diff --git a/.travis.yml b/.travis.yml
index f26a8ad..82b8379 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,5 +1,12 @@
 language: Rust
 cache: cargo
 sudo: false
+
 rust:
-- nightly
+  - stable
+  - nightly
+env:
+  - FEATURES=""
+  - FEATURES="proposed"
+
+script: cargo build --verbose; cargo test --verbose --features ${FEATURES:-""}
diff --git a/Cargo.toml b/Cargo.toml
index 9f0b58e..3a1c26d 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -24,3 +24,8 @@ serde_json = "1.0.0"
 url = "1.1.0"
 url_serde = "0.2.0"
 
+[features]
+default = []
+# Enables proposed LSP extensions.
+# NOTE: No semver compatibility is guaranteed for types enabled by this feature.
+proposed = []
diff --git a/src/lib.rs b/src/lib.rs
index 3fbbd0e..ffb749f 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1360,6 +1360,19 @@ pub struct TextDocumentClientCapabilities {
     pub folding_range: Option<FoldingRangeCapability>,
 }
 
+/**
+ * Window specific client capabilities.
+ */
+#[derive(Debug, PartialEq, Default, Deserialize, Serialize)]
+#[serde(rename_all = "camelCase")]
+pub struct WindowClientCapabilities {
+    /**
+     * Whether `window/progress` server notifications are supported.
+     */
+    #[cfg(feature = "proposed")]
+    pub progress: Option<bool>,
+}
+
 /**
  * Where ClientCapabilities are currently empty:
  */
@@ -1378,6 +1391,12 @@ pub struct ClientCapabilities {
     #[serde(skip_serializing_if = "Option::is_none")]
     pub text_document: Option<TextDocumentClientCapabilities>,
 
+    /**
+     * Window specific client capabilities.
+     */
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub window: Option<WindowClientCapabilities>,
+
     /**
      * Experimental client capabilities.
      */
@@ -3350,6 +3369,35 @@ pub struct MarkupContent {
     pub value: String,
 }
 
+#[cfg(feature = "proposed")]
+/// The progress notification is sent from the server to the client to ask
+/// the client to indicate progress.
+#[derive(Debug, PartialEq, Deserialize, Serialize, Clone)]
+pub struct ProgressParams {
+    /// A unique identifier to associate multiple progress notifications
+    /// with the same progress.
+    pub id: String,
+
+    /// Mandatory title of the progress operation. Used to briefly inform
+    /// about the kind of operation being performed.
+    /// Examples: "Indexing" or "Linking dependencies".
+    pub title: String,
+
+    /// Optional, more detailed associated progress message. Contains
+    /// complementary information to the `title`.
+    /// Examples: "3/25 files", "project/src/module2", "node_modules/some_dep".
+    /// If unset, the previous progress message (if any) is still valid.
+    pub message: Option<String>,
+
+    /// Optional progress percentage to display (value 100 is considered 100%).
+    /// If unset, the previous progress percentage (if any) is still valid.
+    pub percentage: Option<f64>,
+
+    /// Set to true on the final progress update.
+    /// No more progress notifications with the same ID should be sent.
+    pub done: Option<bool>,
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
diff --git a/src/notification.rs b/src/notification.rs
index 67d2722..c2f2ea7 100644
--- a/src/notification.rs
+++ b/src/notification.rs
@@ -59,6 +59,11 @@ macro_rules! lsp_notification {
     ("workspace/didChangeWorkspaceFolders") => {
         $crate::notification::DidChangeWorkspaceFolders
     };
+
+    // Requires #[cfg(feature = "proposed")]
+    ("window/progress") => {
+        $crate::notification::Progress
+    };
 }
 
 /// The base protocol now offers support for request cancellation. To cancel a request,
@@ -252,6 +257,18 @@ impl Notification for PublishDiagnostics {
     const METHOD: &'static str = "textDocument/publishDiagnostics";
 }
 
+#[cfg(feature = "proposed")]
+/// The progress notification is sent from the server to the client to ask
+/// the client to indicate progress.
+#[derive(Debug)]
+pub enum Progress {}
+
+#[cfg(feature = "proposed")]
+impl Notification for Progress {
+    type Params = ProgressParams;
+    const METHOD: &'static str = "window/progress";
+}
+
 #[cfg(test)]
 mod test {
     use super::*;
@@ -290,5 +307,8 @@ mod test {
         check_macro!("workspace/didChangeConfiguration");
         check_macro!("workspace/didChangeWatchedFiles");
         check_macro!("workspace/didChangeWorkspaceFolders");
+
+        #[cfg(feature = "proposed")]
+        check_macro!("window/progress");
     }
 }