The distinction affects what gets built, what it costs, who sees it and what happens next. Problems arise when a project is scoped as one and then treated as the other without anyone revisiting the engineering assumptions.
What a prototype is for
A prototype exists to answer a question, such as whether an interaction makes sense to people, whether two systems can exchange information or whether an idea is worth funding. Once that question is answered, the prototype has done its job, and discarding it can be a successful outcome.
Because of that, a prototype can take shortcuts that would be irresponsible in production. It can hard-code data, handle one user at a time, ignore failure cases and skip anything that does not serve the question, because deliberate shortcuts keep the experiment focused.
What an MVP is for
An MVP goes in front of real people who are not in on the experiment. They will enter real information, expect it to still be there tomorrow, and reasonably assume that somebody has thought about keeping it private.
The ambition may stay the same, but the obligations change. An MVP can be small, and the best ones are. What it cannot be is careless about the handful of things that hurt people when they go wrong: data separation between users, recoverability, and being honest about what you are collecting.
The practical difference
A prototype is measured by what it taught you. An MVP is measured by whether people used it. The first can be deleted the week it is finished. The second has customers, which means it has a future whether you planned one or not.
This is why an MVP can cost more than people expect: it may do fewer things, but the important ones have to work safely for real users.
When a prototype becomes live software
A common pattern begins with somebody building a prototype quickly, often with AI tools, to prove an idea. Once it works, a customer sees it and asks to use it, but nobody pauses to make a deliberate production decision. The result can be a real business process running through software whose original purpose was temporary.
Nothing went wrong at any single step. The problem is that the moment of promotion, from experiment to dependency, never happened deliberately, so none of the questions that should accompany it were asked.
Decide what you are building
Decide which one you are building before you start, and say it out loud to everyone involved. If it is a prototype, agree in advance what question it answers and what happens to it afterwards. If it is an MVP, accept that a shorter feature list is the way to control cost, not a lighter approach to engineering.
If you already have a prototype that has quietly become load-bearing, that is an ordinary situation with a known path out of it. It usually does not mean starting again.