diff --git a/.gitignore b/.gitignore
index f3dbe4d9..5c16ff0b 100644
--- a/.gitignore
+++ b/.gitignore
@@ -26,3 +26,6 @@ dist/
 
 # scratch workspace
 /workspace
+
+# Codegen sync changelog text, read by `make clients`
+/CODEGEN_SYNC_CHANGELOG.md
diff --git a/Makefile b/Makefile
index 22f2b071..086d5682 100644
--- a/Makefile
+++ b/Makefile
@@ -7,7 +7,7 @@ SMITHY_PYTHON ?= ../smithy-python
 # Clients per gradle build in `make clients`; lower it if the build runs out of heap.
 BATCH_SIZE ?= 25
 
-.PHONY: docs docs-serve docs-clean docs-install docs-lock venv gen clients publish-codegen aio-check static-analysis test-unit test-functional test-integration
+.PHONY: docs docs-serve docs-clean docs-install docs-lock venv gen clients fragments publish-codegen aio-check static-analysis test-unit test-functional test-integration
 
 # Each client and package runs in its own .venv. Dependencies outside this repo,
 # including smithy-python, resolve from PyPI at the versions each one declares.
@@ -60,6 +60,11 @@ test-integration:
 clients:
 	SMITHY_PYTHON=$(abspath $(SMITHY_PYTHON)) uv run python codegen/gen_client.py --all --pinned --batch-size $(BATCH_SIZE)
 
+# Only for a smithy-python pointer move: writes a changelog fragment from
+# CODEGEN_SYNC_CHANGELOG.md for every generated client.
+fragments:
+	uv run --no-project --python $(PYTHON_VERSION) python codegen/gen_fragments.py
+
 ########################## Granular targets below ##########################
 
 # Publishes the smithy-python codegen jars to the local Maven cache so `gen`
diff --git a/codegen/gen_fragments.py b/codegen/gen_fragments.py
new file mode 100644
index 00000000..8647a414
--- /dev/null
+++ b/codegen/gen_fragments.py
@@ -0,0 +1,87 @@
+#!/usr/bin/env python3
+"""Write a codegen sync changelog fragment for every generated client.
+
+Usage: python codegen/gen_fragments.py
+  Only for a smithy-python pointer move; the text comes from CODEGEN_SYNC_CHANGELOG.md
+  in the repo root.
+"""
+
+import json
+import re
+import sys
+import time
+import tomllib
+from pathlib import Path
+
+CODEGEN_DIR = Path(__file__).resolve().parent
+REPO = CODEGEN_DIR.parent
+CLIENTS = REPO / "clients"
+MODELS = CODEGEN_DIR / "aws-models"
+POINTER = CODEGEN_DIR / "smithy-python.toml"
+SYNC_CHANGELOG = REPO / "CODEGEN_SYNC_CHANGELOG.md"
+SMITHY_PYTHON_COMMITS = "https://github.com/smithy-lang/smithy-python/commits"
+# An older file is assumed to be left over from a previous sync.
+SYNC_CHANGELOG_MAX_AGE_SECONDS = 8 * 60 * 60
+
+
+def main() -> None:
+    previous, commit = _pointer_commits()
+    description = _description(previous, commit)
+    for name in _generated_clients():
+        _write_fragment(name, commit, description)
+
+
+def _pointer_commits() -> tuple[str, str]:
+    with POINTER.open("rb") as f:
+        pointer = tomllib.load(f)
+    commits = []
+    for key in ("previous_commit", "commit"):
+        value = pointer.get(key)
+        if not isinstance(value, str) or not re.fullmatch(r"[0-9a-f]{40}", value):
+            sys.exit(
+                f"{POINTER}: {key} must be a full 40-character hash, got {value!r}"
+            )
+        commits.append(value)
+    previous, commit = commits
+    if previous == commit:
+        sys.exit(f"{POINTER}: previous_commit and commit must differ")
+    return previous, commit
+
+
+def _description(previous: str, commit: str) -> str:
+    changes = f"{SMITHY_PYTHON_COMMITS}/{previous}..{commit}"
+    reminder = f"write the changelog text for this codegen sync of {changes}"
+    if not SYNC_CHANGELOG.exists():
+        SYNC_CHANGELOG.touch()
+        sys.exit(f"created empty {SYNC_CHANGELOG}; {reminder}")
+    age = time.time() - SYNC_CHANGELOG.stat().st_mtime
+    if age > SYNC_CHANGELOG_MAX_AGE_SECONDS:
+        sys.exit(f"{SYNC_CHANGELOG} is {age / 3600:.1f} hours old; {reminder}")
+    text = SYNC_CHANGELOG.read_text().strip()
+    if not text:
+        sys.exit(f"{SYNC_CHANGELOG} is empty; {reminder}")
+    link = f"[smithy-python {previous[:7]}..{commit[:7]}]({changes})"
+    return f"Codegen sync for {link}: {text}"
+
+
+def _generated_clients() -> list[str]:
+    return [f"aws-sdk-{model.stem}" for model in sorted(MODELS.glob("*.json"))]
+
+
+def _write_fragment(name: str, commit: str, description: str) -> None:
+    # Keyed by target commit: a rerun for the same pin overwrites, a later sync adds.
+    fragment = (
+        CLIENTS
+        / name
+        / ".changes"
+        / "next-release"
+        / f"{name}-enhancement-codegen-sync-{commit}.json"
+    )
+    fragment.parent.mkdir(parents=True, exist_ok=True)
+    entry = {"type": "enhancement", "description": description}
+    fragment.write_text(json.dumps(entry, indent=2) + "\n")
+    print(f"wrote {fragment}")
+
+
+if __name__ == "__main__":
+    main()
diff --git a/codegen/smithy-python.toml b/codegen/smithy-python.toml
index 6d7079aa..dab7d93c 100644
--- a/codegen/smithy-python.toml
+++ b/codegen/smithy-python.toml
@@ -1,3 +1,6 @@
 # The smithy-python commit `make clients` builds codegen from. May be any commit
 # reachable from the colocated smithy-python checkout, including a local one.
 commit = "b8eceadb0573bd0c757def9a2b26fe7bf938b239"
+# The commit this pointer moved from; with `commit` it bounds the range linked
+# in codegen sync changelog entries.
+previous_commit = "505312562bf78d45265145ae3ae9f874c00464d1"