IndexNow is an open protocol jointly announced by Microsoft Bing and Yandex that lets a site push new or changed URLs to participating search engines in near real time — and it matters for ChatGPT because ChatGPT Search's live web results are anchored on Bing's index.
The protocol is documented at indexnow.org. A publisher generates a UUID-style key, hosts it as a plain-text file at a well-known URL (/{key}.txt), and then submits a JSON body to https://api.indexnow.org/indexnow containing the site host, the key, its key location, and the list of URLs. Bing and Yandex fetch and confirm the key, then queue the URLs for crawling.
Bing announced the protocol in its October 2021 Webmaster blog post and integrated it into Bing Webmaster Tools. Because ChatGPT Search uses Bing as its primary web result source, an IndexNow push is the fastest documented path to make a new URL eligible for ChatGPT Search results — often within minutes instead of the days a passive crawl might take.
Two practices to keep it working: fire a ping on every publish or meaningful update (not only on a batch schedule), and ensure the key file at /{key}.txt actually resolves — if it 404s, the submission is discarded.
Google is not currently an IndexNow participant. For Google discovery, use Search Console's URL Inspection tool and a valid sitemap.