In ultrarelativistic heavy ion collisions at the LHC, each nucleus acts a sources of high-energy real photons that can scatter off the opposing nucleus in ultraperipheral photonuclear (<a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mi>γ</a:mi><a:mo>+</a:mo><a:mi>A</a:mi></a:math>) collisions. Hard scattering processes initiated by the photons in such collisions provide a novel method for probing nuclear parton distributions in a kinematic region not easily accessible to other measurements. ATLAS has measured production of dijet and multijet final states in ultraperipheral <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:mrow><c:mi>Pb</c:mi><c:mo>+</c:mo><c:mi>Pb</c:mi></c:mrow></c:math> collisions at <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:msqrt><e:msub><e:mi>s</e:mi><e:mi>NN</e:mi></e:msub></e:msqrt><e:mo>=</e:mo><e:mn>5.02</e:mn><e:mtext> </e:mtext><e:mtext> </e:mtext><e:mi>TeV</e:mi></e:math> using a dataset recorded in 2018 with an integrated luminosity of <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"><g:mn>1.72</g:mn><g:mtext> </g:mtext><g:mtext> </g:mtext><g:msup><g:mi>nb</g:mi><g:mrow><g:mo>−</g:mo><g:mn>1</g:mn></g:mrow></g:msup></g:math>. Photonuclear final states are selected by requiring a rapidity gap in the photon direction; this selects events where one of the outgoing nuclei remains intact. Jets are reconstructed using the anti-<i:math xmlns:i="http://www.w3.org/1998/Math/MathML" display="inline"><i:msub><i:mi>k</i:mi><i:mi mathvariant="normal">t</i:mi></i:msub></i:math> algorithm with radius parameter, <l:math xmlns:l="http://www.w3.org/1998/Math/MathML" display="inline"><l:mi>R</l:mi><l:mo>=</l:mo><l:mn>0.4</l:mn></l:math>. Triple-differential cross sections, unfolded for detector response, are measured and presented using two sets of kinematic variables. The first set consists of the total transverse momentum (<n:math xmlns:n="http://www.w3.org/1998/Math/MathML" display="inline"><n:msub><n:mi>H</n:mi><n:mi mathvariant="normal">T</n:mi></n:msub></n:math>), rapidity, and mass of the jet system. The second set uses <q:math xmlns:q="http://www.w3.org/1998/Math/MathML" display="inline"><q:msub><q:mi>H</q:mi><q:mi mathvariant="normal">T</q:mi></q:msub></q:math> and particle-level nuclear and photon parton momentum fractions, <t:math xmlns:t="http://www.w3.org/1998/Math/MathML" display="inline"><t:msub><t:mi>x</t:mi><t:mi mathvariant="normal">A</t:mi></t:msub></t:math> and <w:math xmlns:w="http://www.w3.org/1998/Math/MathML" display="inline"><w:msub><w:mi>z</w:mi><w:mi>γ</w:mi></w:msub></w:math>, respectively. The results are compared with leading-order perturbative QCD calculations of photonuclear jet production cross sections, where all leading order predictions using existing fits fall below the data in the shadowing region. More detailed theoretical comparisons will allow these results to strongly constrain nuclear parton distributions, and these data provide results from the LHC directly comparable to early physics results at the planned Electron-Ion Collider. © 2025 CERN, for the ATLAS Collaboration 2025 CERN