Overview

Halfbill is an API service that resells Anthropic Claude and OpenAI GPT models. You get one API key, a base URL, and a dashboard; the request and response formats are the ones you already use.

Endpoints

The OpenAI-compatible base URL is https://api.halfbill.uk/v1. The Anthropic SDK and Claude Code take https://api.halfbill.uk and append /v1/messages themselves.

Models

Halfbill serves a short, current list rather than a marketplace:

• Anthropic: claude-sonnet-5, claude-opus-5, claude-fable-5, claude-haiku-4-5, claude-sonnet-4-6, claude-opus-4-6, claude-opus-4-7, claude-opus-4-8
• OpenAI: gpt-5.5, gpt-5.6-terra, gpt-5.6-sol, gpt-6-astra

Claude models accept up to 200K input tokens and return up to 32K; GPT models accept up to 400K and return up to 128K. Streaming, tool calls, vision, structured outputs, and prompt caching (Claude) are supported. Context limits, capabilities, and per-token prices are listed on the models page; when the catalogue changes, that page changes with it.

Billing

• Credits — prepaid, pay as you go, no subscription required. Standard models are billed at half the vendor list price.
• Subscriptions — Chat plans for Halfbill Chat and Code plans for coding agents, each with a monthly allowance that overflows to credits.
• Limits — per-key spend limits, plus organization rate limits described in Rate limits.

Details, top-up packs, and the VAT note are in Pricing & billing.

Dashboard

The dashboard at halfbill.uk/dashboard shows usage and cost per model, key, and project, request logs, spend limits per key, invoices, and team members. The Knowledge base walks through each page.

First request

curl https://api.halfbill.uk/v1/chat/completions \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer $HALFBILL_API_KEY" \
  -d '{
    "model": "claude-sonnet-5",
    "messages": [{"role": "user", "content": "Hello!"}]
  }'

Continue with the Quickstart for SDK and coding-agent snippets.