AIBase Pillar
Claude — Guide, Setup & How to Use
Claude is Anthropic's family of AI models, built for careful reasoning, long-context work, and dependable coding. It powers everything from quick Q&A to Claude Code, an agentic command-line tool that reads, writes, and runs code across a whole project. This pillar walks through what Claude does well, which model tier to pick, how to wire up Claude Code, and how to get more out of every call — including cheaper access to the same models through Izzi API.
What Claude is good at
Claude's strengths cluster around three areas: writing that holds a consistent voice and structure, multi-step reasoning that stays coherent over long chains, and coding across large, interconnected files. Its long context window lets you paste whole documents, specs, or codebases and reason over them in one pass instead of chunking. It tends to follow detailed instructions closely and to flag uncertainty rather than inventing an answer, which makes it a good fit for work where correctness matters more than speed.
Opus vs Sonnet vs Haiku — which tier to use
The Claude family is tiered by capability and cost. Opus is the most capable tier, worth it for hard reasoning, tricky refactors, and tasks where a wrong answer is expensive. Sonnet is the balanced middle — fast enough for interactive use, strong enough for most coding and writing, and the default most people should reach for. Haiku is the lightweight tier for high-volume, latency-sensitive jobs like classification, extraction, and routing where you call the model thousands of times. A common pattern is to route cheap-first: Haiku or Sonnet for the bulk, Opus only when a task genuinely needs it.
Setting up Claude Code
Claude Code is a terminal tool that turns Claude into a hands-on coding agent — it can open files, make edits, run commands, and iterate. It reads its endpoint and credentials from environment variables: point `ANTHROPIC_BASE_URL` at your provider and set `ANTHROPIC_API_KEY` to your key. Because it speaks the Anthropic-compatible API, you can route it through Izzi API with one key to reach the same Claude models at lower cost, without changing how the tool works. After that, run it from any project root and give it a task in plain language.
Extended Thinking and prompt caching
Extended Thinking lets Claude spend more internal reasoning before answering, which measurably improves results on math, planning, and multi-constraint problems — at the cost of extra tokens, so reserve it for hard tasks. Prompt caching stores a large, reused prefix (a long system prompt, a codebase, or reference docs) so repeat calls skip re-processing it, cutting both latency and cost on iterative workflows. Used together with a clear, specific system prompt, these two features are the biggest quality-and-cost levers most users overlook.
Claude for coding vs writing
For coding, Claude works best when you give it the surrounding context — related files, the error, and the goal — rather than an isolated snippet; Claude Code automates that context-gathering for you. For writing, it responds well to a brief: audience, tone, length, and a few examples of the style you want. In both cases the failure mode is vagueness, so treat the prompt like a spec. Pairing a strong system prompt with one or two worked examples reliably lifts output quality.
Pricing and access
Claude is billed per token, with input and output priced separately and higher tiers costing more than lighter ones. You can access it directly through Anthropic, through cloud marketplaces, or through an aggregator like Izzi API that gives you one key across models and typically lower effective pricing. For predictable workloads, combining the right tier with prompt caching keeps costs down without sacrificing quality. Check current provider pricing before committing to a tier, since rates change over time.
Frequently asked questions
- How is Claude different from GPT?
- Both are strong general-purpose model families, but Claude is often preferred for long-context reasoning, careful instruction-following, and coding across large projects, while GPT has a very broad ecosystem and tooling. In practice the best choice depends on the task, so many teams keep access to both — an aggregator like Izzi API makes switching between them a one-line change.
- Is Claude Code free?
- The Claude Code tool itself is free to install, but it needs a paid backend to run — either Anthropic API credits or an eligible Claude subscription. If you route it through Izzi API you pay per token for the underlying model calls, usually at a lower effective rate than going direct.
- How large is Claude's context window?
- Claude supports long context windows, large enough to hold whole documents or sizeable codebases in a single request, and some tiers offer an extended context beyond the standard size. Because exact token limits vary by model and change over time, check the current model card for the specific number before relying on it.
- Claude Code vs Cursor — what's the difference?
- Claude Code is a terminal-based agentic tool that works from the command line across your whole project, while Cursor is an AI-native code editor (a VS Code–style IDE) with inline assistance. They solve overlapping problems from different angles, and both can be pointed at Claude models — Claude Code suits automation and headless workflows, Cursor suits interactive editing.