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HomeDocsClaude Developer Platform 19 Aug 2026
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API usage primer for Claude changedclaude_api_primer

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2121 
2222### Basic request and response
2323 
24<CodeGroup>
24<CodeGroup exclude="shell:cURL, typescript, csharp, go, java, php, ruby">
2525 ```bash CLI
2626 ant messages create \
2727 --model claude-opus-5 \
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6666 
6767The Messages API is stateless, which means that you always send the full conversational history to the API. You can use this pattern to build up a conversation over time. Earlier conversational turns don't necessarily need to actually originate from Claude. You can use synthetic `assistant` messages.
6868 
69<CodeGroup>
69<CodeGroup exclude="shell:cURL, typescript, csharp, go, java, php, ruby">
7070 ```bash CLI
7171 ant messages create <<'YAML'
7272 model: claude-opus-5
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105105 Claude 4.6 and later models and Claude Mythos Preview do not support assistant message prefill; requests to those models must end with a user message. The examples below use a model that supports prefill.
106106</Note>
107107 
108<CodeGroup>
108<CodeGroup exclude="shell:cURL, typescript, csharp, go, java, php, ruby">
109109 ```bash CLI
110110 ant messages create <<'YAML'
111111 model: claude-sonnet-4-5
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140140 
141141Claude can read both text and images in requests. Both `base64` and `url` source types are supported for images, along with the `image/jpeg`, `image/png`, `image/gif`, and `image/webp` media types.
142142 
143<CodeGroup>
143<CodeGroup exclude="shell:cURL, typescript, csharp, go, java, php, ruby">
144144 ```bash CLI
145145 IMAGE_URL="https://platform.claude.com/docs/images/vision-example.jpg"
146146 
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260260 
261261When thinking is on, Claude creates `thinking` content blocks where it outputs its internal reasoning. The API response includes `thinking` content blocks, followed by `text` content blocks.
262262 
263<CodeGroup>
263<CodeGroup exclude="shell:cURL, typescript, csharp, go, java, php, ruby">
264264 ```bash CLI
265265 ant messages create \
266266 --transform content --format yaml <<'YAML'
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314314 
315315### Preserving thinking blocks
316316 
317<CodeGroup>
317<CodeGroup exclude="shell:cURL, typescript, csharp, go, java, php, ruby">
318318 ```bash CLI
319319 # First request: capture the assistant content array (thinking + tool_use
320320 # blocks, signatures intact) as compact JSON.
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448448 
449449On older models that use manual extended thinking (Claude 4, 4.5, and Sonnet 4.6 models), enable interleaved thinking by adding the beta header `interleaved-thinking-2025-05-14` to your API request:
450450 
451<CodeGroup>
451<CodeGroup exclude="shell:cURL, typescript, csharp, go, java, php, ruby">
452452 ```bash CLI
453453 ant beta:messages create --beta interleaved-thinking-2025-05-14 <<'YAML'
454454 model: claude-sonnet-4-6
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719719 
720720### Streaming with SDKs
721721 
722<CodeGroup>
722<CodeGroup exclude="shell:cURL, typescript, csharp, go, java, php, ruby">
723723 ```bash CLI
724724 ant messages create --stream --format jsonl \
725725 --model claude-opus-5 \
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