Claude Sonnet 4.5 API

Name: Claude Sonnet 4.5 API
Brand: Anthropic

$3/Mtok in

Anthropic · text

Frontier-quality text and reasoning through one OpenAI-compatible endpoint.

Overview

About Claude Sonnet 4.5

Claude Sonnet 4.5 is the model most coding agents default to: frontier tool-calling reliability, prompt caching, and 200k context at mid-tier pricing. Through CompanyFabric it shares one key, one prepaid balance, and one rate-limit envelope with every other model in the library — switch to GPT-5.5 or an open model by changing one string. Every model on CompanyFabric shares the same API key, billing balance, and rate-limit envelope — one integration covers the entire library.

Facts

At a glance

Availability

Live

Pricing

$3/Mtok in

Metered exactly per call

Context window

200k tokens

Commercial use

See license

Commercial output use permitted per Anthropic terms.

Variants

All endpoints

Claude Sonnet 4.5

$3/Mtok in

Frontier-quality text and reasoning through one OpenAI-compatible endpoint.

Chat Completions

Claude Haiku 4.5

$1/Mtok in

Fast, cheap frontier-family model for high-volume tasks.

Chat Completions

Claude Opus 4.6

$15/Mtok in

The frontier tier for the hardest reasoning and agentic work.

Chat Completions

Prompt library

Example runs

Summarize the three biggest risks in this launch plan, then rewrite the executive summary in half the words.

1. Timeline compression assumes zero provider churn…

This exact run cost $0.014

Review this pull request for correctness bugs. Explain each finding with the failing input.

1. `parseWindow()` returns NaN when `end` precedes `start`…

This exact run cost $0.019

Turn these 12 support tickets into a prioritized product backlog with effort estimates.

P0 — Billing page 500s on annual plans (7 tickets)…

This exact run cost $0.012

Quickstart

How to use the Claude Sonnet 4.5 API

1
Create a free CompanyFabric account — starter credits are included, no card required.
2
Copy your API key from the dashboard. One key covers every model in the library.
3
Point any OpenAI SDK at api.companyfabric.com/v1 and set model to "anthropic/claude-sonnet-4-5".
4
Read the exact metered cost of the call from the response — the same number shown in the playground.

Use cases

What teams build with it

Coding agents

The main loop of agentic coding tools — reliable tool calls, low hallucination rate on file edits, strong repo comprehension.

claude codecoding agenttool use

Long-document analysis

Contracts, specs, and research packs up to 200k tokens with dependable citation of the source text.

long contextdocument analysis

Production copilots

Customer-facing assistants that must stay on policy — strong instruction hierarchy and refusal behavior.

copilotassistantproduction

Get better output

Prompting tips

Give it a role and an output contract up front; Sonnet holds structure across very long outputs.
For agents, prefer many small tools over one mega-tool — tool-choice accuracy is a strength, use it.
Turn on prompt caching for agent loops — repeated system prompts drop to a tenth of the input price.

Exact, metered, prepaid

Pricing

Endpoint	Type	Price
Claude Sonnet 4.5	Chat	$3 / M input · $15 / M output
Claude Haiku 4.5	Chat	$1 / M input · $5 / M output
Claude Opus 4.6	Chat	$15 / M input · $75 / M output

Production-grade

Code samples

import OpenAI from "openai"

const client = new OpenAI({
  baseURL: "https://api.companyfabric.com/v1",
  apiKey: process.env.COMPANYFABRIC_API_KEY,
})

const res = await client.chat.completions.create({
  model: "anthropic/claude-sonnet-4-5",
  max_tokens: 1024,
  temperature: 0.7,
  messages: [{ role: "user", content: "Say hello from the fabric." }],
})

console.log(res.choices[0].message.content)

Playground

Try it in the browser

Playground$3 in / $15 out per 1M tokens

Model

Max output tokens

Prompt

≈ $0.0154

Comparisons

Claude Sonnet 4.5 vs the alternatives

Claude Sonnet 4.5 vs GPT-5.5

GPT-5.5 wins on raw reasoning benchmarks and cheap input tokens; Sonnet 4.5 wins on tool-calling reliability and sustained code-edit quality. Most teams route the agent loop to Sonnet and heavy one-shot analysis to GPT-5.5 — with one key, that split is a config line, not a second vendor contract.

Claude Sonnet 4.5 vs Gemini 3.1 Pro

Gemini 3.1 Pro brings a bigger context window and strong multimodal input; Sonnet 4.5 is the steadier hand inside agent loops. Route by shape of work: massive-context analysis to Gemini, iterative tool-driven execution to Sonnet.

FAQ

Frequently asked questions

How much does the Claude Sonnet 4.5 API cost?

$3 / M input · $15 / M output. Every call is metered exactly and shown before you run it.

How do I get a Claude Sonnet 4.5 API key?

Create a CompanyFabric account, and one key unlocks Claude Sonnet 4.5 and every other model in the library. Free starter credits are included — no subscription, no card required to try it.

Why use Claude Sonnet 4.5 on CompanyFabric instead of going direct?

One key, one prepaid balance, and one rate-limit envelope across the whole library, at pricing at parity with or below the direct API. Model switching is a one-line change, and BYOK routing is 0% fee.

Is the API OpenAI-compatible?

Yes — point any OpenAI SDK at api.companyfabric.com/v1 and set model to "anthropic/claude-sonnet-4-5".

Can I use the output commercially?

Commercial output use permitted per Anthropic terms.

How does billing work?

Prepaid credits via card, or BYOK with your own provider keys at 0% platform fee. No subscription required; balances never expire.

Does the Claude Sonnet API support tool use and streaming through CompanyFabric?

Yes — tools, streaming, vision, and prompt caching pass through the OpenAI-compatible endpoint unchanged. Anthropic-native /v1/messages is also on the roadmap.

Provider

About Anthropic

Anthropic publishes the claude family. Also in this family: Claude Haiku 4.5, Claude Opus 4.6. License: Commercial output use permitted per Anthropic terms.

Explore