Prompt injection benchmark: delimiter and strict prompt took Gemma 4 from 21% to 100% defense rate

Prompt injection benchmark: delimiter + strict prompt took Gemma 4 from 21% to 100% defense rate (15 models, 6100+ tests)

A Reddit user posted a prompt-injection benchmark covering 15 models, 7 attack types, and 6,100+ cases. The setup wraps untrusted documents in long random delimiters; Gemma 4 E4B rose from 21.6% to 100% defense. The key detail is the reproducible metric: blocked/(blocked+failed).

Why it matters: HKR-H/K/R all pass: Gemma 4’s defense-rate jump is clickable, the test setup is concrete, and prompt injection matters to builders. Single Reddit benchmark keeps it in the 78–84 band.