Claude Sonnet 5.5

anthropic/claude-sonnet-5.5

A chat model with a 1M-token context window, at $2.10 per million input tokens and $10.50 per million output tokens.

Details

Maker: anthropic
Kind: Chat
Context window: 1,000,000 tokens
Max output: 128,000 tokens
Input: $2.10 per million tokens
Cached input: $0.105 per million tokens, 95% off
Cache write: $2.625 per million tokens
Output: $10.50 per million tokens
Capabilities: Reasoning, tool use, vision, file input, web search
Takes: Text, image, pdf
Returns: Text
Zero data retention: Yes, on every provider
No training on requests: Yes, on every provider
Released: 2026-09-28
Newer model: anthropic/claude-haiku-5.5Released later by the same maker, costs no more, and lists the same capabilities. Compare the two
phantom-1: phantom-1 sends hard problems here: race conditions, proofs and contest problems. How phantom-1 picks

Description

Claude Sonnet 5.5 is a step-change improvement over Sonnet 5 for well-scoped everyday work like building features, fixing bugs, and creating polished documents, slides, and spreadsheets. It also writes more clearly than Sonnet 5.

Call it

curl

curl https://phantom.codes/v1/chat/completions \
  -H "Authorization: Bearer $PHANTOM_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "anthropic/claude-sonnet-5.5",
    "messages": [
      {"role": "user", "content": "Hello"}
    ]
  }'

Set PHANTOM_KEY to your key. Any OpenAI client works with the base URL https://phantom.codes/v1.

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