Claude Code with DeepSeek Anthropic-compatible API fails during project analysis: Invalid user_id

## Description I encountered a compatibility issue when using Claude Code with DeepSeek's Anthropic-compatible API endpoint. Claude Code can start successfully, and it works in a clean empty directory. However, when I run it inside a real project directory and ask it to read or analyse the codebase, it starts by searching/listing files and then fails during a subsequent API request with the following error: ```text API Error: 400 Invalid 'user_id': string does not match pattern. Expected a string that matches the pattern '^[a-zA-Z0-9_-]+$'. ``` Environment Tool: Claude Code API endpoint: https://api.deepseek.com/anthropic Model: deepseek-v4-pro[1m] OS: macOS Usage scenario: Claude Code project-level code analysis My environment variables are configured as follows: export ANTHROPIC_BASE_URL=https://api.deepseek.com/anthropic export ANTHROPIC_AUTH_TOKEN=sk-xxxx export ANTHROPIC_MODEL='deepseek-v4-pro[1m]' export ANTHROPIC_DEFAULT_OPUS_MODEL='deepseek-v4-pro[1m]' export ANTHROPIC_DEFAULT_SONNET_MODEL='deepseek-v4-pro[1m]' export ANTHROPIC_DEFAULT_HAIKU_MODEL=deepseek-v4-flash I also previously tested with: export CLAUDE_CODE_SUBAGENT_MODEL=deepseek-v4-flash export CLAUDE_CODE_EFFORT_LEVEL=max But the issue still appears after disabling these two variables. Steps to reproduce Configure Claude Code to use DeepSeek's Anthropic-compatible endpoint. Run Claude Code in a clean empty directory. It starts successfully. Run Claude Code inside an actual code project. Ask Claude ...