diff --git a/.github/workflows/ci.yaml b/.github/workflows/ci.yaml
index d74432949..b913fcbbb 100644
--- a/.github/workflows/ci.yaml
+++ b/.github/workflows/ci.yaml
@@ -216,10 +216,10 @@ jobs:
         # tests the endpoints of the supported range. The wheel build process
         # (in a separate workflow) *does* use all the versions.
         os:
-          - ubuntu-24.04
+          - ubuntu-24.04-x64-8-core
           - macos-14
           - macos-15
-          - windows-2025
+          - windows-2025-x64-8-core
         python_version:
           - '3.10'
           - '3.13'
@@ -247,13 +247,13 @@ jobs:
         with:
           debug: ${{inputs.debug}}
 
-      - if: matrix.os != 'windows-2025'
+      - if: ${{! startsWith(matrix.os, 'windows-')}}
         name: Build the qsim C++ library and run tests (non-Windows case)
         run: |
           alias bazel=bazelisk
           dev_tools/test_libs.sh ${{inputs.debug && '--config=verbose'}}
 
-      - if: matrix.os == 'windows-2025'
+      - if: ${{startsWith(matrix.os, 'windows-')}}
         name: Build the qsim C++ library and run tests (Windows case)
         # On GitHub Windows runners, Bazel ends up finding a different "python3"
         # binary than what's installed by setup-python unless we tell Bazel what
@@ -301,7 +301,7 @@ jobs:
       - python-checks
       - shell-lint
       - yaml-lint
-    runs-on: ubuntu-24.04
+    runs-on: ubuntu-24.04-x64-16-core
     timeout-minutes: 60
     strategy:
       matrix:
@@ -356,7 +356,7 @@ jobs:
       - python-checks
       - shell-lint
       - yaml-lint
-    runs-on: ubuntu-24.04
+    runs-on: ubuntu-24.04-x64-16-core
     timeout-minutes: 60
     env:
       common_args: >-
@@ -411,7 +411,7 @@ jobs:
       - python-checks
       - shell-lint
       - yaml-lint
-    runs-on: ubuntu-24.04
+    runs-on: ubuntu-24.04-x64-16-core
     timeout-minutes: 60
     env:
       # The next environment variable is used by Docker.