From 9521f38d2ac1ff1add7bf92ee03af62613833afd Mon Sep 17 00:00:00 2001
From: igerber <isaac.gerber@gmail.com>
Date: Mon, 16 Feb 2026 15:37:17 -0500
Subject: [PATCH] Bump version to 2.4.0

Update version numbers in __init__.py, pyproject.toml, and rust/Cargo.toml.
Add CHANGELOG entry for v2.4.0 with Two-Stage DiD estimator and related fixes.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
---
 CHANGELOG.md          | 21 +++++++++++++++++++++
 diff_diff/__init__.py |  2 +-
 pyproject.toml        |  2 +-
 rust/Cargo.toml       |  2 +-
 4 files changed, 24 insertions(+), 3 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 1745866e..c38c03ff 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,26 @@ 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).
 
+## [2.4.0] - 2026-02-16
+
+### Added
+- **Gardner (2022) Two-Stage DiD estimator** (`TwoStageDiD`)
+  - Two-stage estimator: (1) estimate unit+time FE on untreated obs, (2) regress residualized outcomes on treatment indicators
+  - `TwoStageDiDResults` with overall ATT, event study, group effects, per-observation treatment effects
+  - `TwoStageBootstrapResults` for multiplier bootstrap inference on GMM influence function
+  - `two_stage_did()` convenience function for quick estimation
+  - Point estimates identical to ImputationDiD; different variance estimator (GMM sandwich vs. conservative)
+  - No finite-sample adjustments (raw asymptotic sandwich, matching R `did2s`)
+- Proposition 5 detection for unidentified long-run horizons without never-treated units
+
+### Changed
+- Workflow improvements to reduce PR review rounds
+
+### Fixed
+- Zero-observation horizons/cohorts producing se=0 instead of NaN in TwoStageDiD
+- Edge case fixes for TwoStageDiD (PR review feedback)
+- Grep PCRE patterns updated to use POSIX character classes
+
 ## [2.3.2] - 2026-02-16
 
 ### Added
@@ -719,6 +739,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   - `to_dict()` and `to_dataframe()` export methods
   - `is_significant` and `significance_stars` properties
 
+[2.4.0]: https://github.com/igerber/diff-diff/compare/v2.3.2...v2.4.0
 [2.3.2]: https://github.com/igerber/diff-diff/compare/v2.3.1...v2.3.2
 [2.3.1]: https://github.com/igerber/diff-diff/compare/v2.3.0...v2.3.1
 [2.3.0]: https://github.com/igerber/diff-diff/compare/v2.2.1...v2.3.0
diff --git a/diff_diff/__init__.py b/diff_diff/__init__.py
index 01c50e75..05e3f517 100644
--- a/diff_diff/__init__.py
+++ b/diff_diff/__init__.py
@@ -148,7 +148,7 @@
     load_mpdta,
 )
 
-__version__ = "2.3.2"
+__version__ = "2.4.0"
 __all__ = [
     # Estimators
     "DifferenceInDifferences",
diff --git a/pyproject.toml b/pyproject.toml
index 67c22abf..6e411d64 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -4,7 +4,7 @@ build-backend = "maturin"
 
 [project]
 name = "diff-diff"
-version = "2.3.2"
+version = "2.4.0"
 description = "A library for Difference-in-Differences causal inference analysis"
 readme = "README.md"
 license = "MIT"
diff --git a/rust/Cargo.toml b/rust/Cargo.toml
index 450777cf..3b7f6178 100644
--- a/rust/Cargo.toml
+++ b/rust/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "diff_diff_rust"
-version = "2.3.2"
+version = "2.4.0"
 edition = "2021"
 description = "Rust backend for diff-diff DiD library"
 license = "MIT"