Claude Sonnet 5.5 - Unifically

Claude Sonnet 5.5 is Anthropic’s Sonnet model from the Claude 5.5 family, released September 28, 2026, for everyday coding, bug fixing, and document, slide, and spreadsheet work. It takes text and image input, outputs text, and carries a 1M token context window with up to 128k output tokens. It uses adaptive thinking steered by effort, which defaults to high; to keep up-front thinking off, use the between_tools setting. Try it in the browser: Claude Sonnet 5.5 API playground.

Model

anthropic/claude-sonnet-5-5


Provider	Anthropic
Name	Claude Sonnet 5.5

Supported Endpoints

All three API formats are supported:

Chat Completions — POST /v1/chat/completions
Responses — POST /v1/responses
Messages — POST /v1/messages

Send LLM requests to https://direct-api.unifically.com, not https://api.unifically.com. The main host sits behind Cloudflare, and Cloudflare’s proxy timeout cuts most LLM requests short before the model has finished writing. When that happens you receive a truncated reply and are still charged for every token generated up to the cut-off. direct-api.unifically.com reaches the same API without the Cloudflare proxy, so long responses complete in full.

Example

curl -X POST https://direct-api.unifically.com/v1/messages \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "anthropic-version: 2023-06-01" \
  -d '{
    "model": "anthropic/claude-sonnet-5-5",
    "max_tokens": 4096,
    "messages": [
      {"role": "user", "content": "Design a distributed job queue with exactly-once semantics."}
    ]
  }'

Volume discounts are available for almost all models. Reach out at contact@unifically.com to discuss custom pricing.