VARIANT · Anthropic / Claude

claude-sonnet-4-5-20250929 API

Anthropic / Claude

Use claude-sonnet-4-5-20250929 from the Claude family via RunAPI. Per-call pricing, no subscription, and failed generations are never charged.

Operational · text · Commercial OK
runapi.ai
# Base URL
https://runapi.ai

# Endpoints
POST /v1/messages
curl https://runapi.ai/v1/messages \
  -H "Authorization: Bearer $RUNAPI_KEY" \
  -H "Content-Type: application/json" \
  -d '{
  "model": "claude-sonnet-4-5-20250929",
  "max_tokens": 1024,
  "messages": [
    {
      "role": "user",
      "content": "Review this pull request for security vulnerabilities, performance issues, and suggest concrete improvements."
    }
  ]
}'
import anthropic

client = anthropic.Anthropic(
    base_url="https://runapi.ai",
    api_key="your-runapi-key"
)

message = client.messages.create(
    model="claude-sonnet-4-5-20250929",
    max_tokens=1024,
    messages=[{"role": "user", "content": "Review this pull request for security vulnerabilities, performance issues, and suggest concrete improvements."}]
)
import Anthropic from "@anthropic-ai/sdk";

const client = new Anthropic({
  baseURL: "https://runapi.ai",
  apiKey: "your-runapi-key"
});

const message = await client.messages.create({
  model: "claude-sonnet-4-5-20250929",
  max_tokens: 1024,
  messages: [{ role: "user", content: "Review this pull request for security vulnerabilities, performance issues, and suggest concrete improvements." }]
});
https://runapi.ai /v1/messages
Switch variant
OVERVIEW

claude-sonnet-4-5-20250929 targets the sweet spot of quality and cost within the Claude family. It shares the same API key, request shape, and async task lifecycle as every other RunAPI model — switch to this variant by changing one model ID parameter. Install the Claude skill to load docs, typed schemas, pricing notes, and setup steps into your coding workspace. Billing is metered per completed request in USD with no subscription or minimum spend, and failed generations are never charged.

  • Pay-per-call pricing in USD with no subscription
  • Failed generations are never charged
  • Streaming when supported by the model
  • Schema-validated parameters and tool calls
  • Switch variant by changing one model ID parameter
  • Unified billing across all models and providers
PRICING

Pricing

Failed generations are not charged
Messages API
Input $1.50 / 1M tokens
Output $7.50 / 1M tokens
Cache read $0.15
Cache write 5m $1.88
SPEC SHEET

Technical details

Model ID claude-sonnet-4-5-20250929
Provider Anthropic
Modality text
Task type synchronous
Billing unit 1K tokens
API endpoint /v1/messages
Commercial license Yes — included via API
Status Operational
SKILLS

Model skill — claude-sonnet-4-5-20250929

Install the skill once, then use the variant ID from this page while building.

Endpoint Protocol
/v1/messages Anthropic compatible
HOW IT WORKS

Use claude-sonnet-4-5-20250929 with a model skill

01

Install

Install the model skill for the %{model} line. The skill loads docs, typed schemas, pricing notes, and setup steps into your coding workspace so your agent has the right context.

02

Configure

Set the model field to the full model ID shown on this page and configure your RunAPI API key as an environment variable. The same key works across all models and providers.

03

Call

Use the skill instructions while adding prompt, input, and callback handling to your application. RunAPI routes the request to the provider, manages the async lifecycle, and returns structured JSON.

04

Receive

Read the task response by polling the task ID, streaming when supported, or handling the webhook callback at your configured URL. Generated outputs are stored and retrievable by task ID.

DIFFERENCES

What's different about claude-sonnet-4-5-20250929

VS CLAUDE-FABLE-5

claude-sonnet-4-5-20250929

Mythos-class 1M context; state-of-the-art coding, reasoning, and vision

VS CLAUDE-HAIKU-4-5-20251001

claude-sonnet-4-5-20250929

Dated snapshot of Haiku 4.5 for reproducible outputs

VS CLAUDE-OPUS-4-1-20250805

claude-sonnet-4-5-20250929

claude-opus-4-1-20250805

USE CASES

Best for

Customer support

Answer customer questions from a private knowledge base, reducing ticket volume.

Document analysis

Draft contract summaries and flag key clauses for attorney review.

Code generation

Auto-generate unit tests, code reviews, and refactoring suggestions in CI.

FAQ

Frequently asked questions about claude-sonnet-4-5-20250929

Is the model ID stable across versions?

Yes. RunAPI keeps the model ID stable and handles compatible version refreshes without changing your request shape. You do not need to update your code when the provider releases a new compatible version.

What's the rate limit on this variant?

Per-key rate limits scale with your usage tier. The pricing page shows current limits. If you need higher throughput, contact support to discuss tier upgrades.

Can I switch variants later?

Yes. Variant is a parameter in the request. Switch by changing the model ID — no code changes, no re-authentication, no separate billing setup. All variants share the same API key and request shape.

Does it stream?

Where streaming is available, RunAPI streams end-to-end. LLM models support token-level streaming. Media models use async task polling or webhook callbacks for result delivery.

Where do I report quality issues?

Open an issue on the public GitHub repo or email support at [email protected]. Include the task ID and model ID so the team can investigate the specific generation.

Do I need a separate provider account?

No. Your RunAPI API key is enough to access this variant and every other model in the catalog. You do not need accounts with the underlying provider.

START NOW

Start building with Claude.