I've been using GLM 5.3 and 5.3 Flash to reverse-engineer some old firmwares, and it hasn't protested at all. Full 5.3 has a scary-good grasp of debugging assembly, QEMU and hex dumps in my experience, it would make for a good "sleuth" model to find potential vulns. 5.3 Flash is closer to 5.5 Sonnet/6 Luna capabilities-wise, but still smart enough to implement the easy fixes or steer your red team agent.
It's been about a year since I switched from Claude Code to Z.AI, so I don't know what I'm missing out on. But I also don't really feel any FOMO, I'd rather support open model releases than amortize another gated-release model like Mythos.