The Fermi GRB is one of the instruments listed in the article as detecting the initial burst and would had generated a redirection request for a whole family of different telescopes, including Fermi itself.
Actually, this is a better page with both the swift and fermi images.
Longevity: The explanation on NASA's APOD page states:
" In low Earth orbit Fermi’s Large Area Telescope recorded gamma-ray photons from the burst for more than 10 hours as high-energy radiation from GRB 221009A swept over planet Earth last Sunday, October 9. "
while the second is more specific: "the afterglow of GRB 221009A faded over the course of about 10 hours."
Related interest: The Earth's atmosphere itself produces gamma flashes up to 20MeV:
" In low Earth orbit Fermi’s Large Area Telescope recorded gamma-ray photons from the burst for more than 10 hours as high-energy radiation from GRB 221009A swept over planet Earth last Sunday, October 9. "
while the second is more specific: "the afterglow of GRB 221009A faded over the course of about 10 hours."
Related interest: The Earth's atmosphere itself produces gamma flashes up to 20MeV:
https://en.wikipedia.org/wiki/Terrestrial_gamma-ray_flash
And: "Possible Role of Gamma Ray Bursts on Life Extinction in the Universe" (abstract only):
https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.11...