diff --git a/.github/workflows/build-element-call.yaml b/.github/workflows/build-element-call.yaml
index f4071975e..2eeb8b577 100644
--- a/.github/workflows/build-element-call.yaml
+++ b/.github/workflows/build-element-call.yaml
@@ -14,6 +14,11 @@ on:
         description: The build mode for vite. Must be either 'development' or 'production'
         required: false
         default: production
+      layered:
+        type: boolean
+        description: Build against the matching branch of matrix-js-sdk (if any) instead of the locked commit.
+        required: false
+        default: false
     secrets:
       SENTRY_ORG:
         required: true
@@ -43,8 +48,15 @@ jobs:
           cache: "pnpm"
           node-version-file: ".node-version"
       - name: Install dependencies
+        if: ${{ !inputs.layered }}
         # ignore-pnpmfile should never be commited. Make CI crash if it happened (`pnpmfileChecksum` is present)
         run: "pnpm install --frozen-lockfile --ignore-pnpmfile"
+      - name: Install dependencies (layered)
+        if: ${{ inputs.layered }}
+        # ignore-pnpmfile should never be commited. Make CI crash if it happened (`pnpmfileChecksum` is present)
+        run: "scripts/layered.sh --ignore-pnpmfile"
+        env:
+          PR_HEAD_REPO_OWNER: ${{ github.event.pull_request.head.repo.owner.login }}
       - name: Build Element Call
         run: pnpm run build:"$PACKAGE":"$BUILD_MODE"
         env:
diff --git a/.github/workflows/build.yaml b/.github/workflows/build.yaml
index 3fe10723d..aa14a3dff 100644
--- a/.github/workflows/build.yaml
+++ b/.github/workflows/build.yaml
@@ -15,6 +15,7 @@ jobs:
       package: full
       vite_app_version: ${{ github.event.release.tag_name || github.sha }}
       build_mode: ${{ github.event_name == 'pull_request' && contains(github.event.pull_request.labels.*.name, 'development build') && 'development' || 'production' }}
+      layered: ${{ github.event_name == 'pull_request' }}
     secrets:
       SENTRY_ORG: ${{ secrets.SENTRY_ORG }}
       SENTRY_PROJECT: ${{ secrets.SENTRY_PROJECT }}
@@ -65,6 +66,7 @@ jobs:
       package: embedded
       vite_app_version: ${{ github.event.release.tag_name || github.sha }}
       build_mode: ${{ github.event_name == 'pull_request' && contains(github.event.pull_request.labels.*.name, 'development build') && 'development' || 'production' }}
+      layered: ${{ github.event_name == 'pull_request' }}
     secrets:
       SENTRY_ORG: ${{ secrets.SENTRY_ORG }}
       SENTRY_PROJECT: ${{ secrets.SENTRY_PROJECT }}
@@ -79,6 +81,7 @@ jobs:
       package: sdk
       vite_app_version: ${{ github.event.release.tag_name || github.sha }}
       build_mode: ${{ github.event_name == 'pull_request' && contains(github.event.pull_request.labels.*.name, 'development build') && 'development' || 'production' }}
+      layered: ${{ github.event_name == 'pull_request' }}
     secrets:
       SENTRY_ORG: ${{ secrets.SENTRY_ORG }}
       SENTRY_PROJECT: ${{ secrets.SENTRY_PROJECT }}
diff --git a/.github/workflows/lint.yaml b/.github/workflows/lint.yaml
index ad92e7d1a..89d0baf62 100644
--- a/.github/workflows/lint.yaml
+++ b/.github/workflows/lint.yaml
@@ -17,9 +17,11 @@ jobs:
         with:
           cache: "pnpm"
           node-version-file: ".node-version"
-      - name: Install dependencies
+      - name: Install dependencies (layered)
         # ignore-pnpmfile should never be commited. Make CI crash if it happened (`pnpmfileChecksum` is present)
-        run: "pnpm install --frozen-lockfile --ignore-pnpmfile"
+        run: "scripts/layered.sh --ignore-pnpmfile"
+        env:
+          PR_HEAD_REPO_OWNER: ${{ github.event.pull_request.head.repo.owner.login }}
       - name: Formatting
         run: "pnpm run format:check"
       - name: i18n
diff --git a/.github/workflows/test.yaml b/.github/workflows/test.yaml
index 3f86f093d..582e8ab2f 100644
--- a/.github/workflows/test.yaml
+++ b/.github/workflows/test.yaml
@@ -20,8 +20,15 @@ jobs:
           cache: "pnpm"
           node-version-file: ".node-version"
       - name: Install dependencies
+        if: github.event_name != 'pull_request'
         # ignore-pnpmfile should never be commited. Make CI crash if it happened (`pnpmfileChecksum` is present)
         run: "pnpm install --frozen-lockfile --ignore-pnpmfile"
+      - name: Install dependencies (layered)
+        if: github.event_name == 'pull_request'
+        # ignore-pnpmfile should never be commited. Make CI crash if it happened (`pnpmfileChecksum` is present)
+        run: "scripts/layered.sh --ignore-pnpmfile"
+        env:
+          PR_HEAD_REPO_OWNER: ${{ github.event.pull_request.head.repo.owner.login }}
       - name: Get Playwright version
         run: echo "PLAYWRIGHT_VERSION=$(pnpm list @playwright/test --depth=0 --json | jq -r '.[0].devDependencies["@playwright/test"].version')" >> $GITHUB_ENV
       - name: Cache Playwright binaries
@@ -58,8 +65,14 @@ jobs:
           cache: "pnpm"
           node-version-file: ".node-version"
       - name: Install dependencies
+        if: github.event_name != 'pull_request'
         # ignore-pnpmfile should never be commited. Make CI crash if it happened (`pnpmfileChecksum` is present)
         run: pnpm install --frozen-lockfile --ignore-pnpmfile
+      - name: Install dependencies (layered)
+        if: github.event_name == 'pull_request'
+        run: scripts/layered.sh --ignore-pnpmfile
+        env:
+          PR_HEAD_REPO_OWNER: ${{ github.event.pull_request.head.repo.owner.login }}
       - name: Get Playwright version
         run: echo "PLAYWRIGHT_VERSION=$(pnpm list @playwright/test --depth=0 --json | jq -r '.[0].devDependencies["@playwright/test"].version')" >> $GITHUB_ENV
       - name: Cache Playwright binaries
diff --git a/.gitignore b/.gitignore
index 14e96439a..4233ecbeb 100644
--- a/.gitignore
+++ b/.gitignore
@@ -41,3 +41,6 @@ yarn-error.log
 
 *storybook.log
 storybook-static
+
+# Nested checkout made by scripts/layered.sh
+/matrix-js-sdk/
diff --git a/docs/linking.md b/docs/linking.md
index 3a18844d4..3ee49a1a9 100644
--- a/docs/linking.md
+++ b/docs/linking.md
@@ -60,6 +60,21 @@ git config --local core.hooksPath .githooks
 
 This will add the hook path for this repository only to .gihooks. which is a tracked (by git) folder containing the pre-commit hook.
 
+## Testing against a matrix-js-sdk branch in CI
+
+Linking covers local development. In CI, `scripts/layered.sh` plays the same
+role for `matrix-js-sdk`: after the usual frozen install, `scripts/fetchdep.sh`
+looks for a matrix-js-sdk branch with the same name as the pull request's head
+branch (in the fork first, when the pull request comes from one). If there is
+one, it is cloned, packed and installed over the locked version. If there is
+none, the install stays as `pnpm-lock.yaml` pins it.
+
+This means a change that needs a not yet merged matrix-js-sdk change can be tested
+by giving both branches the same name. This mirrors how element-web tests against
+matrix-js-sdk. Once the matrix-js-sdk branch is merged and deleted, the pull
+request falls back to the lockfile and needs a lockfile bump to stay green,
+which is also what keeps `main` consistent after the merge.
+
 ## Background
 
 Information, why this approach is used can be found in the [linking concept reasoning](./linking_concept_reasoning.md) document.
diff --git a/scripts/fetchdep.sh b/scripts/fetchdep.sh
new file mode 100755
index 000000000..705b3b80a
--- /dev/null
+++ b/scripts/fetchdep.sh
@@ -0,0 +1,73 @@
+#!/usr/bin/env bash
+
+# Clones the branch of a dependency's repository that has the same name as
+# the pull request branch under test, so a change spanning both repositories
+# can be tested before either side is merged. Inspired by scripts/fetchdep.sh 
+# element-web.
+#
+# Usage: scripts/fetchdep.sh <org> <repo> [ref]
+#
+# The clone lands in ./<repo>. When the pull request comes from a fork and
+# PR_HEAD_REPO_OWNER was set, the fork's own copy of the repository is tried
+# before <org>'s. Exits 0 when a branch was cloned and 1 when there is none,
+# so the caller can keep the locked version in that case. Without a ref,
+# nothing is closed outside a pull request.
+
+set -eu
+
+org=$1
+repo=$2
+ref=${3:-}
+
+rm -rf "$repo"
+
+# If a ref was passed, try to clone it or die.
+if [ -n "$ref" ]; then
+    echo "fetchdep.sh: Using $org/$repo at $ref"
+    git clone --depth 1 "https://github.com/$org/$repo.git" "$repo"
+    git -C "$repo" fetch --depth 1 origin "$ref"
+    git -C "$repo" -c advice.detachedHead=false checkout FETCH_HEAD
+    git -C "$repo" log -1
+    exit 0
+fi
+
+# Otherwise ensure that we're on a pull request.
+head_ref=${GITHUB_HEAD_REF:-}
+if [ -z "$head_ref" ]; then
+    echo "fetchdep.sh: Not a pull request, nothing to match"
+    exit 1
+fi
+
+# Bots name their branches the same way in every repository, so a match on
+# one of theirs would be a coincidence rather than a paired change.
+case "$head_ref" in
+    renovate/* | dependabot/*)
+        echo "fetchdep.sh: Not matching bot branch $head_ref"
+        exit 1
+        ;;
+esac
+
+# Clones a branch if it exists and ends the script on success.
+clone() {
+    local try_org=$1
+    local branch=$2
+    echo "fetchdep.sh: Trying to use $try_org/$repo#$branch"
+    # Disable auth prompts: https://serverfault.com/a/665959
+    if GIT_TERMINAL_PROMPT=0 git clone "https://github.com/$try_org/$repo.git" "$repo" --branch "$branch" --depth 1; then
+        git -C "$repo" log -1
+        # Surface the match on the workflow run summary.
+        echo "::notice title=Matched $repo branch::Using $try_org/$repo#$branch at $(git -C "$repo" rev-parse HEAD)"
+        exit 0
+    fi
+}
+
+# Try cloning from the fork, then from the org.
+head_owner=${PR_HEAD_REPO_OWNER:-}
+if [ -n "$head_owner" ] && [ "$head_owner" != "${GITHUB_REPOSITORY_OWNER:-}" ]; then
+    clone "$head_owner" "$head_ref"
+fi
+clone "$org" "$head_ref"
+
+# Nothing worked. Die.
+echo "fetchdep.sh: No branch named $head_ref in $org/$repo"
+exit 1
diff --git a/scripts/layered.sh b/scripts/layered.sh
new file mode 100755
index 000000000..878d7dc84
--- /dev/null
+++ b/scripts/layered.sh
@@ -0,0 +1,59 @@
+#!/usr/bin/env bash
+
+# Installs dependencies, then swaps matrix-js-sdk for a branch of the same
+# name as the pull request branch under test if one exists. This is what
+# lets CI test an Element Call branch together with a matrix-js-sdk branch
+# before either is merged. Without a matching branch the install is left as
+# pnpm-lock.yaml pins it. Inspired by scripts/layered.sh in element-web.
+#
+# Usage: scripts/layered.sh [pnpm install flags]
+#
+# The matrix-js-sdk checkout is nested inside this directory because some CI
+# systems do not allow moving above the primary checkout. It is git-ignored.
+#
+# Set JS_SDK_GITHUB_BASE_REF to a ref to use that exact ref of matrix-js-sdk
+# instead of looking for a matching branch.
+#
+# This script is only meant to be used in CI. For local development use
+# see docs/linking.md.
+
+set -ex
+
+# Paths below are relative to the repository root.
+cd "$(dirname "$0")/.."
+
+pnpm install --frozen-lockfile "$@"
+
+js_sdk_dep=$(jq -r '.devDependencies["matrix-js-sdk"]' < package.json)
+
+# Only layer when package.json follows the branch head rather than pinning a
+# release, so a release build keeps its pinned version.
+if [ "$js_sdk_dep" != "github:matrix-org/matrix-js-sdk#develop" ]; then
+    echo "layered.sh: Skipping matrix-js-sdk fetch and install as package.json pins $js_sdk_dep"
+    exit 0
+fi
+
+if ! scripts/fetchdep.sh matrix-org matrix-js-sdk "${JS_SDK_GITHUB_BASE_REF:-}"; then
+    echo "layered.sh: No matching matrix-js-sdk branch, keeping the locked version"
+    exit 0
+fi
+
+# matrix-js-sdk pins its pnpm version in `devEngines` only. Under corepack,
+# pnpm does not switch versions on its own and corepack, finding no
+# `packageManager` field there, would walk up to this project's and use
+# ours. Pinning it in the clone makes every pnpm invocation inside that
+# directory, including the `prepare` script run by pack, use the right one.
+js_sdk_pnpm="pnpm@$(jq -r '.devEngines.packageManager.version' < matrix-js-sdk/package.json)"
+jq --arg pm "$js_sdk_pnpm" '.packageManager = $pm' matrix-js-sdk/package.json > matrix-js-sdk/package.json.tmp
+mv matrix-js-sdk/package.json.tmp matrix-js-sdk/package.json
+export COREPACK_ENABLE_DOWNLOAD_PROMPT=0
+
+# Install matrix-js-sdk's build dependencies. `prepare` runs on pack below,
+# so it is skipped here.
+(cd matrix-js-sdk && pnpm install --frozen-lockfile --ignore-scripts)
+
+# Rather than `pnpm link`, build matrix-js-sdk into a tarball and install
+# that. This better reflects a clean install: dependencies may be hoisted
+# and shared, and there is no tsconfig.json to pick up sources from.
+(cd matrix-js-sdk && pnpm pack --out matrix-js-sdk.tgz)
+pnpm install "$(pwd)/matrix-js-sdk/matrix-js-sdk.tgz" "$@"