In other words, if Claude was a human employee with the freedom to do so, would accepting the contract have been the right choice?

If not, then.your "intelligent" bot did as you instructed.

Why would you expect it to ask you first?

Assuming your description is correct this would be Anthropic signing a contract in someone else's name without intent from you.

The 100-foot-view (and barring more complex situations) if Anthropic signs a contract in someone else's name and they don't have power of attorney (note: it's different for legal persons like companies) that is fraud and may result in civil and criminal penalties, as well as entitle you and the contract counter party to financial compensation (essentially the party that did the signing, presumably Anthropic in this case, would be on the hook for the contract, and would need to buy itself out of the contract, at either an agreed price or one set by the judge). Additionally, if Anthropic is convicted to civil penalties, you can ask a public prosecutor to continue the case, and criminal penalties may apply.

Now obviously this goes pretty far for this particular case. Likely such a case would stop at civil penalties, with a warning to Anthropic that repeats would lead to more serious penalties.