---
title: 'Claude Sonnet 5.5 API: Pricing, Model ID and Migration Notes | RunAPI'
description: Call claude-sonnet-5-5 through the Anthropic Messages API on RunAPI. Per-token rates, 1M context, effort defaults, and the request changes coming from Sonnet 5.
url: https://runapi.ai/models/claude/sonnet-5-5.md
canonical: https://runapi.ai/models/claude/sonnet-5-5
locale: en
site: RunAPI
image: https://runapi.ai/assets/opengraph-bfaaa0f0.png
alternates:
en: https://runapi.ai/models/claude/sonnet-5-5
zh-CN: https://runapi.ai/zh-CN/models/claude/sonnet-5-5
es: https://runapi.ai/es/models/claude/sonnet-5-5
ja: https://runapi.ai/ja/models/claude/sonnet-5-5
de: https://runapi.ai/de/models/claude/sonnet-5-5
fr: https://runapi.ai/fr/models/claude/sonnet-5-5
pt-BR: https://runapi.ai/pt-BR/models/claude/sonnet-5-5
ko: https://runapi.ai/ko/models/claude/sonnet-5-5
it: https://runapi.ai/it/models/claude/sonnet-5-5
nl: https://runapi.ai/nl/models/claude/sonnet-5-5
pl: https://runapi.ai/pl/models/claude/sonnet-5-5
tr: https://runapi.ai/tr/models/claude/sonnet-5-5
zh-TW: https://runapi.ai/zh-TW/models/claude/sonnet-5-5
zh-HK: https://runapi.ai/zh-HK/models/claude/sonnet-5-5
ar: https://runapi.ai/ar/models/claude/sonnet-5-5
x-default: https://runapi.ai/models/claude/sonnet-5-5
model: Claude
provider: Anthropic
variant_id: claude-sonnet-5-5
sdk_model_id: claude-sonnet-5-5
modality: text
billing_unit: 1K tokens
status: active
---
> HTML version: https://runapi.ai/models/claude/sonnet-5-5
> Site index for agents: https://runapi.ai/llms.txt
# claude-sonnet-5-5 API
Call claude-sonnet-5-5 from the Claude family through RunAPI. Billing is per token with no subscription, and a request that fails before its response starts is not charged.
**Anthropic / [Claude](https://runapi.ai/models/claude.md)**
**Operational · text · Commercial OK**
## What changes when you move to Claude Sonnet 5.5
Anthropic released Claude Sonnet 5.5 on September 28, 2026. It keeps the per-token input and output rates of Sonnet 5, and since October 7, 2026 its cache reads cost half of what Sonnet 5 charges. Anthropic aims it at well-scoped everyday work that has a clear definition of done, such as fixing bugs or producing documents, and recommends Opus 5.5 for open-ended problems.
Code written for Sonnet 5 needs a few request changes. Turning thinking off with thinking: {type: "disabled"} now returns a 400; send {type: "between_tools"} at high effort or below instead. Forced tool use, with tool_choice set to any or to a named tool, also returns a 400, so switch to auto and strict tool definitions. Sonnet 5.5 also rejects non-default temperature, top_p, or top_k values.
On RunAPI, claude-sonnet-5-5 is served through the Anthropic Messages endpoint (/v1/messages) only. RunAPI rejects requests for this model in the OpenAI Chat Completions, Responses, or Gemini formats, so call it from an Anthropic SDK or from Claude Code.
**Model ID:** claude-sonnet-5-5
**Released:** September 28, 2026
**Context window:** 1M tokens
**Max output:** 128K tokens
**Knowledge cutoff:** June 2026
**Default effort (API):** high
**Protocol on RunAPI:** Anthropic Messages
## Try Claude Sonnet 5.5
Pick any model and generate in seconds.
**Model:**
- **Message** — `message` · `claude-sonnet-5-5` · Input $1.60 / 1M tokens | Output $8.00 / 1M tokens
**Prompt:** Describe what you want to create...
**Estimated:** Input $1.60 / 1M tokens | Output $8.00 / 1M tokens
- [Generate](https://runapi.ai/login)
Sign in to generate with RunAPI.
### Switch variant
- [claude-fable-5](https://runapi.ai/models/claude/fable-5.md)
- [claude-fable-5-1](https://runapi.ai/models/claude/fable-5-1.md)
- [claude-haiku-4-5-20251001](https://runapi.ai/models/claude/haiku-4-5-20251001.md)
- [claude-haiku-5-5](https://runapi.ai/models/claude/haiku-5-5.md)
- [claude-opus-4-1-20250805](https://runapi.ai/models/claude/opus-4-1-20250805.md)
- [claude-opus-4-5-20251101](https://runapi.ai/models/claude/opus-4-5-20251101.md)
- [claude-opus-4-6](https://runapi.ai/models/claude/opus-4-6.md)
- [claude-opus-4-7](https://runapi.ai/models/claude/opus-4-7.md)
- [claude-opus-4-8](https://runapi.ai/models/claude/opus-4-8.md)
- [claude-opus-5](https://runapi.ai/models/claude/opus-5.md)
- [claude-opus-5-5](https://runapi.ai/models/claude/opus-5-5.md)
- [claude-sonnet-4-5-20250929](https://runapi.ai/models/claude/sonnet-4-5-20250929.md)
- [claude-sonnet-4-6](https://runapi.ai/models/claude/sonnet-4-6.md)
- [claude-sonnet-5](https://runapi.ai/models/claude/sonnet-5.md)
- **claude-sonnet-5-5** (current)
15 versions available
claude-sonnet-5-5 is one of the Claude models on RunAPI. It uses the same API key as every other model, and you switch to it by changing the model ID in your request. Each call is synchronous and billed in USD by input, output, and cache tokens, with no subscription or minimum spend. A request that fails before the response starts is not charged; once a response is streaming, the tokens already generated are billed, even if the client disconnects.
- Per-token billing in USD with no subscription
- No charge when a request fails before its response starts
- Token-by-token streaming
- Switch models by changing one model ID
- One API key and one bill for every model and provider
## Usage metrics
- **API Calls / Day:** 1
- **Success Rate:** 100.0%
- **Avg Generation:** 2.1s
Verified customer feedback is not available for this model yet.
## Technical details
| Field | Value |
|---|---|
| Provider | Anthropic |
| Model ID | claude-sonnet-5-5 |
| Modality | Text |
| Task types | Synchronous |
| API endpoint | `/v1/messages` |
| Billing unit | 1K tokens |
| Catalog status | Operational |
**HOW IT WORKS**
## Use This Model in 3 Steps
1. **Get Your Key** - Sign up for free and create an API key for claude-sonnet-5-5 from the dashboard.
2. **Send a Request** - POST to /v1/messages with the claude-sonnet-5-5 model slug and your parameters.
3. **Get Results** - Read the completed claude-sonnet-5-5 response directly from the endpoint.
## What this model offers
- **Endpoint coverage** — Exposes 1 public endpoint(s): message.
- **Usage-based billing** — Metered by 1K tokens with no subscription requirement.
## Claude Sonnet 5.5 Pricing
| Endpoint | Price |
|---|---|
| `message` | Input: $1.60 / 1M tokens
Output: $8.00 / 1M tokens
Cache read: $0.08 / 1M tokens
Cache write 5m: $2.00 / 1M tokens
Cache write 1h: $3.20 / 1M tokens |
**API REFERENCE**
## Endpoint Specification
| Field | Value |
|---|---|
| Endpoint | `POST /v1/messages` |
| Model ID | `claude-sonnet-5-5` |
| Task Types | `message` |
## Request parameters
No request parameters are published for this endpoint.
**Request example**
```json
{
"model": "claude-sonnet-5-5",
"max_tokens": 1024,
"messages": [
{
"role": "user",
"content": "Review this pull request for security vulnerabilities, performance issues, and suggest concrete improvements."
}
]
}
```
### Model skill — claude-sonnet-5-5
Install the skill once, then use the variant ID from this page while building.
Base URL: `https://runapi.ai`
| Endpoint | Protocol |
|---|---|
| `POST /v1/messages` | Anthropic compatible |
Use the Anthropic SDK with your RunAPI API key and `model: "claude-sonnet-5-5"`.
### Use claude-sonnet-5-5 with a model skill
1. **Install** — Install the model skill for the Claude line. It loads docs, request formats, and pricing notes into your coding workspace.
2. **Configure** — Point your SDK at https://runapi.ai and set your RunAPI API key. The same key works for every model and provider.
3. **Call** — Send a request in an API format this model supports, with the model field set to the model ID on this page. RunAPI forwards it to the provider.
4. **Receive** — Read the response from the same call, or stream it as it is generated. The usage field shows the tokens you are billed for.
### What's different about claude-sonnet-5-5
- **VS CLAUDE-FABLE-5: 1M context; Sonnet 5 successor for everyday coding and agent work** — Mythos-class 1M context; state-of-the-art coding, reasoning, and vision
- **VS CLAUDE-FABLE-5-1: 1M context; Sonnet 5 successor for everyday coding and agent work** — 1M context; successor to Fable 5
- **VS CLAUDE-HAIKU-4-5-20251001: 1M context; Sonnet 5 successor for everyday coding and agent work** — Haiku 4.5 for reproducible outputs
## USE CASES
**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.
## Frequently asked questions about Claude Sonnet 5.5
### How much does the Claude Sonnet 5.5 API cost?
Sonnet 5.5 is billed per token for input, output, cache writes, and cache reads; the pricing table on this page shows RunAPI's current rate for each. Anthropic kept the Sonnet 5 input and output rates and, on October 7, 2026, cut the cache-read rate to half of Sonnet 5's. There is no long-context surcharge, so a 900K-token prompt pays the same per-token rate as a short one.
### Is Claude Sonnet 5.5 cheaper than Sonnet 5?
Per token, input and output cost the same and cache reads cost half as much. Anthropic says a typical task costs up to 30% less because Sonnet 5.5 reaches an answer with fewer tokens. Token use depends on the effort level you set, so compare the usage field of your own requests before moving a large workload.
### Should I use Sonnet 5.5 or Opus 5.5?
Anthropic recommends Sonnet 5.5 when the task has a clear spec and a way to check the result, and Opus 5.5 for complex, open-ended work. Both run on RunAPI under the same API key, so you can route each job by changing the model ID.
### Which effort level should I use with Sonnet 5.5?
The API default is high. Anthropic suggests starting at medium for agentic coding and multi-step tool use with a clear spec, moving to high for hard tasks, and using medium or low for chat. Higher levels spend more thinking tokens, and thinking tokens are billed at the output rate.
### Why does my Sonnet 5 code return a 400 error on Sonnet 5.5?
Sonnet 5.5 rejects three request shapes that Sonnet 5 accepted: thinking set to disabled (use between_tools at high effort or below), tool_choice set to any or to a named tool (use auto with strict tools), and non-default temperature, top_p, or top_k. Thinking blocks are also tied to the conversation that produced them, so replaying an edited history can fail.
### Why did a request come back with stop_reason refusal?
Sonnet 5.5 runs Anthropic's safety classifiers. A declined request returns HTTP 200 with stop_reason set to refusal and a stop_details object that names the category. Check stop_reason before reading the content. RunAPI returns this response to you unchanged.
### Can I call Claude Sonnet 5.5 with the OpenAI SDK on RunAPI?
No. RunAPI serves claude-sonnet-5-5 through the Anthropic Messages API only. Use the Anthropic SDK with ANTHROPIC_BASE_URL set to https://runapi.ai and your RunAPI key, or a Messages client such as Claude Code.
### How do I select claude-sonnet-5-5?
Pass the model ID shown in the quickstart.
### 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 contact@runapi.ai. 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.
### RELATED
- [claude-haiku-5-5](https://runapi.ai/models/claude/haiku-5-5.md) — by Anthropic · Input $0.08-$0.40 / 1M tokens | Output $0.40-$2.00 / 1M tokens
- [claude-haiku-4-5-20251001](https://runapi.ai/models/claude/haiku-4-5-20251001.md) — by Anthropic · Input $0.80 / 1M tokens | Output $4.00 / 1M tokens
- [claude-sonnet-5](https://runapi.ai/models/claude/sonnet-5.md) — by Anthropic · Input $1.60 / 1M tokens | Output $8.00 / 1M tokens
- [claude-sonnet-4-5-20250929](https://runapi.ai/models/claude/sonnet-4-5-20250929.md) — by Anthropic · Input $2.40 / 1M tokens | Output $12.00 / 1M tokens
### Start building with Claude.
- [Create free account](https://runapi.ai/login)
- [Read the quickstart →](https://runapi.ai/docs/api/anthropic/messages)
## Building with a team?
We're here to help with enterprise setup, integrations, and technical questions.
[Contact Us](https://runapi.ai/contact.md)
---
## More from RunAPI
- [Home](https://runapi.ai/.md)
### Product
- [Model Catalog](https://runapi.ai/models.md)
- [Pricing](https://runapi.ai/pricing.md)
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### Guides
- [Claude Code vs Cursor](https://runapi.ai/claude-code-vs-cursor.md)
- [Cursor API Setup](https://runapi.ai/cursor-api-setup.md)
- [RunAPI vs OpenRouter](https://runapi.ai/openrouter-alternative.md)
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- [Enterprise](https://runapi.ai/contact.md)
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- [Privacy](https://runapi.ai/privacy.md)
- [Site index for agents](https://runapi.ai/llms.txt)
Contact: contact@runapi.ai
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}
},
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"@type": "Question",
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"acceptedAnswer": {
"@type": "Answer",
"text": "Sonnet 5.5 rejects three request shapes that Sonnet 5 accepted: thinking set to disabled (use between_tools at high effort or below), tool_choice set to any or to a named tool (use auto with strict tools), and non-default temperature, top_p, or top_k. Thinking blocks are also tied to the conversation that produced them, so replaying an edited history can fail."
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"acceptedAnswer": {
"@type": "Answer",
"text": "Sonnet 5.5 runs Anthropic's safety classifiers. A declined request returns HTTP 200 with stop_reason set to refusal and a stop_details object that names the category. Check stop_reason before reading the content. RunAPI returns this response to you unchanged."
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"@type": "Answer",
"text": "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."
}
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"@type": "Answer",
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},
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"@type": "Question",
"name": "Does it stream?",
"acceptedAnswer": {
"@type": "Answer",
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}
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```