diff --git a/.github/workflows/lockfiles.yml b/.github/workflows/lockfiles.yml
index 8f363f3a2..158b41b71 100644
--- a/.github/workflows/lockfiles.yml
+++ b/.github/workflows/lockfiles.yml
@@ -24,10 +24,13 @@ on:
     branches: [main]
   pull_request:
 
+# Runs on `linux-arm64`, not `linux`: these jobs read files and run scripts, so the CPU
+# architecture does not matter to them, and the one `linux` (x86_64) runner is the
+# fleet's bottleneck, with every Rust workspace's tests queued on it.
 jobs:
   current:
     name: every Cargo.lock is current
-    runs-on: linux
+    runs-on: linux-arm64
     timeout-minutes: 15
     steps:
       - uses: actions/checkout@v4
diff --git a/.github/workflows/no-vanity-metrics.yml b/.github/workflows/no-vanity-metrics.yml
index 43e35cd52..8f51fec8c 100644
--- a/.github/workflows/no-vanity-metrics.yml
+++ b/.github/workflows/no-vanity-metrics.yml
@@ -88,10 +88,13 @@ on:
       - 'scripts/check-public-names.sh'
       - 'scripts/test-public-text-checks.sh'
 
+# Runs on `linux-arm64`, not `linux`: these jobs read files and run scripts, so the CPU
+# architecture does not matter to them, and the one `linux` (x86_64) runner is the
+# fleet's bottleneck, with every Rust workspace's tests queued on it.
 jobs:
   scan:
     name: Scan committed Markdown for vanity metrics
-    runs-on: linux
+    runs-on: linux-arm64
     steps:
       - name: Checkout
         uses: actions/checkout@v4
@@ -101,7 +104,7 @@ jobs:
 
   wai-comparative-prose:
     name: WAI public text names no comparison
-    runs-on: linux
+    runs-on: linux-arm64
     steps:
       - name: Checkout
         uses: actions/checkout@v4
@@ -112,7 +115,7 @@ jobs:
 
   wai-public-names:
     name: WAI public text names no company or product
-    runs-on: linux
+    runs-on: linux-arm64
     steps:
       - name: Checkout
         uses: actions/checkout@v4
@@ -159,7 +162,7 @@ jobs:
   # pre-existing condition, and so the count can only ratchet down.
   orphan-sources:
     name: No new orphan source files
-    runs-on: linux
+    runs-on: linux-arm64
     steps:
       - name: Checkout
         uses: actions/checkout@v4
diff --git a/.github/workflows/tests-in-ci.yml b/.github/workflows/tests-in-ci.yml
index 8fc926dde..89dca38a8 100644
--- a/.github/workflows/tests-in-ci.yml
+++ b/.github/workflows/tests-in-ci.yml
@@ -25,10 +25,13 @@ on:
     branches: [main]
   pull_request:
 
+# Runs on `linux-arm64`, not `linux`: these jobs read files and run scripts, so the CPU
+# architecture does not matter to them, and the one `linux` (x86_64) runner is the
+# fleet's bottleneck, with every Rust workspace's tests queued on it.
 jobs:
   covered:
     name: every test file is run by a job or listed with its reason
-    runs-on: linux
+    runs-on: linux-arm64
     timeout-minutes: 10
     steps:
       - uses: actions/checkout@v4
diff --git a/.github/workflows/wai-section-refs.yml b/.github/workflows/wai-section-refs.yml
index 5352e46bc..62844cbad 100644
--- a/.github/workflows/wai-section-refs.yml
+++ b/.github/workflows/wai-section-refs.yml
@@ -45,10 +45,13 @@ on:
       - 'scripts/check-wai-section-refs.py'
       - '.github/workflows/wai-section-refs.yml'
 
+# Runs on `linux-arm64`, not `linux`: these jobs read files and run scripts, so the CPU
+# architecture does not matter to them, and the one `linux` (x86_64) runner is the
+# fleet's bottleneck, with every Rust workspace's tests queued on it.
 jobs:
   section-refs:
     name: cited sections exist
-    runs-on: linux
+    runs-on: linux-arm64
     steps:
       - uses: actions/checkout@v5
       - uses: actions/setup-python@v5
diff --git a/.github/workflows/workflow-hygiene.yml b/.github/workflows/workflow-hygiene.yml
index 94255e69b..f40794e6d 100644
--- a/.github/workflows/workflow-hygiene.yml
+++ b/.github/workflows/workflow-hygiene.yml
@@ -40,10 +40,13 @@ concurrency:
   group: ${{ github.workflow }}-${{ github.ref }}
   cancel-in-progress: true
 
+# Runs on `linux-arm64`, not `linux`: these jobs read files and run scripts, so the CPU
+# architecture does not matter to them, and the one `linux` (x86_64) runner is the
+# fleet's bottleneck, with every Rust workspace's tests queued on it.
 jobs:
   concurrency-groups:
     name: every workflow supersedes its own queue
-    runs-on: linux
+    runs-on: linux-arm64
     steps:
       - uses: actions/checkout@v4