diff --git a/src/core_plugins/kibana/index.js b/src/core_plugins/kibana/index.js
index 82859b388967..9c8ed813cd84 100644
--- a/src/core_plugins/kibana/index.js
+++ b/src/core_plugins/kibana/index.js
@@ -29,13 +29,14 @@ import { homeApi } from './server/routes/api/home';
 import { managementApi } from './server/routes/api/management';
 import { scriptsApi } from './server/routes/api/scripts';
 import { registerSuggestionsApi } from './server/routes/api/suggestions';
+import { registerKqlTelemetryApi } from './server/routes/api/kql_telemetry';
 import { registerFieldFormats } from './server/field_formats/register';
 import { registerTutorials } from './server/tutorials/register';
 import * as systemApi from './server/lib/system_api';
 import handleEsError from './server/lib/handle_es_error';
 import mappings from './mappings.json';
 import { getUiSettingDefaults } from './ui_setting_defaults';
-
+import { makeKQLUsageCollector } from './server/lib/kql_usage_collector';
 import { injectVars } from './inject_vars';
 
 const mkdirp = Promise.promisify(mkdirpNode);
@@ -119,6 +120,12 @@ export default function (kibana) {
         },
       ],
 
+      savedObjectSchemas: {
+        'kql-telemetry': {
+          isNamespaceAgnostic: true,
+        },
+      },
+
       injectDefaultVars(server, options) {
         return {
           kbnIndex: options.index,
@@ -156,8 +163,10 @@ export default function (kibana) {
       homeApi(server);
       managementApi(server);
       registerSuggestionsApi(server);
+      registerKqlTelemetryApi(server);
       registerFieldFormats(server);
       registerTutorials(server);
+      makeKQLUsageCollector(server);
       server.expose('systemApi', systemApi);
       server.expose('handleEsError', handleEsError);
       server.injectUiAppVars('kibana', () => injectVars(server));
diff --git a/src/core_plugins/kibana/mappings.json b/src/core_plugins/kibana/mappings.json
index 471cee57da56..2ccdd5cd8a36 100644
--- a/src/core_plugins/kibana/mappings.json
+++ b/src/core_plugins/kibana/mappings.json
@@ -167,5 +167,15 @@
         "type": "keyword"
       }
     }
+  },
+  "kql-telemetry": {
+    "properties": {
+      "optInCount": {
+        "type": "long"
+      },
+      "optOutCount": {
+        "type": "long"
+      }
+    }
   }
 }
diff --git a/src/core_plugins/kibana/server/lib/kql_usage_collector/fetch.js b/src/core_plugins/kibana/server/lib/kql_usage_collector/fetch.js
new file mode 100644
index 000000000000..20008fdb47c4
--- /dev/null
+++ b/src/core_plugins/kibana/server/lib/kql_usage_collector/fetch.js
@@ -0,0 +1,70 @@
+/*
+ * Licensed to Elasticsearch B.V. under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch B.V. licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+import { getUiSettingDefaults } from '../../../ui_setting_defaults';
+import { get } from 'lodash';
+
+const uiSettingDefaults = getUiSettingDefaults();
+const defaultSearchQueryLanguageSetting = uiSettingDefaults['search:queryLanguage'].value;
+
+export async function fetch(callCluster) {
+  const [response, config] = await Promise.all([
+    callCluster('get', {
+      index: '.kibana',
+      type: 'doc',
+      id: 'kql-telemetry:kql-telemetry',
+      ignore: [404],
+    }),
+    callCluster('search', {
+      index: '.kibana',
+      body: { query: { term: { type: 'config' } } },
+      ignore: [404],
+    }),
+  ]);
+
+  const queryLanguageConfigValue = get(config, 'hits.hits[0]._source.config.search:queryLanguage');
+
+  // search:queryLanguage can potentially be in four states in the .kibana index:
+  // 1. undefined: this means the user has never touched this setting
+  // 2. null: this means the user has touched the setting, but the current value matches the default
+  // 3. 'kuery' or 'lucene': this means the user has explicitly selected the given non-default language
+  //
+  // It's nice to know if the user has never touched the setting or if they tried kuery then
+  // went back to the default, so I preserve this info by prefixing the language name with
+  // 'default-' when the value in .kibana is undefined (case #1).
+  let defaultLanguage;
+  if (queryLanguageConfigValue === undefined) {
+    defaultLanguage = `default-${defaultSearchQueryLanguageSetting}`;
+  } else if (queryLanguageConfigValue === null) {
+    defaultLanguage = defaultSearchQueryLanguageSetting;
+  } else {
+    defaultLanguage = queryLanguageConfigValue;
+  }
+
+  const kqlTelemetryDoc = {
+    optInCount: 0,
+    optOutCount: 0,
+    ...get(response, '_source.kql-telemetry', {}),
+  };
+
+  return {
+    ...kqlTelemetryDoc,
+    defaultQueryLanguage: defaultLanguage,
+  };
+}
diff --git a/src/core_plugins/kibana/server/lib/kql_usage_collector/fetch.test.js b/src/core_plugins/kibana/server/lib/kql_usage_collector/fetch.test.js
new file mode 100644
index 000000000000..17903dbbcb34
--- /dev/null
+++ b/src/core_plugins/kibana/server/lib/kql_usage_collector/fetch.test.js
@@ -0,0 +1,116 @@
+/*
+ * Licensed to Elasticsearch B.V. under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch B.V. licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+jest.mock('../../../ui_setting_defaults', () => ({
+  getUiSettingDefaults: () => ({ 'search:queryLanguage': { value: 'lucene' } }),
+}));
+
+import { fetch } from './fetch';
+
+let callCluster;
+
+function setupMockCallCluster(optCount, language) {
+  callCluster = jest.fn((method, params) => {
+    if ('id' in params && params.id === 'kql-telemetry:kql-telemetry') {
+      if (optCount === null) {
+        return Promise.resolve({
+          _index: '.kibana_1',
+          _type: 'doc',
+          _id: 'kql-telemetry:kql-telemetry',
+          found: false,
+        });
+      } else {
+        return Promise.resolve({
+          _source: {
+            'kql-telemetry': {
+              ...optCount,
+            },
+            type: 'kql-telemetry',
+            updated_at: '2018-10-05T20:20:56.258Z',
+          },
+        });
+      }
+    } else if ('body' in params && params.body.query.term.type === 'config') {
+      if (language === 'missingConfigDoc') {
+        Promise.resolve({
+          hits: {
+            hits: [],
+          },
+        });
+      } else {
+        return Promise.resolve({
+          hits: {
+            hits: [
+              {
+                _source: {
+                  config: {
+                    'search:queryLanguage': language,
+                  },
+                },
+              },
+            ],
+          },
+        });
+      }
+    }
+  });
+}
+
+describe('makeKQLUsageCollector', () => {
+  describe('fetch method', () => {
+    it('should return opt in data from the .kibana/kql-telemetry doc', async () => {
+      setupMockCallCluster({ optInCount: 1 }, 'kuery');
+      const fetchResponse = await fetch(callCluster);
+      expect(fetchResponse.optInCount).toBe(1);
+      expect(fetchResponse.optOutCount).toBe(0);
+    });
+
+    it('should return the default query language set in advanced settings', async () => {
+      setupMockCallCluster({ optInCount: 1 }, 'kuery');
+      const fetchResponse = await fetch(callCluster);
+      expect(fetchResponse.defaultQueryLanguage).toBe('kuery');
+    });
+
+    // Indicates the user has modified the setting at some point but the value is currently the default
+    it('should return the kibana default query language if the config value is null', async () => {
+      setupMockCallCluster({ optInCount: 1 }, null);
+      const fetchResponse = await fetch(callCluster);
+      expect(fetchResponse.defaultQueryLanguage).toBe('lucene');
+    });
+
+    it('should indicate when the default language has never been modified by the user', async () => {
+      setupMockCallCluster({ optInCount: 1 }, undefined);
+      const fetchResponse = await fetch(callCluster);
+      expect(fetchResponse.defaultQueryLanguage).toBe('default-lucene');
+    });
+
+    it('should default to 0 opt in counts if the .kibana/kql-telemetry doc does not exist', async () => {
+      setupMockCallCluster(null, 'kuery');
+      const fetchResponse = await fetch(callCluster);
+      expect(fetchResponse.optInCount).toBe(0);
+      expect(fetchResponse.optOutCount).toBe(0);
+    });
+
+    it('should default to the kibana default language if the config document does not exist', async () => {
+      setupMockCallCluster(null, 'missingConfigDoc');
+      const fetchResponse = await fetch(callCluster);
+      expect(fetchResponse.defaultQueryLanguage).toBe('default-lucene');
+    });
+  });
+});
diff --git a/src/core_plugins/kibana/server/lib/kql_usage_collector/index.js b/src/core_plugins/kibana/server/lib/kql_usage_collector/index.js
new file mode 100644
index 000000000000..ea2979834be3
--- /dev/null
+++ b/src/core_plugins/kibana/server/lib/kql_usage_collector/index.js
@@ -0,0 +1,20 @@
+/*
+ * Licensed to Elasticsearch B.V. under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch B.V. licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+export { makeKQLUsageCollector } from './make_kql_usage_collector';
diff --git a/src/core_plugins/kibana/server/lib/kql_usage_collector/make_kql_usage_collector.js b/src/core_plugins/kibana/server/lib/kql_usage_collector/make_kql_usage_collector.js
new file mode 100644
index 000000000000..3ceff0fee504
--- /dev/null
+++ b/src/core_plugins/kibana/server/lib/kql_usage_collector/make_kql_usage_collector.js
@@ -0,0 +1,29 @@
+/*
+ * Licensed to Elasticsearch B.V. under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch B.V. licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+import { fetch } from './fetch';
+
+export function makeKQLUsageCollector(server) {
+  const kqlUsageCollector = server.usage.collectorSet.makeUsageCollector({
+    type: 'kql',
+    fetch,
+  });
+
+  server.usage.collectorSet.register(kqlUsageCollector);
+}
diff --git a/src/core_plugins/kibana/server/lib/kql_usage_collector/make_kql_usage_collector.test.js b/src/core_plugins/kibana/server/lib/kql_usage_collector/make_kql_usage_collector.test.js
new file mode 100644
index 000000000000..7fd19fbcccc6
--- /dev/null
+++ b/src/core_plugins/kibana/server/lib/kql_usage_collector/make_kql_usage_collector.test.js
@@ -0,0 +1,48 @@
+/*
+ * Licensed to Elasticsearch B.V. under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch B.V. licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+import { makeKQLUsageCollector } from './make_kql_usage_collector';
+
+describe('makeKQLUsageCollector', () => {
+
+  let server;
+  let makeUsageCollectorStub;
+  let registerStub;
+
+  beforeEach(() => {
+    makeUsageCollectorStub = jest.fn();
+    registerStub = jest.fn();
+    server = {
+      usage: {
+        collectorSet: { makeUsageCollector: makeUsageCollectorStub, register: registerStub },
+      },
+    };
+  });
+
+  it('should call collectorSet.register', () => {
+    makeKQLUsageCollector(server);
+    expect(registerStub).toHaveBeenCalledTimes(1);
+  });
+
+  it('should call makeUsageCollector with type = kql', () => {
+    makeKQLUsageCollector(server);
+    expect(makeUsageCollectorStub).toHaveBeenCalledTimes(1);
+    expect(makeUsageCollectorStub.mock.calls[0][0].type).toBe('kql');
+  });
+});
diff --git a/src/core_plugins/kibana/server/routes/api/kql_telemetry/index.js b/src/core_plugins/kibana/server/routes/api/kql_telemetry/index.js
new file mode 100644
index 000000000000..028f3062be9e
--- /dev/null
+++ b/src/core_plugins/kibana/server/routes/api/kql_telemetry/index.js
@@ -0,0 +1,60 @@
+/*
+ * Licensed to Elasticsearch B.V. under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch B.V. licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+import Joi from 'joi';
+import Boom from 'boom';
+
+export function registerKqlTelemetryApi(server) {
+  server.route({
+    path: '/api/kibana/kql_opt_in_telemetry',
+    method: 'POST',
+    config: {
+      validate: {
+        payload: {
+          opt_in: Joi.bool().required(),
+        },
+      },
+      tags: ['api'],
+    },
+    handler: async function (request, reply) {
+      const { savedObjects: { getSavedObjectsRepository } } = server;
+      const { callWithInternalUser } = server.plugins.elasticsearch.getCluster('admin');
+      const internalRepository = getSavedObjectsRepository(callWithInternalUser);
+
+      const {
+        payload: { opt_in: optIn },
+      } = request;
+
+      const counterName = optIn ? 'optInCount' : 'optOutCount';
+
+      try {
+        await internalRepository.incrementCounter(
+          'kql-telemetry',
+          'kql-telemetry',
+          counterName,
+        );
+      }
+      catch (error) {
+        reply(new Boom('Something went wrong', { statusCode: error.status, data: { success: false } }));
+      }
+
+      reply({ success: true });
+    },
+  });
+}
diff --git a/src/server/saved_objects/service/lib/repository.js b/src/server/saved_objects/service/lib/repository.js
index b01b893fc93b..992386ac4c8c 100644
--- a/src/server/saved_objects/service/lib/repository.js
+++ b/src/server/saved_objects/service/lib/repository.js
@@ -500,6 +500,82 @@ export class SavedObjectsRepository {
     };
   }
 
+  /**
+   * Increases a counter field by one. Creates the document if one doesn't exist for the given id.
+   *
+   * @param {string} type
+   * @param {string} id
+   * @param {string} counterFieldName
+   * @param {object} [options={}]
+   * @property {object} [options.migrationVersion=undefined]
+   * @returns {promise}
+   */
+  async incrementCounter(type, id, counterFieldName, options = {}) {
+    if (typeof type !== 'string') {
+      throw new Error('"type" argument must be a string');
+    }
+    if (typeof counterFieldName !== 'string') {
+      throw new Error('"counterFieldName" argument must be a string');
+    }
+
+    const {
+      migrationVersion,
+      namespace,
+    } = options;
+
+    const time = this._getCurrentTime();
+
+
+    const migrated = this._migrator.migrateDocument({
+      id,
+      type,
+      attributes: { [counterFieldName]: 1 },
+      migrationVersion,
+      updated_at: time,
+    });
+
+    const raw = this._serializer.savedObjectToRaw(migrated);
+
+    const response = await this._writeToCluster('update', {
+      id: this._serializer.generateRawId(namespace, type, id),
+      type: this._type,
+      index: this._index,
+      refresh: 'wait_for',
+      _source: true,
+      body: {
+        script: {
+          source: `
+              if (ctx._source[params.type][params.counterFieldName] == null) {
+                ctx._source[params.type][params.counterFieldName] = params.count;
+              }
+              else {
+                ctx._source[params.type][params.counterFieldName] += params.count;
+              }
+              ctx._source.updated_at = params.time;
+            `,
+          lang: 'painless',
+          params: {
+            count: 1,
+            time,
+            type,
+            counterFieldName,
+          },
+        },
+        upsert: raw._source,
+      },
+    });
+
+    return {
+      id,
+      type,
+      updated_at: time,
+      version: response._version,
+      attributes: response.get._source[type],
+    };
+
+
+  }
+
   async _writeToCluster(method, params) {
     try {
       await this._onBeforeWrite();
diff --git a/src/server/saved_objects/service/lib/repository.test.js b/src/server/saved_objects/service/lib/repository.test.js
index c0dbcc964d58..af5050ccc031 100644
--- a/src/server/saved_objects/service/lib/repository.test.js
+++ b/src/server/saved_objects/service/lib/repository.test.js
@@ -1252,6 +1252,219 @@ describe('SavedObjectsRepository', () => {
     });
   });
 
+  describe('#incrementCounter', () => {
+    beforeEach(() => {
+      callAdminCluster.callsFake((method, params) => ({
+        _type: 'doc',
+        _id: params.id,
+        _version: 2,
+        _index: '.kibana',
+        get: {
+          found: true,
+          _source: {
+            type: 'config',
+            ...mockTimestampFields,
+            config: {
+              buildNum: 8468,
+              defaultIndex: 'logstash-*',
+            },
+          },
+        },
+      }));
+    });
+
+    it('formats Elasticsearch response', async () => {
+      callAdminCluster.callsFake((method, params) => ({
+        _type: 'doc',
+        _id: params.id,
+        _version: 2,
+        _index: '.kibana',
+        get: {
+          found: true,
+          _source: {
+            type: 'config',
+            ...mockTimestampFields,
+            config: {
+              buildNum: 8468,
+              defaultIndex: 'logstash-*',
+            },
+          },
+        },
+      }));
+
+
+      const response = await savedObjectsRepository.incrementCounter(
+        'config',
+        '6.0.0-alpha1',
+        'buildNum',
+        {
+          namespace: 'foo-namespace',
+        }
+      );
+
+      expect(response).toEqual({
+        type: 'config',
+        id: '6.0.0-alpha1',
+        ...mockTimestampFields,
+        version: 2,
+        attributes: {
+          buildNum: 8468,
+          defaultIndex: 'logstash-*'
+        }
+      });
+    });
+
+    it('migrates the doc if an upsert is required', async () => {
+      migrator.migrateDocument = (doc) => {
+        doc.attributes.buildNum = 42;
+        doc.migrationVersion = { foo: '2.3.4' };
+        return doc;
+      };
+
+      await savedObjectsRepository.incrementCounter(
+        'config',
+        'doesnotexist',
+        'buildNum',
+        {
+          namespace: 'foo-namespace',
+        }
+      );
+
+      sinon.assert.calledOnce(callAdminCluster);
+      expect(callAdminCluster.firstCall.args[1]).toMatchObject({
+        body: {
+          upsert: {
+            config: { buildNum: 42 },
+            migrationVersion: { foo: '2.3.4' },
+            type: 'config',
+            ...mockTimestampFields
+          }
+        },
+      });
+    });
+
+    it(`prepends namespace to the id but doesn't add namespace to body when providing namespace for namespaced type`, async () => {
+      await savedObjectsRepository.incrementCounter('config', '6.0.0-alpha1', 'buildNum', {
+        namespace: 'foo-namespace',
+      });
+
+      sinon.assert.calledOnce(callAdminCluster);
+
+      const requestDoc = callAdminCluster.firstCall.args[1];
+      expect(requestDoc.id).toBe('foo-namespace:config:6.0.0-alpha1');
+      expect(requestDoc.body.script.params.type).toBe('config');
+      expect(requestDoc.body.upsert.type).toBe('config');
+      expect(requestDoc).toHaveProperty('body.upsert.config');
+
+      sinon.assert.calledOnce(onBeforeWrite);
+    });
+
+    it(`doesn't prepend namespace to the id or add namespace property when providing no namespace for namespaced type`, async () => {
+      await savedObjectsRepository.incrementCounter('config', '6.0.0-alpha1', 'buildNum');
+
+      sinon.assert.calledOnce(callAdminCluster);
+
+      const requestDoc = callAdminCluster.firstCall.args[1];
+      expect(requestDoc.id).toBe('config:6.0.0-alpha1');
+      expect(requestDoc.body.script.params.type).toBe('config');
+      expect(requestDoc.body.upsert.type).toBe('config');
+      expect(requestDoc).toHaveProperty('body.upsert.config');
+
+      sinon.assert.calledOnce(onBeforeWrite);
+    });
+
+    it(`doesn't prepend namespace to the id or add namespace property when providing namespace for namespace agnostic type`, async () => {
+      callAdminCluster.callsFake((method, params) => ({
+        _type: 'doc',
+        _id: params.id,
+        _version: 2,
+        _index: '.kibana',
+        get: {
+          found: true,
+          _source: {
+            type: 'globaltype',
+            ...mockTimestampFields,
+            globaltype: {
+              counter: 1,
+            },
+          },
+        },
+      }));
+
+      await savedObjectsRepository.incrementCounter('globaltype', 'foo', 'counter', {
+        namespace: 'foo-namespace',
+      });
+
+      sinon.assert.calledOnce(callAdminCluster);
+
+      const requestDoc = callAdminCluster.firstCall.args[1];
+      expect(requestDoc.id).toBe('globaltype:foo');
+      expect(requestDoc.body.script.params.type).toBe('globaltype');
+      expect(requestDoc.body.upsert.type).toBe('globaltype');
+      expect(requestDoc).toHaveProperty('body.upsert.globaltype');
+
+      sinon.assert.calledOnce(onBeforeWrite);
+    });
+
+    it('should assert that the "type" and "counterFieldName" arguments are strings', () => {
+      expect.assertions(6);
+
+      expect(savedObjectsRepository.incrementCounter(
+        null,
+        '6.0.0-alpha1',
+        'buildNum',
+        {
+          namespace: 'foo-namespace',
+        }),
+      ).rejects.toEqual(new Error('"type" argument must be a string'));
+
+      expect(savedObjectsRepository.incrementCounter(
+        42,
+        '6.0.0-alpha1',
+        'buildNum',
+        {
+          namespace: 'foo-namespace',
+        }),
+      ).rejects.toEqual(new Error('"type" argument must be a string'));
+
+      expect(savedObjectsRepository.incrementCounter(
+        {},
+        '6.0.0-alpha1',
+        'buildNum',
+        {
+          namespace: 'foo-namespace',
+        }),
+      ).rejects.toEqual(new Error('"type" argument must be a string'));
+
+      expect(savedObjectsRepository.incrementCounter(
+        'config',
+        '6.0.0-alpha1',
+        null,
+        {
+          namespace: 'foo-namespace',
+        }),
+      ).rejects.toEqual(new Error('"counterFieldName" argument must be a string'));
+
+      expect(savedObjectsRepository.incrementCounter(
+        'config',
+        '6.0.0-alpha1',
+        42,
+        {
+          namespace: 'foo-namespace',
+        }),
+      ).rejects.toEqual(new Error('"counterFieldName" argument must be a string'));
+
+      expect(savedObjectsRepository.incrementCounter(
+        'config',
+        '6.0.0-alpha1',
+        {},
+        {
+          namespace: 'foo-namespace',
+        }),
+      ).rejects.toEqual(new Error('"counterFieldName" argument must be a string'));
+    });
+  });
+
   describe('onBeforeWrite', () => {
     it('blocks calls to callCluster of requests', async () => {
       onBeforeWrite.returns(delay(500));
diff --git a/src/ui/public/query_bar/directive/query_popover.js b/src/ui/public/query_bar/directive/query_popover.js
index 6c8cdd69ad57..14be6f41b3c1 100644
--- a/src/ui/public/query_bar/directive/query_popover.js
+++ b/src/ui/public/query_bar/directive/query_popover.js
@@ -21,6 +21,7 @@ import React from 'react';
 import ReactDOM from 'react-dom';
 import { uiModules } from '../../modules';
 import { documentationLinks } from '../../documentation_links/documentation_links';
+import { kfetch } from 'ui/kfetch';
 import {
   EuiPopover,
   EuiButtonEmpty,
@@ -62,8 +63,18 @@ module.directive('queryPopover', function (localStorage) {
       }
 
       function onSwitchChange() {
+        const newLanguage = $scope.language === 'lucene' ? 'kuery' : 'lucene';
+
+        // Send telemetry info every time the user opts in or out of kuery
+        // As a result it is important this function only ever gets called in the
+        // UI component's change handler.
+        kfetch({
+          pathname: '/api/kibana/kql_opt_in_telemetry',
+          method: 'POST',
+          body: JSON.stringify({ opt_in: newLanguage === 'kuery' }),
+        });
+
         $scope.$evalAsync(() => {
-          const newLanguage = $scope.language === 'lucene' ? 'kuery' : 'lucene';
           localStorage.set('kibana.userQueryLanguage', newLanguage);
           $scope.onSelectLanguage({ $language: newLanguage });
         });
diff --git a/test/api_integration/apis/index.js b/test/api_integration/apis/index.js
index 4ec28eca427b..d43199da7a93 100644
--- a/test/api_integration/apis/index.js
+++ b/test/api_integration/apis/index.js
@@ -23,6 +23,7 @@ export default function ({ loadTestFile }) {
     loadTestFile(require.resolve('./general'));
     loadTestFile(require.resolve('./home'));
     loadTestFile(require.resolve('./index_patterns'));
+    loadTestFile(require.resolve('./kql_telemetry'));
     loadTestFile(require.resolve('./management'));
     loadTestFile(require.resolve('./saved_objects'));
     loadTestFile(require.resolve('./scripts'));
diff --git a/test/api_integration/apis/kql_telemetry/index.js b/test/api_integration/apis/kql_telemetry/index.js
new file mode 100644
index 000000000000..bf72fa90ac00
--- /dev/null
+++ b/test/api_integration/apis/kql_telemetry/index.js
@@ -0,0 +1,24 @@
+/*
+ * Licensed to Elasticsearch B.V. under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch B.V. licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+export default function ({ loadTestFile }) {
+  describe('KQL', () => {
+    loadTestFile(require.resolve('./kql_telemetry'));
+  });
+}
diff --git a/test/api_integration/apis/kql_telemetry/kql_telemetry.js b/test/api_integration/apis/kql_telemetry/kql_telemetry.js
new file mode 100644
index 000000000000..6ed48434064e
--- /dev/null
+++ b/test/api_integration/apis/kql_telemetry/kql_telemetry.js
@@ -0,0 +1,124 @@
+/*
+ * Licensed to Elasticsearch B.V. under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch B.V. licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+import expect from 'expect.js';
+import Promise from 'bluebird';
+import { get } from 'lodash';
+
+export default function ({ getService }) {
+  const supertest = getService('supertest');
+  const esArchiver = getService('esArchiver');
+  const es = getService('es');
+
+  describe('telemetry API', () => {
+    before(() => esArchiver.load('saved_objects/basic'));
+    after(() => esArchiver.unload('saved_objects/basic'));
+
+    it('should increment the opt *in* counter in the .kibana/kql-telemetry document', async () => {
+      await supertest
+        .post('/api/kibana/kql_opt_in_telemetry')
+        .set('content-type', 'application/json')
+        .send({ opt_in: true })
+        .expect(200);
+
+      return es.search({
+        index: '.kibana',
+        q: 'type:kql-telemetry',
+      }).then(response => {
+        const kqlTelemetryDoc = get(response, 'hits.hits[0]._source.kql-telemetry');
+        expect(kqlTelemetryDoc.optInCount).to.be(1);
+      });
+    });
+
+    it('should increment the opt *out* counter in the .kibana/kql-telemetry document', async () => {
+      await supertest
+        .post('/api/kibana/kql_opt_in_telemetry')
+        .set('content-type', 'application/json')
+        .send({ opt_in: false })
+        .expect(200);
+
+      return es.search({
+        index: '.kibana',
+        q: 'type:kql-telemetry',
+      }).then(response => {
+        const kqlTelemetryDoc = get(response, 'hits.hits[0]._source.kql-telemetry');
+        expect(kqlTelemetryDoc.optOutCount).to.be(1);
+      });
+
+    });
+
+
+    it('should report success when opt *in* is incremented successfully', () => {
+      return supertest
+        .post('/api/kibana/kql_opt_in_telemetry')
+        .set('content-type', 'application/json')
+        .send({ opt_in: true })
+        .expect('Content-Type', /json/)
+        .expect(200)
+        .then(({ body }) => {
+          expect(body.success).to.be(true);
+        });
+    });
+
+    it('should report success when opt *out* is incremented successfully', () => {
+      return supertest
+        .post('/api/kibana/kql_opt_in_telemetry')
+        .set('content-type', 'application/json')
+        .send({ opt_in: false })
+        .expect('Content-Type', /json/)
+        .expect(200)
+        .then(({ body }) => {
+          expect(body.success).to.be(true);
+        });
+    });
+
+    it('should only accept literal boolean values for the opt_in POST body param', function () {
+      return Promise.all([
+        supertest
+          .post('/api/kibana/kql_opt_in_telemetry')
+          .set('content-type', 'application/json')
+          .send({ opt_in: 'notabool' })
+          .expect(400),
+        supertest
+          .post('/api/kibana/kql_opt_in_telemetry')
+          .set('content-type', 'application/json')
+          .send({ opt_in: 0 })
+          .expect(400),
+        supertest
+          .post('/api/kibana/kql_opt_in_telemetry')
+          .set('content-type', 'application/json')
+          .send({ opt_in: null })
+          .expect(400),
+        supertest
+          .post('/api/kibana/kql_opt_in_telemetry')
+          .set('content-type', 'application/json')
+          .send({ opt_in: undefined })
+          .expect(400),
+        supertest
+          .post('/api/kibana/kql_opt_in_telemetry')
+          .set('content-type', 'application/json')
+          .send({})
+          .expect(400),
+      ]);
+    });
+
+  });
+
+}
+
diff --git a/x-pack/test/api_integration/apis/kibana/index.js b/x-pack/test/api_integration/apis/kibana/index.js
index d84ac9c75154..be0eb513c515 100644
--- a/x-pack/test/api_integration/apis/kibana/index.js
+++ b/x-pack/test/api_integration/apis/kibana/index.js
@@ -7,5 +7,6 @@
 export default function ({ loadTestFile }) {
   describe('kibana', () => {
     loadTestFile(require.resolve('./stats'));
+    loadTestFile(require.resolve('./kql_telemetry'));
   });
 }
diff --git a/x-pack/test/api_integration/apis/kibana/kql_telemetry/index.js b/x-pack/test/api_integration/apis/kibana/kql_telemetry/index.js
new file mode 100644
index 000000000000..e6735de40dfe
--- /dev/null
+++ b/x-pack/test/api_integration/apis/kibana/kql_telemetry/index.js
@@ -0,0 +1,11 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License;
+ * you may not use this file except in compliance with the Elastic License.
+ */
+
+export default function ({ loadTestFile }) {
+  describe('KQL', () => {
+    loadTestFile(require.resolve('./kql_telemetry'));
+  });
+}
diff --git a/x-pack/test/api_integration/apis/kibana/kql_telemetry/kql_telemetry.js b/x-pack/test/api_integration/apis/kibana/kql_telemetry/kql_telemetry.js
new file mode 100644
index 000000000000..ab47576cdc23
--- /dev/null
+++ b/x-pack/test/api_integration/apis/kibana/kql_telemetry/kql_telemetry.js
@@ -0,0 +1,45 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License;
+ * you may not use this file except in compliance with the Elastic License.
+ */
+
+import expect from 'expect.js';
+
+export default function ({ getService }) {
+  const supertestNoAuth = getService('supertestWithoutAuth');
+  const supertest = getService('supertest');
+  const esArchiver = getService('esArchiver');
+
+  describe('telemetry API', () => {
+    before(() => esArchiver.load('empty_kibana'));
+    after(() => esArchiver.unload('empty_kibana'));
+
+    describe('no auth', () => {
+      it('should return 401', async () => {
+        return supertestNoAuth
+          .post('/api/kibana/kql_opt_in_telemetry')
+          .set('content-type', 'application/json')
+          .set('kbn-xsrf', 'much access')
+          .send({ opt_in: true })
+          .expect(401);
+      });
+    });
+
+    describe('with auth', () => {
+      it('should return 200 for a successful request', async () => {
+        return supertest
+          .post('/api/kibana/kql_opt_in_telemetry')
+          .set('content-type', 'application/json')
+          .set('kbn-xsrf', 'such token, wow')
+          .send({ opt_in: true })
+          .expect('Content-Type', /json/)
+          .expect(200)
+          .then(({ body }) => {
+            expect(body.success).to.be(true);
+          });
+      });
+
+    });
+  });
+}