DeepSeek Harness works very well, also used Codewhale which is not too shabby

You can stick with Claude Code if you're already using it. DeepSeek has an Anthropic-compatible endpoint, so you just need to set ANTHROPIC_BASE_URL=https://api.deepseek.com/anthropic and ANTHROPIC_AUTH_TOKEN to your DeepSeek API key.

Pi is very good with open weight models (proprietary ones too)

Pi if you're a minimalist

OpenCode if you want a good, opinionated setup