Claude Code with SeibertGPT

Anthropic's coding agent for the terminal – uses DeepSeek via SeibertGPT's Anthropic-compatible interface.

Developertested with Claude Code 2.1.283 on September 28, 2026 · all tools

Claude Code is closed source, comes with a large system prompt and is optimized for Anthropic's Claude models.

Claude Code in auto mode needs at least 2 concurrent requests

In auto mode, a second model, the classifier, checks actions such as shell commands before Claude Code runs them. With SeibertGPT, Claude Code sends its own requests to the model for this, in addition to the actual requests. Your plan must therefore allow at least 2 concurrent requests. With only one, SeibertGPT briefly holds overlapping requests or rejects them with HTTP 429 (concurrency_limit); if a request is rejected, Claude Code blocks the action. If your plan allows only one concurrent request, press Shift+Tab to switch to a different mode.

Which tool fits which plan? Recommendations in the API docs

1. Prerequisites

You need a SeibertGPT plan and an API key. You get both after signing in.

Sign inView plans

2. Download for macOS

  • In the terminal: curl -fsSL https://claude.ai/install.sh | bash
  • Or with Homebrew: brew install --cask claude-code

3. Set up

Store the key

Run this in the terminal and paste the key when asked. It's stored in the Keychain, and Claude Code reads it from there:

Command
security add-generic-password -U -s seibertgpt -a "$USER" -w

Store the config file

Download settings.json and put it in the folder shown. If there's already a settings.json there, copy over only “apiKeyHelper” and the entries under “env”. After that, Claude Code sends its model requests to SeibertGPT instead of Anthropic; to switch back, remove the entries again.

Start and check

Open a new terminal, start claude and enter /status. “Anthropic base URL” shows https://api.seibert.ai, and the model is deepseek-v41-flash-fast.

Optional: turn off connections to Anthropic

Besides the model requests, Claude Code still calls Anthropic services, e.g. for updates, telemetry and settings, and in some cases sends your SeibertGPT key along (Anthropic rejects it). If you don't want this, add this line as the first line directly below "env": {, including the comma at the end. However, Claude Code then no longer updates itself: run claude update to get updates.

Command
"CLAUDE_CODE_DISABLE_NONESSENTIAL_TRAFFIC": "1",

File: ~/.claude/settings.json · Download settings.json

Important: if settings.json already exists, don't replace it. The file also contains your other settings; copy over only our entries.

settings.json
{
  "apiKeyHelper": "security find-generic-password -ws seibertgpt",
  "env": {
    "ANTHROPIC_BASE_URL": "https://api.seibert.ai",
    "ANTHROPIC_MODEL": "deepseek-v41-flash-fast",
    "ANTHROPIC_DEFAULT_OPUS_MODEL": "deepseek-v41-flash-fast",
    "ANTHROPIC_DEFAULT_SONNET_MODEL": "deepseek-v41-flash-fast",
    "ANTHROPIC_DEFAULT_HAIKU_MODEL": "deepseek-v41-flash-fast",
    "CLAUDE_CODE_SUBAGENT_MODEL": "deepseek-v41-flash-fast",
    "CLAUDE_CODE_MAX_CONTEXT_TOKENS": "1000000"
  }
}

4. Test

In the project folder, ask “What's in the README?” – Claude Code reads the file using a tool and summarizes it.

5. Troubleshooting

Claude Code can't find the key

macOS: if Claude Code reports that the apiKeyHelper script fails, the Keychain entry “seibertgpt” is usually missing. Run the command from “Store the key” again. Windows: if Claude Code doesn't see the variable SEIBERTGPT_API_KEY, it sends the text %SEIBERTGPT_API_KEY% as the key, and SeibertGPT responds with error 401. This happens in windows that were already open before the key was stored, including VS Code. Open a new PowerShell window or quit VS Code completely and restart it.

ANTHROPIC_AUTH_TOKEN or ANTHROPIC_API_KEY is set

In Claude Code, both variables take precedence over “apiKeyHelper”: ANTHROPIC_AUTH_TOKEN replaces the SeibertGPT key (this shows up e.g. as error 401), and Claude Code additionally sends ANTHROPIC_API_KEY to SeibertGPT. Remove both (also from ~/.zshrc or the Windows environment variables) and open a new window. On Windows, for example: [Environment]::SetEnvironmentVariable("ANTHROPIC_AUTH_TOKEN", $null, "User")

Model not found

SeibertGPT doesn't know Claude model names. All model entries under “env” must point to a SeibertGPT model.

Cost display

/cost and total_cost_usd use Anthropic prices and say nothing about your billing at SeibertGPT. The “unrecognized_model” warning in claude -p mode is harmless: Claude Code simply doesn't know the model name.

What doesn't work with SeibertGPT

Anthropic doesn't officially support Claude Code with models from other providers. Features that require a claude.ai account (e.g. Remote Control) aren't available with SeibertGPT.

HTTP 401 – key rejected

The key was copied incorrectly or has been revoked. Create a new key under Account → API keys.

HTTP 403 – IP binding

Your key is currently bound to a different IP (e.g. another device). Wait for the lock period to expire or release the binding under Account → API keys.

HTTP 400 – cold_request_too_large

A new or long-paused session starts with a lot of context. Start a new session or shorten the history.

“Hinweis von SeibertGPT: Der Kontext ist zu … gefüllt” (German context notice)

You're approaching your plan's context limit. Summarize the history (e.g. /compact) or start over.

Nothing works after an update

These tools change quickly. The version the guide was tested with is shown at the top – let us know if something no longer matches.