diff --git a/pkgs/by-name/si/six-sines/package.nix b/pkgs/by-name/si/six-sines/package.nix
new file mode 100644
index 000000000000..14100abc6c98
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+++ b/pkgs/by-name/si/six-sines/package.nix
@@ -0,0 +1,216 @@
+{
+  lib,
+  stdenv,
+  fetchFromGitHub,
+  cmake,
+  pkg-config,
+  autoPatchelfHook,
+  # JUCE graphics / GL
+  freetype,
+  fontconfig,
+  libGL,
+  # JUCE / standalone audio + MIDI
+  alsa-lib,
+  libjack2,
+  libpulseaudio,
+  # JUCE GUI: linked at build time (juce_gui_basics dlopens these at runtime,
+  # but the standalone host's X11 GUI path links them directly)
+  libx11,
+  libxext,
+  libxcursor,
+  libxinerama,
+  libxrandr,
+  libxrender,
+  libxscrnsaver,
+  # clap-wrapper's Linux standalone GUI host (auto-detected via pkg-config;
+  # if absent, the standalone still builds but can't show plugin windows)
+  gtkmm3,
+}:
+
+let
+  # The bundled clap-wrapper hard-codes CLAP_WRAPPER_DOWNLOAD_DEPENDENCIES=TRUE
+  # and CPM-fetches these from GitHub at configure time. We pre-fetch them so
+  # the build is hermetic, and feed the paths in via *_SDK_ROOT cmake flags;
+  # `base_sdks.cmake` short-circuits the CPM path when *_SDK_ROOT is set.
+  #
+  # Revisions are pinned to whatever the clap-wrapper submodule at the
+  # six-sines v1.1.0 tag requests in cmake/base_sdks.cmake. When bumping
+  # six-sines, re-check those tags here.
+  vst3sdk = fetchFromGitHub {
+    owner = "steinbergmedia";
+    repo = "vst3sdk";
+    rev = "v3.7.6_build_18";
+    fetchSubmodules = true;
+    hash = "sha256-MeMb09bM8D4FPHWvvRbmWbiyO9u8JVxyfgv4jmeogLI=";
+    # The `doc` submodule is ~130 MB of PDFs we never reference. The
+    # `vstgui4` submodule isn't touched by clap-wrapper's VST3 glue either,
+    # but it's small (~12 MB) and removing it would diverge further from
+    # upstream Steinberg, so leave it in.
+    postFetch = ''
+      rm -rf $out/doc
+    '';
+  };
+
+  rtaudio-src = fetchFromGitHub {
+    owner = "thestk";
+    repo = "rtaudio";
+    rev = "6.0.1";
+    hash = "sha256-Acsxbnl+V+Y4mKC1gD11n0m03E96HMK+oEY/YV7rlIY=";
+  };
+
+  rtmidi-src = fetchFromGitHub {
+    owner = "thestk";
+    repo = "rtmidi";
+    rev = "6.0.0";
+    hash = "sha256-QuUeFx8rPpe0+exB3chT6dUceDa/7ygVy+cQYykq7e0=";
+  };
+in
+
+stdenv.mkDerivation (finalAttrs: {
+  pname = "six-sines";
+  version = "1.1.0";
+  __structuredAttrs = true;
+  strictDeps = true;
+
+  src = fetchFromGitHub {
+    owner = "baconpaul";
+    repo = "six-sines";
+    rev = "v${finalAttrs.version}";
+    fetchSubmodules = true;
+    hash = "sha256-IQLGC86FqS3dptPzNpHEYKB59MWFDKsOPGM+FuzGcPo=";
+  };
+
+  nativeBuildInputs = [
+    cmake
+    pkg-config
+    autoPatchelfHook
+  ];
+
+  # nixpkgs' default `format` hardening injects `-Wformat -Wformat-security
+  # -Werror=format-security`. clap-wrapper's base_sdks.cmake adds
+  # `-Wno-format` privately to the VST3 SDK targets to silence a known
+  # confusion between `%lld` and `long long int`, which leaves
+  # `-Werror=format-security` dangling — and gcc treats "X ignored without
+  # Y" as a `-Werror=format-security` violation in its own right, breaking
+  # the base-sdk-vst3 compile. Disabling the whole hardening flag is the
+  # smallest change that lets the SDK's own pragma stand.
+  hardeningDisable = [ "format" ];
+
+  buildInputs = [
+    freetype
+    fontconfig
+    libGL
+    alsa-lib
+    libjack2
+    libpulseaudio
+    libx11
+    libxext
+    libxcursor
+    libxinerama
+    libxrandr
+    libxrender
+    libxscrnsaver
+    gtkmm3
+  ];
+
+  # JUCE loads several X11 libraries via dlopen() in juce_XSymbols_linux.h
+  # (libx11.so.6, libxext.so.6, libxcursor.so.1, libxinerama.so.1,
+  # libxrender.so.1, libxrandr.so.2, plus libxss.so.1 from
+  # juce_XWindowSystem_linux.cpp). Listing them in runtimeDependencies makes
+  # autoPatchelfHook bake them into the binaries' RPATH.
+  runtimeDependencies = [
+    libx11
+    libxext
+    libxcursor
+    libxinerama
+    libxrandr
+    libxrender
+    libxscrnsaver
+  ];
+
+  postPatch = ''
+    # sst-plugininfra's version_from_versionfile_or_git() looks for a
+    # BUILD_VERSION file before falling back to `git describe`. fetchFromGitHub
+    # strips .git, so we provide the file directly. The format is 5 lines:
+    # header (ignored), commit hash, tag, branch, display version.
+    cat > BUILD_VERSION <<EOF
+    Six Sines v${finalAttrs.version}
+    v${finalAttrs.version}
+    v${finalAttrs.version}
+    main
+    ${finalAttrs.version}
+    EOF
+  '';
+
+  cmakeFlags = [
+    # Don't try to copy build artefacts into ~/.clap and ~/.vst3 from
+    # within the build (CMake's POST_BUILD step in clap-wrapper's
+    # target_copy_after_build()).
+    (lib.cmakeBool "COPY_AFTER_BUILD" false)
+
+    # Hand clap-wrapper the SDK trees it would otherwise CPM-download.
+    # base_sdks.cmake short-circuits the CPM path whenever a *_SDK_ROOT is
+    # set, so we don't need to additionally flip CLAP_WRAPPER_DOWNLOAD_DEPENDENCIES.
+    (lib.cmakeFeature "VST3_SDK_ROOT" "${vst3sdk}")
+    (lib.cmakeFeature "RTAUDIO_SDK_ROOT" "${rtaudio-src}")
+    (lib.cmakeFeature "RTMIDI_SDK_ROOT" "${rtmidi-src}")
+
+    # CMake 4 hard-removed support for cmake_minimum_required(VERSION < 3.5).
+    # The bundled libsamplerate submodule still declares `VERSION 3.1..3.18`
+    # at the top of its CMakeLists.txt and refuses to configure otherwise.
+    # 3.5 is the value CMake itself suggests in the error.
+    (lib.cmakeFeature "CMAKE_POLICY_VERSION_MINIMUM" "3.5")
+  ];
+
+  # The CMakeLists exposes a `six-sines_all` custom target that aggregates
+  # the `_clap`, `_vst3`, and `_standalone` sub-targets (`_auv2` is
+  # APPLE-gated and absent on Linux). The default ALL target would build
+  # the same outputs in practice — the test subdir is already EXCLUDE_FROM_ALL
+  # — but going through `six-sines_all` matches what upstream documents and
+  # keeps the surface narrow if extra default targets ever land later.
+  buildPhase = ''
+    runHook preBuild
+    cmake --build . --config Release --parallel "$NIX_BUILD_CORES" --target six-sines_all
+    runHook postBuild
+  '';
+
+  installPhase = ''
+    runHook preInstall
+
+    install -d $out/lib/clap $out/lib/vst3 $out/bin
+
+    # The clap-wrapper assets dir is flat on Linux — the CLAP/ and VST3/
+    # subdirectories only get created on Windows (the relevant branches in
+    # make_clapfirst.cmake and wrap_vst3.cmake are gated on WIN32). On
+    # Linux and macOS everything lands directly in ''${CMAKE_BINARY_DIR}/
+    # six-sines_assets/.
+    cp -r 'six-sines_assets/Six Sines.clap' "$out/lib/clap/"
+    cp -r 'six-sines_assets/Six Sines.vst3' "$out/lib/vst3/"
+
+    # Rename the standalone to a Unix-friendly $out/bin name.
+    install -m755 'six-sines_assets/Six Sines' "$out/bin/six-sines"
+
+    runHook postInstall
+  '';
+
+  meta = {
+    description = "Small synthesizer exploring audio-rate inter-modulation of sine waves (FM/PM/AM)";
+    longDescription = ''
+      Six Sines is a six-operator phase-/amplitude-/ring-modulation synthesizer
+      by Paul Walker (baconpaul). It ships as a CLAP plug-in, a VST3 plug-in,
+      and a standalone application backed by RtAudio (ALSA / JACK / PulseAudio).
+    '';
+    homepage = "https://github.com/baconpaul/six-sines";
+    changelog = "https://github.com/baconpaul/six-sines/blob/v${finalAttrs.version}/doc/changelog.md";
+    # Author's own code is MIT (see LICENSE.md), but the binary statically
+    # links GPL3 JUCE, so the combined work is distributed under GPL3+
+    # (resources/LICENSE_GPL3).
+    license = lib.licenses.gpl3Plus;
+    maintainers = with lib.maintainers; [ magnetophon ];
+    mainProgram = "six-sines";
+    # cmake/compile-options.cmake hard-codes `-march=nehalem` for non-Apple
+    # builds, and clap-wrapper hard-codes the VST3 bundle architecture path
+    # to `x86_64-linux`. aarch64-linux would require patching both.
+    platforms = [ "x86_64-linux" ];
+  };
+})