RTK (Rust Token Killer) filters and compresses terminal output before the AI agent reads it. With over 79k GitHub stars, RTK is popular for making AI coding cheaper. One X post claimed RTK could cut Claude Code tokens by up to 60%, reaching 313K views. Yet JetBrains's Skills Bench found no savings. The README warns: RTK cuts up to 90% of bash output, not your bill.

We tested RTK on Terminal-Bench 2.1 with Claude Code + Fable 5.0 and Open Code + DeepSeek V4 Pro 0813. Each task ran five times with and without RTK—1,740 attempts total. With RTK, Fable costs fell 5%, DeepSeek rose 5%. Pass rates dropped 1% and 2%.

Per-task, Fable was 1% more expensive; DeepSeek rose 17%. One task, winning-avg-corewars, drove Fable's savings. RTK reported 349.2M tokens saved across 445 DeepSeek attempts, but costs stayed higher.

Less terminal output does not mean cheaper AI coding.