According to Variety, Krypto will also appear in the Supergirl: Woman of Tomorrow film that's being written by Ana Nogueira.
In the comics, Kara Zor-El is often fairly lonely after arriving on Earth several years after her "baby cousin" Kal-El. While Superman doesn't remember much, if anything about Krypton, Kara is often depicted as a teenager when the doomed planet explodes.
When she eventually arrives on Earth, she's often dismayed by the primitive Earth technology when it's compared to the vast technological wonders of Krypton.
When first describing Woman of Tomorrow, DCU co-chair James Gunn stated, "We see the difference between Superman, who was sent to Earth and raised by loving parents from the time he’s an infant, versus Supergirl, who was raised on a rock chip off of Krypton, and watched everyone around her die and be killed in terrible ways for the first 14 years of her life."
Oftentimes, Kara's lone comfort and remembrance of home is Krypto.
The film is said to be inspired by Tom King's 2021 run on the Supergirl comics, which was collected as a TPB titled, Supergirl: Woman of Tomorrow. The TPB eventually sees Kara leave Earth and venture off into space with Krypto.
The official synopsis for the series reads:
Kara Zor-El has seen some epic adventures over the years, but she now finds her life without meaning or purpose. Here she is, a young woman who saw her planet destroyed and was sent to Earth to protect a baby cousin who ended up not needing her. What was it all for? Wherever she goes, people only see her through the lens of Superman’s fame.
Just when Supergirl thinks she’s had enough, everything changes. An alien girl seeks her out for a vicious mission. Her world has been destroyed, and the bad guys responsible are still out there. She wants revenge, and if Supergirl doesn’t help her, she’ll do it herself, whatever the cost. Now a Kryptonian, a dog, and an angry, heartbroken child head out into space on a journey that will shake them to their very core.
This volume collects Supergirl: Woman of Tomorrow #1-8
To expand on that synopsis, the series opens with Kara celebrating her birthday on a distant planet with a red sun. She travels there with Krypto, with the intent to use her weakened state (due to the red sun) to get drunk. While there, she comes across Ruthye, a young girl who is looking to hire a mercenary to avenge the death of her father.
However, the men behind her father's death catch up to her and they intend to finish the job and wipe out the entire family line. Naturally, Supergirl and Krypto step in and save the girl but Krypto gets poisoned during the confrontation. While Supergirl doesn't want to take on a mission of vengeance she reluctantly agrees to help Ruthye because she needs to acquire a sample of the original poison in order to cure Krypto.
The story has been called a superhero version of True Grit and has gone on to become a definitive story for Kara, despite being a fairly recent publication.
The question on the minds of DC fans now is whether Krypto arrives in Kara's spaceship or if he hitches a ride with Kal.
If it's the latter, then perhaps Krypto will actually be showing up a lot sooner in Superman: Legacy, alongside David Corenswet's Man of Steel?