diff --git a/.github/workflows/build-test.yml b/.github/workflows/build-test.yml
index 1b1abba..8e31c6e 100644
--- a/.github/workflows/build-test.yml
+++ b/.github/workflows/build-test.yml
@@ -36,9 +36,19 @@ jobs:
       # hosted Github Actions runners don't offer much space. Clean up unused
       # dependencies so that we don't run out of disk. Borrowed from
       # https://carlosbecker.com/posts/github-actions-disk-space.
+      # 
+      # Note: deleting these directories can be very slow, so we only remove
+      # enough to allow the build to complete. We'll drop this workaround and
+      # get better build times once we switch to self-hosted runners with
+      # persistent storage and more disk.
       - name: "cleanup"
         run: |
-          sudo rm -rf /usr/share/dotnet /usr/local/lib/android /opt/ghc /opt/hostedtoolcache/CodeQL
+          time du -sh /usr/share/dotnet
+          time du -sh /opt/hostedtoolcache/CodeQL
+
+          time sudo rm -rf /usr/share/dotnet
+          time sudo rm -rf /opt/hostedtoolcache/CodeQL
+
           sudo docker image prune --all --force
           sudo docker builder prune -a
       - uses: actions/checkout@v5
@@ -57,11 +67,15 @@ jobs:
           echo "$(pwd)/bin" >> $GITHUB_PATH
       # Run simulated omicron in the background with docker compose.
       # TODO(jmcarp): support tests against multiple omicron versions.
-      # TODO(jmcarp): publish this image for faster builds.
+      - name: Login to GitHub Container Registry
+        uses: docker/login-action@v3
+        with:
+          registry: ghcr.io
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
       - name: omicron-dev
         working-directory: acctest
         run: |
-          docker compose build
           if ! docker compose up --wait --wait-timeout 1500; then
             docker compose logs
             exit 1
diff --git a/acctest/Dockerfile b/acctest/Dockerfile
index 242f630..2fbc619 100644
--- a/acctest/Dockerfile
+++ b/acctest/Dockerfile
@@ -2,11 +2,15 @@ FROM rust
 
 SHELL ["/bin/bash", "-c"]
 
+ARG OMICRON_REF=main
+
 RUN \
-  git clone https://github.com/oxidecomputer/omicron.git --branch main --depth 1 && \
+  git clone https://github.com/oxidecomputer/omicron.git && \
   cd omicron && \
+  git checkout $OMICRON_REF && \
   source env.sh && \
-  ./tools/install_builder_prerequisites.sh -y -s
+  ./tools/install_builder_prerequisites.sh -y -s && \
+  cargo xtask omicron-dev help
 
 COPY nexus-config.toml omicron
 
diff --git a/acctest/docker-compose.yaml b/acctest/docker-compose.yaml
index 5577714..a7a02f2 100644
--- a/acctest/docker-compose.yaml
+++ b/acctest/docker-compose.yaml
@@ -1,6 +1,6 @@
 services:
   omicron-dev:
-    build: .
+    image: ghcr.io/oxidecomputer/omicron-acceptance-test:4449f0156baa80430eec3a98d53b3c1d8ed06c8d
     command: /bin/bash -c 'source env.sh && cargo xtask omicron-dev run-all --nexus-config ./nexus-config.toml'
     healthcheck:
       test: ["CMD", "curl", "-f", "http://localhost:12220"]
diff --git a/acctest/nexus-config.toml b/acctest/nexus-config.toml
index 7924381..39be41e 100644
--- a/acctest/nexus-config.toml
+++ b/acctest/nexus-config.toml
@@ -98,13 +98,16 @@ metrics_producer_gc.period_secs = 60
 external_endpoints.period_secs = 60
 nat_cleanup.period_secs = 30
 bfd_manager.period_secs = 30
+# How frequently to check for a new inventory collection (made by any Nexus).
+# This is cheap, so we should check frequently.
+inventory.period_secs_load = 15
 # How frequently to collect hardware/software inventory from the whole system
 # (even if we don't have reason to believe anything has changed).
-inventory.period_secs = 600
+inventory.period_secs_collect = 600
 # Maximum number of past collections to keep in the database
 inventory.nkeep = 5
 # Disable inventory collection altogether (for emergencies)
-inventory.disable = false
+inventory.disable_collect = false
 phantom_disks.period_secs = 30
 physical_disk_adoption.period_secs = 30
 support_bundle_collector.period_secs = 30