diff --git a/.github/workflows/ci.yaml b/.github/workflows/ci.yaml
index f6b5e19..81786a3 100644
--- a/.github/workflows/ci.yaml
+++ b/.github/workflows/ci.yaml
@@ -18,7 +18,7 @@ defaults:
 
 jobs:
   test:
-    name: ${{ matrix.os }}, 🐍=${{ matrix.python-version }}, 🟠=${{ matrix.ambertools }}, 👁️=${{ matrix.openeye }}, 🐉=${{ matrix.mamba-executable }}
+    name: ${{ matrix.os }}, 🐍=${{ matrix.python-version }}, 🟠=${{ matrix.ambertools }}, 👁️=${{ matrix.openeye }}, 🐉=${{ matrix.mamba-executable }}@${{ matrix.micromamba-version }}
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
@@ -27,6 +27,11 @@ jobs:
         ambertools: [false, true]
         openeye: [false, true]
         mamba-executable: ["micromamba"]  # TODO: Add "mamba" back
+        # TEMPORARY, for #156: pin both the pre- and post-4202 micromamba
+        # releases to confirm the packages-key fix covers both `list --json`
+        # formats. Revert this axis (and the micromamba-version input below)
+        # before merging.
+        micromamba-version: ["2.8.1-0", "2.9.0-0"]
         exclude:
           - python-version: "3.14"
             ambertools: true
@@ -47,6 +52,7 @@ jobs:
       uses: mamba-org/setup-micromamba@v3
       with:
         environment-file: devtools/conda-envs/test_env.yaml
+        micromamba-version: ${{ matrix.micromamba-version }}
         create-args: >-
           python=${{ matrix.python-version }}
 
diff --git a/openff/utilities/provenance.py b/openff/utilities/provenance.py
index 758e0c2..d5423a6 100644
--- a/openff/utilities/provenance.py
+++ b/openff/utilities/provenance.py
@@ -30,6 +30,12 @@ def _get_conda_list_package_versions() -> dict[str, str]:
 
     output = json.loads(subprocess.check_output(conda_command.split()).decode())
 
+    # micromamba >= 2.9.0 nests the package list under a "packages" key instead
+    # of returning it as the top-level array (mamba-org/mamba#4202, issue #156).
+    # conda, mamba, pixi, and micromamba < 2.9.0 all return the bare array.
+    if isinstance(output, dict):
+        output = output.get("packages", [])
+
     package_versions = {}
     for _package in output:
         package_versions[_package["name"]] = _package["version"]