AnthropicFastUltra

Claude Sonnet 5.5

Anthropic's newest Sonnet model (September 2026), balancing speed, cost, and intelligence at $2/$10 per M tokens. 1M-token context window and 128K max output tokens, with prompt caching (read $0.20/M, 5-minute write $2.50/M) and web search. Compatible with the Anthropic Messages and OpenAI Chat Completions formats.

3,716/18,580credits

input / output · per 1M tokens

Balanced speed, cost, and intelligence

1M token context window

128K max output tokens

Prompt caching (read 10% / 5-min write 125% of input price)

Web search tool support

Vision and tool use

Streaming support

Run it right now

Test this model instantly in the Console Playground — no code required

Use with AI Assistant

Copy usage instructions for Claude, ChatGPT, or other AI

llms.txtllms.txt ↗

Model Specifications

Context Window

tokens

Max Output

128K

tokens

Training Cutoff

Not published

Compatible SDK

Anthropic, OpenAI

Capabilities

Vision

Function Calling

Streaming

JSON Mode

System Prompt

Token Pricing (per 1M tokens)

Token Type	Credits	USD Equivalent
Input Tokens	3,716	$2.48
Output Tokens	18,580	$12.39
Cached Tokens	371.6	$0.25

* 1,500 credits ≈ $1 (actual charges may vary based on usage)

Quick Start

curl -X POST "https://api.core.today/llm/anthropic/v1/messages" \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer cdt_your_api_key" \
  -d '{
  "model": "claude-sonnet-5-5",
  "messages": [
    {
      "role": "system",
      "content": "You are a research analyst. Provide structured, source-aware analysis."
    },
    {
      "role": "user",
      "content": "Summarize the key findings and open questions from this 200-page technical report and flag any inconsistencies."
    }
  ],
  "max_tokens": 6000
}'

Parameters

Parameter	Type	Required	Default	Description
`messages`	array	Yes	-	Array of message objects (OpenAI format)
`max_tokens`	integer	No	4096	Maximum tokens in response (up to 128000)
`stream`	boolean	No	false	Enable Server-Sent Events streaming

Examples

High-throughput Analysis

Fast, cost-efficient analysis over large documents with Claude Sonnet 5.5

curl -X POST "https://api.core.today/llm/anthropic/v1/messages" \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer cdt_your_api_key" \
  -d '{
  "model": "claude-sonnet-5-5",
  "messages": [
    {
      "role": "system",
      "content": "You are a research analyst. Provide structured, source-aware analysis."
    },
    {
      "role": "user",
      "content": "Summarize the key findings and open questions from this 200-page technical report and flag any inconsistencies."
    }
  ],
  "max_tokens": 6000
}'

Production Code Generation

Generate production-ready code with a strong quality-to-cost ratio

curl -X POST "https://api.core.today/llm/anthropic/v1/messages" \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer cdt_your_api_key" \
  -d '{
  "model": "claude-sonnet-5-5",
  "messages": [
    {
      "role": "system",
      "content": "You are a senior software engineer. Write clean, well-tested, production code."
    },
    {
      "role": "user",
      "content": "Implement a token-bucket rate limiter in TypeScript backed by Redis, with unit tests."
    }
  ],
  "max_tokens": 6000
}'

Tips & Best Practices

1Best default Anthropic model when you want strong reasoning at Sonnet-tier speed and cost ($2/$10 per M)

2128K output (vs 64K on Sonnet 5) enables long-form drafts in a single response

3Prompt caching: read $0.20/M (10%), 5-minute write $2.50/M — cache large repeated contexts

4Web search costs about 18.6 credits per request ($10 per 1,000 searches) on top of token usage

5Sampling params (`temperature`, `top_p`, `top_k`) are not accepted by Claude 4.7+ models — omit them (the console strips `temperature` automatically)

6Streaming recommended for long responses

7Compatible with both Anthropic Messages and OpenAI SDK formats

8US-only inference (inference_geo: us) bills token charges at 1.1x