If it's neither written nor explicitly spoken, then it's not a contract of any kind. It's just an - usually naive - expectation.

> Social contracts are typically unwritten

Maybe this is the case, but why is your presumption of entitlement to free labor of others the assumed social contract, the assumed "moral" position, rather than the immoral one?

Why is the assumed social contract that is unwritten not that you can have the free labor we've released to you so far, but we owe you nothing in the future?

There's too much assumption of the premise that "moral" and "social contract" are terms that make the entitled demands of free-loaders the good guys in this debate. Maybe the better "morality" is the selfless workers giving away the product of their labor for free are the actual good guys.