Is it possible to jailbreak?

Is it possible to jailbreak iPhone 4S ios 6.1.3 when the jailbreak for it comes out after ios7 comes out and then update my phone to ios 7 and keep the jailbreak?

No.

When you update it always looses the jailbreak.

No, you can't upgrade and keep your jailbreak at the same time. You need to jailbreak when you're already running the OS. If you want to install iOS 7 early, you can register your device's UDID with a developer account through a site like http://www.udid.in/.It's $5, and then you can try out the new OS before everyone else. That's how I got it on my 4S.

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