I0nic has given his untether for the iOS 4.3.1 jailbreak to the iPhone Dev-Team for testing and integration into their jailbreak utilities.
i0n1c has announced that he will likely release his untether for the iOS 4.3 jailbreak before next weekend.
Because of several changes in iOS 4.3 in comparison to iOS 4.2.1 the jailbreak is NOT READY yet. That is what the *ALPHA* means. I need some time to check what kernel patches are actually required to work 100%ly.
However I recommend the dev-team or chronic-dev to first release a *tethered* iOS 4.3 so that everyone can test if their nice feature actually work. I guess most people require Mobile Substrate to work and AFAIK it does not work due to ASLR. It would be a waste if Apple kills an untethered jailbreak before Mobile Substrate works.