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 b6916bc5a58..101f6628ee5 100644
--- a/packages/opencode/src/cli/cmd/tui/routes/session/index.tsx
+++ b/packages/opencode/src/cli/cmd/tui/routes/session/index.tsx
@@ -155,8 +155,12 @@ export function Session() {
     if (sidebar() === "auto" && wide()) return true
     return false
   })
+  const sidebarOverlay = createMemo(() => {
+    if (sync.data.config.tui?.sidebar_overlay === false) return false
+    return sidebarVisible() && !wide()
+  })
   const showTimestamps = createMemo(() => timestamps() === "show")
-  const contentWidth = createMemo(() => dimensions().width - (sidebarVisible() ? 42 : 0) - 4)
+  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 bf4a6035bd8..25c47271c6f 100644
--- a/packages/opencode/src/config/config.ts
+++ b/packages/opencode/src/config/config.ts
@@ -765,6 +765,12 @@ 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 acc29d9b43e..8e1e404a7ef 100644
--- a/packages/sdk/js/src/v2/gen/types.gen.ts
+++ b/packages/sdk/js/src/v2/gen/types.gen.ts
@@ -1568,6 +1568,10 @@ 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 a31f0d67ab2..5840aa19f37 100644
--- a/packages/sdk/openapi.json
+++ b/packages/sdk/openapi.json
@@ -9119,6 +9119,10 @@
                 "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"
               }
             }
           },