Tesla Dropped Halloween Mode. Two Hours Later, Rivian’s Software Chief Answered in Anagram

At 4:30 p.m. on October 6, Rivian chief software officer Wassym Bensaid posted a single line to X with no words in it: "abcdeeeehhillmnnnoooorttw." Those 25 letters, sorted alphabetically, are the letters of "Halloween Mode October Ninth," with nothing left over.

Tesla's Halloween Mode announcement had gone up on the company's X account at 2:22 p.m. the same afternoon, two hours and eight minutes earlier. It listed a ghost costume for the car's on-screen avatar, a Trick or Treat setting that plays sounds and flickers the lights when visitors approach, a new light show, wraps, a lock sound, a Photobooth, and a way to speak through the app and have the car say it "in a voice of its own."

Bensaid didn't explain the letters, and Rivian announced nothing that day. On October 8 it published its Ghostbusters update, built with Sony Pictures, saying the over-the-air rollout would start the next day. Halloween Mode runs October 9 through November 2. The anagram had the date right. (We went through the Ghostbusters content itself, from the Bill Murray spot to the Ecto-R1 show cars, in our earlier story.)

Rivian's mobile app carries the Trick or Treat and exterior effect controls. Photo: Rivian (manufacturer press image)

Rivian's last two Halloween releases came later in the month: the 2024 "Let's Get Spooky" update, which turned R1s into K.I.T.T. and the Back to the Future time machine (we covered it then), and the 2025 Spooky Swamp update. Rivian's own posts give these windows:

This year's start is 12 days ahead of last year's and three days behind Tesla's.

Nothing on the record says why. Rivian's announcement never mentions Tesla, and neither company has published anything showing when Rivian locked in October 9. A Ghostbusters license, a TV spot directed by Gil Kenan and a set of physical show cars are not things a company assembles in two days, so the program was built well before Tesla's post. Whether the date was always October 9 is a separate question, and Bensaid's post only establishes that he knew it by 4:30 p.m. on October 6.

The two updates share a lot of vocabulary. Rivian's version has its own "Trick or Treat Mode," which takes over the driver and rear displays, starts the Ghostbusters theme and switches the exterior lights and sounds to match. Its Motion Mode sets off a light-and-sound show when someone walks past, which is what Tesla's Trick or Treat does for visitors. Rivian had that motion trigger in last year's Spooky Swamp release, so on that feature Tesla is the one catching up.

Tesla's 2026 headline item is a ghost costume on the car's avatar. Rivian has been calling its themes "Car Costumes" since 2024.

Voice is where they split. Tesla lets you speak through the phone app and have the car repeat it to whoever is standing outside. Rivian says its Rivian Assistant "picks up a distinctively eerie tone" and can run light shows, read scavenger-hunt clues or play sound effects on request. That line carries a footnote, and the footnote is about Connect+: a subscription is required, plus separate accounts for streaming services. Rivian's page doesn't say whether the spooky assistant itself needs Connect+, or whether the footnote is about something else.

The Halloween Mode charging screen on an R1 driver display. Photo: Rivian (manufacturer press image)

Tesla's announcement doesn't say which cars get Halloween Mode or when it switches off. Rivian gives an end date and version numbers (2026.36.0 for R1, 2026.36.40 for R2) and says the update goes to "all Rivian vehicles," but its instructions only name R1 and R2. The electric delivery van Rivian builds for Amazon and fleet buyers isn't mentioned.

Bensaid's post is also the only advance notice Rivian gave. He has spoken for Rivian's software timing before, telling Reddit users in May that Teen Mode was delayed. The anagram reached far fewer people than Tesla's announcement: as of October 19, it showed about 17,500 views to Tesla's 1.5 million.

Rivian's Ghostbusters content turns itself off on November 2, two days after Halloween. Tesla hasn't put an end date in writing. Does shipping first beat shipping Ghostbusters? Pick a side: Tesla's ghost avatar or Rivian's Ecto-R1.

Sources: Wassym Bensaid on X (Oct. 6, 2026); Tesla on X (Oct. 6, 2026); Rivian, "New Software: Who Ya Gonna Call?" (Oct. 8, 2026); Rivian, "New Software: Let's Get Spooky" (Oct. 17, 2024); Rivian, "New Software: Enter Rivian's Spooky Swamp" (Oct. 21, 2025). Images: Rivian press photography.