I've been using V4 flash consistently with Claude. Pretty great fast and darn cheap. I use it about 3h/day and so far haven't crossed $1 USD/week.

FWIW, I this is what I have in my settings.json

  "env": {
    "ANTHROPIC_AUTH_TOKEN":"sk-nope_not_real",   
    "ANTHROPIC_BASE_URL": "https://api.deepseek.com/anthropic",
    "ANTHROPIC_MODEL": "deepseek-v4-flash",
    "ANTHROPIC_DEFAULT_OPUS_MODEL": "deepseek-v4-flash",
    "ANTHROPIC_DEFAULT_SONNET_MODEL": "deepseek-v4-flash",
    "ANTHROPIC_DEFAULT_HAIKU_MODEL": "deepseek-v4-flash",
    "CLAUDE_CODE_DISABLE_NONESSENTIAL_TRAFFIC": "1",
    "CLAUDE_CODE_EFFORT_LEVEL": "low",
    "CLAUDE_CODE_DISABLE_ADAPTIVE_THINKING": "1",
    "CLAUDE_CODE_DISABLE_THINKING": "0",
    "CLAUDE_CODE_ENABLE_AWAY_SUMMARY": "0",
    "CLAUDE_CODE_SUBAGENT_MODEL": "deepseek-v4-flash",
    "CLAUDE_CODE_MAX_OUTPUT_TOKENS": "8000",
    "CLAUDE_CODE_FILE_READ_MAX_OUTPUT_TOKENS": "4000",
    "BASH_MAX_OUTPUT_LENGTH": "20000",
    "CLAUDE_AUTOCOMPACT_PCT_OVERRIDE": "60",
    "CLAUDE_CODE_AUTO_COMPACT_WINDOW": "200000",
    "CLAUDE_CODE_DISABLE_GIT_INSTRUCTIONS": "1"
  }