diff --git a/.gitignore b/.gitignore
index 8965cf832..5290a6187 100644
--- a/.gitignore
+++ b/.gitignore
@@ -6,6 +6,7 @@
 /platform.local.txt
 /loader/VERSION
 /cores/arduino/api/
+/variants/include/
 
 __pycache__/
 
diff --git a/extra/dedupe_includes.py b/extra/dedupe_includes.py
new file mode 100755
index 000000000..b2b449b0f
--- /dev/null
+++ b/extra/dedupe_includes.py
@@ -0,0 +1,204 @@
+#!/usr/bin/env python3
+
+# Copyright (c) Arduino s.r.l. and/or its affiliated companies
+# SPDX-License-Identifier: Apache-2.0
+
+# Finds files that are byte-identical, at the same relative path, in the
+# 'llext-edk/include' directory of every given variant, copies one canonical
+# copy of each into a common variant's directory (dropping the
+# 'llext-edk/include' part of the path), then deletes the duplicate copies
+# from the variants' directories.
+#
+# Each variant's "includes.txt" (a list of "-iwithprefixbefore<path>"
+# compiler flags, each path relative to the variant's own directory) is
+# updated to match: entries fully emptied by the move are repointed at the
+# common variant's directory and their now-empty source directory is removed
+# from disk; entries only partially emptied get an extra entry added for the
+# common directory alongside the original. This only happens when not
+# running with --dry-run.
+
+import argparse
+import hashlib
+import os
+import posixpath
+import shutil
+import sys
+from pathlib import Path
+
+INCLUDE_FLAG = "-iwithprefixbefore"
+VARIANTS_DIR = Path("variants")
+LLEXT_INCLUDE = Path("llext-edk/include")
+
+
+def input_path(name: str) -> Path:
+    return VARIANTS_DIR / name / LLEXT_INCLUDE
+
+
+def strip_variants_prefix(name: str) -> str:
+    name = name.rstrip("/")
+    if name.startswith(f"{VARIANTS_DIR}/"):
+        name = name[len(f"{VARIANTS_DIR}/") :]
+    return name
+
+
+def hash_file(path: Path) -> str:
+    digest = hashlib.sha256()
+    with path.open("rb") as f:
+        for chunk in iter(lambda: f.read(1024 * 1024), b""):
+            digest.update(chunk)
+    return digest.hexdigest()
+
+
+def scan_directory(directory: Path) -> dict[Path, str]:
+    return {
+        path.relative_to(directory): hash_file(path)
+        for path in directory.rglob("*")
+        if path.is_file()
+    }
+
+
+def find_common_files(per_dir_hashes: list[dict[Path, str]]) -> dict[Path, str]:
+    common = {}
+    first, rest = per_dir_hashes[0], per_dir_hashes[1:]
+    for rel_path, digest in first.items():
+        if all(other.get(rel_path) == digest for other in rest):
+            common[rel_path] = digest
+    return common
+
+
+def update_includes_txt(name: str, common_dir: Path, common_rel_paths) -> None:
+    variant_root = VARIANTS_DIR / name
+    input_dir = input_path(name)
+    includes_txt = variant_root / "includes.txt"
+    if not includes_txt.is_file():
+        return
+
+    lines = includes_txt.read_text().splitlines()
+    # Normalize entries such as "a/b/../c" or "a/./b": pathlib keeps ".."
+    # components, so they would never match the deduplicated file paths.
+    entries = [
+        (i, posixpath.normpath(line[len(INCLUDE_FLAG) :]))
+        for i, line in enumerate(lines)
+        if line.startswith(INCLUDE_FLAG)
+    ]
+    # Deepest first, so a child directory is resolved (and possibly removed)
+    # before its parent's emptiness is checked.
+    entries.sort(key=lambda e: e[1].count("/"), reverse=True)
+
+    actions: dict[int, tuple[str, str]] = {}
+    for idx, suffix in entries:
+        real_dir = variant_root / suffix.lstrip("/")
+        if real_dir != input_dir and input_dir not in (real_dir, *real_dir.parents):
+            continue
+
+        affected = any(
+            (input_dir / rel) == real_dir or real_dir in (input_dir / rel).parents
+            for rel in common_rel_paths
+        )
+        if not affected:
+            continue
+
+        if real_dir.exists():
+            has_files = any(p.is_file() for p in real_dir.rglob("*"))
+        else:
+            has_files = False
+
+        sub_path = real_dir.relative_to(input_dir)
+        common_target = common_dir if sub_path == Path(".") else common_dir / sub_path
+        new_suffix = "/" + os.path.relpath(common_target, variant_root).replace(os.sep, "/")
+        new_line = INCLUDE_FLAG + new_suffix
+
+        if not has_files:
+            if real_dir.exists():
+                shutil.rmtree(real_dir)
+            actions[idx] = ("replace", new_line)
+        else:
+            actions[idx] = ("augment", new_line)
+
+    if not actions:
+        return
+
+    new_lines = []
+    for i, line in enumerate(lines):
+        action = actions.get(i)
+        if action is None:
+            new_lines.append(line)
+        elif action[0] == "replace":
+            new_lines.append(action[1])
+        else:
+            new_lines.append(line)
+            new_lines.append(action[1])
+
+    includes_txt.write_text("\n".join(new_lines) + "\n")
+
+
+def main() -> int:
+    parser = argparse.ArgumentParser(description=__doc__)
+    parser.add_argument(
+        "--common-dir",
+        required=True,
+        help="name of the common variant to mirror files into "
+        "(created at variants/<name>; must not already exist)",
+    )
+    parser.add_argument(
+        "--dry-run",
+        action="store_true",
+        help="report what would be done, without touching the filesystem",
+    )
+    parser.add_argument(
+        "variant_names",
+        nargs="+",
+        help="two or more variant names to compare (a leading 'variants/' is ignored)",
+    )
+    args = parser.parse_args()
+
+    variant_names = [strip_variants_prefix(v) for v in args.variant_names]
+    if len(variant_names) < 2:
+        parser.error("need at least 2 variants to compare")
+
+    for name in variant_names:
+        if not (VARIANTS_DIR / name).is_dir():
+            parser.error(f"{VARIANTS_DIR / name} does not exist")
+
+    common_dir = VARIANTS_DIR / strip_variants_prefix(args.common_dir)
+    if common_dir.exists():
+        parser.error(f"--common-dir {common_dir} already exists")
+
+    per_dir_hashes = [scan_directory(input_path(name)) for name in variant_names]
+    common = find_common_files(per_dir_hashes)
+
+    total_size = sum(
+        (input_path(variant_names[0]) / rel_path).stat().st_size for rel_path in common
+    )
+    freed = total_size * (len(variant_names) - 1)
+
+    print(f"{len(variant_names)} variants compared")
+    for name, hashes in zip(variant_names, per_dir_hashes):
+        print(f"  {input_path(name)}: {len(hashes)} files")
+    print(f"{len(common)} files common to all variants")
+    print(f"{freed} bytes would be freed" if args.dry_run else f"{freed} bytes freed")
+
+    if args.dry_run:
+        return 0
+
+    for rel_path in common:
+        src = input_path(variant_names[0]) / rel_path
+        dst = common_dir / rel_path
+        dst.parent.mkdir(parents=True, exist_ok=True)
+        dst.write_bytes(src.read_bytes())
+        if hash_file(dst) != common[rel_path]:
+            print(f"error: mirrored copy of {rel_path} does not match source", file=sys.stderr)
+            return 1
+
+    for rel_path in common:
+        for name in variant_names:
+            (input_path(name) / rel_path).unlink()
+
+    for name in variant_names:
+        update_includes_txt(name, common_dir, common.keys())
+
+    return 0
+
+
+if __name__ == "__main__":
+    sys.exit(main())
diff --git a/extra/package_core.sh b/extra/package_core.sh
index 77b431480..867b565b7 100755
--- a/extra/package_core.sh
+++ b/extra/package_core.sh
@@ -88,6 +88,21 @@ for variant in $INCLUDED_VARIANTS ; do
 	fi
 done
 
+# deduplicate llext-edk headers shared by all included variants
+# (CI only: this modifies the working tree)
+if [ -n "$GITHUB_ACTIONS" ] ; then
+	EDK_VARIANTS=$(for v in $INCLUDED_VARIANTS ; do
+		if [ -d variants/$v/llext-edk/include ] ; then echo $v ; fi
+	done)
+	if [ $(echo $EDK_VARIANTS | wc -w) -ge 2 ] ; then
+		extra/dedupe_includes.py --common-dir include $EDK_VARIANTS
+	fi
+fi
+# shared headers, from the step above or from a synced deduplicated package
+if [ -d variants/include ] ; then
+	echo "variants/include/" >> ${TEMP_INC}
+fi
+
 # create the list of files and directories to exclude
 TEMP_EXC=$(mktemp -p . | sed 's/\.\///')
 declutter_file extra/artifacts/_common.exc >> ${TEMP_EXC}
diff --git a/platform.txt b/platform.txt
index bc8821cf4..de0b9387b 100644
--- a/platform.txt
+++ b/platform.txt
@@ -40,7 +40,7 @@ compiler.zephyr.includes_file={build.variant.path}/includes.txt
 compiler.zephyr.machine_flags_file={build.variant.path}/machine_flags.txt
 compiler.zephyr.cflags_file={build.variant.path}/cflags.txt
 compiler.zephyr.cxxflags_file={build.variant.path}/cxxflags.txt
-compiler.zephyr.macros="-imacros{build.variant.path}/llext-edk/include/zephyr/include/generated/zephyr/autoconf.h" "-imacros{build.variant.path}/llext-edk/include/zephyr/include/zephyr/toolchain/zephyr_stdint.h"
+compiler.zephyr.macros=-imacroszephyr/autoconf.h -imacroszephyr/toolchain/zephyr_stdint.h
 # NOTE: -fno-extern-tls-init prevents the C++ frontend from emitting guarded
 # references to the thread-local init function (e.g. _ZTH5errno) for extern
 # thread_local variables such as picolibc's `errno`. These variables are
diff --git a/tools/sync-zephyr-artifacts/main.go b/tools/sync-zephyr-artifacts/main.go
index 8fdf3b56e..209a68a7d 100644
--- a/tools/sync-zephyr-artifacts/main.go
+++ b/tools/sync-zephyr-artifacts/main.go
@@ -185,8 +185,9 @@ func main() {
 		_ = cmd.Run() // no error check, the api symlink may be gone in the future
 	}
 
-	// Remove old firmwares and variants/*/llext-edk files
+	// Remove old firmwares, variants/*/llext-edk files and shared variant headers
 	os.RemoveAll(filepath.Join(gitCorePath, "firmwares"))
+	os.RemoveAll(filepath.Join(gitCorePath, "variants", "include"))
 	filepath.WalkDir(filepath.Join(gitCorePath, "variants"), func(path string, d os.DirEntry, err error) error {
 		if err != nil {
 			fmt.Println("Error:", err)