Ok so the conversation I remembered wasn't in reference to the lab but the picture was pretty clear. From early May:
https://www.google.com/amp/s/screenrant.com/better-call-saul-gus-gun-superlab-lalo-plan/amp/
"Since learning of Lalo's survival, Gus Fring has expected Lalo Salamanca to turn up at his personal residence - hence the massive security operation. Even in "Black & Blue," Mike stands in Gus' house and utters, "Sooner or later, he's gonna end up right here." Earlier in the episode, however, Gus Fring experienced a sudden epiphany while asking a Los Pollos Hermanos customer if they'd like to try spice curls. After weeks without a peep, Gus realizes Lalo can't kill him without upsetting the cartel. The Salamancas' only option is to find proof of Fring's betrayal, and nothing screams "betrayal" like a massive underground superlab the cartel knew nothing about. Having been constantly wondering where Lalo would attack from, Gus now knows his nemesis will, sooner or later, visit the superlab. This foresight allows Gus to prepare for battle, giving himself a home-field advantage by planting a hidden pistol."