diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 8cd7b05fc..b34a06af9 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -6,6 +6,12 @@ on:
     branches: ["main"]
   pull_request:
     branches: ["main"]
+  workflow_dispatch:
+    inputs:
+      run_macos:
+        description: "Run macOS CI jobs (slow runners, opt-in)"
+        type: boolean
+        default: false
 
 name: CI
 
@@ -361,9 +367,13 @@ jobs:
             --package diskann-quantization \
             -- --skip compile_tests
 
+  # macOS is opt-in since it is slow to provision.
+  # It is excluded from the default push/PR matrix, and only included for manually
+  # dispatched runs when `run_macos: true` is set.
   test-workspace:
     needs: basics
     name: test workspace
+    if: ${{ matrix.os != 'macos-latest' || (github.event_name == 'workflow_dispatch' && inputs.run_macos) }}
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
@@ -371,7 +381,7 @@ jobs:
           - windows-latest
           - ubuntu-latest
           - ubuntu-24.04-arm
-          - macos-latest
+          - macos-latest # skipped unless manually triggered
 
     steps:
       - uses: actions/checkout@v4
@@ -397,13 +407,14 @@ jobs:
   test-workspace-features:
     needs: basics
     name: test workspace (all features)
+    if: ${{ matrix.os != 'macos-latest' || (github.event_name == 'workflow_dispatch' && inputs.run_macos) }}
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
         os:
           - windows-latest
           - ubuntu-latest
-          - macos-latest
+          - macos-latest # skipped unless manually triggered
 
     steps:
       - uses: actions/checkout@v4