diff --git a/CHANGELOG.md b/CHANGELOG.md
index bad43cff..da03535b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,7 +5,7 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
-## [Unreleased]
+## [3.9.1] - 2026-08-17
 
 ### Added
 - **LWDiD Stata parity arm + acceptance-suite re-anchor (ahead of PR #588's merge).**
@@ -5067,6 +5067,7 @@ for the full feature history leading to this release.
 [2.1.2]: https://github.com/igerber/diff-diff/compare/v2.1.1...v2.1.2
 [2.1.1]: https://github.com/igerber/diff-diff/compare/v2.1.0...v2.1.1
 [2.1.0]: https://github.com/igerber/diff-diff/compare/v2.0.3...v2.1.0
+[3.9.1]: https://github.com/igerber/diff-diff/compare/v3.9.0...v3.9.1
 [3.9.0]: https://github.com/igerber/diff-diff/compare/v3.8.0...v3.9.0
 [3.8.0]: https://github.com/igerber/diff-diff/compare/v3.7.0...v3.8.0
 [3.7.0]: https://github.com/igerber/diff-diff/compare/v3.6.2...v3.7.0
diff --git a/CITATION.cff b/CITATION.cff
index 342b13d5..2aef819f 100644
--- a/CITATION.cff
+++ b/CITATION.cff
@@ -7,8 +7,8 @@ authors:
     family-names: Gerber
     orcid: "https://orcid.org/0009-0009-3275-5591"
 license: MIT
-version: "3.9.0"
-date-released: "2026-08-10"
+version: "3.9.1"
+date-released: "2026-08-17"
 doi: "10.5281/zenodo.19646175"
 url: "https://github.com/igerber/diff-diff"
 repository-code: "https://github.com/igerber/diff-diff"
diff --git a/diff_diff/__init__.py b/diff_diff/__init__.py
index 10c34054..0834c3e7 100644
--- a/diff_diff/__init__.py
+++ b/diff_diff/__init__.py
@@ -366,7 +366,7 @@ def __getattr__(name: str) -> _Any:
     raise AttributeError(f"module 'diff_diff' has no attribute {name!r}")
 
 
-__version__ = "3.9.0"
+__version__ = "3.9.1"
 __all__ = [
     # Estimators
     "DifferenceInDifferences",
diff --git a/diff_diff/guides/llms-full.txt b/diff_diff/guides/llms-full.txt
index 6d707851..a8003a59 100644
--- a/diff_diff/guides/llms-full.txt
+++ b/diff_diff/guides/llms-full.txt
@@ -2,7 +2,7 @@
 
 > A Python library for Difference-in-Differences causal inference analysis. Provides sklearn-like estimators with statsmodels-style output for econometric analysis.
 
-- Version: 3.9.0
+- Version: 3.9.1
 - Repository: https://github.com/igerber/diff-diff
 - License: MIT
 - Dependencies: numpy, pandas, scipy (no statsmodels dependency)
diff --git a/pyproject.toml b/pyproject.toml
index d1932915..ee10b168 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -4,7 +4,7 @@ build-backend = "maturin"
 
 [project]
 name = "diff-diff"
-version = "3.9.0"
+version = "3.9.1"
 description = "Difference-in-Differences causal inference with sklearn-like API. Callaway-Sant'Anna, Synthetic DiD, Honest DiD, event studies, parallel trends."
 readme = "README.md"
 license = "MIT"
diff --git a/rust/Cargo.toml b/rust/Cargo.toml
index 9b40f033..2671a86a 100644
--- a/rust/Cargo.toml
+++ b/rust/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "diff_diff_rust"
-version = "3.9.0"
+version = "3.9.1"
 edition = "2021"
 rust-version = "1.85"
 description = "Rust backend for diff-diff DiD library"