diff --git a/flatpak.bzl b/flatpak.bzl
index 48aac85..509c2be 100644
--- a/flatpak.bzl
+++ b/flatpak.bzl
@@ -3,9 +3,13 @@
 # Unlike cargo.bzl's genrules (which shell out to a real `cargo build`),
 # this one doesn't compile anything itself — it packages the *already
 # buck2-built* //:sleek-host binary into a distributable .flatpak bundle,
-# reusing the org.gnome.Platform//49 runtime (baked into toolchains/
-# rbe-image/Containerfile at image-build time, same pattern as the Android
-# NDK/SDK) instead of vendoring every shared library sleek links against.
+# reusing the org.freedesktop.Platform//25.08 runtime (baked into
+# toolchains/rbe-image/Containerfile at image-build time, same pattern as
+# the Android NDK/SDK) instead of vendoring every shared library sleek
+# links against. Freedesktop's base runtime, not GNOME's — `ldd` on the
+# built binary shows only libstdc++/libpipewire/libasound/libc, no
+# GTK/glib/adwaita, so the GNOME layer GNOME's runtime adds on top of
+# Freedesktop's own was pure unused weight (eframe/glow, not GTK).
 #
 # Ports flake.nix's old `nix2flatpak.lib.${system}.mkFlatpak` derivation
 # (see git history) to buck2 — nix2flatpak itself has no buck2 equivalent
@@ -113,7 +117,7 @@ def flatpak_genrule(name, manifest, app_id, host_target = "//:sleek-host"):
             # build-init sets up build-dir/{files,var,metadata} — no bwrap
             # involved, unlike flatpak-builder's own build-command
             # execution (see module docstring).
-            "  flatpak build-init build-dir {} org.gnome.Sdk org.gnome.Platform 49".format(app_id),
+            "  flatpak build-init build-dir {} org.freedesktop.Sdk org.freedesktop.Platform 25.08".format(app_id),
             # Hand-replicated from flatpak/uk.nandi.sleek.json's
             # build-commands — /app/... there maps to build-dir/files/...
             # here (what build-init's build-dir becomes once exported).
diff --git a/flatpak/uk.nandi.sleek.json b/flatpak/uk.nandi.sleek.json
index ac1bfbd..54109cf 100644
--- a/flatpak/uk.nandi.sleek.json
+++ b/flatpak/uk.nandi.sleek.json
@@ -1,8 +1,8 @@
 {
     "app-id": "uk.nandi.sleek",
-    "runtime": "org.gnome.Platform",
-    "runtime-version": "49",
-    "sdk": "org.gnome.Sdk",
+    "runtime": "org.freedesktop.Platform",
+    "runtime-version": "25.08",
+    "sdk": "org.freedesktop.Sdk",
     "command": "sleek",
     "appstream-compose": false,
     "finish-args": [
diff --git a/toolchains/rbe-image/Containerfile b/toolchains/rbe-image/Containerfile
index ad8b29c..5efb64d 100644
--- a/toolchains/rbe-image/Containerfile
+++ b/toolchains/rbe-image/Containerfile
@@ -7,11 +7,11 @@
 # devShell env exactly, so sleek-android-lib's `cargo build` has
 # everything it needs without depending on this machine's local pixi/NDK
 # install. Also bakes in flatpak + flatpak-builder + a system-wide
-# org.gnome.Platform//49 + org.gnome.Sdk//49 install for flatpak.bzl's
-# sleek-flatpak genrule (see near the bottom of this file) — same
-# "pre-install so RE actions don't need Flathub network access" pattern as
-# the Android NDK/SDK. See README.md in this directory for how to build +
-# push it.
+# org.freedesktop.Platform//25.08 + org.freedesktop.Sdk//25.08 install for
+# flatpak.bzl's sleek-flatpak genrule (see near the bottom of this file) —
+# same "pre-install so RE actions don't need Flathub network access"
+# pattern as the Android NDK/SDK. See README.md in this directory for how
+# to build + push it.
 FROM gcr.io/flame-public/rbe-ubuntu22-04:latest
 
 # build-essential: pixi's own clang/libclang (bindgen's dependency, see
@@ -112,12 +112,18 @@ RUN cd /tmp/sleek-pixi && pixi install --locked \
     && rm -rf /tmp/sleek-pixi
 
 # flatpak + flatpak-builder — for flatpak.bzl's sleek-flatpak genrule
-# (packages //:sleek-host into a distributable .flatpak using the GNOME
-# Platform/49 runtime; ports flake.nix's old nix2flatpak-based
-# sleek-flatpak derivation, see that file's git history). Jammy's stock
-# apt versions (flatpak 1.12.7, flatpak-builder 1.2.2 — both quite old)
-# confirmed able to pull a current GNOME 49 runtime from Flathub fine, no
-# PPA needed.
+# (packages //:sleek-host into a distributable .flatpak using the
+# Freedesktop Platform/25.08 runtime, not GNOME's — `ldd` on the built
+# binary shows only libstdc++/libpipewire/libasound/libc, no GTK/glib, so
+# GNOME's runtime was pulling in a desktop stack the app never uses;
+# org.freedesktop.Platform.GL//25.08 is what org.gnome.Platform//49
+# itself declares as its own GL extension version, confirmed via
+# `flatpak remote-info --show-metadata`, so 25.08 is the correctly-paired
+# base version). Ports flake.nix's old nix2flatpak-based sleek-flatpak
+# derivation, see that file's git history. Jammy's stock apt versions
+# (flatpak 1.12.7, flatpak-builder 1.2.2 — both quite old) confirmed able
+# to pull a current Freedesktop 25.08 runtime from Flathub fine, no PPA
+# needed.
 RUN apt-get update && apt-get install -y --no-install-recommends \
     flatpak flatpak-builder \
     && rm -rf /var/lib/apt/lists/*
@@ -149,4 +155,4 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
 # jammy's own `appstream` package (0.15.2) doesn't ship it anyway (that
 # subcommand only exists in much newer libappstream releases).
 RUN flatpak remote-add --if-not-exists flathub https://flathub.org/repo/flathub.flatpakrepo \
-    && flatpak install -y --noninteractive --system flathub org.gnome.Platform//49 org.gnome.Sdk//49
+    && flatpak install -y --noninteractive --system flathub org.freedesktop.Platform//25.08 org.freedesktop.Sdk//25.08