  The highest energy gamma-rays from gamma-ray bursts (GRBs) have important
implications for their radiation mechanism. Here we report for the first time
the detection of gamma-rays up to 13 TeV from the brightest GRB 221009A by the
Large High Altitude Air-shower Observatory (LHAASO). The LHAASO-KM2A detector
registered more than 140 gamma-rays with energies above 3 TeV during 230$-$900s
after the trigger. The intrinsic energy spectrum of gamma-rays can be described
by a power-law after correcting for extragalactic background light (EBL)
absorption. Such a hard spectrum challenges the synchrotron self-Compton (SSC)
scenario of relativistic electrons for the afterglow emission above several
TeV. Observations of gamma-rays up to 13 TeV from a source with a measured
redshift of z=0.151 hints more transparency in intergalactic space than
previously expected. Alternatively, one may invoke new physics such as Lorentz
Invariance Violation (LIV) or an axion origin of very high energy (VHE)
signals.
