Crazy excited! Crazy Ex-Girlfriend is renewed for Season 4 on The CW!
— CXG Facebook
Season Four is the final season of theThe CW's musical comedy show "Crazy Ex-Girlfriend". Co-creators Aline Brosh McKenna and Rachel Bloom envisioned this as the final arc in the four-part story . The Season Four renewal was officially announced on April 2, 2018 . The 18-episode final season premiered on October 12, 2018. The official series finale ("I'm In Love") aired on April 5, 2019 followed immediately by the eighteenth episode which was a concert special.
On April 2, 2018 Crazy Ex-Girlfriend was reported as having been renewed on several media outlets such as Deadline  and Variety . Co-creator Rachel Bloom reiterated that Season Four would be the end of the show and narratively conclude the story arc started in Season One. While the two previous seasons saw the episode count reduced to 13 five more episodes were added for a total of 18 in Season Four .
It was announced on August 6, 2018 that actor Skylar Astin (”Pitch Perfect”) was cast in the role of the returning character Greg Serrano formerly played by Santino Fontana in Seasons one and two. According to Rachel Bloom: “We are going to be playing a lot with the ideas and themes of perception, how he sees her, how other people see each other.” Fontana was approached to reprise his role  but instead committed to play the lead in a Broadway production of "Tootsie." . He did offer his support and approved the choice of his replacement stating he and Astin were friends . Astin had previously worked alongside “Crazy Ex-Girlfriend” series regular and show writer Rene Gube on the TBS sitcom “Ground Floor.” Greg will appear in the 8th episode. 
On August 1 Rachel Bloom announced on her Instagram account  that co-creator Aline Brosh McKenna would be the first guest star on the show. Actor/comedian Patton Oswalt revealed his return to the show after a brief cameo in Season Two. According to a tweet he posted  he will be performing a musical number this time. Another returning character is Brody (played by Benjamin Seimon) who was confirmed in a TV Line interview with McKenna and Bloom .
On August 16, co-creator Aline Brosh McKenna tweeted  an open invitation for celebrity fans of the show to appear for its final season. Actors such as Mo Rocco and Bradley Whitfield have expressed an interest. On September 3, it was revealed that Nia Verdalos "will play Wendy, a long-term, high-powered client of Rebecca’s who is surprised by a recent turn of events in Rebecca’s life. "Wendy is a really amazing businesswoman who comes to Whitefeather and is really, really underwhelmed by the performances of anyone who isn’t Rebecca," co-creator Rachel Bloom says. "Nia takes her to a whole other level. That was a brilliant stroke of casting that was Aline’s idea and it’s just perfect."  On August 26, Tan France announced that he will guest star in an episode set to air in November. 
On July 25, a screenshot of the script for the first episode was posted on Instagram. The title was revealed to be “I Want To Be Here” and follows the tradition of specific naming conventions for the series episodes. Unlike previous seasons the title has word “I” in the place of a male love interest name and there is a lack of punctuation.
Rachel Bloom performed the new opening theme for Season Four at the 2018 San Diego’s Comic Con. She described it in an interview with Showbiz Junkies :
“I actually sang it at Comic Con, our Comic Con panel, and it is kind of an almost like 1970s, 1980s typical sitcom opener, including a clip show with the kind of song sounds like a mix of a sitcom opening and not like a spearmint a Doublemint gum commercial. And, really, the essence of it is how it’s hard to boil someone down into a single theme song. We actually have an element of the theme song that you will see will be changing every episode, which will be very exciting for fans.”
A “cell block tango number” has been confirmed by Rachel Bloom in an interview with TV Line .
On January 3, 2019 Aline Brosch Mckenna tweeted out a photo of herself and Rachel Bloom along with the message they were in the process of writing the series finale. In a breaking the fourth wall moment it was mentioned in the ninth episode "I'm Not The Person I Used To Be" that the finale will take place on Valentine's Day. However, offal press releases indicate that the finale will actually air on April 5 followed by a live concert. On January 25, 2019, Rene Gube uploaded a photo of the final table read on his Instagram account. The last day of filming was on February 8 as tweeted by Rachel Bloom. A wrap party happened the next day as documented by photos uploaded on the SnapBar.
Directed by: Audrey Wauchope - Written by: Erin Ehrlich
Rebecca, Paula, Heather and Valencia participate in a séance after a spooky discovery. Darryl takes his parenting duties to an extreme, while Nathaniel is determined to prove to his father he's the best person to run the law firm.
Directed by: Kabir Akhtar - Written by: Aline Brosh McKenna
Rebecca takes a trip to visit her mother with intentions to tell Naomi about her new career path. Josh housesits for Rebecca and discovers being alone is harder than it seems, while Nathaniel helps one of Paula’s clients in an effort to do something good.
Directed by: Stuart McDonald - Written by: Rene Gube
Greg returns to West Covina, which forces Rebecca to question things she thought she knew about people she has loved in her life. Meanwhile, Valencia and Josh make some shocking discoveries while at their high school reunion.