diff --git a/runtimes/steamrt3c.yaml b/runtimes/steamrt3c.yaml
new file mode 100644
index 0000000000000000000000000000000000000000..418f4ae491db7a7323672a817722e69dc8ae2209
--- /dev/null
+++ b/runtimes/steamrt3c.yaml
@@ -0,0 +1,128 @@
+---
+# Copyright © 2013-2016 Valve Corporation
+# Copyright © 2017-2020 Collabora Ltd.
+# SPDX-License-Identifier: MIT
+#
+# Permission is hereby granted, free of charge, to any person obtaining
+# a copy of these scripts and associated documentation files (the
+# "Software"), to deal in the Software without restriction, including
+# without limitation the rights to use, copy, modify, merge, publish,
+# distribute, sublicense, and/or sell copies of the Software, and to
+# permit persons to whom the Software is furnished to do so, subject to
+# the following conditions:
+#
+# The above copyright notice and this permission notice shall be included
+# in all copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+# IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+# CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+# TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
+# SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+id_prefix: com.valvesoftware.SteamRuntime
+toolbx: true
+
+add_packages_multiarch:
+  - steamrt-container-host-compat
+  - steamrt-libs
+
+add_packages:
+  - steamrt-container
+
+post_script: |
+  set -eux
+
+  if [ -e /usr/share/i18n/locales/en_US ]; then
+    echo "en_US.UTF-8 UTF-8" > /etc/locale.gen
+    localedef -v -i en_US -c -f UTF-8 en_US.UTF-8 || :
+    test -e /usr/lib/locale/locale-archive
+  fi
+
+  test -d /usr/lib/gconv
+  test -d /usr/lib/locale
+  test -d /usr/share/i18n
+  test -d /usr/share/libdrm
+  if dpkg-query -W steamrt-container-host-compat:amd64; then
+    test -d /usr/lib64
+    test -d /usr/lib64/gconv
+    test -d /usr/lib64/locale
+    test -d /usr/lib/x86_64-linux-gnu/gconv
+    # Arch Linux uses a non-standard ELF interpreter for some binaries in
+    # the glibc package. We can't create this from
+    # steamrt-container-host-compat, because that breaks dpkg-shlibdeps.
+    ln -fns /lib64/ld-linux-x86-64.so.2 /usr/lib/ld-linux-x86-64.so.2
+    if ! [ -e /usr/lib/x86_64-linux-gnu/ld-linux-x86-64.so.2 ] \
+      && ! [ -L /usr/lib/x86_64-linux-gnu/ld-linux-x86-64.so.2 ] \
+    ; then
+      install -d /usr/lib/x86_64-linux-gnu
+      ln -s /lib/x86_64-linux-gnu/ld-linux-x86-64.so.2 \
+        /usr/lib/x86_64-linux-gnu/ld-linux-x86-64.so.2
+    fi
+    test -e /usr/x86_64-pc-linux-gnu/lib/ld-linux-x86-64.so.2
+  fi
+  if dpkg-query -W steamrt-container-host-compat:i386; then
+    test -d /usr/lib32
+    test -d /usr/lib32/gconv
+    test -d /usr/lib32/locale
+    test -d /usr/lib/i386-linux-gnu/gconv
+    if ! [ -e /usr/lib/i386-linux-gnu/ld-linux.so.2 ] \
+      && ! [ -L /usr/lib/i386-linux-gnu/ld-linux.so.2 ] \
+    ; then
+      install -d /usr/lib/i386-linux-gnu
+      ln -s /lib/i386-linux-gnu/ld-linux.so.2 \
+        /usr/lib/i386-linux-gnu/ld-linux.so.2
+    fi
+    test -e /usr/i686-pc-linux-gnu/lib/ld-linux.so.2
+  fi
+  # https://github.com/ValveSoftware/steam-runtime/issues/302
+  # https://github.com/ValveSoftware/steam-for-linux/issues/6310
+  for prefix in /usr /usr/local; do
+    install -d "${prefix}/share/steam"
+    ln -fns "/run/host${prefix}/share/steam/compatibilitytools.d" \
+                     "${prefix}/share/steam/compatibilitytools.d"
+  done
+
+platform:
+  pre_apt_script: |
+    set -eux
+    rm -f /etc/apt/preferences.d/*steamrt-no-runtime-overlay.pref
+    apt-get -y full-upgrade
+
+sdk:
+  add_packages_multiarch:
+    - steamrt-libdebug:
+        debug_symbols: true
+    - steamrt-libdevel
+
+  add_packages:
+    - steamrt-dev
+    - steamrt-libdebug-non-multiarch:
+        debug_symbols: true
+
+  post_script: |
+    set -eux
+
+    for bin in \
+      dos2unix \
+      ifconfig \
+      ip \
+      nc \
+      ping \
+      ping6 \
+      route \
+      telnet \
+      traceroute \
+      traceroute6 \
+      unix2dos \
+      vi \
+      xxd \
+    ; do
+      if [ -e /bin/busybox ] && ! [ -e "/bin/$bin" ] && ! [ -e "/usr/bin/$bin" ]; then
+        ln -fnsv busybox "/bin/$bin"
+      fi
+    done
+
+...
diff --git a/suites/steamrt3c.yaml b/suites/steamrt3c.yaml
new file mode 100644
index 0000000000000000000000000000000000000000..c493a3ced286b93876c44d183c42f1a72427f156
--- /dev/null
+++ b/suites/steamrt3c.yaml
@@ -0,0 +1,57 @@
+---
+# Copyright 2017-2025 Collabora Ltd.
+# SPDX-License-Identifier: MIT
+additional_base_packages:
+  - steamrt-customizations
+apt_components:
+  - main
+  - contrib
+  - non-free
+can_merge_usr: after_sysroot
+has_automatic_dbgsym: true
+strip_source_version_suffix: '\+bsrt3c?[.~].*'
+bootstrap_keyring: '0d6c9793-debian-archive-bullseye-stable.gpg'
+sources:
+  - label: debian
+    apt_uri: 'http://deb.debian.org/debian'
+    apt_suite: 'bullseye'
+    keyrings:
+      - '8dd47936-debian-archive-bullseye-automatic.gpg'
+      - '4aad5c5d-debian-archive-bullseye-security-automatic.gpg'
+      - '0d6c9793-debian-archive-bullseye-stable.gpg'
+  - label: debian-debug
+    apt_uri: 'http://deb.debian.org/debian-debug'
+    apt_suite: 'bullseye-debug'
+    keyrings:
+      - '8dd47936-debian-archive-bullseye-automatic.gpg'
+      - '4aad5c5d-debian-archive-bullseye-security-automatic.gpg'
+      - '0d6c9793-debian-archive-bullseye-stable.gpg'
+    deb-src: false
+  # For security updates' detached debug symbols
+  - label: debian-pu-debug
+    apt_uri: 'http://deb.debian.org/debian-debug'
+    apt_suite: 'bullseye-proposed-updates-debug'
+    keyrings:
+      - '8dd47936-debian-archive-bullseye-automatic.gpg'
+      - '4aad5c5d-debian-archive-bullseye-security-automatic.gpg'
+      - '0d6c9793-debian-archive-bullseye-stable.gpg'
+    deb-src: false
+  - label: debian-security
+    apt_uri: 'http://security.debian.org/debian-security'
+    apt_suite: 'bullseye-security'
+    keyrings:
+      - '8dd47936-debian-archive-bullseye-automatic.gpg'
+      - '4aad5c5d-debian-archive-bullseye-security-automatic.gpg'
+      - '0d6c9793-debian-archive-bullseye-stable.gpg'
+  - label: steamrt
+    apt_uri: 'https://repo.steampowered.com/steamrt3c/apt'
+    keyrings:
+      - 'd0bbf5ae-valve-archive-builder.gpg'
+      - '8abddd96-valve-archive-steamos-release-key.gpg'
+  - label: steamrt-runtime-overlay
+    apt_uri: 'https://repo.steampowered.com/steamrt3c/apt'
+    apt_suite: steamrt3c-runtime-overlay
+    keyrings:
+      - 'd0bbf5ae-valve-archive-builder.gpg'
+      - '8abddd96-valve-archive-steamos-release-key.gpg'
+...