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RTK reports token savings, but our cost benchmarks disagree

Quesma's $1,500 benchmark found RTK cuts reported token output but changes Claude Code and DeepSeek coding costs by only about 5% on Terminal-Bench 2.1.

Quesma benchmarked RTK (Rust Token Killer), a popular tool with 79k GitHub stars that filters terminal output for AI coding agents, whose README claims up to 90% output reduction. Across 1,740 Terminal-Bench 2.1 attempts running Claude Code with Fable 5.0 and OpenCode with DeepSeek V4 Pro 0813, total costs moved only -5% for Fable and +5% for DeepSeek, with pass rates dropping 1-2%. RTK's own rtk gain metric reported 349.2 million tokens saved (an 89% reduction) across 445 DeepSeek attempts, but this did not correlate with actual cost savings, and cached terminal-output reads cost as little as 1/10 to 1/30 of regular input tokens. A bug in rtk find 0.45.0 caused one agent to loop with 339 consecutive errors, costing roughly 9x the baseline attempt, though the task still passed.

Video compressor

Simon Willison built a browser-based video compressor using the WebAssembly FFmpeg build, generated by Claude Fable 5.1 in Claude Code for web.

Willison recorded a demo video of his Equal Earth animation and wanted an optimized web-publishable version. He had Claude Fable 5.1 running in Claude Code for web build a compressor around the WebAssembly port of FFmpeg. The post is a short vibe-coding demonstration, not a model release or security event.

Simon Willison · 9d agoAI tools & infra

llm-anthropic 0.28

llm-anthropic 0.28 released with Claude Fable 5.1 support, default reasoning traces and a new ClaudeRefusal exception.

Developer Simon Willison released version 0.28 of the llm-anthropic Python plugin, adding support for Claude Fable 5.1. Reasoning traces are now displayed by default for models that support them, and a new llm_anthropic.ClaudeRefusal exception is raised when Claude returns a refusal.

Simon Willison · 14d agoAI tools & infra2

GeoJSON Map Viewer

Simon Willison built a GeoJSON map viewer with PNG export using GPT-5.6-Sol, Claude Code for web, and Fable 5.1.

Simon Willison describes building a GeoJSON map viewer that displays boundary files and exports maps as PNGs. GPT-5.6-Sol proactively offered to create the tool, and iterations used Claude Code for web and Fable 5.1. He also notes ChatGPT Work will assemble boundary polygons from government data sources when asked.

Simon Willison · 15d agoAI tools & infra

Ask HN: How do you manage skills files?

A Hacker News thread debates whether agent skill files are worth managing, citing 2–4x output-token reductions on flagship models in one company's testing.

Commenters argue skills are stored prompts that help less-technical users compensate for weak prompting, while one participant reports company testing found skills reduce flagship-model output tokens by roughly 2–4x, a gap growing with newer models. Others note skills can bundle reusable scripts and inline commands for deterministic context building, and that harnesses now execute backticked commands before the agent sees the skill. Some argue improving model capability makes downloadable skills redundant.

Show HN: How Stale Is Your AI? Release age and training cutoff for 20 models

A new site tracks release dates and training cutoffs for 20 AI models across 8 labs, exposing months-long staleness gaps.

A community-built page, launched via Show HN, tracks release dates and training cutoff dates for 20 current models from 8 labs including OpenAI, Anthropic, Google DeepMind, Meta, Mistral AI, Alibaba, DeepSeek, and xAI. Only 10 of the 20 models have lab-published cutoff dates, with data available as models.json. For example, GPT-6 Astra shipped September 3, 2026 with an April 30, 2026 cutoff. The page argues web search tools paper over, but never close, the staleness gap.