diff --git a/.planning/PROJECT.md b/.planning/PROJECT.md
index da53fb1..4b500c0 100644
--- a/.planning/PROJECT.md
+++ b/.planning/PROJECT.md
@@ -20,8 +20,11 @@ icon, i18n, Hilt, DataStore, green CI.
 
 ## Stack
 
-Kotlin 2.3, Jetpack Compose + Material 3 Expressive (alpha for 1.5 APIs),
-Hilt, DataStore. Gradle Kotlin DSL with Version Catalog. AGP 9.1, Gradle 9.5.
+Kotlin 2.3.21 (paired with KSP 2.3.9 — Kotlin 2.4.0 has no KSP release
+yet, do not upgrade until one ships). Jetpack Compose + Material 3
+Expressive 1.5.0-alpha21 (alpha is intentional — Expressive APIs only
+live in the 1.5 alpha line). Hilt 2.59.2, DataStore. Gradle Kotlin DSL
+with Version Catalog. AGP 9.1.1, Gradle 9.5.1. JVM target 17.
 
 Read-only V1, write support V2.
 
diff --git a/.planning/REQUIREMENTS.md b/.planning/REQUIREMENTS.md
index fb7820e..b33fadf 100644
--- a/.planning/REQUIREMENTS.md
+++ b/.planning/REQUIREMENTS.md
@@ -37,6 +37,7 @@ See full design spec: `docs/superpowers/specs/2026-06-08-calendar-app-design.md`
 ## Constraints
 
 - **Tech stack:** Kotlin + Jetpack Compose + Material 3 Expressive, Hilt, DataStore
+- **Tech stack pin:** Hilt 2.59.2 + KSP 2.3.9; Kotlin 2.3.21 (KSP for Kotlin 2.4.0 not released yet). Material 3 pinned to `1.5.0-alpha21` (Expressive APIs only exist in alpha). Re-evaluate when KSP/Material3 stable land.
 - **Platform:** Android 10+ (API 29 minimum), Android 16 (API 36) target
 - **Offline-first:** all data lives in `CalendarContract`; no app-side network
 - **Privacy:** zero telemetry, no analytics