diff --git a/.github/workflows/build-yggdrasil-engine.yml b/.github/workflows/build-yggdrasil-engine.yml
new file mode 100644
index 0000000000..2ca6282d1d
--- /dev/null
+++ b/.github/workflows/build-yggdrasil-engine.yml
@@ -0,0 +1,167 @@
+# SPDX-FileCopyrightText: 2026 The RISE Project
+# SPDX-License-Identifier: MIT
+---
+# Based on upstream's own Python build/publish tooling at this tag:
+#   https://github.com/Unleash/yggdrasil-bindings/blob/python-engine-v1.3.1/python-engine/{build.sh,tox.ini,scripts/repair_wheel.py}
+# The PyPI package `yggdrasil-engine` is Unleash's ctypes binding to their
+# Rust `yggdrasilffi` cdylib, not Google's Yggdrasil Decision Forests.
+name: Build yggdrasil-engine wheels (riscv64)
+
+on:
+  workflow_dispatch:
+    inputs:
+      version:
+        description: 'yggdrasil-engine version to build (git tag python-engine-v<version>, e.g. 1.3.1)'
+        required: true
+        default: '1.3.1'
+  pull_request:
+    paths:
+      - '.github/workflows/build-yggdrasil-engine.yml'
+
+concurrency:
+  group: ${{ github.workflow }}-${{ inputs.version || '1.3.1' }}-${{ github.head_ref || github.run_id }}
+  cancel-in-progress: true
+
+permissions:
+  contents: read
+
+env:
+  YGGDRASIL_ENGINE_VERSION: ${{ inputs.version || '1.3.1' }}
+  MANYLINUX_RISCV64_IMAGE: quay.io/pypa/manylinux_2_39_riscv64
+
+jobs:
+  setup:
+    uses: $/.github/workflows/_setup.yml
+
+  build_wheel:
+    needs: [setup]
+    name: Build yggdrasil-engine ${{ inputs.version || '1.3.1' }} cp312-abi3-manylinux_riscv64
+    runs-on: ubuntu-24.04-riscv
+    timeout-minutes: 60
+    steps:
+      - name: Checkout yggdrasil-bindings python-engine-v${{ env.YGGDRASIL_ENGINE_VERSION }}
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1  # v7.0.1
+        with:
+          repository: Unleash/yggdrasil-bindings
+          ref: python-engine-v${{ env.YGGDRASIL_ENGINE_VERSION }}
+          persist-credentials: false
+
+      # build-python.yml's own "Get client spec" step.
+      - name: Get client spec
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1  # v7.0.1
+        with:
+          repository: Unleash/client-specification
+          ref: v6.1.0
+          path: client-specification
+          persist-credentials: false
+
+      - name: Checkout python-wheels
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1  # v7.0.1
+        with:
+          path: python-wheels
+          persist-credentials: false
+
+      # compat_glibc.rs defines SYS_GETTID/SYS_STATX for x86_64 and aarch64
+      # only but compiles unconditionally, so the crate fails to build on
+      # riscv64. See patches/yggdrasil-engine/1.3.1 for the full rationale.
+      - name: Patch yggdrasilffi source
+        run: git apply python-wheels/patches/yggdrasil-engine/${{ env.YGGDRASIL_ENGINE_VERSION }}/00*.patch
+
+      # LICENSE.md lives at the repo root; poetry-core only auto-bundles a
+      # licence file that sits beside pyproject.toml, and upstream's own
+      # published wheel carries none either (same gap build-valkey-glide.yml
+      # hit).
+      - name: Stage the project licence beside pyproject.toml
+        run: cp LICENSE.md python-engine/LICENSE.md
+
+      # Mirrors build-python.yml (build the ffi, `poetry run pytest`) and
+      # python-engine/build.sh + tox.ini (vendor the binary, `poetry build`,
+      # repair_wheel.py retags the resulting py3-none-any wheel): upstream
+      # downloads a prebuilt binary here instead of building it, but ships
+      # none for riscv64, so this builds it natively in-container. musllinux
+      # is skipped: rustup ships no riscv64gc-unknown-linux-musl host
+      # toolchain (gotcha 10).
+      - name: Write in-container build script
+        run: |
+          cat > "$RUNNER_TEMP/build.sh" <<'SCRIPT'
+          set -euxo pipefail
+          curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y
+          source "$HOME/.cargo/env"
+          cargo build --release -p yggdrasilffi
+
+          pybin=/opt/python/cp312-cp312/bin
+          "$pybin/pip" install -q poetry-core setuptools build pytest
+          mkdir -p python-engine/yggdrasil_engine/lib python-engine/staging
+          cp target/release/libyggdrasilffi.so python-engine/yggdrasil_engine/lib/
+
+          cd python-engine
+          "$pybin/python3" -m pytest
+          "$pybin/python3" -m build --wheel --no-isolation
+          PLATFORM_TAG=manylinux_2_39_riscv64 "$pybin/python3" scripts/repair_wheel.py
+          SCRIPT
+
+      - name: Build wheel
+        run: |
+          docker run --rm \
+            -v "$(pwd)":/workspace \
+            -v "$RUNNER_TEMP/build.sh":/build.sh \
+            -w /workspace \
+            "${MANYLINUX_RISCV64_IMAGE}" \
+            bash /build.sh
+
+      - uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a  # v7.0.1
+        with:
+          name: yggdrasil-engine-${{ env.YGGDRASIL_ENGINE_VERSION }}-cp312-abi3-manylinux_riscv64
+          path: python-engine/staging/*.whl
+          if-no-files-found: error
+
+  test_wheel:
+    name: Test yggdrasil-engine ${{ inputs.version || '1.3.1' }} on Python ${{ matrix.python-version }}
+    needs: [setup, build_wheel]
+    runs-on: ubuntu-24.04-riscv
+    timeout-minutes: 30
+    strategy:
+      fail-fast: false
+      matrix:
+        # abi3 wheels are not compatible with free-threaded interpreters
+        # (packaging.tags._abi3_applies), matching upstream, which ships no
+        # cp3XXt wheel either; 3.12/3.13/3.14 exercise the same cp312-abi3
+        # wheel via abi3 forward compatibility.
+        python-version: ['3.12', '3.13', '3.14']
+    steps:
+      - name: Download wheel
+        uses: actions/download-artifact@3e5f45b2cfb9172054b4087a40e8e0b5a5461e7c  # v8.0.1
+        with:
+          name: yggdrasil-engine-${{ env.YGGDRASIL_ENGINE_VERSION }}-cp312-abi3-manylinux_riscv64
+
+      - name: Install Python
+        uses: astral-sh/setup-uv@20cfd1bf945f4377ade1205e4dbc17946fc9a30d  # v10.0.1
+        with:
+          python-version: ${{ matrix.python-version }}
+          activate-environment: true
+          enable-cache: false
+
+      - name: Install wheel
+        run: uv pip install --reinstall --no-index --find-links . yggdrasil-engine==${{ env.YGGDRASIL_ENGINE_VERSION }}
+
+      - name: Test wheel
+        run: |
+          python -c "
+          from yggdrasil_engine.engine import UnleashEngine
+
+          engine = UnleashEngine()
+          engine.take_state('{\"version\": 2, \"features\": [{\"name\": \"my-toggle\", \"enabled\": true, \"strategies\": [{\"name\": \"default\"}]}]}')
+          assert engine.is_enabled('my-toggle', {}) is True
+          assert engine.is_enabled('missing-toggle', {}) is None
+          print('Smoke test passed')
+          "
+
+  publish:
+    name: Publish yggdrasil-engine ${{ inputs.version || '1.3.1' }}
+    needs: [setup, build_wheel, test_wheel]
+    permissions:
+      contents: write
+      pull-requests: write
+    uses: $/.github/workflows/_publish-wheel.yml
+    with:
+      artifact-pattern: yggdrasil-engine-${{ inputs.version || '1.3.1' }}-cp312-abi3-manylinux_riscv64
diff --git a/patches/yggdrasil-engine/1.3.1/0001-yggdrasilffi-riscv64-syscall-numbers.patch b/patches/yggdrasil-engine/1.3.1/0001-yggdrasilffi-riscv64-syscall-numbers.patch
new file mode 100644
index 0000000000..8cad8aea45
--- /dev/null
+++ b/patches/yggdrasil-engine/1.3.1/0001-yggdrasilffi-riscv64-syscall-numbers.patch
@@ -0,0 +1,47 @@
+From 79a1d5318f08a15066d691f90d263496edd4b227 Mon Sep 17 00:00:00 2001
+From: Ludovic Henry <git@ludovic.dev>
+Date: Sun, 13 Sep 2026 01:34:34 +0200
+Subject: [PATCH] yggdrasilffi: add riscv64 syscall numbers for gettid/statx
+ compat shim
+
+compat_glibc.rs hand-rolls gettid(2)/statx(2) via raw syscall(2) to
+avoid depending on the libc crate's own bindings, which would require
+a newer glibc than the zigbuild-targeted GLIBC_2.25 floor. It defines
+SYS_GETTID/SYS_STATX for x86_64 and aarch64 only; mod compat_glibc is
+included unconditionally (no target_arch gate), so on any other arch
+- riscv64 included - the crate fails to compile with two
+cannot-find-value errors for the two undefined consts.
+
+riscv64 and aarch64 both use the Linux kernel's generic syscall table
+(include/uapi/asm-generic/unistd.h: __NR_gettid 178, __NR_statx 291,
+confirmed also in the libc crate's own riscv64 module), unlike x86_64,
+which has its own legacy numbering. Add the same two constants under
+target_arch = "riscv64".
+
+Upstream-Status: To upstream [not filed upstream from this porting session, which does not open issues/PRs on repos other than riseproject-dev/python-wheels; genuinely worth upstreaming, it only adds an arch branch matching aarch64's already-supported case]
+
+Signed-off-by: Ludovic Henry <git@ludovic.dev>
+---
+ yggdrasilffi/src/compat_glibc.rs | 6 ++++++
+ 1 file changed, 6 insertions(+)
+
+diff --git a/yggdrasilffi/src/compat_glibc.rs b/yggdrasilffi/src/compat_glibc.rs
+index c13446d..1a115ac 100644
+--- a/yggdrasilffi/src/compat_glibc.rs
++++ b/yggdrasilffi/src/compat_glibc.rs
+@@ -32,6 +32,12 @@ const SYS_GETTID: c_long = 178;
+ #[cfg(target_arch = "aarch64")]
+ const SYS_STATX: c_long = 291;
+ 
++// riscv64 syscall numbers (riscv64 shares aarch64's asm-generic/unistd.h table)
++#[cfg(target_arch = "riscv64")]
++const SYS_GETTID: c_long = 178;
++#[cfg(target_arch = "riscv64")]
++const SYS_STATX: c_long = 291;
++
+ #[no_mangle]
+ pub unsafe extern "C" fn gettid() -> pid_t {
+     syscall(SYS_GETTID) as pid_t
+-- 
+2.50.1 (Apple Git-155)
+