@v6
 
       # check that trace compiles with no optional deps
       - run: opam install -t trace --deps-only
@@ -37,11 +30,11 @@ jobs:
 
       # install all packages
       - run: opam install -t trace trace-tef trace-fuchsia --deps-only
-      - run: opam install ppx_trace --deps-only # no tests
-        if: matrix.ocaml-compiler != '4.08.x'
+      - run: opam install ppx_trace --deps-only
+        if: ${{ !contains(matrix.container, 'ci-4.08') }}
       - run: opam exec -- dune build '@install' -p trace,trace-tef,trace-fuchsia
       - run: opam exec -- dune build '@install' -p ppx_trace
-        if: matrix.ocaml-compiler != '4.08.x'
+        if: ${{ !contains(matrix.container, 'ci-4.08') }}
       - run: opam exec -- dune runtest -p trace
       - run: opam install trace
       - run: opam exec -- dune runtest -p trace-tef,trace-fuchsia
@@ -51,9 +44,9 @@ jobs:
       - run: opam exec -- dune build '@install' -p trace,trace-tef,trace-fuchsia
 
       - run: opam install picos_aux
-        if: matrix.ocaml-compiler != '4.08.x' && matrix.ocaml-compiler != '4.12.x'
+        if: ${{ !contains(matrix.container, 'ci-4.') }}
       - run: opam exec -- dune build '@install' -p trace,trace-tef,trace-fuchsia
-        if: matrix.ocaml-compiler != '4.08.x' && matrix.ocaml-compiler != '4.12.x'
+        if: ${{ !contains(matrix.container, 'ci-4.') }}
 
       - run: opam install mtime
       - run: opam exec -- dune build '@install' -p trace,trace-tef,trace-fuchsia