diff --git a/packages/opencode/src/cli/cmd/tui/routes/session/index.tsx b/packages/opencode/src/cli/cmd/tui/routes/session/index.tsx
index e1423e22c22..543c784ed46 100644
--- a/packages/opencode/src/cli/cmd/tui/routes/session/index.tsx
+++ b/packages/opencode/src/cli/cmd/tui/routes/session/index.tsx
@@ -149,7 +149,11 @@ export function Session() {
     if (sidebar() === "auto" && wide()) return true
     return false
   })
-  const contentWidth = createMemo(() => dimensions().width - (sidebarVisible() ? 42 : 0) - 4)
+  const sidebarOverlay = createMemo(() => {
+    if (sync.data.config.tui?.sidebar_overlay === false) return false
+    return sidebarVisible() && !wide()
+  })
+  const contentWidth = createMemo(() => dimensions().width - (sidebarVisible() && !sidebarOverlay() ? 42 : 0) - 4)
 
   const scrollAcceleration = createMemo(() => {
     const tui = sync.data.config.tui
diff --git a/packages/opencode/src/config/config.ts b/packages/opencode/src/config/config.ts
index 6f04ecc6854..64e2fe79eb2 100644
--- a/packages/opencode/src/config/config.ts
+++ b/packages/opencode/src/config/config.ts
@@ -715,6 +715,12 @@ export namespace Config {
       .enum(["auto", "stacked"])
       .optional()
       .describe("Control diff rendering style: 'auto' adapts to terminal width, 'stacked' always shows single column"),
+    sidebar_overlay: z
+      .boolean()
+      .optional()
+      .describe(
+        "Enable sidebar overlay mode on narrow screens (default: true). Set to false to always show sidebar side-by-side with content",
+      ),
   })
 
   export const Server = z
diff --git a/packages/sdk/js/src/v2/gen/types.gen.ts b/packages/sdk/js/src/v2/gen/types.gen.ts
index 97a695162ed..eaa5be24c20 100644
--- a/packages/sdk/js/src/v2/gen/types.gen.ts
+++ b/packages/sdk/js/src/v2/gen/types.gen.ts
@@ -1492,6 +1492,10 @@ export type Config = {
      * Control diff rendering style: 'auto' adapts to terminal width, 'stacked' always shows single column
      */
     diff_style?: "auto" | "stacked"
+    /**
+     * Enable sidebar overlay mode on narrow screens (default: true). Set to false to always show sidebar side-by-side with content
+     */
+    sidebar_overlay?: boolean
   }
   server?: ServerConfig
   /**
diff --git a/packages/sdk/openapi.json b/packages/sdk/openapi.json
index f697f6e3f3e..7ba96f6ad0e 100644
--- a/packages/sdk/openapi.json
+++ b/packages/sdk/openapi.json
@@ -8778,6 +8778,10 @@
                 "description": "Control diff rendering style: 'auto' adapts to terminal width, 'stacked' always shows single column",
                 "type": "string",
                 "enum": ["auto", "stacked"]
+              },
+              "sidebar_overlay": {
+                "description": "Enable sidebar overlay mode on narrow screens (default: true). Set to false to always show sidebar side-by-side with content",
+                "type": "boolean"
               }
             }
           },