diff --git a/chrome/content/zotero/xpcom/sync/syncAPIClient.js b/chrome/content/zotero/xpcom/sync/syncAPIClient.js
index 5931e41d90..99a0a9481c 100644
--- a/chrome/content/zotero/xpcom/sync/syncAPIClient.js
+++ b/chrome/content/zotero/xpcom/sync/syncAPIClient.js
@@ -617,7 +617,99 @@ Zotero.Sync.APIClient.prototype = {
 	},
 
 
+	// Hidden prefs for Read Aloud custom endpoints:
+	//   extensions.zotero.reader.readAloud.customEndpoint
+	//     "{mode}=[url]". Empty/invalid falls back to the normal Zotero API
+	//     endpoint. Only "openai" is currently supported as a mode, where the
+	//     server must implement OpenAI's /audio/speech
+	//     (e.g. https://api.openai.com/v1).
+	//   extensions.zotero.reader.readAloud.customEndpoint.voices
+	//     Comma-separated voice IDs (openai mode only). Defaults to the
+	//     OpenAI TTS voice list.
+	//   extensions.zotero.reader.readAloud.customEndpoint.apiKey
+	//     Sent as "Authorization: Bearer <key>" (openai mode only).
+	//   extensions.zotero.reader.readAloud.customEndpoint.model
+	//     Model name sent in the request body (openai mode only).
+	_getReadAloudCustomEndpoint() {
+		let pref = Zotero.Prefs.get('reader.readAloud.customEndpoint');
+		if (!pref || typeof pref !== 'string') return null;
+		let match = pref.match(/^(\w+)=(.+)$/);
+		if (!match) return null;
+		let [, mode, url] = match;
+		if (mode !== 'openai') {
+			Zotero.debug(`Unsupported customEndpoint mode '${mode}'`);
+			return null;
+		}
+		try {
+			// eslint-disable-next-line no-new
+			new URL(url);
+		}
+		catch {
+			Zotero.debug('Invalid customEndpoint pref value: ' + pref);
+			return null;
+		}
+		if (!url.endsWith('/')) {
+			url += '/';
+		}
+		let voicesPref = Zotero.Prefs.get('reader.readAloud.customEndpoint.voices');
+		let voices = typeof voicesPref === 'string'
+			? voicesPref.split(',').map(s => s.trim()).filter(Boolean)
+			: null;
+		let apiKey = Zotero.Prefs.get('reader.readAloud.customEndpoint.apiKey');
+		if (typeof apiKey !== 'string' || !apiKey) {
+			apiKey = null;
+		}
+		let model = Zotero.Prefs.get('reader.readAloud.customEndpoint.model');
+		if (typeof model !== 'string' || !model) {
+			model = 'gpt-4o-mini-tts';
+		}
+		return { mode, url, voices, apiKey, model };
+	},
+
+
 	async getReadAloudVoices() {
+		let custom = this._getReadAloudCustomEndpoint();
+		if (custom?.mode === 'openai') {
+			// Fall back to OpenAI's voice IDs
+			let voiceIDs = custom.voices ?? [
+				'alloy',
+				'ash',
+				'ballad',
+				'coral',
+				'echo',
+				'fable',
+				'nova',
+				'onyx',
+				'sage',
+				'shimmer',
+				'verse',
+			];
+			let voices = Object.fromEntries(voiceIDs.map(id => [id, { label: id }]));
+			// Derive a cache version from the endpoint and model so that
+			// changing either one invalidates previously cached audio
+			let cacheVersion = parseInt(
+				Zotero.Utilities.Internal.md5(custom.url + '|' + custom.model).slice(0, 8),
+				16
+			);
+			// OpenAI's TTS endpoint auto-detects language from the input
+			// text, so use the wildcard locale.
+			// The reader treats '*' as matching any language.
+			return {
+				voices: {
+					standard: [{
+						creditsPerMinute: 0,
+						segmentGranularity: 'sentence',
+						cacheVersion,
+						voices,
+						locales: { '*': voiceIDs },
+					}],
+				},
+				standardCreditsRemaining: null,
+				premiumCreditsRemaining: null,
+				devMode: false,
+			};
+		}
+
 		let url = this.baseURL + "tts/voices";
 		let params = new URLSearchParams();
 		params.set("lang", Services.locale.appLocaleAsBCP47);
@@ -669,6 +761,47 @@ Zotero.Sync.APIClient.prototype = {
 
 
 	async getReadAloudAudio(segment, voiceID) {
+		let custom = this._getReadAloudCustomEndpoint();
+		if (custom?.mode === 'openai') {
+			let text = segment === 'sample'
+				? "Isn't it nice to have a computer that will talk to you?"
+				: segment.text;
+			let headers = { "Content-Type": "application/json" };
+			if (custom.apiKey) {
+				headers.Authorization = `Bearer ${custom.apiKey}`;
+			}
+			try {
+				let xmlhttp = await Zotero.HTTP.request("POST", custom.url + "audio/speech", {
+					responseType: "blob",
+					headers,
+					body: JSON.stringify({
+						model: custom.model,
+						voice: voiceID,
+						input: text,
+						// eslint-disable-next-line camelcase
+						response_format: 'mp3',
+					}),
+					errorDelayMax: 8000,
+				});
+				return { audio: xmlhttp.response };
+			}
+			catch (e) {
+				Zotero.logError(e);
+
+				let error;
+				if (e instanceof Zotero.HTTP.BrowserOfflineException) {
+					error = 'network';
+				}
+				else {
+					error = 'unknown';
+				}
+				return {
+					audio: null,
+					error,
+				};
+			}
+		}
+
 		let method;
 		let url;
 		let options = {
@@ -741,6 +874,10 @@ Zotero.Sync.APIClient.prototype = {
 
 
 	async getReadAloudCreditsRemaining() {
+		let custom = this._getReadAloudCustomEndpoint();
+		if (custom?.mode === 'openai') {
+			return { standardCreditsRemaining: null, premiumCreditsRemaining: null };
+		}
 		let uri = this.baseURL + "tts/credits";
 		try {
 			let xmlhttp = await this.makeRequest("GET", uri, {
@@ -761,6 +898,10 @@ Zotero.Sync.APIClient.prototype = {
 
 
 	async resetReadAloudCredits() {
+		let custom = this._getReadAloudCustomEndpoint();
+		if (custom?.mode === 'openai') {
+			return { standardCreditsRemaining: null, premiumCreditsRemaining: null };
+		}
 		let uri = this.baseURL + "tts/reset";
 		try {
 			let xmlhttp = await this.makeRequest("POST", uri, {
diff --git a/defaults/preferences/zotero.js b/defaults/preferences/zotero.js
index c51de7cda2..f0c527a358 100644
--- a/defaults/preferences/zotero.js
+++ b/defaults/preferences/zotero.js
@@ -250,6 +250,7 @@ pref("extensions.zotero.reader.autoDisableTool.image", true);
 pref("extensions.zotero.reader.lastSidebarTab", "annotations");
 pref("extensions.zotero.reader.popupPositions", "{}");
 pref("extensions.zotero.reader.readAloud.highlightGranularity", "sentence");
+pref("extensions.zotero.reader.readAloud.customEndpoint.model", "gpt-4o-mini-tts");
 
 // Set color scheme to auto by default
 pref("browser.theme.toolbar-theme", 2);