diff --git a/.release-please-manifest.json b/.release-please-manifest.json
index 5612636..6d6aa7c 100644
--- a/.release-please-manifest.json
+++ b/.release-please-manifest.json
@@ -1,5 +1,5 @@
 {
-  "packages/sandbox": "0.4.20",
+  "packages/sandbox": "0.4.21",
   "packages/agent": "0.11.4",
   "packages/provider": "0.4.17"
 }
diff --git a/packages/sandbox/CHANGELOG.md b/packages/sandbox/CHANGELOG.md
index fb1791f..2b10e2f 100644
--- a/packages/sandbox/CHANGELOG.md
+++ b/packages/sandbox/CHANGELOG.md
@@ -1,5 +1,9 @@
 # Changelog
 
+## [0.4.21](https://github.com/coder/ai-sdk/compare/sandbox-v0.4.20...sandbox-v0.4.21) (2026-09-20)
+
+A maintenance release with no notable user-facing changes.
+
 ## [0.4.20](https://github.com/coder/ai-sdk/compare/sandbox-v0.4.19...sandbox-v0.4.20) (2026-09-18)
 
 A maintenance release of the sandbox package with no user-facing changes documented.
diff --git a/packages/sandbox/package.json b/packages/sandbox/package.json
index 77c89a5..6a9f633 100644
--- a/packages/sandbox/package.json
+++ b/packages/sandbox/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@coder/ai-sdk-sandbox",
-  "version": "0.4.20",
+  "version": "0.4.21",
   "description": "Coder workspace sandbox provider for the Vercel AI SDK v7 HarnessAgent",
   "keywords": [
     "ai-sdk",