diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 625466151e34de..6aa99928278294 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -414,6 +414,29 @@ jobs:
       - name: Build and test
         run: ./Android/android.py ci --fast-ci ${{ matrix.arch }}-linux-android
 
+  build-ios:
+    name: iOS
+    needs: build-context
+    if: needs.build-context.outputs.run-tests == 'true'
+    timeout-minutes: 60
+    runs-on: macos-15
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          persist-credentials: false
+
+      # GitHub recommends explicitly selecting the desired Xcode version:
+      # https://github.com/actions/runner-images/issues/12541#issuecomment-3083850140
+      # This became a necessity as a result of
+      # https://github.com/actions/runner-images/issues/12541 and
+      # https://github.com/actions/runner-images/issues/12751.
+      - name: Select Xcode version
+        run: |
+          sudo xcode-select --switch /Applications/Xcode_16.4.app
+
+      - name: Build and test
+        run: python3 Apple ci iOS --fast-ci --simulator 'iPhone 16e,OS=18.5'
+
   build-wasi:
     name: 'WASI'
     needs: build-context
@@ -723,6 +746,7 @@ jobs:
     - build-ubuntu-ssltests-awslc
     - build-ubuntu-ssltests-openssl
     - build-android
+    - build-ios
     - build-wasi
     - test-hypothesis
     - build-asan
@@ -759,6 +783,7 @@ jobs:
             build-ubuntu-ssltests-awslc,
             build-ubuntu-ssltests-openssl,
             build-android,
+            build-ios,
             build-wasi,
             test-hypothesis,
             build-asan,
diff --git a/Apple/__main__.py b/Apple/__main__.py
index 96c2d34fbe0959..34744871f681ea 100644
--- a/Apple/__main__.py
+++ b/Apple/__main__.py
@@ -823,7 +823,7 @@ def test(context: argparse.Namespace, host: str | None = None) -> None:
             + [
                 "--",
                 "test",
-                "--slow-ci" if context.slow else "--fast-ci",
+                f"--{context.ci_mode}-ci",
                 "--single-process",
                 "--no-randomize",
                 # Timeout handling requires subprocesses; explicitly setting
@@ -836,11 +836,39 @@ def test(context: argparse.Namespace, host: str | None = None) -> None:
         )
 
 
+def apple_sim_host(platform_name: str) -> str:
+    """Determine the native simulator target for this platform."""
+    for _, slice_parts in HOSTS[platform_name].items():
+        for host_triple in slice_parts:
+            parts = host_triple.split('-')
+            if parts[0] == platform.machine() and parts[-1] == "simulator":
+                return host_triple
+
+    raise KeyError(platform_name)
+
+
 def ci(context: argparse.Namespace) -> None:
-    """The implementation of the "ci" command."""
+    """The implementation of the "ci" command.
+
+    In "Fast" mode, this compiles the build python, and the simulator for the
+    build machine's architecture; and runs the test suite with `--fast-ci`
+    configuration.
+
+    In "Slow" mode, it compiles the build python, plus all candidate
+    architectures (both device and simulator); then runs the test suite with
+    `--slow-ci` configuration.
+    """
     clean(context, "all")
-    build(context, host="all")
-    test(context, host="all")
+    if context.ci_mode == "slow":
+        # In slow mode, build and test the full XCframework
+        build(context, host="all")
+        test(context, host="all")
+    else:
+        # In fast mode, just build the simulator platform.
+        sim_host = apple_sim_host(context.platform)
+        build(context, host="build")
+        build(context, host=sim_host)
+        test(context, host=sim_host)
 
 
 def parse_args() -> argparse.Namespace:
@@ -947,11 +975,13 @@ def parse_args() -> argparse.Namespace:
                 "an ARM64 iPhone 16 Pro simulator running iOS 26.0."
             ),
         )
-        cmd.add_argument(
-            "--slow",
-            action="store_true",
-            help="Run tests with --slow-ci options.",
-        )
+        group = cmd.add_mutually_exclusive_group()
+        group.add_argument(
+            "--fast-ci", action="store_const", dest="ci_mode", const="fast",
+            help="Add test arguments for GitHub Actions")
+        group.add_argument(
+            "--slow-ci", action="store_const", dest="ci_mode", const="slow",
+            help="Add test arguments for buildbots")
 
     for subcommand in [configure_build, configure_host, build, ci]:
         subcommand.add_argument(
@@ -1012,4 +1042,10 @@ def signal_handler(*args):
 
 
 if __name__ == "__main__":
+    # Under the buildbot, stdout is not a TTY, but we must still flush after
+    # every line to make sure our output appears in the correct order relative
+    # to the output of our subprocesses.
+    for stream in [sys.stdout, sys.stderr]:
+        stream.reconfigure(line_buffering=True)
+
     main()
diff --git a/Apple/testbed/__main__.py b/Apple/testbed/__main__.py
index 4a1333380cdb6d..f3407ecdf7e734 100644
--- a/Apple/testbed/__main__.py
+++ b/Apple/testbed/__main__.py
@@ -412,4 +412,9 @@ def main():
 
 
 if __name__ == "__main__":
+    # Under the buildbot, stdout is not a TTY, but we must still flush after
+    # every line to make sure our output appears in the correct order relative
+    # to the output of our subprocesses.
+    for stream in [sys.stdout, sys.stderr]:
+        stream.reconfigure(line_buffering=True)
     main()
diff --git a/Misc/NEWS.d/next/Build/2025-10-16-11-30-53.gh-issue-140189.YCrUyt.rst b/Misc/NEWS.d/next/Build/2025-10-16-11-30-53.gh-issue-140189.YCrUyt.rst
new file mode 100644
index 00000000000000..a1b81659242670
--- /dev/null
+++ b/Misc/NEWS.d/next/Build/2025-10-16-11-30-53.gh-issue-140189.YCrUyt.rst
@@ -0,0 +1 @@
+iOS builds were added to CI.