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The passage around this formula

With a closed, API-served model, both arguments are partly opaque: $\theta$ is asserted rather than shown, and $\theta$' — whatever the endpoint is actually running today — cannot be confirmed to equal $\theta$ . A reproduction attempt is chasing two unknowns with one equation. With an open-weight release, $\theta$ is a downloadable file, and a downloaded file can be checksummed against the one a vendor states it evaluated. That does not resolve the equation, but it removes a whole term from it: if the checksums match, $\theta$ = $\theta$' is no longer a hypothesis, it is a verified fact, and any gap between s and s' has to be attributed to H $\neq$ H' . That is a strictly smaller, more tractable problem…

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