diff --git a/.changeset/patch-bump-gemini-cli-0-40-0.md b/.changeset/patch-bump-gemini-cli-0-40-0.md
new file mode 100644
index 00000000000..83af05f06fb
--- /dev/null
+++ b/.changeset/patch-bump-gemini-cli-0-40-0.md
@@ -0,0 +1,5 @@
+---
+"gh-aw": patch
+---
+
+Bump default Gemini CLI version to 0.40.0 to restore Smoke Gemini health (API_KEY_INVALID failures with 0.39.1 since 2026-04-29).
diff --git a/.github/workflows/smoke-gemini.lock.yml b/.github/workflows/smoke-gemini.lock.yml
index 40951194a7c..506a1f05f05 100644
--- a/.github/workflows/smoke-gemini.lock.yml
+++ b/.github/workflows/smoke-gemini.lock.yml
@@ -487,7 +487,7 @@ jobs:
       - name: Install AWF binary
         run: bash "${RUNNER_TEMP}/gh-aw/actions/install_awf_binary.sh" v0.25.29
       - name: Install Gemini CLI
-        run: npm install --ignore-scripts -g @google/gemini-cli@0.39.1
+        run: npm install --ignore-scripts -g @google/gemini-cli@0.40.0
       - name: Determine automatic lockdown mode for GitHub MCP Server
         id: determine-automatic-lockdown
         uses: actions/github-script@373c709c69115d41ff229c7e5df9f8788daa9553 # v9
@@ -1431,7 +1431,7 @@ jobs:
       - name: Install AWF binary
         run: bash "${RUNNER_TEMP}/gh-aw/actions/install_awf_binary.sh" v0.25.29
       - name: Install Gemini CLI
-        run: npm install --ignore-scripts -g @google/gemini-cli@0.39.1
+        run: npm install --ignore-scripts -g @google/gemini-cli@0.40.0
       - name: Write Gemini Config
         if: always() && steps.detection_guard.outputs.run_detection == 'true'
         continue-on-error: true
diff --git a/pkg/constants/version_constants.go b/pkg/constants/version_constants.go
index d30b190f316..0d0e2962122 100644
--- a/pkg/constants/version_constants.go
+++ b/pkg/constants/version_constants.go
@@ -45,7 +45,7 @@ const DefaultCopilotVersion Version = "1.0.36"
 const DefaultCodexVersion Version = "0.125.0"
 
 // DefaultGeminiVersion is the default version of the Google Gemini CLI
-const DefaultGeminiVersion Version = "0.39.1"
+const DefaultGeminiVersion Version = "0.40.0"
 
 // DefaultCrushVersion is the default version of the Crush CLI
 const DefaultCrushVersion Version = "0.59.0"