Configuring Claude Code with DeepSeek V4 PRO APIs

Motivation

PawnDB is a C++17 in-memory database. Modern C++ involves a lot of boilerplate and repetitive patterns. AI coding assistants can absorb that, but the major options are proprietary, expensive, or tied to specific models. DeepSeek V4 PRO provides a capable, cost-effective alternative — and Claude Code supports it through an Anthropic-compatible API endpoint.

This post walks through how PawnDB's dev container is set up to use DeepSeek V4 PRO as the backend for Claude Code, so anyone can reproduce the same setup.

Prerequisites: Dev Container with Node.js

Claude Code is a VS Code extension that runs on Node.js. A base Ubuntu image doesn't include it, so the Dockerfile installs it explicitly:

RUN apt-get update \
    && apt-get install -y curl \
    && curl -fsSL https://deb.nodesource.com/setup_22.x | bash - \
    && apt-get install -y nodejs \
    && apt-get clean \
    && rm -rf /var/lib/apt/lists/*

The dev container JSON installs the extension and wires the API key:

{
  "customizations": {
    "vscode": {
      "extensions": [
        "anthropic.claude-code"
      ],
      "settings": {
        "claude-code.primaryApiKey": "${env:ANTHROPIC_AUTH_TOKEN}"
      }
    }
  },
  "runArgs": [
    "--env-file=${localWorkspaceFolder}/.devcontainer/.env"
  ]
}

The .env file (gitignored) supplies the API key:

ANTHROPIC_AUTH_TOKEN=<your-deepseek-api-key>

Claude Code Configuration

Claude Code natively targets the Anthropic API. DeepSeek exposes an Anthropic-compatible endpoint that accepts the same request/response shapes, so you can redirect Claude Code by changing the base URL, the model name, and setting a few environment variables.

PawnDB's .claude/settings.json:

{
  "env": {
    "ANTHROPIC_BASE_URL": "https://api.deepseek.com/anthropic",
    "ANTHROPIC_MODEL": "deepseek-v4-pro[1m]",
    "ANTHROPIC_DEFAULT_OPUS_MODEL": "deepseek-v4-pro[1m]",
    "ANTHROPIC_DEFAULT_SONNET_MODEL": "deepseek-v4-pro[1m]",
    "ANTHROPIC_DEFAULT_HAIKU_MODEL": "deepseek-v4-flash",
    "CLAUDE_CODE_SUBAGENT_MODEL": "deepseek-v4-flash",
    "CLAUDE_CODE_EFFORT_LEVEL": "max"
  }
}

Alternatively, if you're migrating an existing Claude Code installation without a settings file, you can export these as shell environment variables:

export ANTHROPIC_BASE_URL=https://api.deepseek.com/anthropic
export ANTHROPIC_AUTH_TOKEN=<your DeepSeek API Key>
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
export CLAUDE_CODE_SUBAGENT_MODEL=deepseek-v4-flash
export CLAUDE_CODE_EFFORT_LEVEL=max

Key details

Base URL — ANTHROPIC_BASE_URL points to https://api.deepseek.com/anthropic. This is the DeepSeek endpoint that speaks the Anthropic Messages API. Claude Code sends all requests here instead of https://api.anthropic.com.

Model mapping — Claude Code has several "slots" for different model sizes. These are all mapped to DeepSeek equivalents:

Haiku and subagent models point to deepseek-v4-flash for quick, cheap tasks (file reads, simple edits). Opus, Sonnet, and the primary model all use deepseek-v4-pro[1m] for heavier reasoning. The [1m] suffix enables the 1-million-token context window.

Effort level — CLAUDE_CODE_EFFORT_LEVEL=max sets maximum reasoning depth for the primary model. This lets deepseek-v4-pro spend more thinking tokens on complex refactors and multi-file changes.

How It Fits Together

From a cold start:

1. Build the image — docker build runs the Dockerfile, installing Node.js alongside the C++ toolchain.
2. Open in dev container — VS Code starts the container, mounts the repo volume, and loads the .env file.
3. Extension activates — Claude Code reads .claude/settings.json and redirects all chat/agent traffic to api.deepseek.com/anthropic.
4. Workflow — You chat with Claude Code for complex tasks (refactoring, generating tests, explaining code), all powered by DeepSeek's models.

All of this is committed to the repo (except the .env secrets), so anyone who clones PawnDB and provides their own DeepSeek API key gets the same setup.

Trade-offs

Why DeepSeek over Anthropic's own models? Cost and access. DeepSeek V4 PRO is substantially cheaper per token while being competitive on reasoning-heavy C++ tasks. It also avoids the need for a separate Anthropic billing account.

What you lose. DeepSeek's Anthropic-compatible endpoint doesn't implement every Claude feature. Sometimes the agent gets interrupted and you have to prompt again to continue. Prompt caching and some advanced tool-use patterns may behave differently than on Anthropic's native API.