# DeepSeek-Reasonix: DeepSeek-native terminal AI coding agent > An MIT-licensed, terminal-first AI coding agent built only for DeepSeek, engineered around its prefix-cache to keep token costs low across long sessions. Published: 2026-05-27 URL: https://daniliants.com/insights/deepseek-reasonix-deepseek-native-ai-coding-agent/ Tags: ai-coding-agent, deepseek, prefix-cache, cli-tools, cost-optimization, terminal, open-source --- ## Summary Reasonix is an MIT-licensed, terminal-first AI coding agent built exclusively for DeepSeek, with its entire loop engineered around DeepSeek's byte-stable prefix-cache mechanic to keep token costs low across long sessions. It is a direct alternative to Claude Code / Cursor / Aider, trading multi-provider flexibility for deep single-backend cost efficiency. ## Key Insight - **Cache stability as an architectural invariant, not a toggle.** The loop is designed so the prompt prefix stays byte-stable, maximizing DeepSeek's prefix-cache hits. This is why it is DeepSeek-only by design - coupling to one backend is the feature. - **Hard cost number:** one real user's single day (01-05-2026) logged 435M input tokens at 99.82% cache hit, costing ~$12 vs ~$61 with no cache. ~5x savings purely from cache discipline. - **Three architecture pillars:** (1) cache-first loop, (2) tool-call repair, (3) cost control. These solve problems generic agent frameworks "don't even see" because they target a different cache mechanic. - **Drop-in Claude compatibility:** reads `.claude/skills//SKILL.md` and `~/.claude/skills/` alongside its native paths, so Claude-format skills (e.g. OpenSpec workflows) load without an adapter. - **Two modes:** `code` (filesystem + shell tools, SEARCH/REPLACE review, plan mode, project memory) vs `chat` (tools-off thinking partner with MCP, global memory only). - **Honest non-goals:** for hardest-leaderboard reasoning / PhD proofs they recommend Claude Opus; for air-gapped/zero-cost they point to Aider + Ollama. DeepSeek positioned as competitive on coding, cheap per task. - Requires Node >= 22; needs a paid DeepSeek API key. Desktop is a Tauri GUI prerelease (unsigned installers).