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What Is Fidelity on Westworld?

How does fidelity work on Westworld?

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When Westworld Season 4 Episode 4 ended, an older plot point was reintroduced in the most unexpected way. If you’re needing a refresher on fidelity, then you’ve come to the right place. 

Note: This article has major spoilers for Season 4 Episode 4 of Westworld. 


Caleb Is Undergoing Fidelity Testing

At the end of Season 4 Episode 4, Dolores-as-Charlotte (known as Halores or Charlores) reveals to Caleb that he’s actually far in the future and is on his 278th fidelity test. 

This means that Caleb was killed the first time that Maeve and Caleb confronted Halores and Host William at the construction site. Ever since then, Charlotte has been trying to reawaken him in a host body. 

It’s not clear at the end of S4E4 why she wants Caleb revived and has tried 278 times so far. And as it always is, the revelation is shocking to Caleb. It carries so many implications — including that his daughter is now an adult and his wife is likely long gone. 

Perhaps Halores wants him because Caleb was taken over by the flies and was able to resist them. At the time, Halores is surprised by Caleb’s ability to resist her. But later on, we learn that many adults weren’t actually able to fully come under the flies’ control due to having rigid minds, while children were more malleable. So it’s unclear to me if Caleb resisting Halores was a sign of what many adults would be able to do, or something unique to him. 

Caleb marks the third time that we’ve seen fidelity on the show. So let’s look back at the previous examples. 


James Delos Underwent Fidelity Testing that Ultimately Failed

The story of James Delos in Season 2 was the first time we were introduced to the concept of fidelity testing. At the time, it was a human attempt to move a human’s consciousness into a pearl (and thus into a host.) Caleb’s process is likely similar, only done at the behest of a host rather than a human. 

James Delos had an official baseline interview with young William before he died, because he wanted to be transferred into a host and achieve immortality. The idea is that if the new human host responds to the interview exactly like his human counterpart, then it means his consciousness was successfully transferred or replicated into a pearl. 

With Delos, he broke down mentally every time he underwent his baseline interview. He would malfunction or glitch, and 149 attempts were all unsuccessful. Each time it didn’t work, his host was incinerated and they tried again. You can see a YouTube video of his encounter with William about the topic here.

There’s also a YouTube video below showing the creepy time that Bernard and Elsie saw a glitched James Delos host, left on its own. 

Every attempt with James Delos failed.

It sounds like they’re trying more frequently with Caleb, and he’s broken down more often than Delos did. But the very last attempt might have worked.


William Has Undergone Fidelity Testing Too

There’s also been an attempt to turn William into a host and replicate his consciousness. At the end of Season 2, during the post-credits scene (which you can watch in the embedded video above), we’re introduced to a Delos laboratory that appears to be far in the future, where everything has broken down and sand has encroached inside.

William’s daughter (who is dead in real life, so this must be a host) tells him that she’s going to ask him questions for the purpose of fidelity. 

So in this case, we see that at some point in the future, a host is testing William for fidelity. In fact, there are many ways where William’s test parallels Caleb’s more, because it seems like neither had willingly undergone a baseline interview in the first place. Instead, they are being tested via scenarios. 

We know that Halores has created a William Host, but I don’t think it’s the same as a Fidelity William Host. The Halores William Host is just a copy under her control. I’m going to guess that the post-credits William fidelity test marks a completely different test than what Charlotte did for the William Host we currently know. 


So What Is Fidelity? 

In summary, fidelity is the attempt to transfer (or perfectly replicate) a human’s consciousness into a pearl that resides in a host’s body. The concept was originally created by James Delos, the owner of Delos, before he died and William took over the company.

For the official version that Delos created, a human is asked a series of questions just before they die. Once they’re transferred into a host, they achieve “fidelity” if they give the exact same responses to the same set of questions. 

If they die before they can create that baseline interview (or someone else wants to try to achieve fidelity for them), then they are run through a scenario instead and tested to see if they will react exactly the same as their human counterpart.

As far as we know, fidelity has never worked. There is something in the human psyche that causes them to break down mentally or glitch uncontrollably when transferred. 

However, in Caleb’s case, the 278th try might have actually succeeded. 

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    Stephanie Dwilson started Post Apocalyptic Media with her husband Derek. She's a licensed attorney and has a master's in science and technology journalism. You can reach her at [email protected].

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    1 Comment

    1. Thank you for this article, I have been a bit confused about this. I think I understand the fidelity stuff now. So the “non-fidelity” human-based hosts like William (in the current season), the politician and his wife from ep 2, Jay, etc…these are just physical replicas only basically? I get confused, because there seems to be SOME knowledge they have of the human they are replicas of, like when William was golfing and mentioned something about his wife’s funeral I think. Didn’t he say to the guy he whacked with the club that he didn’t show up to it or something? I can’t recall, but it was as if the host William had the real William’s memories.