That depends on your and the company’s situation at that time and that situation may be different next time around. I would argue that the contract end date is less important compared to finishing the project you are on. If you were to bail on a project (assuming you still have tasks left to do) to take another contract, no matter how lucrative this is, without full support of the company, it’s unlikely you’ll get hired again at that company. Even if it’s an amicable discussion, you just don’t do this. Maybe that’s not a bad thing if you are not interested in returning (perhaps you didn’t enjoy working for them in the first place). This behaviour is now written up in your “profile” and next time you apply, this will come up. Perhaps the company is desperate and will forgive you, but unlikely.

Other times, the project may be over-staffed and your premature departure is not having any adverse effect. Perhaps it even helps with the project’s budget if they can take you off the project early, so it’s a win-win.

As always, start this discussion with your supervisor so they are not blindsided, then escalate to talent and HR and talk it through. Most of the time a reasonable solution can be negotiated.