diff --git a/.changeset/weak-cameras-hope.md b/.changeset/weak-cameras-hope.md
new file mode 100644
index 0000000000..62eecb7fe0
--- /dev/null
+++ b/.changeset/weak-cameras-hope.md
@@ -0,0 +1,5 @@
+---
+"roo-cline": patch
+---
+
+Default middle-out compression to on for OpenRouter
diff --git a/src/api/providers/openrouter.ts b/src/api/providers/openrouter.ts
index b65c06b98b..0bf98ba18e 100644
--- a/src/api/providers/openrouter.ts
+++ b/src/api/providers/openrouter.ts
@@ -114,7 +114,7 @@ export class OpenRouterHandler extends BaseProvider implements SingleCompletionH
 			stream: true,
 			include_reasoning: true,
 			// This way, the transforms field will only be included in the parameters when openRouterUseMiddleOutTransform is true.
-			...(this.options.openRouterUseMiddleOutTransform && { transforms: ["middle-out"] }),
+			...((this.options.openRouterUseMiddleOutTransform ?? true) && { transforms: ["middle-out"] }),
 		}
 
 		const stream = await this.client.chat.completions.create(completionParams)
diff --git a/src/core/webview/ClineProvider.ts b/src/core/webview/ClineProvider.ts
index e25f46bde3..e23e8762a7 100644
--- a/src/core/webview/ClineProvider.ts
+++ b/src/core/webview/ClineProvider.ts
@@ -2430,6 +2430,7 @@ export class ClineProvider implements vscode.WebviewViewProvider {
 			autoApprovalEnabled: autoApprovalEnabled ?? false,
 			customModes,
 			maxOpenTabsContext: maxOpenTabsContext ?? 20,
+			openRouterUseMiddleOutTransform: openRouterUseMiddleOutTransform ?? true,
 		}
 	}
 
diff --git a/webview-ui/src/components/settings/ApiOptions.tsx b/webview-ui/src/components/settings/ApiOptions.tsx
index 6f0dba9f00..4b1707afa6 100644
--- a/webview-ui/src/components/settings/ApiOptions.tsx
+++ b/webview-ui/src/components/settings/ApiOptions.tsx
@@ -498,7 +498,7 @@ const ApiOptions = ({
 								/>
 							)}
 							<Checkbox
-								checked={apiConfiguration?.openRouterUseMiddleOutTransform || false}
+								checked={apiConfiguration?.openRouterUseMiddleOutTransform ?? true}
 								onChange={handleInputChange("openRouterUseMiddleOutTransform", noTransform)}>
 								Compress prompts and message chains to the context size (
 								<a href="https://openrouter.ai/docs/transforms">OpenRouter Transforms</a>)