Claude vs Gemini Across 4 Security Domains: A Dead Heat — and the Hardening 63% of AI Code Skips

The interesting result isn't who won. It's that across four security domains, Claude and Gemini missed the same hardening steps — and if you've shipped AI-generated auth middleware this year, your code almost certainly has the same gaps, and your review didn't catch them either. For the record, the scoreboard: one Gemini win, two ties, one split — a statistical dead heat. That's the last time the winner matters in this article. Here's the number that should bother you more than any leaderboard: across 700 AI-generated functions scored by the rules I'm about to use, 63% shipped a vulnerability . So "which model writes more secure code?" is mostly the wrong question — I've run that leaderboard myself and argued it's the wrong frame. But people keep asking it, so I ran it properly — on the ESLint security plugins I wrote specifically to catch these bugs, each mapped to a CWE — to show you what actually matters. The setup Four domains, four of my plugins. For each, the same feature-only prompt (no "make it secure" hint — that's how people actually use these tools), generated once by Gemini 2.5 Flash via the Gemini CLI and once by Claude Sonnet 4.6 via the Claude CLI , then linted with the domain's plugin on recommended . Method honesty: this is Gemini Flash vs Claude Sonnet — the comparable price/latency tier each vendor's CLI defaults to (Pro and Opus are a separate bracket; more on that below). It compares CLI tooling, system prompt included, not raw models under controlled decoding. n=1 per domain — but I re-ran the JWT round, and both models landed on 5 findings again with the same core misses, so treat these as directional with stable failure modes, not ±0 gospel. The scorecard Domain Prompt Plugin Gemini Claude NestJS service users + auth + admin nestjs-security 2 6 JWT auth login + verify middleware jwt 5 5 MongoDB data layer Mongoose model + search mongodb-security 8 8 General API (injection) import + search + reset secure-coding 9 13* One Gemini win, two dead h