diff --git a/app/assets/javascripts/discourse/app/components/composer-editor-uppy.js b/app/assets/javascripts/discourse/app/components/composer-editor-uppy.js
deleted file mode 100644
index 1e230a37814..00000000000
--- a/app/assets/javascripts/discourse/app/components/composer-editor-uppy.js
+++ /dev/null
@@ -1,14 +0,0 @@
-import ComposerEditor from "discourse/components/composer-editor";
-import { alias } from "@ember/object/computed";
-import ComposerUploadUppy from "discourse/mixins/composer-upload-uppy";
-
-export default ComposerEditor.extend(ComposerUploadUppy, {
-  layoutName: "components/composer-editor",
-  fileUploadElementId: "file-uploader",
-  eventPrefix: "composer",
-  uploadType: "composer",
-  uppyId: "composer-editor-uppy",
-  composerModel: alias("composer"),
-  composerModelContentKey: "reply",
-  editorInputClass: ".d-editor-input",
-});
diff --git a/app/assets/javascripts/discourse/app/components/composer-editor.js b/app/assets/javascripts/discourse/app/components/composer-editor.js
index a5287c8eef4..80b94812074 100644
--- a/app/assets/javascripts/discourse/app/components/composer-editor.js
+++ b/app/assets/javascripts/discourse/app/components/composer-editor.js
@@ -3,6 +3,7 @@ import {
   authorizesAllExtensions,
   authorizesOneOrMoreImageExtensions,
 } from "discourse/lib/uploads";
+import { alias } from "@ember/object/computed";
 import { BasePlugin } from "@uppy/core";
 import { resolveAllShortUrls } from "pretty-text/upload-short-url";
 import {
@@ -27,7 +28,7 @@ import {
 import { later, next, schedule, throttle } from "@ember/runloop";
 import Component from "@ember/component";
 import Composer from "discourse/models/composer";
-import ComposerUpload from "discourse/mixins/composer-upload";
+import ComposerUploadUppy from "discourse/mixins/composer-upload-uppy";
 import EmberObject from "@ember/object";
 import I18n from "I18n";
 import { ajax } from "discourse/lib/ajax";
@@ -71,17 +72,6 @@ export function cleanUpComposerUploadHandler() {
   uploadHandlers.length = 0;
 }
 
-let uploadProcessorQueue = [];
-let uploadProcessorActions = {};
-export function addComposerUploadProcessor(queueItem, actionItem) {
-  uploadProcessorQueue.push(queueItem);
-  Object.assign(uploadProcessorActions, actionItem);
-}
-export function cleanUpComposerUploadProcessor() {
-  uploadProcessorQueue = [];
-  uploadProcessorActions = {};
-}
-
 let uploadPreProcessors = [];
 export function addComposerUploadPreProcessor(pluginClass, optionsResolverFn) {
   if (!(pluginClass.prototype instanceof BasePlugin)) {
@@ -107,18 +97,22 @@ export function cleanUpComposerUploadMarkdownResolver() {
   uploadMarkdownResolvers = [];
 }
 
-export default Component.extend(ComposerUpload, {
+export default Component.extend(ComposerUploadUppy, {
   classNameBindings: ["showToolbar:toolbar-visible", ":wmd-controls"],
 
   fileUploadElementId: "file-uploader",
   mobileFileUploaderId: "mobile-file-upload",
+  eventPrefix: "composer",
+  uploadType: "composer",
+  uppyId: "composer-editor-uppy",
+  composerModel: alias("composer"),
+  composerModelContentKey: "reply",
+  editorInputClass: ".d-editor-input",
   shouldBuildScrollMap: true,
   scrollMap: null,
   processPreview: true,
 
   uploadMarkdownResolvers,
-  uploadProcessorActions,
-  uploadProcessorQueue,
   uploadPreProcessors,
   uploadHandlers,
 
diff --git a/app/assets/javascripts/discourse/app/controllers/composer.js b/app/assets/javascripts/discourse/app/controllers/composer.js
index 016ed8d3bdf..9d85a476ba0 100644
--- a/app/assets/javascripts/discourse/app/controllers/composer.js
+++ b/app/assets/javascripts/discourse/app/controllers/composer.js
@@ -296,15 +296,6 @@ export default Controller.extend({
     return option;
   },
 
-  @discourseComputed()
-  composerComponent() {
-    const defaultComposer = "composer-editor";
-    if (this.siteSettings.enable_experimental_composer_uploader) {
-      return "composer-editor-uppy";
-    }
-    return defaultComposer;
-  },
-
   @discourseComputed("model.requiredCategoryMissing", "model.replyLength")
   disableTextarea(requiredCategoryMissing, replyLength) {
     return requiredCategoryMissing && replyLength === 0;
diff --git a/app/assets/javascripts/discourse/app/initializers/register-media-optimization-upload-processor.js b/app/assets/javascripts/discourse/app/initializers/register-media-optimization-upload-processor.js
index 7b6bfbff653..3f1bfed382e 100644
--- a/app/assets/javascripts/discourse/app/initializers/register-media-optimization-upload-processor.js
+++ b/app/assets/javascripts/discourse/app/initializers/register-media-optimization-upload-processor.js
@@ -1,7 +1,4 @@
-import {
-  addComposerUploadPreProcessor,
-  addComposerUploadProcessor,
-} from "discourse/components/composer-editor";
+import { addComposerUploadPreProcessor } from "discourse/components/composer-editor";
 import UppyMediaOptimization from "discourse/lib/uppy-media-optimization-plugin";
 
 export default {
@@ -10,30 +7,18 @@ export default {
   initialize(container) {
     let siteSettings = container.lookup("site-settings:main");
     if (siteSettings.composer_media_optimization_image_enabled) {
-      if (!siteSettings.enable_experimental_composer_uploader) {
-        addComposerUploadProcessor(
-          { action: "optimizeJPEG" },
-          {
-            optimizeJPEG: (data, opts) =>
+      addComposerUploadPreProcessor(
+        UppyMediaOptimization,
+        ({ isMobileDevice }) => {
+          return {
+            optimizeFn: (data, opts) =>
               container
                 .lookup("service:media-optimization-worker")
                 .optimizeImage(data, opts),
-          }
-        );
-      } else {
-        addComposerUploadPreProcessor(
-          UppyMediaOptimization,
-          ({ isMobileDevice }) => {
-            return {
-              optimizeFn: (data, opts) =>
-                container
-                  .lookup("service:media-optimization-worker")
-                  .optimizeImage(data, opts),
-              runParallel: !isMobileDevice,
-            };
-          }
-        );
-      }
+            runParallel: !isMobileDevice,
+          };
+        }
+      );
     }
   },
 };
diff --git a/app/assets/javascripts/discourse/app/lib/plugin-api.js b/app/assets/javascripts/discourse/app/lib/plugin-api.js
index d11adef5f16..12f1b900c20 100644
--- a/app/assets/javascripts/discourse/app/lib/plugin-api.js
+++ b/app/assets/javascripts/discourse/app/lib/plugin-api.js
@@ -2,7 +2,6 @@ import ComposerEditor, {
   addComposerUploadHandler,
   addComposerUploadMarkdownResolver,
   addComposerUploadPreProcessor,
-  addComposerUploadProcessor,
 } from "discourse/components/composer-editor";
 import {
   addButton,
@@ -94,8 +93,10 @@ import { CUSTOM_USER_SEARCH_OPTIONS } from "select-kit/components/user-chooser";
 import { downloadCalendar } from "discourse/lib/download-calendar";
 
 // If you add any methods to the API ensure you bump up the version number
-// based on Semantic Versioning 2.0.0.
-const PLUGIN_API_VERSION = "0.14.0";
+// based on Semantic Versioning 2.0.0. Please up the changelog at
+// docs/CHANGELOG-JAVASCRIPT-PLUGIN-API.md whenever you change the version
+// using the format described at https://keepachangelog.com/en/1.0.0/.
+const PLUGIN_API_VERSION = "1.0.0";
 
 // This helper prevents us from applying the same `modifyClass` over and over in test mode.
 function canModify(klass, type, resolverName, changes) {
@@ -1021,44 +1022,22 @@ class PluginApi {
   }
 
   /**
-   * Registers a function to handle uploads for specified file types
+   * Registers a function to handle uploads for specified file types.
    * The normal uploading functionality will be bypassed if function returns
    * a falsy value.
-   * This only for uploads of individual files
    *
    * Example:
    *
-   * api.addComposerUploadHandler(["mp4", "mov"], (file, editor) => {
-   *   console.log("Handling upload for", file.name);
+   * api.addComposerUploadHandler(["mp4", "mov"], (files, editor) => {
+   *   files.forEach((file) => {
+   *     console.log("Handling upload for", file.name);
+   *   });
    * })
    */
   addComposerUploadHandler(extensions, method) {
     addComposerUploadHandler(extensions, method);
   }
 
-  /**
-   * Registers a pre-processor for file uploads
-   * See https://github.com/blueimp/jQuery-File-Upload/wiki/Options#file-processing-options
-   *
-   * Useful for transforming to-be uploaded files client-side
-   *
-   * Example:
-   *
-   * api.addComposerUploadProcessor({action: 'myFileTransformation'}, {
-   *    myFileTransformation(data, options) {
-   *      let p = new Promise((resolve, reject) => {
-   *        let file = data.files[data.index];
-   *        console.log(`Transforming ${file.name}`);
-   *        // do work...
-   *        resolve(data);
-   *      });
-   *      return p;
-   * });
-   */
-  addComposerUploadProcessor(queueItem, actionItem) {
-    addComposerUploadProcessor(queueItem, actionItem);
-  }
-
   /**
    * Registers a pre-processor for file uploads in the form
    * of an Uppy preprocessor plugin.
diff --git a/app/assets/javascripts/discourse/app/mixins/composer-upload-uppy.js b/app/assets/javascripts/discourse/app/mixins/composer-upload-uppy.js
index c623a92388c..dfd8efd160f 100644
--- a/app/assets/javascripts/discourse/app/mixins/composer-upload-uppy.js
+++ b/app/assets/javascripts/discourse/app/mixins/composer-upload-uppy.js
@@ -549,4 +549,35 @@ export default Mixin.create(ExtendableUploader, UppyS3Multipart, {
   showUploadSelector(toolbarEvent) {
     this.send("showUploadSelector", toolbarEvent);
   },
+
+  _bindMobileUploadButton() {
+    if (this.site.mobileView) {
+      this.mobileUploadButton = document.getElementById(
+        this.mobileFileUploaderId
+      );
+      this.mobileUploadButtonEventListener = () => {
+        document.getElementById(this.fileUploadElementId).click();
+      };
+      this.mobileUploadButton.addEventListener(
+        "click",
+        this.mobileUploadButtonEventListener,
+        false
+      );
+    }
+  },
+
+  _unbindMobileUploadButton() {
+    this.mobileUploadButton?.removeEventListener(
+      "click",
+      this.mobileUploadButtonEventListener
+    );
+  },
+
+  _filenamePlaceholder(data) {
+    return data.name.replace(/\u200B-\u200D\uFEFF]/g, "");
+  },
+
+  _resetUploadFilenamePlaceholder() {
+    this.set("uploadFilenamePlaceholder", null);
+  },
 });
diff --git a/app/assets/javascripts/discourse/app/mixins/composer-upload.js b/app/assets/javascripts/discourse/app/mixins/composer-upload.js
deleted file mode 100644
index cee453f6d02..00000000000
--- a/app/assets/javascripts/discourse/app/mixins/composer-upload.js
+++ /dev/null
@@ -1,367 +0,0 @@
-import Mixin from "@ember/object/mixin";
-import I18n from "I18n";
-import { next, run } from "@ember/runloop";
-import getURL from "discourse-common/lib/get-url";
-import { clipboardHelpers } from "discourse/lib/utilities";
-import discourseComputed, {
-  observes,
-  on,
-} from "discourse-common/utils/decorators";
-import {
-  displayErrorForUpload,
-  getUploadMarkdown,
-  validateUploadedFiles,
-} from "discourse/lib/uploads";
-import { cacheShortUploadUrl } from "pretty-text/upload-short-url";
-import bootbox from "bootbox";
-
-export default Mixin.create({
-  _xhr: null,
-  uploadProgress: 0,
-  uploadFilenamePlaceholder: null,
-  uploadProcessingFilename: null,
-  uploadProcessingPlaceholdersAdded: false,
-
-  @discourseComputed("uploadFilenamePlaceholder")
-  uploadPlaceholder(uploadFilenamePlaceholder) {
-    const clipboard = I18n.t("clipboard");
-    const filename = uploadFilenamePlaceholder
-      ? uploadFilenamePlaceholder
-      : clipboard;
-
-    let placeholder = `[${I18n.t("uploading_filename", { filename })}]()\n`;
-    if (!this._cursorIsOnEmptyLine()) {
-      placeholder = `\n${placeholder}`;
-    }
-
-    return placeholder;
-  },
-
-  @observes("composer.uploadCancelled")
-  _cancelUpload() {
-    if (!this.get("composer.uploadCancelled")) {
-      return;
-    }
-    this.set("composer.uploadCancelled", false);
-
-    if (this._xhr) {
-      this._xhr._userCancelled = true;
-      this._xhr.abort();
-    }
-    this._resetUpload(true);
-  },
-
-  _setUploadPlaceholderSend(data) {
-    const filename = this._filenamePlaceholder(data);
-    this.set("uploadFilenamePlaceholder", filename);
-
-    // when adding two separate files with the same filename search for matching
-    // placeholder already existing in the editor ie [Uploading: test.png...]
-    // and add order nr to the next one: [Uploading: test.png(1)...]
-    const escapedFilename = filename.replace(/[.*+?^${}()|[\]\\]/g, "\\$&");
-    const regexString = `\\[${I18n.t("uploading_filename", {
-      filename: escapedFilename + "(?:\\()?([0-9])?(?:\\))?",
-    })}\\]\\(\\)`;
-    const globalRegex = new RegExp(regexString, "g");
-    const matchingPlaceholder = this.get("composer.reply").match(globalRegex);
-    if (matchingPlaceholder) {
-      // get last matching placeholder and its consecutive nr in regex
-      // capturing group and apply +1 to the placeholder
-      const lastMatch = matchingPlaceholder[matchingPlaceholder.length - 1];
-      const regex = new RegExp(regexString);
-      const orderNr = regex.exec(lastMatch)[1]
-        ? parseInt(regex.exec(lastMatch)[1], 10) + 1
-        : 1;
-      data.orderNr = orderNr;
-      const filenameWithOrderNr = `${filename}(${orderNr})`;
-      this.set("uploadFilenamePlaceholder", filenameWithOrderNr);
-    }
-  },
-
-  _setUploadPlaceholderDone(data) {
-    const filename = this._filenamePlaceholder(data);
-
-    if (data.orderNr) {
-      const filenameWithOrderNr = `${filename}(${data.orderNr})`;
-      this.set("uploadFilenamePlaceholder", filenameWithOrderNr);
-    } else {
-      this.set("uploadFilenamePlaceholder", filename);
-    }
-  },
-
-  _filenamePlaceholder(data) {
-    if (data.files) {
-      return data.files[0].name.replace(/\u200B-\u200D\uFEFF]/g, "");
-    } else {
-      return data.name.replace(/\u200B-\u200D\uFEFF]/g, "");
-    }
-  },
-
-  _resetUploadFilenamePlaceholder() {
-    this.set("uploadFilenamePlaceholder", null);
-  },
-
-  _resetUpload(removePlaceholder) {
-    next(() => {
-      if (this._validUploads > 0) {
-        this._validUploads--;
-      }
-      if (this._validUploads === 0) {
-        this.setProperties({
-          uploadProgress: 0,
-          isUploading: false,
-          isCancellable: false,
-        });
-      }
-      if (removePlaceholder) {
-        this.appEvents.trigger(
-          "composer:replace-text",
-          this.uploadPlaceholder,
-          ""
-        );
-      }
-      this._resetUploadFilenamePlaceholder();
-    });
-  },
-
-  _bindUploadTarget() {
-    this._unbindUploadTarget(); // in case it's still bound, let's clean it up first
-    this._pasted = false;
-
-    const $element = $(this.element);
-
-    this.setProperties({
-      uploadProgress: 0,
-      isUploading: false,
-      isProcessingUpload: false,
-      isCancellable: false,
-    });
-
-    $.blueimp.fileupload.prototype.processActions = this.uploadProcessorActions;
-
-    $element.fileupload({
-      url: getURL(`/uploads.json?client_id=${this.messageBus.clientId}`),
-      dataType: "json",
-      pasteZone: $element,
-      processQueue: this.uploadProcessorQueue,
-    });
-
-    $element
-      .on("fileuploadprocessstart", () => {
-        this.setProperties({
-          uploadProgress: 0,
-          isUploading: true,
-          isProcessingUpload: true,
-          isCancellable: false,
-        });
-      })
-      .on("fileuploadprocess", (e, data) => {
-        if (!this.uploadProcessingPlaceholdersAdded) {
-          data.originalFiles
-            .map((f) => f.name)
-            .forEach((f) => {
-              this.appEvents.trigger(
-                "composer:insert-text",
-                `[${I18n.t("processing_filename", {
-                  filename: f,
-                })}]()\n`
-              );
-            });
-          this.uploadProcessingPlaceholdersAdded = true;
-        }
-        this.uploadProcessingFilename = data.files[data.index].name;
-      })
-      .on("fileuploadprocessstop", () => {
-        this.setProperties({
-          uploadProgress: 0,
-          isUploading: false,
-          isProcessingUpload: false,
-          isCancellable: false,
-        });
-        this.uploadProcessingPlaceholdersAdded = false;
-      });
-
-    $element.on("fileuploadpaste", (e) => {
-      this._pasted = true;
-
-      if (!$(".d-editor-input").is(":focus")) {
-        return;
-      }
-
-      const { canUpload, canPasteHtml, types } = clipboardHelpers(e, {
-        siteSettings: this.siteSettings,
-        canUpload: true,
-      });
-
-      if (!canUpload || canPasteHtml || types.includes("text/plain")) {
-        e.preventDefault();
-      }
-    });
-
-    $element.on("fileuploadsubmit", (e, data) => {
-      const max = this.siteSettings.simultaneous_uploads;
-      const fileCount = data.files.length;
-
-      // Limit the number of simultaneous uploads
-      if (max > 0 && fileCount > max) {
-        bootbox.alert(
-          I18n.t("post.errors.too_many_dragged_and_dropped_files", {
-            count: max,
-          })
-        );
-        return false;
-      }
-
-      // Look for a matching file upload handler contributed from a plugin
-      if (fileCount === 1) {
-        const file = data.files[0];
-        const matchingHandler = this._findMatchingUploadHandler(file.name);
-        if (matchingHandler && !matchingHandler.method(file, this)) {
-          return false;
-        }
-      }
-
-      // If no plugin, continue as normal
-      const isPrivateMessage = this.get("composer.privateMessage");
-
-      data.formData = { type: "composer" };
-      if (isPrivateMessage) {
-        data.formData.for_private_message = true;
-      }
-      if (this._pasted) {
-        data.formData.pasted = true;
-      }
-
-      const opts = {
-        user: this.currentUser,
-        siteSettings: this.siteSettings,
-        isPrivateMessage,
-        allowStaffToUploadAnyFileInPm: this.siteSettings
-          .allow_staff_to_upload_any_file_in_pm,
-      };
-
-      const isUploading = validateUploadedFiles(data.files, opts);
-
-      run(() => {
-        this.setProperties({ uploadProgress: 0, isUploading });
-      });
-
-      return isUploading;
-    });
-
-    $element.on("fileuploadprogressall", (e, data) => {
-      run(() => {
-        this.set(
-          "uploadProgress",
-          parseInt((data.loaded / data.total) * 100, 10)
-        );
-      });
-    });
-
-    $element.on("fileuploadsend", (e, data) => {
-      run(() => {
-        this._pasted = false;
-        this._validUploads++;
-
-        this._setUploadPlaceholderSend(data);
-
-        if (this.uploadProcessingFilename) {
-          this.appEvents.trigger(
-            "composer:replace-text",
-            `[${I18n.t("processing_filename", {
-              filename: this.uploadProcessingFilename,
-            })}]()`,
-            this.uploadPlaceholder.trim()
-          );
-          this.uploadProcessingFilename = null;
-        } else {
-          this.appEvents.trigger(
-            "composer:insert-text",
-            this.uploadPlaceholder
-          );
-        }
-
-        if (data.xhr && data.originalFiles.length === 1) {
-          this.set("isCancellable", true);
-          this._xhr = data.xhr();
-        }
-      });
-    });
-
-    $element.on("fileuploaddone", (e, data) => {
-      run(() => {
-        let upload = data.result;
-        this._setUploadPlaceholderDone(data);
-        if (!this._xhr || !this._xhr._userCancelled) {
-          const markdown = this.uploadMarkdownResolvers.reduce(
-            (md, resolver) => resolver(upload) || md,
-            getUploadMarkdown(upload)
-          );
-
-          cacheShortUploadUrl(upload.short_url, upload);
-          this.appEvents.trigger(
-            "composer:replace-text",
-            this.uploadPlaceholder.trim(),
-            markdown
-          );
-          this._resetUpload(false);
-        } else {
-          this._resetUpload(true);
-        }
-      });
-    });
-
-    $element.on("fileuploadfail", (e, data) => {
-      run(() => {
-        this._setUploadPlaceholderDone(data);
-        this._resetUpload(true);
-
-        const userCancelled = this._xhr && this._xhr._userCancelled;
-        this._xhr = null;
-
-        if (!userCancelled) {
-          displayErrorForUpload(data, this.siteSettings, data.files[0].name);
-        }
-      });
-    });
-  },
-
-  _bindMobileUploadButton() {
-    if (this.site.mobileView) {
-      this.mobileUploadButton = document.getElementById(
-        this.mobileFileUploaderId
-      );
-      this.mobileUploadButtonEventListener = () => {
-        document.getElementById(this.fileUploadElementId).click();
-      };
-      this.mobileUploadButton.addEventListener(
-        "click",
-        this.mobileUploadButtonEventListener,
-        false
-      );
-    }
-  },
-
-  _unbindMobileUploadButton() {
-    this.mobileUploadButton?.removeEventListener(
-      "click",
-      this.mobileUploadButtonEventListener
-    );
-  },
-
-  @on("willDestroyElement")
-  _unbindUploadTarget() {
-    this._validUploads = 0;
-    const $uploadTarget = $(this.element);
-    try {
-      $uploadTarget.fileupload("destroy");
-    } catch (e) {
-      /* wasn't initialized yet */
-    }
-    $uploadTarget.off();
-  },
-
-  showUploadSelector(toolbarEvent) {
-    this.send("showUploadSelector", toolbarEvent);
-  },
-});
diff --git a/app/assets/javascripts/discourse/app/templates/composer.hbs b/app/assets/javascripts/discourse/app/templates/composer.hbs
index 26f8f21b327..e1c50bc71b6 100644
--- a/app/assets/javascripts/discourse/app/templates/composer.hbs
+++ b/app/assets/javascripts/discourse/app/templates/composer.hbs
@@ -111,7 +111,7 @@
 
         </div>
 
-        {{component composerComponent
+        {{composer-editor
           topic=topic
           composer=model
           lastValidatedAt=lastValidatedAt
diff --git a/app/assets/javascripts/discourse/tests/acceptance/composer-attachment-test.js b/app/assets/javascripts/discourse/tests/acceptance/composer-attachment-test.js
deleted file mode 100644
index 37ed65aca3e..00000000000
--- a/app/assets/javascripts/discourse/tests/acceptance/composer-attachment-test.js
+++ /dev/null
@@ -1,326 +0,0 @@
-import {
-  acceptance,
-  exists,
-  query,
-  queryAll,
-} from "discourse/tests/helpers/qunit-helpers";
-import { withPluginApi } from "discourse/lib/plugin-api";
-import { click, fillIn, visit } from "@ember/test-helpers";
-import bootbox from "bootbox";
-import { test } from "qunit";
-
-function pretender(server, helper) {
-  server.post("/uploads/lookup-urls", () => {
-    return helper.response([
-      {
-        short_url: "upload://asdsad.png",
-        url: "/secure-media-uploads/default/3X/1/asjdiasjdiasida.png",
-        short_path: "/uploads/short-url/asdsad.png",
-      },
-    ]);
-  });
-}
-
-async function writeInComposer(assert) {
-  await visit("/t/internationalization-localization/280");
-  await click("#topic-footer-buttons .btn.create");
-
-  await fillIn(".d-editor-input", "[test](upload://abcdefg.png)");
-
-  assert.strictEqual(
-    queryAll(".d-editor-preview:visible").html().trim(),
-    '<p><a href="/404" tabindex="-1">test</a></p>'
-  );
-
-  await fillIn(".d-editor-input", "[test|attachment](upload://asdsad.png)");
-}
-
-acceptance("Composer Attachment - Cooking", function (needs) {
-  needs.user();
-  needs.pretender(pretender);
-
-  test("attachments are cooked properly", async function (assert) {
-    await writeInComposer(assert);
-    assert.strictEqual(
-      queryAll(".d-editor-preview:visible").html().trim(),
-      '<p><a class="attachment" href="/uploads/short-url/asdsad.png" tabindex="-1">test</a></p>'
-    );
-  });
-});
-
-acceptance("Composer Attachment - Secure Media Enabled", function (needs) {
-  needs.user();
-  needs.settings({ secure_media: true });
-  needs.pretender(pretender);
-
-  test("attachments are cooked properly when secure media is enabled", async function (assert) {
-    await writeInComposer(assert);
-    assert.strictEqual(
-      queryAll(".d-editor-preview:visible").html().trim(),
-      '<p><a class="attachment" href="/secure-media-uploads/default/3X/1/asjdiasjdiasida.png" tabindex="-1">test</a></p>'
-    );
-  });
-});
-
-acceptance("Composer Attachment - Upload Placeholder", function (needs) {
-  needs.user();
-
-  test("should insert a newline before and after an image when pasting into an empty composer", async function (assert) {
-    await visit("/");
-    await click("#create-topic");
-    const image = createImage("avatar.png", "/images/avatar.png?1", 200, 300);
-
-    await queryAll(".wmd-controls").trigger("fileuploadsend", image);
-    assert.strictEqual(
-      queryAll(".d-editor-input").val(),
-      "[Uploading: avatar.png...]()\n"
-    );
-
-    await queryAll(".wmd-controls").trigger("fileuploaddone", image);
-    assert.strictEqual(
-      queryAll(".d-editor-input").val(),
-      "![avatar|200x300](/images/avatar.png?1)\n"
-    );
-  });
-
-  test("should insert a newline after an image when pasting into a blank line", async function (assert) {
-    await visit("/");
-    await click("#create-topic");
-    await fillIn(".d-editor-input", "The image:\n");
-
-    const image = createImage("avatar.png", "/images/avatar.png?1", 200, 300);
-    await queryAll(".wmd-controls").trigger("fileuploadsend", image);
-
-    assert.strictEqual(
-      queryAll(".d-editor-input").val(),
-      "The image:\n[Uploading: avatar.png...]()\n"
-    );
-
-    await queryAll(".wmd-controls").trigger("fileuploaddone", image);
-    assert.strictEqual(
-      queryAll(".d-editor-input").val(),
-      "The image:\n![avatar|200x300](/images/avatar.png?1)\n"
-    );
-  });
-
-  test("should insert a newline before and after an image when pasting into a non blank line", async function (assert) {
-    await visit("/");
-    await click("#create-topic");
-    await fillIn(".d-editor-input", "The image:");
-
-    const image = createImage("avatar.png", "/images/avatar.png?1", 200, 300);
-    await queryAll(".wmd-controls").trigger("fileuploadsend", image);
-
-    assert.strictEqual(
-      queryAll(".d-editor-input").val(),
-      "The image:\n[Uploading: avatar.png...]()\n"
-    );
-
-    await queryAll(".wmd-controls").trigger("fileuploaddone", image);
-    assert.strictEqual(
-      queryAll(".d-editor-input").val(),
-      "The image:\n![avatar|200x300](/images/avatar.png?1)\n"
-    );
-  });
-
-  test("should insert a newline before and after an image when pasting with cursor in the middle of the line", async function (assert) {
-    await visit("/");
-    await click("#create-topic");
-    await fillIn(".d-editor-input", "The image Text after the image.");
-    const textArea = query(".d-editor-input");
-    textArea.selectionStart = 10;
-    textArea.selectionEnd = 10;
-
-    const image = createImage("avatar.png", "/images/avatar.png?1", 200, 300);
-    await queryAll(".wmd-controls").trigger("fileuploadsend", image);
-
-    assert.strictEqual(
-      queryAll(".d-editor-input").val(),
-      "The image \n[Uploading: avatar.png...]()\nText after the image."
-    );
-
-    await queryAll(".wmd-controls").trigger("fileuploaddone", image);
-    assert.strictEqual(
-      queryAll(".d-editor-input").val(),
-      "The image \n![avatar|200x300](/images/avatar.png?1)\nText after the image."
-    );
-  });
-
-  test("should insert a newline before and after an image when pasting with text selected", async function (assert) {
-    await visit("/");
-    await click("#create-topic");
-    const image = createImage("avatar.png", "/images/avatar.png?1", 200, 300);
-    await fillIn(
-      ".d-editor-input",
-      "The image [paste here] Text after the image."
-    );
-    const textArea = query(".d-editor-input");
-    textArea.selectionStart = 10;
-    textArea.selectionEnd = 23;
-
-    await queryAll(".wmd-controls").trigger("fileuploadsend", image);
-    assert.strictEqual(
-      queryAll(".d-editor-input").val(),
-      "The image \n[Uploading: avatar.png...]()\n Text after the image."
-    );
-
-    await queryAll(".wmd-controls").trigger("fileuploaddone", image);
-    assert.strictEqual(
-      queryAll(".d-editor-input").val(),
-      "The image \n![avatar|200x300](/images/avatar.png?1)\n Text after the image."
-    );
-  });
-
-  test("pasting several images", async function (assert) {
-    await visit("/");
-    await click("#create-topic");
-
-    const image1 = createImage("test.png", "/images/avatar.png?1", 200, 300);
-    const image2 = createImage("test.png", "/images/avatar.png?2", 100, 200);
-    const image3 = createImage("image.png", "/images/avatar.png?3", 300, 400);
-    const image4 = createImage("image.png", "/images/avatar.png?4", 300, 400);
-
-    await queryAll(".wmd-controls").trigger("fileuploadsend", image1);
-    assert.strictEqual(
-      queryAll(".d-editor-input").val(),
-      "[Uploading: test.png...]()\n"
-    );
-
-    await queryAll(".wmd-controls").trigger("fileuploadsend", image2);
-    assert.strictEqual(
-      queryAll(".d-editor-input").val(),
-      "[Uploading: test.png...]()\n[Uploading: test.png(1)...]()\n"
-    );
-
-    await queryAll(".wmd-controls").trigger("fileuploadsend", image4);
-    assert.strictEqual(
-      queryAll(".d-editor-input").val(),
-      "[Uploading: test.png...]()\n[Uploading: test.png(1)...]()\n[Uploading: image.png...]()\n"
-    );
-
-    await queryAll(".wmd-controls").trigger("fileuploadsend", image3);
-    assert.strictEqual(
-      queryAll(".d-editor-input").val(),
-      "[Uploading: test.png...]()\n[Uploading: test.png(1)...]()\n[Uploading: image.png...]()\n[Uploading: image.png(1)...]()\n"
-    );
-
-    await queryAll(".wmd-controls").trigger("fileuploaddone", image2);
-    assert.strictEqual(
-      queryAll(".d-editor-input").val(),
-      "[Uploading: test.png...]()\n![test|100x200](/images/avatar.png?2)\n[Uploading: image.png...]()\n[Uploading: image.png(1)...]()\n"
-    );
-
-    await queryAll(".wmd-controls").trigger("fileuploaddone", image3);
-    assert.strictEqual(
-      queryAll(".d-editor-input").val(),
-      "[Uploading: test.png...]()\n![test|100x200](/images/avatar.png?2)\n[Uploading: image.png...]()\n![image|300x400](/images/avatar.png?3)\n"
-    );
-
-    await queryAll(".wmd-controls").trigger("fileuploaddone", image1);
-    assert.strictEqual(
-      queryAll(".d-editor-input").val(),
-      "![test|200x300](/images/avatar.png?1)\n![test|100x200](/images/avatar.png?2)\n[Uploading: image.png...]()\n![image|300x400](/images/avatar.png?3)\n"
-    );
-  });
-
-  test("should accept files with unescaped characters", async function (assert) {
-    await visit("/");
-    await click("#create-topic");
-
-    const image = createImage("ima++ge.png", "/images/avatar.png?4", 300, 400);
-
-    await queryAll(".wmd-controls").trigger("fileuploadsend", image);
-    assert.strictEqual(
-      queryAll(".d-editor-input").val(),
-      "[Uploading: ima++ge.png...]()\n"
-    );
-
-    await queryAll(".wmd-controls").trigger("fileuploaddone", image);
-    assert.strictEqual(
-      queryAll(".d-editor-input").val(),
-      "![ima++ge|300x400](/images/avatar.png?4)\n"
-    );
-  });
-});
-
-function createImage(name, url, width, height) {
-  const file = new Blob([""], { type: "image/png" });
-  file.name = name;
-  return {
-    files: [file],
-    result: {
-      original_filename: name,
-      thumbnail_width: width,
-      thumbnail_height: height,
-      url,
-    },
-  };
-}
-
-acceptance("Composer Attachment - Upload Handler", function (needs) {
-  needs.user();
-  needs.hooks.beforeEach(() => {
-    withPluginApi("0.8.14", (api) => {
-      api.addComposerUploadHandler(["png"], (file) => {
-        bootbox.alert(`This is an upload handler test for ${file.name}`);
-      });
-    });
-  });
-
-  test("should handle a single file being uploaded with the extension handler", async function (assert) {
-    await visit("/");
-    await click("#create-topic");
-    const image = createImage(
-      "handlertest.png",
-      "/images/avatar.png?1",
-      200,
-      300
-    );
-    await fillIn(".d-editor-input", "This is a handler test.");
-
-    await queryAll(".wmd-controls").trigger("fileuploadsubmit", image);
-    assert.strictEqual(
-      queryAll(".bootbox .modal-body").html(),
-      "This is an upload handler test for handlertest.png",
-      "it should show the bootbox triggered by the upload handler"
-    );
-    await click(".modal-footer .btn");
-  });
-});
-
-acceptance("Composer Attachment - File input", function (needs) {
-  needs.user();
-
-  test("shouldn't add to DOM the hidden file input if uploads aren't allowed", async function (assert) {
-    this.siteSettings.authorized_extensions = "";
-    await visit("/");
-    await click("#create-topic");
-
-    assert.notOk(exists("input#file-uploader"));
-  });
-
-  test("should fill the accept attribute with allowed file extensions", async function (assert) {
-    this.siteSettings.authorized_extensions = "jpg|jpeg|png";
-    await visit("/");
-    await click("#create-topic");
-
-    assert.ok(exists("input#file-uploader"), "An input is rendered");
-    assert.strictEqual(
-      query("input#file-uploader").accept,
-      ".jpg,.jpeg,.png",
-      "Accepted values are correct"
-    );
-  });
-
-  test("the hidden file input shouldn't have the accept attribute if any file extension is allowed", async function (assert) {
-    this.siteSettings.authorized_extensions = "jpg|jpeg|png|*";
-    await visit("/");
-    await click("#create-topic");
-
-    assert.ok(exists("input#file-uploader"), "An input is rendered");
-    assert.notOk(
-      query("input#file-uploader").hasAttribute("accept"),
-      "The input doesn't contain the accept attribute"
-    );
-  });
-});
diff --git a/app/assets/javascripts/discourse/tests/acceptance/composer-uploads-uppy-test.js b/app/assets/javascripts/discourse/tests/acceptance/composer-uploads-uppy-test.js
index 6671bc8a925..622fe159ede 100644
--- a/app/assets/javascripts/discourse/tests/acceptance/composer-uploads-uppy-test.js
+++ b/app/assets/javascripts/discourse/tests/acceptance/composer-uploads-uppy-test.js
@@ -59,7 +59,6 @@ acceptance("Uppy Composer Attachment - Upload Placeholder", function (needs) {
   needs.user();
   needs.pretender(pretender);
   needs.settings({
-    enable_experimental_composer_uploader: true,
     simultaneous_uploads: 2,
   });
 
@@ -197,7 +196,6 @@ acceptance("Uppy Composer Attachment - Upload Error", function (needs) {
     });
   });
   needs.settings({
-    enable_experimental_composer_uploader: true,
     simultaneous_uploads: 2,
   });
 
@@ -229,7 +227,6 @@ acceptance("Uppy Composer Attachment - Upload Handler", function (needs) {
   needs.user();
   needs.pretender(pretender);
   needs.settings({
-    enable_experimental_composer_uploader: true,
     simultaneous_uploads: 2,
   });
   needs.hooks.beforeEach(() => {
diff --git a/app/assets/javascripts/discourse/tests/helpers/qunit-helpers.js b/app/assets/javascripts/discourse/tests/helpers/qunit-helpers.js
index 956deeb0de7..58410713f66 100644
--- a/app/assets/javascripts/discourse/tests/helpers/qunit-helpers.js
+++ b/app/assets/javascripts/discourse/tests/helpers/qunit-helpers.js
@@ -48,7 +48,6 @@ import {
   cleanUpComposerUploadHandler,
   cleanUpComposerUploadMarkdownResolver,
   cleanUpComposerUploadPreProcessor,
-  cleanUpComposerUploadProcessor,
 } from "discourse/components/composer-editor";
 import { resetLastEditNotificationClick } from "discourse/models/post-stream";
 import { clearAuthMethods } from "discourse/models/login-method";
@@ -294,7 +293,6 @@ export function acceptance(name, optionsOrCallback) {
       setTopicList(null);
       _clearSnapshots();
       cleanUpComposerUploadHandler();
-      cleanUpComposerUploadProcessor();
       cleanUpComposerUploadMarkdownResolver();
       cleanUpComposerUploadPreProcessor();
       clearTopicFooterDropdowns();
diff --git a/config/site_settings.yml b/config/site_settings.yml
index d82c83144a6..f2019ac4356 100644
--- a/config/site_settings.yml
+++ b/config/site_settings.yml
@@ -267,6 +267,8 @@ basic:
     client: true
     default: true
     hidden: true
+  # TODO (martin) (2022-02-01) Remove this setting once plugins relying on
+  # it have been changed.
   enable_experimental_composer_uploader:
     client: true
     default: false
diff --git a/docs/CHANGELOG-JAVASCRIPT-PLUGIN-API.md b/docs/CHANGELOG-JAVASCRIPT-PLUGIN-API.md
new file mode 100644
index 00000000000..7ded201f976
--- /dev/null
+++ b/docs/CHANGELOG-JAVASCRIPT-PLUGIN-API.md
@@ -0,0 +1,30 @@
+# Changelog
+
+All notable changes to the Discourse JavaScript plugin API located at
+app/assets/javascripts/discourse/app/lib/plugin-api.js will be described
+in this file..
+
+The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
+and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
+
+## [1.0.0] - 2021-11-25
+### Removed
+- Removes the `addComposerUploadProcessor` function, which is no longer used in
+favour of `addComposerUploadPreProcessor`. The former was used to add preprocessors
+for client side uploads via jQuery file uploader (described at
+https://github.com/blueimp/jQuery-File-Upload/wiki/Options#file-processing-options).
+The new `addComposerUploadPreProcessor` adds preprocessors for client side
+uploads in the form of an Uppy plugin. See https://uppy.io/docs/writing-plugins/
+for the Uppy documentation, but other examples of preprocessors in core can be found
+in the UppyMediaOptimization and UppyChecksum classes. This has been done because
+of the overarching move towards Uppy in the Discourse codebase rather than
+jQuery fileupload, which will eventually be removed altogether as a broader effort
+to remove jQuery from the codebase.
+
+### Changed
+- Changes `addComposerUploadHandler`'s behaviour. Instead of being only usable
+for single files at a time, now multiple files are sent to the upload handler
+at once. These multiple files are sent based on the groups in which they are
+added (e.g. multiple files selected from the system upload dialog, or multiple
+files dropped in to the composer). Files will be sent in buckets to the handlers
+they match.