diff --git a/.github/workflows/llvm.yml b/.github/workflows/llvm.yml
index 4d8929492a82..6857f23cbbf4 100644
--- a/.github/workflows/llvm.yml
+++ b/.github/workflows/llvm.yml
@@ -41,17 +41,22 @@ jobs:
           - {llvm_version: 18, runs-on: ubuntu-24.04, codename: noble}
           - {llvm_version: 19, runs-on: ubuntu-24.04, codename: noble}
           - {llvm_version: 20, runs-on: ubuntu-24.04, codename: noble}
-    name: "LLVM ${{ matrix.llvm_version }}"
+          - {runs-on: ubuntu-24.04, codename: noble}
+    name: "LLVM ${{ matrix.llvm_version || 'Nightly' }}"
     steps:
       - name: Checkout Crystal source
         uses: actions/checkout@v4
 
-      - name: Install LLVM ${{ matrix.llvm_version }}
+      - name: Install LLVM ${{ matrix.llvm_version || 'Nightly' }}
         run: |
           sudo apt remove 'llvm-*' 'libllvm*'
           wget -qO- https://apt.llvm.org/llvm-snapshot.gpg.key | sudo tee /etc/apt/trusted.gpg.d/apt.llvm.org.asc
-          sudo apt-add-repository -y deb http://apt.llvm.org/${{ matrix.codename }}/ llvm-toolchain-${{ matrix.codename }}-${{ matrix.llvm_version }} main
-          sudo apt install -y llvm-${{ matrix.llvm_version }}-dev lld
+          sudo apt-add-repository -y \
+            deb \
+            http://apt.llvm.org/${{ matrix.codename }}/ \
+            llvm-toolchain-${{ matrix.codename }}${{ matrix.llvm_version && format('-{0}', matrix.llvm_version) || '' }} \
+            main
+          sudo apt install -y llvm${{ matrix.llvm_version && format('-{0}', matrix.llvm_version) || '' }}-dev lld
 
       - name: Install Crystal
         uses: crystal-lang/install-crystal@v1
diff --git a/src/compiler/crystal/codegen/codegen.cr b/src/compiler/crystal/codegen/codegen.cr
index 07153e3a7789..c6b4b3d7bca7 100644
--- a/src/compiler/crystal/codegen/codegen.cr
+++ b/src/compiler/crystal/codegen/codegen.cr
@@ -2544,7 +2544,7 @@ module Crystal
       name = "'#{name}'"
       key = StringKey.new(@llvm_mod, str)
       @strings[key] ||= begin
-        global = @llvm_mod.globals.add(@llvm_typer.llvm_string_type(str.bytesize), name)
+        global = @llvm_mod.globals.add(@llvm_typer.llvm_string_type(str.bytesize), name.gsub('\\', "\\\\"))
         global.linkage = LLVM::Linkage::Private
         global.global_constant = true
         global.initializer = llvm_context.const_struct [
diff --git a/src/llvm/enums.cr b/src/llvm/enums.cr
index c944e360574d..8203df32da8a 100644
--- a/src/llvm/enums.cr
+++ b/src/llvm/enums.cr
@@ -57,6 +57,7 @@ module LLVM
     WillReturn
     WriteOnly
     ZExt
+    Captures
 
     # NOTE: enum body does not allow `class_getter` or `TypeDeclaration`, hence
     # the nil cast
@@ -91,6 +92,7 @@ module LLVM
       kinds[ArgMemOnly] = kind_for_name("argmemonly")
       kinds[Builtin] = kind_for_name("builtin")
       kinds[ByVal] = kind_for_name("byval")
+      kinds[Captures] = kind_for_name("captures")
       kinds[Cold] = kind_for_name("cold")
       kinds[Convergent] = kind_for_name("convergent")
       kinds[Dereferenceable] = kind_for_name("dereferenceable")
diff --git a/src/llvm/ext/llvm-versions.txt b/src/llvm/ext/llvm-versions.txt
index a5d4cfac2515..7e0184868f7b 100644
--- a/src/llvm/ext/llvm-versions.txt
+++ b/src/llvm/ext/llvm-versions.txt
@@ -1 +1 @@
-20.1 19.1 18.1 17.0 16.0 15.0 14.0 13.0 12.0 11.1 11.0 10.0 9.0 8.0
+21.0 20.1 19.1 18.1 17.0 16.0 15.0 14.0 13.0 12.0 11.1 11.0 10.0 9.0 8.0
diff --git a/src/llvm/lib_llvm.cr b/src/llvm/lib_llvm.cr
index 7369026e12a5..db82fae25b72 100644
--- a/src/llvm/lib_llvm.cr
+++ b/src/llvm/lib_llvm.cr
@@ -73,6 +73,7 @@
     IS_LT_180 = {{compare_versions(LibLLVM::VERSION, "18.0.0") < 0}}
     IS_LT_190 = {{compare_versions(LibLLVM::VERSION, "19.0.0") < 0}}
     IS_LT_200 = {{compare_versions(LibLLVM::VERSION, "20.0.0") < 0}}
+    IS_LT_210 = {{compare_versions(LibLLVM::VERSION, "21.0.0") < 0}}
   end
 {% end %}