diff --git a/.github/renovate.json b/.github/renovate.json
index a9ea19d..d46582a 100644
--- a/.github/renovate.json
+++ b/.github/renovate.json
@@ -23,6 +23,20 @@
       "groupName": "kotlin",
       "allowedVersions": "/^\\d+\\.\\d+\\.\\d+$/"
     },
+    {
+      "description": "Hold the bundled Analysis API at 2.4.10 until 2.5.0: from 2.4.20 kotlin-compiler can no longer host a standalone session (see libs.versions.toml)",
+      "matchPackageNames": [
+        "org.jetbrains.kotlin:kotlin-compiler",
+        "org.jetbrains.kotlin:analysis-api-for-ide",
+        "org.jetbrains.kotlin:analysis-api-impl-base-for-ide",
+        "org.jetbrains.kotlin:analysis-api-platform-interface-for-ide",
+        "org.jetbrains.kotlin:analysis-api-standalone-for-ide",
+        "org.jetbrains.kotlin:analysis-api-k2-for-ide",
+        "org.jetbrains.kotlin:low-level-api-fir-for-ide",
+        "org.jetbrains.kotlin:symbol-light-classes-for-ide"
+      ],
+      "allowedVersions": "/^(2\\.4\\.10|2\\.([5-9]|[1-9]\\d)\\.\\d+|[3-9]\\.\\d+\\.\\d+)$/"
+    },
     {
       "matchPackageNames": [
         "org.junit:junit-bom",
diff --git a/CLAUDE.md b/CLAUDE.md
index 5a14267..7397705 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -53,7 +53,7 @@ Runs inside the worker's isolated classloader. Bundles the Kotlin Analysis API (
 
 - Korro's own version lives in `gradle.properties` (`version=...`). Both subprojects inherit it via `subprojects { version = rootProject.version }` in the root `build.gradle.kts`. At runtime the plugin reads it from a generated `META-INF/korro-gradle-plugin.properties` resource (`KorroPlugin.readKorroPluginVersion`).
 - Every other version lives in `gradle/libs.versions.toml`. The catalog is the single source of truth — do not hard-code versions in subproject scripts; add to the catalog and reference as `libs.*` / `libs.plugins.*`.
-- `libs.versions.kotlin` — pinned Kotlin / Analysis API version. `libs.versions.kotlinLanguage` — Kotlin `languageVersion`/`apiVersion` used to compile Korro itself; unrelated to the bundled Analysis API. JVM target is hard-coded to `17` in the root `build.gradle.kts`.
+- `libs.versions.kotlin` — Kotlin Gradle plugin and stdlib used to build Korro. `libs.versions.analysisApi` — the bundled Analysis API (`*-for-ide` artifacts) together with the `kotlin-compiler` jar it runs on; they always move as one and may lag `kotlin` (the catalog comment says why). `libs.versions.kotlinLanguage` — Kotlin `languageVersion`/`apiVersion` used to compile Korro itself; unrelated to the bundled Analysis API. JVM target is hard-coded to `17` in the root `build.gradle.kts`.
 
 ## Invariants to preserve
 
diff --git a/gradle/libs.versions.toml b/gradle/libs.versions.toml
index 000a72d..dae5283 100644
--- a/gradle/libs.versions.toml
+++ b/gradle/libs.versions.toml
@@ -1,5 +1,8 @@
 [versions]
-kotlin = "2.4.10"
+kotlin = "2.4.21"
+# Bundled Analysis API + the kotlin-compiler jar it runs on. Held at 2.4.10 until 2.5.0: from 2.4.20 kotlin-compiler lacks
+# the decompiler and IntelliJ classes a standalone session needs (NoClassDefFoundError: ClsKotlinBinaryClassCache).
+analysisApi = "2.4.10"
 kotlinLanguage = "2.1"
 shadow = "9.6.1"
 pluginPublish = "2.1.1"
@@ -10,15 +13,15 @@ mavenPublish = "0.37.0"
 
 [libraries]
 kotlin-stdlib = { module = "org.jetbrains.kotlin:kotlin-stdlib", version.ref = "kotlin" }
-kotlin-compiler = { module = "org.jetbrains.kotlin:kotlin-compiler", version.ref = "kotlin" }
+kotlin-compiler = { module = "org.jetbrains.kotlin:kotlin-compiler", version.ref = "analysisApi" }
 
-kotlin-analysisApi = { module = "org.jetbrains.kotlin:analysis-api-for-ide", version.ref = "kotlin" }
-kotlin-analysisApi-implBase = { module = "org.jetbrains.kotlin:analysis-api-impl-base-for-ide", version.ref = "kotlin" }
-kotlin-analysisApi-platformInterface = { module = "org.jetbrains.kotlin:analysis-api-platform-interface-for-ide", version.ref = "kotlin" }
-kotlin-analysisApi-standalone = { module = "org.jetbrains.kotlin:analysis-api-standalone-for-ide", version.ref = "kotlin" }
-kotlin-analysisApi-k2 = { module = "org.jetbrains.kotlin:analysis-api-k2-for-ide", version.ref = "kotlin" }
-kotlin-lowLevelApiFir = { module = "org.jetbrains.kotlin:low-level-api-fir-for-ide", version.ref = "kotlin" }
-kotlin-symbolLightClasses = { module = "org.jetbrains.kotlin:symbol-light-classes-for-ide", version.ref = "kotlin" }
+kotlin-analysisApi = { module = "org.jetbrains.kotlin:analysis-api-for-ide", version.ref = "analysisApi" }
+kotlin-analysisApi-implBase = { module = "org.jetbrains.kotlin:analysis-api-impl-base-for-ide", version.ref = "analysisApi" }
+kotlin-analysisApi-platformInterface = { module = "org.jetbrains.kotlin:analysis-api-platform-interface-for-ide", version.ref = "analysisApi" }
+kotlin-analysisApi-standalone = { module = "org.jetbrains.kotlin:analysis-api-standalone-for-ide", version.ref = "analysisApi" }
+kotlin-analysisApi-k2 = { module = "org.jetbrains.kotlin:analysis-api-k2-for-ide", version.ref = "analysisApi" }
+kotlin-lowLevelApiFir = { module = "org.jetbrains.kotlin:low-level-api-fir-for-ide", version.ref = "analysisApi" }
+kotlin-symbolLightClasses = { module = "org.jetbrains.kotlin:symbol-light-classes-for-ide", version.ref = "analysisApi" }
 
 kotlinx-serialization-core = { module = "org.jetbrains.kotlinx:kotlinx-serialization-core", version.ref = "kotlinxSerialization" }
 caffeine = { module = "com.github.ben-manes.caffeine:caffeine", version.ref = "caffeine" }