diff --git a/externs/olx.js b/externs/olx.js
index 819dc4127c..4f18e4eef9 100644
--- a/externs/olx.js
+++ b/externs/olx.js
@@ -5668,23 +5668,23 @@ olx.source.WMTSOptions.prototype.projection;
 /**
  * Request encoding. Default is `KVP`.
  * @type {ol.source.WMTSRequestEncoding|string|undefined}
- * @api
+ * @api stable
  */
 olx.source.WMTSOptions.prototype.requestEncoding;
 
 
 /**
- * Layer.
+ * Layer name as advertised in the WMTS capabilities.
  * @type {string}
- * @api
+ * @api stable
  */
 olx.source.WMTSOptions.prototype.layer;
 
 
 /**
- * Style.
+ * Style name as advertised in the WMTS capabilities.
  * @type {string}
- * @api
+ * @api stable
  */
 olx.source.WMTSOptions.prototype.style;
 
@@ -5713,7 +5713,7 @@ olx.source.WMTSOptions.prototype.tilePixelRatio;
 /**
  * WMTS version. Default is `1.0.0`.
  * @type {string|undefined}
- * @api
+ * @api stable
  */
 olx.source.WMTSOptions.prototype.version;
 
@@ -5721,7 +5721,7 @@ olx.source.WMTSOptions.prototype.version;
 /**
  * Image format. Default is `image/jpeg`.
  * @type {string|undefined}
- * @api
+ * @api stable
  */
 olx.source.WMTSOptions.prototype.format;
 
@@ -5729,23 +5729,25 @@ olx.source.WMTSOptions.prototype.format;
 /**
  * Matrix set.
  * @type {string}
- * @api
+ * @api stable
  */
 olx.source.WMTSOptions.prototype.matrixSet;
 
 
 /**
- * Dimensions.
+ * Additional "dimensions" for tile requests.  This is an object with properties
+ * named like the advertised WMTS dimensions.
  * @type {Object|undefined}
- * @api
+ * @api stable
  */
 olx.source.WMTSOptions.prototype.dimensions;
 
 
 /**
- * URL.
+ * A URL for the service.  For the RESTful request encoding, this is a URL
+ * template.  For KVP encoding, it is normal URL.
  * @type {string|undefined}
- * @api
+ * @api stable
  */
 olx.source.WMTSOptions.prototype.url;
 
@@ -5767,9 +5769,9 @@ olx.source.WMTSOptions.prototype.tileLoadFunction;
 
 
 /**
- * Urls.
+ * An array of URLs.  Requests will be distributed among the URLs in this array.
  * @type {Array.<string>|undefined}
- * @api
+ * @api stable
  */
 olx.source.WMTSOptions.prototype.urls;
 
diff --git a/src/ol/source/wmtssource.js b/src/ol/source/wmtssource.js
index f1bd00fc02..0028ee6100 100644
--- a/src/ol/source/wmtssource.js
+++ b/src/ol/source/wmtssource.js
@@ -34,7 +34,7 @@ ol.source.WMTSRequestEncoding = {
  * @constructor
  * @extends {ol.source.TileImage}
  * @param {olx.source.WMTSOptions} options WMTS options.
- * @api
+ * @api stable
  */
 ol.source.WMTS = function(options) {