Twitter / X data API: search, profiles, timelines, followers, DMs, write actions.
TwitterAPIs API is a free Social API that requires apiKey authentication, is served over HTTPS and has unconfirmed CORS support.
TwitterAPIs is the cheapest pay-as-you-go Twitter and X API. $0.0008 per call returns ~20 tweets ($0.04/1,000). No subscription, no X developer account.
Details from twitterapis.com.

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Public Twitter/X data: profiles, tweets, replies, search, followers, lists, communities, trends
The TwitterAPIs API is provided by TwitterAPIs (twitterapis.com). TwitterAPIs is the cheapest pay-as-you-go Twitter and X API. $0.0008 per call returns ~20 tweets ($0.04/1,000). No subscription, no X developer account.
Yes. The TwitterAPIs API is listed in the Social category of the public-apis directory, which only includes APIs that are free or have a free tier. Check its documentation for rate limits and paid plans.
Yes. The TwitterAPIs API uses apiKey authentication, so you need to register for credentials before making requests.
CORS support for the TwitterAPIs API is unknown. Test a request from the browser, and fall back to a server-side call if it is blocked.
Yes. The TwitterAPIs API is served over HTTPS, so it's safe to use in production.