I’ve noticed some fans of the show claiming that BoJack never changed.
To me it’s rather clear that he changed but in a very “1 step forward, 5 steps back” kind of way.

For example:

1. season 1, episode 11, his own brain tells him that " You can’t force love, you blockhead. All you can do is be good to the people in your life and keep your heart open."
   This is a halucination of a Peanuts-looking Diane, but it’s BoJack’s own mind giving himself the answers. As everyone of us, BoJack has most of the tools to
   heal and help himself, but he hasn’t unlocked them yet. Sometimes we need therapy to learn how to effectively use them.

2. season 2, episode 12, coming to the ship to save Todd and remembering hashbrowns details, even though it is established that BoJack “never remembers anything” that is important to others and not to him. It is one of the few postive steps towards wanting to selflessly do something for Todd, to the point where his brain out-does itself and brings out hashbrown memories.

3. season 3, episode 4, the entire saving the baby seahorse thing. Yes, this episode is full of BoJack’s mistakes and fails but his motivation to help the baby and his willingness to go extra miles, without any of his usual pick me ups like nicotine or alcohol, putting in energy, hard work and brainstorming just to get the child safely home is step in the right direction.
   season 3, episode 12 - his approach to the girl on Ethan Around shows he wants to be better to child actors than he has been before and make sure she has what she really needs - validation from her parents.

4. season 4, episode 12. despite absolutely hating standing in lines, and despite knowing that he will not get to see Hollyhock again, he finds her real mother and begs her fathers to give her the information, even if they never let him see Hollyhock.
   It’s all about making sure she’s happy, she finds what she’s been looking for and he put the annoying tedious long work into achieving this goal for her.

5. season 5, episode 7, he asks the actress who’s playing the girl on the submarine if she’s ok, because she’s shivering. She’s probably already in character, but there is nothing in it for BoJack, he doesn’t need to care how co-stars feel, but he’s getting more interested in how people around him feel regardless of whether it benefits him.
   season 5, episode 12 - accepting that he needs rehab.

Season 6:

a) listening to what Maude actually says, offering her Todd’s dating app and never taking credit to Todd’s face about it - that is unbelievable, because season 1 BoJack would not even notice that Maude is an Ace, like Todd.
He would only think about himself, and whine and complain about why isn’t she getting him his order faster.
When Todd refuses to let BoJack in his party, BoJack doesn’t bring up Maude to make Todd feel like he owes BoJack something - season 3 BoJack did this in episode 10, but season 6 BoJack keeps it to himself, that he brought Maude and Todd together.

b) cleaning Diane’s appartment. There is no way he’d ever do that in season 1 or 2.

c) Actively suggesting to play with Mr Peanutbutter the Mr Peanutbutter’s house in Washington DC. Clearly the only motivation there is the fact that it makes Mr Peanutbutter happy. This is both something that would annoy BoJack before as well as feel “unfair” because he envies Mr PB for always seeming so happy - he admits it multiple times, even to Mr PB’s face.

d) Staying sober for the entire seson 6 until Hollyhock’s letter.

e) Actively trying to help Jameson and then empathise with her father. Nothing in it for him.

The Xerox of a Xerox is a terrible relapse to his old pattern.
The drinking after reading Hollyhock’s letter is a relapse to his addiction.

In the finale, he treats everyone much better than he did pre-season 6, including himself.

Todd responds to his fear that relapse could happen again:

“you’ll get sober again”.
To me,
this was a happy ending.

As for the rest of the main 5 - they all ended up happier than in season 1.

​

PC - she’s got a great husband, they’re both in love, and a child as she always wanted. Her career is still going strong. (it seems she’ll still be in contact with BoJack but with more boundaries)
Mr Peanutbutter - he started therapy, trying to face the toxic parts of his positivity and the reason his relationships keep falling apart. He’s finally growing. (it seems he’ll still be in contact with BoJack)

Todd - he complained to Diane in the Chickens episode in season 2, that his life is just a series of random adventures. In the finale he found a steady job that he really likes and is good at. (it seems that he’s willing to stay in some contact with BoJack, but with more boundaries)
Diane - she has a great husband, they’re both in love, and her career took her to a place where she can write fun stuff for kids, something exiting and positive she never expected before. She left L.A. and
she sees that as a good thing.
(the only part that seems a bit sad is that Diane and BoJack won’t be in contact anymore)