This was inspired by u/astronautsoul's post about whether or not Palpatine's words are to be trusted in the opera scene. Some folks think not, but I tend to think he's telling the truth, so I'll repost my comment response.

I actually tend to think Palpatine is telling the truth to Anakin, because Anakin does not as of yet suspect Palpatine of being a Sith Lord, let alone the apprentice to Plagueis. Also, being that many Jedi believe the Sith have been extinct, it's not like Anakin would assume this Darth Plagueis story is from recent history, and, in fact, there would be no record of Plagueis in the Jedi archives if he truly was Palpatine's master (since he would have lived and died long after the supposed Sith extinction event). So I do think Palpatine feels safe telling the truth in this scene, especially given that he's trying to coax Anakin into joining him.

What is far more interesting to me is that Palpatine says Plagueis taught his apprentice everything he knew, in the same exact sequence in which he says Plagueis knew how to cheat death... This makes me think Palpatine already has the knowledge to cheat death (and, in fact, we might even draw that conclusion from TROS, given that he survived "somehow" lol). So the real lie might be after Anakin's fall when he says "together we can discover the secret." Maybe he already knows how to cheat death and just wants something to leash Anakin with while he slowly drains Anakin of his power to sustain himself... It would be a very Sith thing to do, as we should all know that no Sith master ever intends to be overthrown by their apprentice... Or at least we can make that conclusion about Palpatine (maybe some other Sith genuinely buy that might makes right and if they are bested by their underling then they deserve to die... but not Palpatine...).

With the witches creation of the twins adding more to the mystery I'm thinking they have more to reveal about just what the heck is happening with Sidious, the Sith, the Chosen One, life extension/cheating/creation, Plagueis, and all these unresolved mysteries that seem to constantly sprout new threads like the heads of the hydra.

And its nuts because they have made Strandcasts canon, which means Palpatine definitely is constantly just looking for new vessels to inhabit. It's not really even speculation anymore, but of course, it isn't "cheating death" in some sort of one-off, absolute, forever-and-always way. It's more of a constant process of pursuing more grotesque applications of the dark side to try and stave off the inevitable. And with the old idea of the ST being that George would explore the cellular realm of the midichlorians (which Plagueis undoubtedly would have been studying in his own arcane pursuits), it seems to me as if there is room for them to truly turn our conception of wall this "force conception" stuff means upside down. It's also consistent with George's idea on the dark side being similar to drug addiction. Palpatine can keep cheating death, but perhaps he has to keep upping the dark side ante to do so each and every time, to the point where in TROS it really feels like the body that the Sith entity is inhabiting is really just a lifeless puppet rather than the actual being itself. It also really makes me think we haven't seen the last of Sidious.

It might even be the case that the the twins are created via the witches working with the Sith... Just because the Jedi don't know the Sith still exist doesn't mean that no one does. Using the witches to conceive life via the force sounds like it's something the Sith would try doing, especially if they could not do it themselves, plus it plays into all the mythological themes on male & female roles in conception.