AnthropicText / ChatClaude Sonnet 5.5 API: Anthropic on Vertex (Claude)'s chat / LLM model, one key away
Claude Sonnet 5.5 via the ApexApi gateway
Anthropic's newest Sonnet, priced below Sonnet 4.6 with a 1M token context window and up to 128K tokens of output. A good default for coding, agent tasks and knowledge work at volume; pick Opus when a task needs more depth. Call it through ApexApi's unified, OpenAI-compatible API with one `ak-` key, alongside every other model in the catalog. It supports a 1,000,000-token context window, tool / function calling, image (vision) input, and streaming responses. Pricing is $2.40 input and $12.00 output per 1M tokens, billed pay-per-use from your credit balance with no subscription.
Claude Sonnet 5.5 is served through ApexApi's unified, OpenAI-compatible API. One key, one format, with smart routing and automatic failover. Provider: Anthropic on Vertex (Claude).
Why Claude Sonnet 5.5
1,000,000-token context
Reason over long documents, codebases, and multi-turn history in a single request.
Tool & function calling
Structured outputs and tool orchestration for agentic and automation workloads.
Vision input
Send images alongside text for document, UI, and visual-understanding tasks.
Specifications
- Modality
- chat
- Context window
- 1000K tokens
- Max output
- 128K tokens
- Streaming
- Yes
- Tool / function calling
- Yes
- Vision input
- Yes
Claude Sonnet 5.5 pricing
- A million tokens in and a million out costs $14.40 here, all-in.
- It runs 2.5× cheaper than Claude Opus 4.5, the pricier option from the same maker.
- It is one of 37 chat models here with a 1M-token context window.
Getting started with Claude Sonnet 5.5
OpenAI-compatible. Point your client at ApexApi, swap your key, and call it. No new SDK to learn.
from openai import OpenAI
client = OpenAI(
base_url="https://api.apexapi.dev/v1",
api_key="<YOUR_APEXAPI_KEY>",
)
response = client.chat.completions.create(
model="anthropic/claude-sonnet-5.5",
messages=[{"role": "user", "content": "Hello!"}],
)
print(response.choices[0].message.content)Claude Sonnet 5.5 use cases
What teams build with Claude Sonnet 5.5 on ApexApi.
Agents & automation
Tool-using agents that orchestrate multi-step workflows and call APIs.
Coding assistants
Code generation, refactoring, reviews, and multi-file reasoning.
RAG & knowledge apps
Summarization and long-document Q&A grounded in your own data.
Claude Sonnet 5.5 vs other models
How it compares, and on ApexApi you can switch between any of them with a single string change, same key, same endpoint.
Claude Sonnet 5.5 vs Claude Opus 4.7
Compare Claude Sonnet 5.5 against this model on price, capabilities, and latency. A/B them with a single key on ApexApi.
Learn more about Claude Opus 4.7 API →Claude Sonnet 5.5 vs GPT-5.5
Compare Claude Sonnet 5.5 against this model on price, capabilities, and latency. A/B them with a single key on ApexApi.
Learn more about GPT-5.5 API →Claude Sonnet 5.5 vs Gemini 3.1 Pro Preview
Compare Claude Sonnet 5.5 against this model on price, capabilities, and latency. A/B them with a single key on ApexApi.
Learn more about Gemini 3.1 Pro Preview API →Claude Sonnet 5.5 API: FAQ
How do I call Claude Sonnet 5.5 through ApexApi?
Create an ApexApi key, point your client at https://api.apexapi.dev/v1, and POST to /v1/chat/completions with the model set to `anthropic/claude-sonnet-5.5`. The API is OpenAI-compatible, so an existing OpenAI SDK works once you change the base URL and key.
How much does Claude Sonnet 5.5 cost on ApexApi?
$2.40 per million input tokens and $12.00 per million output tokens, all-in with no separate platform fee. You buy credits and pay per call, with no subscription or minimum.
What is the context window for Claude Sonnet 5.5?
1,000,000 tokens. It can return up to 128,000 tokens in a single response.
Does Claude Sonnet 5.5 support tool calling and image input?
Claude Sonnet 5.5 supports tool / function calling, image (vision) input, and streaming responses.
What should I use instead of Claude Sonnet 5.5?
From the same maker, Claude Haiku 4.5 costs less for lighter work and Claude Sonnet 4.6 is the step up when this one falls short. Switching is one string: both run on the same endpoint and the same key, so there is nothing to re-integrate.
Ready to build with Claude Sonnet 5.5?
One API key. Every major AI model. Pay only for what you use.
Try Claude Sonnet 5.5, pay as you go from $5