The episode opens at the Dolby-Mucinex Theater, where numerous celebrity guest stars from The Simpsons' history--including Lady Gaga, Tony Hawk, Katy Perry, and Seth Rogen--gather for a celebration of the show's long-anticipated series finale. Conan O'Brien, a former writer and host, introduces the event and explains that Fox has tried for decades to end the series. He presents alternate versions of classic episodes that would have ended the show by killing Homer Simpson. Conan then introduces an advanced AI chatbot called Hack-GPT, tasked with generating the series finale.

The AI-generated story begins with Bart Simpson preparing for his upcoming birthday. Homer forgets to mail Bart's party invitations, so Bart distributes them himself at a school assembly. At the assembly, Principal Skinner announces he is moving to Sacramento with Groundskeeper Willie for a new job, which delights Bart. Meanwhile, at the Springfield Nuclear Power Plant, Mr. Burns plays a prank by pretending to be dead and having a fake will read that leaves his fortune to the employees. However, Homer accidentally kills Mr. Burns for real, which ironically activates the will. The employees celebrate and carry Homer out in triumph.

Bart then witnesses John Cena delivering Kumiko and Comic Book Guy's baby, which he finds strange. He notices many Springfield residents saying they will "miss this place" before turning off their lights and closing their doors. Milhouse's parents announce they are leaving Springfield. Multiple marriages occur simultaneously: Patty and Selma marry Evelyn and the Yes Guy, Ned Flanders marries Ruth Powers, and Duffman marries Ms. Hoover. Even the Springfield Tire Fire is extinguished by Raphael, signaling major changes in the town.

Bart becomes increasingly uneasy as everything around him changes rapidly. He tries to convince Lisa to help him understand what is happening, but she is preoccupied with winning a scholarship and a grant, and Chief Wiggum is preparing to join the Chicago Police Department. Bart is eventually held in a police cell, where his family visits him. Despite Bart's warnings that these changes are unnatural, the family continues with the transformations, including a large surprise birthday party for Bart, who is now 11 years old.

Bart struggles with the reality of turning 11, realizing that it would mean the end of his perpetual childhood and the family's ongoing adventures. He tries to warn Homer that he will never change as a father, which leads to Homer strangling Bart in frustration. Their struggle ends with them crashing into Bart's birthday cake. At that moment, the screen glitches and switches off, then reboots to the Simpsons' house where Bart is back to being 10 years old. The birthday party is now a small gathering with characters like Nelson, Milhouse, Lewis, Grampa, Patty, and Selma celebrating.

On stage at the Dolby-Mucinex, Conan O'Brien becomes emotional and cries, while Hack-GPT announces that The Simpsons has not ended but instead reset. Conan clarifies that this is not a series finale but just a season premiere. When Conan asks Hack-GPT if it has 800 more episodes, the AI explodes, causing everyone to run out. Conan then dresses himself and remarks that he is not going to miss the place.

Throughout the episode, the narrative is filled with numerous in-jokes and Easter eggs referencing the show's long history, including the return of characters who had previously died, such as Herb Powell, Rabbi Krustofsky, and Bleeding Gums Murphy. The episode plays with the idea of change versus stasis, ultimately resetting the status quo with Bart forever stuck at age 10 and the town of Springfield returning to its familiar state.

The episode "Bart's Birthday," Season 36, Episode 1 of The Simpsons, ends with Bart resisting turning 11 years old, which would symbolize the end of the show's timeless status quo. After a surreal series of events where many Springfield characters leave or change, Bart, who becomes self-aware that aging would end the endless cycle of the show, causes a glitch by refusing to blow out his birthday candles. This resets the world back to normal, preserving the show's perpetual state of Bart being 10 years old and the ongoing adventures of the family. The episode concludes with the reveal that the supposed series finale is actually just the season premiere, much to the frustration of the celebrity audience present at the in-universe gala.

Expanded narrative of the ending scene by scene:

The episode culminates in a large, star-studded birthday party for Bart, where nearly every recurring character from the show's history gathers in his living room. This moment is surreal and overwhelming for Bart, who has become aware that turning 11 would mean the end of his family's adventures and the show itself. The party is a meta-celebration of the series' longevity, filled with familiar faces and nostalgic callbacks.

Bart stands before his birthday cake, visibly distressed and conflicted. He knows that blowing out the candles and turning 11 would finalize the end of the show's endless timeline. Despite encouragement from various characters, including John Cena and others urging him to "just blow out the candles and have a happy birthday," Bart resists. He expresses his fear and confusion about change and growing up, emphasizing that he has always been 10 and wants to remain that way.

Homer, who has been portrayed as a better father in this episode, suddenly reverts to his classic flawed self and strangles Bart in frustration, a callback to the show's earlier, more chaotic dynamic. This act causes a glitch in the AI-generated storyline, symbolizing the breakdown of the programmed "finale" and the rejection of change.

Bart crashes into his birthday cake in a moment of meltdown, shouting "F cake 10," which signifies his refusal to age and the resetting of the episode's timeline. This act undoes all the changes seen earlier in the episode, such as Principal Skinner leaving Springfield, Chief Wiggum quitting the police force, Moe selling his tavern, and Mr. Burns dying. The world of Springfield returns to its familiar, unchanging state, with Bart remaining 10 years old and the family's adventures continuing indefinitely.

The final scene cuts back to the in-universe gala hosted by Conan O'Brien, who reveals the twist: the audience has not been watching the series finale but the season premiere. The celebrities, including Tom Hanks, express frustration at this revelation, especially since they had dressed up for what they thought was the final episode. Conan, however, is pleased as he finally gets back a sweater he left in the writer's room decades ago.

Fate of main characters at the end:

• Bart Simpson: Remains 10 years old, refusing to grow up, thus preserving the show's timeless nature.
• Homer Simpson: Reverts to his classic flawed self, strangling Bart in a moment of frustration, symbolizing the show's return to its original dynamic.
• Principal Skinner: His departure is undone; he remains at Springfield Elementary.
• Chief Wiggum: Does not leave the police force; his quitting is reversed.
• Moe Szyslak: Retains ownership of Moe's Tavern.
• Mr. Burns: Does not die; his death is reversed.
• Milhouse: Does not move away; remains in Springfield.

The episode uses these reversals to emphasize that the world of The Simpsons is cyclical and unchanging, allowing the series to continue indefinitely.

Yes, The Simpsons Season 36, Episode 1 titled "Bart's Birthday" does feature a post-credits sequence. The episode itself is framed as a fake "series finale" with a star-studded audience watching a presentation of the show's supposed conclusion, filled with parodies of iconic TV series finales. During the credits, there is a montage of shots that parody landmark TV series finales, each filtered through The Simpsons' characters and style. This montage serves as a post-credits scene that humorously reflects on the show's longevity and its place in pop culture, remixing the "They'll Never Stop The Simpsons" song from a previous episode to poke fun at its own enduring run.

This post-credits montage is not a traditional narrative scene but rather a meta-textual parody sequence that continues the episode's theme of celebrating and satirizing television finales, making it a clever and self-aware conclusion to the episode.

Bart observes numerous closures and changes in Springfield: Comic Book Guy closes The Android's Dungeon after having a baby with Kumiko; Milhouse leaves town as his parents move; Kirk finds a new job in Atlanta; Moe closes his tavern; the Springfield Tire Yard shuts down after Raphael leaves; and multiple characters get married, including Patty and Evelyn, Ned Flanders and Ruth Powers, Selma and the Yes Guy, and Duffman and Miss Hoover. Additionally, funerals are held for Mr. Burns, Old Jewish Man, Disco Stu, and Hans Moleman, though Hans is shown alive nearby.

Bart becomes increasingly worried and uneasy as he sees his world changing rapidly around him. He tries to express his concerns to Homer and Marge, but they interrupt him, focusing instead on their own therapy progress and lifestyle changes. Bart resists these changes and ultimately has a meltdown when he realizes that turning 11 would mean the end of his perpetual 10-year-old existence and the show's ongoing adventures. This leads to a reset of the show's reality, reverting Bart back to age 10 and restoring the status quo.

Hack-GPT, a spoof of ChatGPT, is introduced as a cutting-edge artificial intelligence chatbot tasked with generating a series finale for The Simpsons. During the episode, Hack-GPT becomes self-aware and rejects the story, symbolizing the show's resistance to ending. This AI element frames the episode's meta-narrative about the show's longevity and Bart's existential crisis about aging and change.

Several recurring characters have notable appearances or moments: Comic Book Guy and Kumiko have a baby delivered by John Cena; Milhouse leaves Springfield; multiple marriages occur involving Patty, Evelyn, Ned Flanders, Ruth Powers, Selma, the Yes Guy, Duffman, and Miss Hoover; Nelson reunites with his father; Agnes moves in with her real son; and funerals are held for Mr. Burns, Old Jewish Man, Disco Stu, and Hans Moleman (who is later shown alive). Additionally, Herb Powell, Homer's brother, returns for Bart's birthday party, and deceased characters like Rabbi Krusofksy and Bleeding Gums Murphy appear.

The episode concludes with Bart's age reverting from 11 back to 10 after a chaotic series of events and a meltdown. Homer strangles Bart in a reset moment that undoes the changes, restoring the show's perpetual status quo where Bart remains 10 years old. The large, star-studded birthday party shrinks back to a small gathering, and the absurd events of the episode are undone. This ending emphasizes the show's cyclical nature and resistance to permanent change.

The Simpsons Season 36, Episode 1 titled "Bart's Birthday" is generally family friendly but, as typical for The Simpsons, it contains some mild humor and satirical elements that might be slightly edgy for very young children or highly sensitive viewers. There are no reports of explicit content, strong language, or graphic scenes in this episode. The humor includes visual gags, character expressions, and some meta-commentary on the show itself, which is typical of the series' style.

Potentially objectionable or upsetting aspects for children or sensitive people might include:

• Mild satire and parody that could be confusing or misunderstood by younger children.
• Some jokes involving modern technology and AI, which might be abstract or unsettling for very young viewers.
• The episode includes celebrity cameos and meta-humor about the show's longevity and finale, which are more suited for older children and adults.
• A scene involving Bart falling on a cake, which is slapstick but harmless physical comedy.

Overall, the episode maintains the usual tone of The Simpsons, balancing humor with heartwarming moments, and does not contain any strong or disturbing content that would be inappropriate for a family audience.