Data centers take time to build. The capital investment to build these DCs is needed now in expectation that future revenue streams will pay for that capital.

That's not what OpenAI announced. They said initial spend would be $100B, and I'm sure until the ink is dry on each contract, that they can change their mind at any time. No business is going to be placing ironclad commitments four years out.

Commitments here means money that people have agreed to lend them in future.

Does it mean have agreed to lend them in a binding agreement that OpenAI can sue to enforce?

Yes. The capital is not needed immediately, but they have agreed to provide it if/when called upon in future.

This is highly unlikely. Imagine OpenAI struggling, and in year 4 of this "commitment" call upon the lenders to provide over $100B in capital. The lenders will definitely have recourse if the risk is too high. Otherwise this would simply be a commercial line of credit, or they would be investing the funds directly in OpenAI now.

The contract would obviously not be no strings attached.