It's a pretty jam-packed first hour, with Kim Kardashian, Kanye West and Kylie Jenner making an appearance, as well as Caitlyn's wider family. Here are the 9 bits you absolutely need to know about:
1. She told her sisters YEARS ago
"He confided in me over 30 years ago," reveals Caitlyn's sister, Pam. "But I thought it was something maybe counselling would help him with. Then about 2 years ago, he started talking to me about 'living an authentic life'."
Pam goes on to admit: "I initially discouraged him [from going public]. I was quite apprehensive."
2. Her mum was the last to know
"I was able to tell everyone in my family first, before my mum," admits Caitlyn and the moment they meet requires ALL of the tissues it's so emotional. "It's okay, it's okay," Caitlyn repeats as they hug.
"I love him so much," Esther says. "I always have, I always will. It's a lot of getting used to, but I will. I will." But breaking down in tears, she admits, "It's going to be so difficult for me to think of you as a she! It's not easy."
3. Kylie met Caitlyn over FaceTime
While Kim met Caitlyn for the first time at her Vanity Fair shoot, Caitlyn admits Kourtney, Khloe, Rob and her other children were less eager. "They never show up, so you know something is going on in their head."
But Kylie had the most unusual meeting of all, when she FacetTimed her dad after a dentist appointment. "Kylie hasn't met Caitlyn yet and she FaceTime's me! I didn't know what to do, should I turn away?" she explains.
"I don't want to scare you," says a worried Caitlyn, as Kylie replies: "You're not scaring me. You look pretty!" So sweet.
4. She struggled with gender identity as a child
As Caitlyn sits her mum and sisters down with a counsellor, her mum describes how, in hindsight, Caitlyn had always found it hard to identify as a male.
She recalls one shopping trip where, as a young boy, she took her son to buy new clothes after he had grown out of what he had. But he began pulling the clothes off. What she thought was just a little boy being difficult, was actually Caitlyn not wanting to wear boy's clothing.
5. Kanye West's appearance is so amazing
If you struggle to imagine Kanye West as a normal human being, laughing, smiling and awkwardly hugging relatives he's just met for the first time, you HAVE to watch I Am Cait. But the great thing, is how proud of Caitlyn he is (in his own Kanye way).
"This is one of the strongest things that has happened in our existence as human beings that are so controlled by perception. Because you couldn't have been up against more - your daughter's a supermodel, you're a celebrity, you have every type of thing and it was still like, 'Fuck it! This is who I am!'"
Caitlyn adds: "I love his open-mindedness. I love how he's helped Kim come to grips with everything."
6. There are a LOT of wardrobe clashes
In one of the funniest and most heartwarming moments in the episode, Kim and Caitlyn return to her closet, for the first time since she first helped Bruce decide on her 'look'. As Caitlyn starts pulling out items, she says, "I love this Tom Ford dress."
Kim replies, "Mum has that." But with zero awkwardness, Caitlyn laughs, "It would be like Who Wore It Best! We gotta do that, wouldn't that be the funniest?!"
7. She contemplated suicide
In the most shocking moment of the episode, Caitlyn reveals she once came close to ending her life. "I've been in some dark places, I have been in my house with a gun and said, 'Let's just end it right there, no more pain, no more suffering, that struggle, it's real and I've been there."
It opens a much deeper conversation on the show, about the horrifically high rates of suicide among the trans community, as well as the number of murder victims who are trans.
8. It's actually really really good
It is a reality show, but don't expect a KUWTK-style hour of sass and drama and super-zoomed in shots of shocked expressions. I Am Cait actually handles some really serious issues and could be a great force for changing attitudes.
The most moving part of the first episode comes when Cait visits the family of Kyler Prescott, a trans teen who committed suicide. And with visits to support groups and LGBT events in upcoming episodes, it's good to see the show is handling trans issues sensitively and seriously. Bravo.
9. Oh and Cait gets a date...
There's been weeks of rumours about a romance between Caitlyn and trans actress Candis Cayne and it seems those rumours are true. "Would you like to go on a date?" she asks Caitlyn. Watch this space.
By Claire Hodgson
See the full story on Cosmopolitan.co.uk