diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3ec3d2b5..0e0e7497 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,31 @@ 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).
 
+## [2.1.5] - 2026-01-22
+
+### Added
+- **METHODOLOGY_REVIEW.md** tracking document for methodology review progress
+  - Review status summary table for all 12 estimators
+  - Detailed notes template for each estimator by category
+  - Review process guidelines with checklist and priority ordering
+- **`base_period` parameter** for CallawaySantAnna pre-treatment effect computation
+  - "varying" (default): Pre-treatment uses t-1 as base (consecutive comparisons)
+  - "universal": All comparisons use g-anticipation-1 as base
+  - Matches R `did::att_gt()` base_period parameter
+- **Pre-merge-check skill** (`/pre-merge-check`) for automated PR validation
+  - Pattern checks for NaN handling consistency
+  - Context-specific checklist generation
+
+### Changed
+- **Tutorial 02 improvements**: Added pre-trends section, clarified base_period interaction with anticipation
+
+### Fixed
+- Not-yet-treated control group now properly excludes cohort g when computing ATT(g,t)
+- Aggregation t_stat uses NaN (not 0.0) when SE is non-finite or zero
+- Bootstrap inference for pre-treatment effects with `base_period="varying"`
+- NaN propagation for empty post-treatment effects in CallawaySantAnna
+- Grep word boundary pattern in pre-merge-check skill
+
 ## [2.1.4] - 2026-01-20
 
 ### Added
@@ -492,6 +517,7 @@ 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
 
+[2.1.5]: https://github.com/igerber/diff-diff/compare/v2.1.4...v2.1.5
 [2.1.4]: https://github.com/igerber/diff-diff/compare/v2.1.3...v2.1.4
 [2.1.3]: https://github.com/igerber/diff-diff/compare/v2.1.2...v2.1.3
 [2.1.2]: https://github.com/igerber/diff-diff/compare/v2.1.1...v2.1.2
diff --git a/diff_diff/__init__.py b/diff_diff/__init__.py
index 55b426c5..799d9f47 100644
--- a/diff_diff/__init__.py
+++ b/diff_diff/__init__.py
@@ -136,7 +136,7 @@
     load_mpdta,
 )
 
-__version__ = "2.1.4"
+__version__ = "2.1.5"
 __all__ = [
     # Estimators
     "DifferenceInDifferences",
diff --git a/pyproject.toml b/pyproject.toml
index 7ebbc10b..5733e2d3 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -4,7 +4,7 @@ build-backend = "maturin"
 
 [project]
 name = "diff-diff"
-version = "2.1.4"
+version = "2.1.5"
 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 557a5850..528b8a39 100644
--- a/rust/Cargo.toml
+++ b/rust/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "diff_diff_rust"
-version = "2.1.4"
+version = "2.1.5"
 edition = "2021"
 description = "Rust backend for diff-diff DiD library"
 license = "MIT"