diff --git a/.github/acton-programs.sh b/.github/acton-programs.sh
new file mode 100755
index 00000000..61c51586
--- /dev/null
+++ b/.github/acton-programs.sh
@@ -0,0 +1,43 @@
+#!/usr/bin/env bash
+# Replace the Acton programs (.act files) in bench/algorithm with the programs
+# maintained in test/perf-benchgames of the Acton repository. Each problem gets
+# exactly the .act files of its directory there. ACTON_REPO and ACTON_REF select
+# the source; the default is the commit of the published Acton tip build.
+set -euo pipefail
+shopt -s nullglob
+cd "$(dirname "$0")/.."
+repo="${ACTON_REPO:-https://github.com/actonlang/acton.git}"
+ref="${ACTON_REF:-tip}"
+
+source_dir="$(mktemp -d)"
+trap 'rm -rf "$source_dir"' EXIT
+git -c advice.detachedHead=false clone --quiet --depth 1 --branch "$ref" --filter=blob:none --sparse "$repo" "$source_dir"
+git -C "$source_dir" sparse-checkout set test/perf-benchgames
+commit="$(git -C "$source_dir" rev-parse HEAD)"
+programs="$source_dir/test/perf-benchgames"
+
+missing=()
+for problem_dir in bench/algorithm/*/; do
+  problem="$(basename "$problem_dir")"
+  ours=("$problem_dir"*.act)
+  theirs=("$programs/$problem/"*.act)
+  if (( ${#ours[@]} > 0 && ${#theirs[@]} == 0 )); then
+    missing+=("$problem")
+  fi
+done
+if (( ${#missing[@]} )); then
+  echo "Acton programs missing from $repo at $ref ($commit): ${missing[*]}" >&2
+  exit 1
+fi
+for problem_dir in "$programs"/*/; do
+  problem="$(basename "$problem_dir")"
+  theirs=("$problem_dir"*.act)
+  (( ${#theirs[@]} )) || continue
+  if [[ -d "bench/algorithm/$problem" ]]; then
+    rm -f "bench/algorithm/$problem/"*.act
+    cp "${theirs[@]}" "bench/algorithm/$problem/"
+  else
+    echo "Acton programs without a benchmark problem here: $problem" >&2
+  fi
+done
+echo "Acton programs: $repo $ref $commit"
diff --git a/.github/run-language.sh b/.github/run-language.sh
index 42f05965..4c524446 100644
--- a/.github/run-language.sh
+++ b/.github/run-language.sh
@@ -5,6 +5,11 @@ mode="${1:?check or measure}"
 language="${2:?language}"
 [[ "$mode" == check || "$mode" == measure ]]
 toolchain_image="$(python3 -c 'import json,sys; print(json.load(open(".github/languages.json"))[sys.argv[1]].get("image", "mcr.microsoft.com/dotnet/sdk:9.0-noble"))' "$language")"
+acton_programs=""
+if [[ "$language" == acton || "$language" == acton-tip ]]; then
+  acton_programs="$(bash .github/acton-programs.sh)"
+  echo "$acton_programs"
+fi
 
 mkdir -p "${XDG_STATE_HOME:-$HOME/.local/state}"
 exec 9>"${XDG_STATE_HOME:-$HOME/.local/state}/acton-perf.lock"
@@ -58,3 +63,6 @@ echo "::endgroup::"
 
 "${engine[@]}" image inspect "$image" --format '{{.Id}}' \
   >> "bench/build/environment-${language}.txt" 9>&-
+if [[ -n "$acton_programs" ]]; then
+  echo "$acton_programs" >> "bench/build/environment-${language}.txt"
+fi
diff --git a/README.md b/README.md
index 6067283c..eb9d199f 100644
--- a/README.md
+++ b/README.md
@@ -70,6 +70,18 @@ Use `acton-tip` to select the development build in workflow inputs or local
 commands. Go uses one 1.26 toolchain throughout the job; dependencies cannot
 silently select another compiler.
 
+The Acton programs are maintained in `test/perf-benchgames` of the
+[Acton repository](https://github.com/actonlang/acton). Before building, both
+Acton jobs run `.github/acton-programs.sh`. It gives each problem in
+`bench/algorithm` exactly the `.act` files of the same problem directory at the
+Acton `tip` tag, the commit of the published development build. The `source`
+lists in `bench/bench_acton.yaml` and `bench/bench_acton_tip.yaml` still choose
+which programs to build. The job records the Acton commit in its environment
+file. A program that needs a newer compiler than the latest release fails the
+stable Acton job, so that run has no stable Acton results. `ACTON_REPO` and
+`ACTON_REF` select another source, for example a branch in a local Acton
+checkout: `ACTON_REPO=file:///path/to/acton ACTON_REF=my-branch`.
+
 ## Running locally
 
 Install .NET 9 and the compilers or runtimes you want to compare. Run commands
@@ -87,6 +99,9 @@ dotnet run --no-launch-profile -c Release --project tool -- --task bench --langs
 dotnet run --no-launch-profile -c Release --project tool -- --task build --langs python --compilers cpython --problems binarytrees --no-docker
 ```
 
+Run `bash .github/acton-programs.sh` first to build the Acton programs from the
+Acton repository instead of the copies in `bench/algorithm`.
+
 `bench/bench.yaml` defines the inputs and expected outputs. Language configurations
 are in `bench/bench_*.yaml`. `--no-docker` uses locally installed compilers instead
 of the container images in those configurations. On Linux with sudo access, the CI wrapper installs Podman if needed and uses
diff --git a/bench/bench_acton.yaml b/bench/bench_acton.yaml
index a6c6c921..4713119a 100644
--- a/bench/bench_acton.yaml
+++ b/bench/bench_acton.yaml
@@ -1,3 +1,6 @@
+# The programs come from test/perf-benchgames in the Acton repository:
+# .github/acton-programs.sh copies their .act files into bench/algorithm before
+# each run. A program is built only when it is listed under source.
 lang: acton
 problems:
   - name: binarytrees
diff --git a/bench/bench_acton_tip.yaml b/bench/bench_acton_tip.yaml
index 6e07f196..d5a8d469 100644
--- a/bench/bench_acton_tip.yaml
+++ b/bench/bench_acton_tip.yaml
@@ -1,3 +1,6 @@
+# The programs come from test/perf-benchgames in the Acton repository:
+# .github/acton-programs.sh copies their .act files into bench/algorithm before
+# each run. A program is built only when it is listed under source.
 lang: acton-tip
 problems:
   - name: binarytrees