What are the differences around endorsing beliefs and expressing them, e.g. Moore’s paradox, also Railton’s Locke lectures. Judging is commitment, which is consenting to being held to certain norms
Brandom takes commitment to truth to be (roughly) claiming to be able to defend your claim under scrutiny and granting others authority to assert on the basis of one’s speech. If you’re not really going to honour these commitments or youre skilful enough to defend any position, then we shouldnt take your assertion as expressing belief or knowledge, its not a good signal
(How would the uncertainty expressed in The Thing affect the possibility of assertions on these views?)
See various common ground theories of assertion (and lying) in Philosophy of Language and Mind.