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Anthropic’s Claude is a model family prized for code, agents and long-document work. Every model speaks the OpenAI-compatible protocol, so you connect with any OpenAI SDK — just change the base_url. Below: how the three tiers are organized, how to read the version numbers, and how to send a first request.

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Three tiers: Haiku, Sonnet, Opus

Claude has three named tiers. The idea is simple: the “higher” the tier, the more capable the model, but the slower and pricier it is.
Not sure? Start with Sonnet (the latest is claude-sonnet-5). It covers most work. Move up to Opus when Sonnet stops keeping up with the complexity; drop to Haiku when speed and cost matter more than peak quality.

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Reading the version numbers

An ID encodes both the tier and the generation, e.g. claude-sonnet-5 or claude-opus-5. One rule: higher numbers are newer and more capable within a tier.
  • claude-haiku-4-5-20251001 — the fast Haiku tier. Some snapshots carry a release-date suffix like this one.
  • claude-sonnet-4-5-20250929, claude-sonnet-4-6, claude-sonnet-5 — the Sonnet tier; -5 is newer than -4-6, which is newer than -4-5.
  • claude-opus-4-5-20251101, claude-opus-4-6, claude-opus-4-7, claude-opus-4-8, claude-opus-5 — the Opus tier; claude-opus-5 is the newest generation and supersedes the whole 4-x branch.
  • claude-fable-5 — Fable, a standalone flagship that sits above the tiers (see below); it isn’t part of the numeric ladder.
Comparing numbers across tiers is meaningless: opus-4-8 beats sonnet-5 not because of the number but because it’s the Opus tier.
Exact current IDs, versions and per-token prices are on the Pricing page at www.ruapi.ai. Names match Anthropic’s official ones, and new versions appear in the catalog automatically.

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Claude Fable 5 — the flagship

claude-fable-5 is Anthropic’s most capable widely released model, built for the most demanding reasoning and long-horizon agentic work: large migrations, complex multi-step implementations, and agent runs that stay on task for hours. It has a 1M-token context window and leads the Opus tier on hard, long-horizon coding and analysis — though on short, well-scoped tasks Opus stays close and costs less. Fable or Opus? Reach for claude-fable-5 on the hardest jobs: big refactors, multi-day agents, deep analytical work. For everyday coding and chat, claude-opus-5 is faster and about half the price. Fable sits at the top of the price range — the exact per-token rate is on the Pricing page.
Fable 5 ships with safety classifiers that decline a small share of requests (cybersecurity, biological and chemical topics, model distillation). A declined request comes back as a normal HTTP 200 with stop_reason: "refusal" — not an error — so have your client handle that case. Haiku, Sonnet and Opus don’t behave this way.

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What Claude is best at

  • Code — writing, refactoring and debugging; one of the family’s strongest suits, especially in Sonnet and Opus.
  • Agents and tool use — the model returns structured function calls that agents and pipelines are built on (see function calling for an example).
  • Long documents — a large context window fits whole codebases and long texts.
  • Vision — you can pass images as input: screenshots, diagrams, scans (see image input for the request format).

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Connecting Claude

The base_url is always https://www.ruapi.ai/v1. Take any OpenAI SDK and put the model ID in the model field:
Step-by-step key, base_url and first-request setup in Python and curl are in the Quickstart. For long answers, streaming is handy. Get your key and balance on the top-up page.

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Next

Connect and first request

base_url, key, Python and curl code.

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Google Gemini: tiers and capabilities.