diff --git a/CHANGELOG.md b/CHANGELOG.md
index 49bf0db2..25c65802 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]
+## [3.3.1] - 2026-04-25
 
 ### Changed
 - **HAD survey-design API consolidated to single `survey_design=` kwarg** across all 8 HAD surfaces: `HeterogeneousAdoptionDiD.fit`, `did_had_pretest_workflow`, `qug_test`, `stute_test`, `yatchew_hr_test`, `stute_joint_pretest`, `joint_pretrends_test`, `joint_homogeneity_test`. Matches the rest of the library (`ContinuousDiD`, `EfficientDiD`, `ChaisemartinDHaultfoeuille` already used `survey_design=`). On data-in surfaces (HAD.fit, workflow, joint data-in wrappers) `survey_design=` accepts a `SurveyDesign` instance (column references resolved against `data` at fit time, same convention as the rest of the library). On the three array-in linearity helpers (`stute_test`, `yatchew_hr_test`, `stute_joint_pretest`) `survey_design=` accepts a pre-resolved `ResolvedSurveyDesign`; passing a `SurveyDesign` raises `TypeError` with migration guidance to `make_pweight_design(arr)` (pweight-only) or pre-resolution. `qug_test` is the 8th surface and accepts the same kwarg signature for consistency, but **all** non-`None` values raise `NotImplementedError` per the Phase 4.5 C0 permanent deferral (no migration path; the qug-specific mutex error reflects this). New public helper `make_pweight_design(weights: np.ndarray) -> ResolvedSurveyDesign` exported from the `diff_diff` top level for the pweight-only convenience on the three array-in linearity helpers (formerly the private `survey._make_trivial_resolved`, kept as a permanent private alias); validates 1-D input at the front door. Three-way mutex (`survey_design + survey + weights`) extends the prior 2-way (`survey + weights`) — at most one may be non-None per call. Patch-level addition (additive new kwarg + permanent alias for the helper; no breaking changes this release).
@@ -1408,6 +1408,7 @@ 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
+[3.3.1]: https://github.com/igerber/diff-diff/compare/v3.3.0...v3.3.1
 [3.3.0]: https://github.com/igerber/diff-diff/compare/v3.2.0...v3.3.0
 [3.2.0]: https://github.com/igerber/diff-diff/compare/v3.1.3...v3.2.0
 [3.1.3]: https://github.com/igerber/diff-diff/compare/v3.1.2...v3.1.3
diff --git a/CITATION.cff b/CITATION.cff
index 9f3a07e8..3a8e4c25 100644
--- a/CITATION.cff
+++ b/CITATION.cff
@@ -7,7 +7,7 @@ authors:
     family-names: Gerber
     orcid: "https://orcid.org/0009-0009-3275-5591"
 license: MIT
-version: "3.3.0"
+version: "3.3.1"
 date-released: "2026-04-25"
 doi: "10.5281/zenodo.19646175"
 url: "https://github.com/igerber/diff-diff"
diff --git a/diff_diff/__init__.py b/diff_diff/__init__.py
index e95ec008..4b92d692 100644
--- a/diff_diff/__init__.py
+++ b/diff_diff/__init__.py
@@ -287,7 +287,7 @@
 DCDH = ChaisemartinDHaultfoeuille
 HAD = HeterogeneousAdoptionDiD
 
-__version__ = "3.3.0"
+__version__ = "3.3.1"
 __all__ = [
     # Estimators
     "DifferenceInDifferences",
diff --git a/diff_diff/guides/llms-full.txt b/diff_diff/guides/llms-full.txt
index 6346da64..b3270c97 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: 3.3.0
+- Version: 3.3.1
 - 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 f5b7d15c..98504b70 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -4,7 +4,7 @@ build-backend = "maturin"
 
 [project]
 name = "diff-diff"
-version = "3.3.0"
+version = "3.3.1"
 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 d6690c08..b2878c35 100644
--- a/rust/Cargo.toml
+++ b/rust/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "diff_diff_rust"
-version = "3.3.0"
+version = "3.3.1"
 edition = "2021"
 rust-version = "1.84"
 description = "Rust backend for diff-diff DiD library"