diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 93316b9cff7b1..972e2f1793c93 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -145,6 +145,9 @@ jobs:
       - name: show the current environment
         run: src/ci/scripts/dump-environment.sh
 
+      - name: install rust
+        run: src/ci/scripts/install-rust.sh
+
       - name: install awscli
         run: src/ci/scripts/install-awscli.sh
 
@@ -225,8 +228,7 @@ jobs:
           fi
           exit ${STATUS}
         env:
-          AWS_ACCESS_KEY_ID: ${{ env.CACHES_AWS_ACCESS_KEY_ID }}
-          AWS_SECRET_ACCESS_KEY: ${{ secrets[format('AWS_SECRET_ACCESS_KEY_{0}', env.CACHES_AWS_ACCESS_KEY_ID)] }}
+          SCCACHE_S3_NO_CREDENTIALS: 1
 
       - name: create github artifacts
         run: src/ci/scripts/create-doc-artifacts.sh
diff --git a/compiler/rustc_target/src/spec/targets/aarch64_pc_windows_msvc.rs b/compiler/rustc_target/src/spec/targets/aarch64_pc_windows_msvc.rs
index 98d78520c9838..94671b4e209b5 100644
--- a/compiler/rustc_target/src/spec/targets/aarch64_pc_windows_msvc.rs
+++ b/compiler/rustc_target/src/spec/targets/aarch64_pc_windows_msvc.rs
@@ -1,10 +1,18 @@
-use crate::spec::{Target, TargetMetadata, base};
+use std::borrow::Cow;
+
+use crate::spec::{LinkerFlavor, Lld, Target, TargetMetadata, base};
 
 pub(crate) fn target() -> Target {
     let mut base = base::windows_msvc::opts();
     base.max_atomic_width = Some(128);
     base.features = "+v8a,+neon,+fp-armv8".into();
 
+    // MSVC emits a warning about code that may trip "Cortex-A53 MPCore processor bug #843419" which
+    // is sometimes emitted by LLVM. Since Arm64 Windows 10+ isn't supported on that processor, it's
+    // safe to disable the warning.
+    let msvc_pre_link_args = base.pre_link_args.get_mut(&LinkerFlavor::Msvc(Lld::No)).unwrap();
+    msvc_pre_link_args.push(Cow::Borrowed("/arm64hazardfree"));
+
     Target {
         llvm_target: "aarch64-pc-windows-msvc".into(),
         metadata: TargetMetadata {
diff --git a/library/std/src/fs/tests.rs b/library/std/src/fs/tests.rs
index 4712e58980cc6..a9062bea09e90 100644
--- a/library/std/src/fs/tests.rs
+++ b/library/std/src/fs/tests.rs
@@ -714,6 +714,10 @@ fn recursive_mkdir_empty() {
 }
 
 #[test]
+#[cfg_attr(
+    all(windows, target_arch = "aarch64"),
+    ignore = "SymLinks not enabled on Arm64 Windows runners https://github.com/actions/partner-runner-images/issues/94"
+)]
 fn recursive_rmdir() {
     let tmpdir = tmpdir();
     let d1 = tmpdir.join("d1");
@@ -733,6 +737,10 @@ fn recursive_rmdir() {
 }
 
 #[test]
+#[cfg_attr(
+    all(windows, target_arch = "aarch64"),
+    ignore = "SymLinks not enabled on Arm64 Windows runners https://github.com/actions/partner-runner-images/issues/94"
+)]
 fn recursive_rmdir_of_symlink() {
     // test we do not recursively delete a symlink but only dirs.
     let tmpdir = tmpdir();
@@ -1517,6 +1525,10 @@ fn file_open_not_found() {
 }
 
 #[test]
+#[cfg_attr(
+    all(windows, target_arch = "aarch64"),
+    ignore = "SymLinks not enabled on Arm64 Windows runners https://github.com/actions/partner-runner-images/issues/94"
+)]
 fn create_dir_all_with_junctions() {
     let tmpdir = tmpdir();
     let target = tmpdir.join("target");
@@ -1995,6 +2007,10 @@ fn test_rename_symlink() {
 
 #[test]
 #[cfg(windows)]
+#[cfg_attr(
+    all(windows, target_arch = "aarch64"),
+    ignore = "SymLinks not enabled on Arm64 Windows runners https://github.com/actions/partner-runner-images/issues/94"
+)]
 fn test_rename_junction() {
     let tmpdir = tmpdir();
     let original = tmpdir.join("original");
diff --git a/src/ci/github-actions/jobs.yml b/src/ci/github-actions/jobs.yml
index afcc092e78e8d..2f957baef635e 100644
--- a/src/ci/github-actions/jobs.yml
+++ b/src/ci/github-actions/jobs.yml
@@ -47,6 +47,10 @@ runners:
     os: windows-2025-8core-32gb
     <<: *base-job
 
+  - &job-windows-aarch64
+    os: windows-11-arm
+    <<: *base-job
+
   - &job-aarch64-linux
     # Free some disk space to avoid running out of space during the build.
     free_disk: true
@@ -115,18 +119,18 @@ envs:
 # These jobs automatically inherit envs.pr, to avoid repeating
 # it in each job definition.
 pr:
-  - name: mingw-check
-    <<: *job-linux-4c
-  - name: mingw-check-tidy
-    continue_on_error: true
-    <<: *job-linux-4c
-  - name: x86_64-gnu-llvm-19
+  # aarch64-msvc is split into two jobs to run tests in parallel.
+  - name: aarch64-msvc-1
     env:
-      ENABLE_GCC_CODEGEN: "1"
-      DOCKER_SCRIPT: x86_64-gnu-llvm.sh
-    <<: *job-linux-16c
-  - name: x86_64-gnu-tools
-    <<: *job-linux-16c
+      RUST_CONFIGURE_ARGS: --build=aarch64-pc-windows-msvc
+      SCRIPT: make ci-msvc-py
+    <<: *job-windows-aarch64
+
+  - name: aarch64-msvc-2
+    env:
+      RUST_CONFIGURE_ARGS: --build=aarch64-pc-windows-msvc
+      SCRIPT: make ci-msvc-ps1
+    <<: *job-windows-aarch64
 
 # Jobs that run when you perform a try build (@bors try)
 # These jobs automatically inherit envs.try, to avoid repeating
diff --git a/src/ci/scripts/install-clang.sh b/src/ci/scripts/install-clang.sh
index 5522095e3049b..228d14fc0138b 100755
--- a/src/ci/scripts/install-clang.sh
+++ b/src/ci/scripts/install-clang.sh
@@ -11,7 +11,7 @@ source "$(cd "$(dirname "$0")" && pwd)/../shared.sh"
 
 # Update both macOS's and Windows's tarballs when bumping the version here.
 # Try to keep this in sync with src/ci/docker/host-x86_64/dist-x86_64-linux/build-clang.sh
-LLVM_VERSION="18.1.4"
+LLVM_VERSION="20.1.3"
 
 if isMacOS; then
     # FIXME: This is the latest pre-built version of LLVM that's available for
@@ -56,9 +56,19 @@ elif isWindows && ! isKnownToBeMingwBuild; then
 
     mkdir -p citools/clang-rust
     cd citools
-    retry curl -f "${MIRRORS_BASE}/LLVM-${LLVM_VERSION}-win64.exe" \
-        -o "LLVM-${LLVM_VERSION}-win64.exe"
-    7z x -oclang-rust/ "LLVM-${LLVM_VERSION}-win64.exe"
+
+    if [[ "${CI_JOB_NAME}" = *aarch64* ]]; then
+        suffix=woa64
+
+        # On Arm64, the Ring crate requires that Clang be on the PATH.
+        # https://github.com/briansmith/ring/blob/main/BUILDING.md
+        ciCommandAddPath "$(cygpath -m "$(pwd)/clang-rust/bin")"
+    else
+        suffix=win64
+    fi
+    retry curl -f "${MIRRORS_BASE}/LLVM-${LLVM_VERSION}-${suffix}.exe" \
+        -o "LLVM-${LLVM_VERSION}-${suffix}.exe"
+    7z x -oclang-rust/ "LLVM-${LLVM_VERSION}-${suffix}.exe"
     ciCommandSetEnv RUST_CONFIGURE_ARGS \
         "${RUST_CONFIGURE_ARGS} --set llvm.clang-cl=$(pwd)/clang-rust/bin/clang-cl.exe"
 
diff --git a/src/ci/scripts/install-mingw.sh b/src/ci/scripts/install-mingw.sh
index c8c501e646a9d..ad852071f2950 100755
--- a/src/ci/scripts/install-mingw.sh
+++ b/src/ci/scripts/install-mingw.sh
@@ -42,5 +42,5 @@ if isWindows && isKnownToBeMingwBuild; then
 
     curl -o mingw.7z "${MIRRORS_BASE}/${mingw_archive}"
     7z x -y mingw.7z > /dev/null
-    ciCommandAddPath "$(pwd)/${mingw_dir}/bin"
+    ciCommandAddPath "$(cygpath -m "$(pwd)/${mingw_dir}/bin")"
 fi
diff --git a/src/ci/scripts/install-ninja.sh b/src/ci/scripts/install-ninja.sh
index 23cbc2eb6d107..7ac19173923cf 100755
--- a/src/ci/scripts/install-ninja.sh
+++ b/src/ci/scripts/install-ninja.sh
@@ -12,7 +12,7 @@ if isWindows; then
     7z x -oninja ninja.zip
     rm ninja.zip
     ciCommandSetEnv "RUST_CONFIGURE_ARGS" "${RUST_CONFIGURE_ARGS} --enable-ninja"
-    ciCommandAddPath "$(pwd)/ninja"
+    ciCommandAddPath "$(cygpath -m "$(pwd)/ninja")"
 elif isMacOS; then
     brew install ninja
 fi
diff --git a/src/ci/scripts/install-rust.sh b/src/ci/scripts/install-rust.sh
new file mode 100644
index 0000000000000..d87bb28aa303b
--- /dev/null
+++ b/src/ci/scripts/install-rust.sh
@@ -0,0 +1,15 @@
+#!/bin/bash
+
+# The Arm64 Windows Runner does not have Rust already installed
+# https://github.com/actions/partner-runner-images/issues/93
+
+set -euo pipefail
+IFS=$'\n\t'
+
+source "$(cd "$(dirname "$0")" && pwd)/../shared.sh"
+
+if [[ "${CI_JOB_NAME}" = *aarch64* ]] && isWindows; then
+    curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | \
+    sh -s -- -y -q --default-host aarch64-pc-windows-msvc
+    ciCommandAddPath "${USERPROFILE}/.cargo/bin"
+fi
diff --git a/src/ci/scripts/install-sccache.sh b/src/ci/scripts/install-sccache.sh
index b055e76a80504..fed06063fa0b3 100755
--- a/src/ci/scripts/install-sccache.sh
+++ b/src/ci/scripts/install-sccache.sh
@@ -15,7 +15,7 @@ elif isWindows; then
     mkdir -p sccache
     curl -fo sccache/sccache.exe \
       "${MIRRORS_BASE}/2025-02-24-sccache-v0.10.0-x86_64-pc-windows-msvc.exe"
-    ciCommandAddPath "$(pwd)/sccache"
+    ciCommandAddPath "$(cygpath -m "$(pwd)/sccache")"
 fi
 
 # FIXME: we should probably install sccache outside the containers and then
diff --git a/src/doc/nomicon b/src/doc/nomicon
index c76a20f0d9871..0c10c30cc5473 160000
--- a/src/doc/nomicon
+++ b/src/doc/nomicon
@@ -1 +1 @@
-Subproject commit c76a20f0d987145dcedf05c5c073ce8d91f2e82a
+Subproject commit 0c10c30cc54736c5c194ce98c50e2de84eeb6e79
diff --git a/src/doc/reference b/src/doc/reference
index 3bf3402aea982..3340922df189b 160000
--- a/src/doc/reference
+++ b/src/doc/reference
@@ -1 +1 @@
-Subproject commit 3bf3402aea982b876eb56c87da17b0685c6461d5
+Subproject commit 3340922df189bddcbaad17dc3927d51a76bcd5ed
diff --git a/src/tools/compiletest/src/directive-list.rs b/src/tools/compiletest/src/directive-list.rs
index 1449e9af19aa5..5757e422ae21e 100644
--- a/src/tools/compiletest/src/directive-list.rs
+++ b/src/tools/compiletest/src/directive-list.rs
@@ -35,6 +35,7 @@ const KNOWN_DIRECTIVE_NAMES: &[&str] = &[
     "ignore-32bit",
     "ignore-64bit",
     "ignore-aarch64",
+    "ignore-aarch64-pc-windows-msvc",
     "ignore-aarch64-unknown-linux-gnu",
     "ignore-aix",
     "ignore-android",
diff --git a/tests/debuginfo/step-into-match.rs b/tests/debuginfo/step-into-match.rs
index 577e553c11985..a4abe9a29aae3 100644
--- a/tests/debuginfo/step-into-match.rs
+++ b/tests/debuginfo/step-into-match.rs
@@ -1,6 +1,10 @@
 //@ compile-flags: -g
 //@ ignore-android: FIXME(#10381)
 
+// On Arm64 Windows, stepping at the end of a funciton on goes to the callsite, not the instruction
+// after it.
+//@ ignore-aarch64-pc-windows-msvc: Stepping out of functions behaves differently.
+
 // === GDB TESTS ==============================================================
 
 // gdb-command: r
diff --git a/tests/debuginfo/type-names.rs b/tests/debuginfo/type-names.rs
index 4df6daf7b6ef0..3c7eab7e8d718 100644
--- a/tests/debuginfo/type-names.rs
+++ b/tests/debuginfo/type-names.rs
@@ -1,5 +1,7 @@
 //@ ignore-lldb
 
+//@ ignore-aarch64-pc-windows-msvc: Arm64 Windows cdb doesn't support JavaScript extensions.
+
 // GDB changed the way that it formatted Foreign types
 //@ min-gdb-version: 9.2
 
diff --git a/tests/ui/runtime/backtrace-debuginfo.rs b/tests/ui/runtime/backtrace-debuginfo.rs
index afc96d6bb5f54..37fce2788b7f0 100644
--- a/tests/ui/runtime/backtrace-debuginfo.rs
+++ b/tests/ui/runtime/backtrace-debuginfo.rs
@@ -42,9 +42,13 @@ macro_rules! dump_and_die {
         // there, even on i686-pc-windows-msvc. We do the best we can in
         // rust-lang/rust to test it as well, but sometimes we just gotta keep
         // landing PRs.
+        //
+        // aarch64-msvc is broken as its backtraces are truncated.
+        // See https://github.com/rust-lang/rust/issues/140489
         if cfg!(any(target_os = "android",
                     all(target_os = "linux", target_arch = "arm"),
                     all(target_env = "msvc", target_arch = "x86"),
+                    all(target_env = "msvc", target_arch = "aarch64"),
                     target_os = "freebsd",
                     target_os = "dragonfly",
                     target_os = "openbsd")) {