You seem to be implying that achievements of internal models are exaggerated, but that's rather implausible. The public does have access to, for example, Opus and Fable, and so we know what those models are capable of - finding real vulnerabilities in multiple codebases, for example. If you extrapolate from these capabilities one more generation, you'll get pretty much the same feats that the internal models are claimed to be capable of - so why should we doubt those claims? It's not like they're claiming that their internal models developed psychic powers and learned to teleport - the claim is pretty much just "we have models a few months ahead of what we're making available, and in those months they've been improving at the same rate as usual".