Compare Duolingo and MIT OpenCourseWare free tiers side by side. Pricing, limits, change history, and risk assessment for developers.
We are not publishing a free-tier verdict for either Duolingo or MIT OpenCourseWare. The page we cite for Duolingo states no amount, tier or rate we can read when we last looked, on 2026-10-22. The page we cite for MIT OpenCourseWare states no amount, tier or rate we can read when we last looked, on 2026-11-09. We are not comparing the two pricing histories.
A verdict here is not a fixed property of the vendor. A one-off pricing event demotes a vendor while its recorded date falls in the last 180 days and then lapses on its own, with nothing about the vendor having changed; a standing condition — a free tier withdrawn and not restored, a product retired — does not lapse with time. A badge carrying a date states the record it rests on; a badge with no date rests on no record in force.
No recorded pricing changes for Duolingo.
No recorded pricing changes for MIT OpenCourseWare.
We do not push notifications. Every change we record is readable the moment it lands, and the JSON answer carries an ETag — send it back as If-None-Match and an unchanged answer costs one 304.
curl https://agentdeals.dev/api/changes?vendor=Duolingo
curl https://agentdeals.dev/pricing-changes/feed.xml?vendor=Duolingo
curl https://agentdeals.dev/api/changes?vendor=MIT%20OpenCourseWare
curl https://agentdeals.dev/pricing-changes/feed.xml?vendor=MIT%20OpenCourseWare