API support matrix

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Responses API

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Supported features

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Supercache usage

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Response status and output validation

• completed means the response finished normally.
• incomplete means generation stopped early. A reason of "max_output_tokens" is Sail’s normalized truncation/cap reason: it is reported whenever generation stops because of a length-based limit, such as the request’s max_output_tokens, the model’s context window, or another provider length signal. It does not by itself prove the request’s output limit alone was reached. A reason of "content_filter" means generation stopped because of a content filter. When present, usage is preserved. A response limited by max_output_tokens can include partial output; tokens reported in usage are billed normally. An incomplete response is not an API error.
• failed includes generations that Sail rejects because the result does not satisfy the request after its retry attempts are exhausted. A request with tool_choice: "required" can fail with error.code: "server_error" and the message "The model did not return a tool call required by the request." A generation with no visible text, refusal, or tool call can fail with error.code: "server_error" and the message "The model did not return visible text, a refusal, or a tool call." instead of returning an empty completed response.
• cancelled means no further output will be produced.

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Not yet supported

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Chat Completions API

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Supported features

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Not yet supported

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Response notes

• Responses always contain exactly one choice (n=1).
• finish_reason reflects the provider result when available, including "stop", "tool_calls", "length", and "content_filter".
• system_fingerprint and service_tier are not included in responses.
• logprobs is always null.

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Messages API

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Supported features

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Not yet supported

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Response notes

• stop_reason reflects the outcome. Sail returns "end_turn" normally, "tool_use" for tool calls, "max_tokens" for token limits, and "refusal" when the provider reports a refusal. Sail returns "model_context_window_exceeded" when the provider reports that the model’s context window was exceeded.
• Responses contain text content blocks, plus tool_use blocks when the model calls a tool.
• Cache-related usage fields (cache_creation_input_tokens, cache_read_input_tokens) are not included (prompt caching isn’t applied yet).
• Thinking output does not include an Anthropic cryptographic signature. thinking.budget_tokens is approximated as medium reasoning effort unless output_config.effort provides an explicit effort.
• When reasoning is present, Messages content begins with a thinking block before the text block. Select content by block type rather than assuming content[0] is text. The Chat Completions response exposes the same reasoning through reasoning_content.
• Token counting applies the same replay-block policy as message creation: redacted thinking is omitted and tool-result images count as the replacement text marker.
• Non-streaming requests wait for up to nine minutes. If generation is still running, Sail returns a 408 timeout_error and includes the response ID in X-Sail-Message-Id. Sail also returns X-Should-Retry: false so Anthropic SDKs do not create a second task. The original task continues. Retrieve it with GET /v1/messages/{id}, or use stream: true for long-running requests. Streaming requests use heartbeats and remain connected for up to 20 minutes. If that wait expires, the stream emits a timeout error with the response ID. The task continues and remains retrievable with GET /v1/messages/{id}.

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Compatibility notes

• Sail accepts both the Anthropic x-api-key header and Authorization: Bearer <key>. If both are present, Authorization takes precedence.

from anthropic import Anthropic

client = Anthropic(
    api_key="YOUR_SAIL_API_KEY",
    base_url="https://api.sailresearch.com",
)

import Anthropic from "@anthropic-ai/sdk";

const client = new Anthropic({
  apiKey: process.env.SAIL_API_KEY,
  baseURL: "https://api.sailresearch.com",
});

• The Anthropic Python and TypeScript SDKs type metadata with only user_id. Sail also accepts completion_window. Keep the additional cast or type assertion scoped to the metadata value:

from typing import cast

from anthropic.types import MetadataParam

metadata = cast(MetadataParam, {"completion_window": "balanced"})

metadata: {
  completion_window: "balanced",
} as Anthropic.Messages.Metadata & { completion_window: string },

• The anthropic-version header is not required or checked.
• Errors use the Anthropic envelope {"type":"error","error":{"type":"...","message":"..."},"request_id":"..."} and Anthropic error types such as invalid_request_error, rate_limit_error, and overloaded_error.

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Batch API

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Cross-API behavior

• Streaming: The Chat Completions API supports stream: true, returning Server-Sent Events (chat.completion.chunk); set stream_options.include_usage for a final usage chunk. The Messages API supports stream: true, returning Anthropic SSE events after generation completes rather than incremental token delivery. The Responses API supports foreground stream: true, returning OpenAI Responses SSE events. background: true requests return 202 immediately and cannot be streamed; use polling or webhooks for long-running background work.
• Completion windows: Express latency tolerance in exchange for lower token costs. See Completion Windows and Pricing.
• Context windows: For each text request, Sail reserves at least 512 tokens, or 0.5% on larger windows, from the model’s published context window. The input token count plus the requested maximum output must fit in the remaining budget. This allowance covers model-specific request formatting that can add tokens when the request runs. On the non-batch Responses endpoint (POST /v1/responses), requests that provide raw_prompt_tokens skip text formatting and use the exact raw-token count without this reserve, requiring the raw token count plus max_output_tokens to fit within the model’s context window. The Batch API does not yet apply this raw_prompt_tokens admission arithmetic.
• Webhooks: Set metadata.completion_webhook to receive a POST when processing finishes. See Webhooks.
• Response storage: store: false is accepted for OpenAI compatibility, but does not change Sail’s normal temporary request/response storage for processing, retries, polling, and idempotency. Customer Data remains governed by Sail’s DPA retention and deletion terms.