Claude Mythos 5 vs GPT-5.4-Cyber (OpenAI)

GPT-5.4-Cyber (OpenAI) edges out Claude Mythos 5 by 0.7 points (7.2 vs 6.5) -- a B-tier vs C-tier split that's narrow but real. Not a blowout; both belong on a shortlist. The score gap shows up most clearly in the categories that matter for GPT-5.4-Cyber (OpenAI)'s strengths, so if those categories are your priority, the lead translates.

Neither tool offers a free tier. Claude Mythos 5 starts at Invite only, GPT-5.4-Cyber (OpenAI) at Not publicly disclosed. Plan to budget for whichever you pick. The cheap tier usually caps out faster than buyers expect, so look at what the entry plan actually includes -- both vendors have raised list prices in 2026 and the limits are where most of the cost surprise lives.

By use case: pick Claude Mythos 5 when partner organizations in project glasswing doing cybersecurity research, defensive red-teaming, threat intelligence, or large-scale vulnerability triage. Pick GPT-5.4-Cyber (OpenAI) when enterprise soc teams, established security research orgs, and vetted individual defenders who can qualify for trusted access for cyber. The two tools aren't fighting for the same person -- they're aiming at adjacent jobs that occasionally overlap. If you're squarely in GPT-5.4-Cyber (OpenAI)'s lane, the tier-list ranking and the use-case fit point the same direction; if you're in Claude Mythos 5's lane, the score gap matters less than the fit.

Bottom line: GPT-5.4-Cyber (OpenAI) is the safer default for most readers, but Claude Mythos 5 is competitive enough that the tie-breaker is your specific workload, not the spec sheet.