API support matrix

What each Sail inference API supports today, and what’s coming soon

Sail provides inference endpoints compatible with the OpenAI Responses API, the OpenAI Chat Completions API, and the Anthropic Messages API. All three inference APIs accept the same models and completion windows.

Additionally, Sail offers a Batch API for running large numbers of Responses API requests efficiently in a single asynchronous job.

API	Endpoint	Maturity
OpenAI Responses	POST /v1/responses	Stable
OpenAI Chat Completions	POST /v1/chat/completions	Stable
Anthropic Messages	POST /v1/messages	Beta
Batch	POST /v1/batches	Stable

---

Responses API

RecommendedOpenAI SDK compatible

API reference →

Supported features

Feature	Details
Core parameters	model, input (string or message array), max_output_tokens, temperature, top_p, user, prompt_cache_key
Instructions	instructions is prepended to the input as a system message.
Structured outputs	text.format with type: "text" or type: "json_schema"
Reasoning	reasoning.effort (none / minimal / low / medium / high / xhigh), reasoning.generate_summary (auto / concise / detailed)
Function tools	tools with type: "function" — client-side function calling with name, description, parameters, strict
Custom tools	tools with type: "custom"
Tool choice	tool_choice: "none", "auto", "required", or a specific function/custom tool
Background mode	background: true returns 202 immediately; poll with GET /v1/responses/{id}
Streaming	stream: true on foreground requests returns Server-Sent Events using OpenAI Responses event names.
Prompt cache routing	prompt_cache_key is an optional routing hint for requests that share a large prompt prefix
Image input	input_image content blocks on multimodal models. Non-multimodal models accept text only.
Video input	input_video content blocks on models that declare video input support. The video_url value can be a URL string or an object with url and model-specific controls.
Output logprobs	include: ["message.output_text.logprobs"] returns one logprob per output token (best effort; omitted when unavailable).

Not yet supported

Feature	Notes
Conversation chaining	previous_response_id and conversation are not supported. Send the full input each request.
Prompt templates	The prompt parameter is not supported.
Server-side tools	web_search, web_search_preview, and image_generation tools are accepted for OpenAI-client compatibility and removed from the request; the model has no such tool to call. file_search, code_interpreter, computer_use, mcp, shell, and apply_patch are not supported.
Multimodal input	Audio and file input blocks are not supported. Image and video input are supported on models that declare those input modalities (see above).
Include	Accepted for compatibility when it is an array of strings. reasoning.encrypted_content is accepted for OpenAI-client compatibility, but reasoning items are returned without encrypted content. Requests that include web_search_call.action.sources, code_interpreter_call.outputs, computer_call_output.output.image_url, or file_search_call.results are rejected.
Truncation	Only "disabled" is accepted. Custom truncation strategies are not supported.
Parallel tool calls	parallel_tool_calls is accepted for compatibility. Models decide their own tool-call cadence, so the field has no effect.
json_object format	text.format.type: "json_object" is not supported. Use "json_schema" instead.
Service tier	Only "auto" is accepted. Use metadata.completion_window to control response timing instead.
Delete / cancel	DELETE /v1/responses/{id} and cancel endpoints are not implemented.

---

Chat Completions API

OpenAI SDK compatible

API reference →

Supported features

Feature	Details
Core parameters	model, messages, max_completion_tokens, temperature, top_p, user, prompt_cache_key
Message roles	system, user, assistant, tool, function (deprecated), developer
Structured outputs	response_format with type: "text", "json_object", or "json_schema"
Reasoning	reasoning_effort (none / minimal / low / medium / high / xhigh)
Function tools	tools with type: "function" — standard {type, function: {name, description, parameters, strict}} format
Custom tools	tools with type: "custom"
Tool choice	tool_choice: "none", "auto", "required", or a specific function/custom tool
Parallel tool calls	parallel_tool_calls is passed through
Metadata	metadata with string key-value pairs, including completion_window and completion_webhook
Prompt cache routing	prompt_cache_key is an optional routing hint for requests that share a large prompt prefix
Streaming	stream: true returns Server-Sent Events (chat.completion.chunk); stream_options.include_usage adds a final usage chunk. Reasoning is streamed as reasoning_content deltas and tool calls are emitted atomically.
Image input	image_url content parts on multimodal models. Non-multimodal models accept text only.
Video input	video_url content parts on models that declare video input support. URL objects and model-specific controls such as num_frames and fps are preserved.

Not yet supported

Feature	Notes
Multiple choices	n must be 1.
Multimodal content	Audio (input_audio) content parts are not supported. Image and video input are supported on models that declare those input modalities (see above).
Sampling controls	frequency_penalty, presence_penalty, logit_bias, stop, seed, top_logprobs, logprobs, verbosity are not supported.
Audio modality	audio and modalities: ["audio"] are not supported.
Predicted output	prediction is not supported.
Web search	web_search_options is not supported.
Service tier	Only "auto" is accepted.
CRUD endpoints	GET, POST, DELETE on stored completions are not implemented.
Deprecated fields	max_tokens, functions, function_call are rejected. Use their modern replacements.

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.

---

Messages API

Anthropic Messages formatAnthropic SDK compatible

API reference →

The Messages API is Anthropic-compatible for agentic use: system prompts, tool calling, and streaming (SSE) are supported. Prompt caching (cache_control) is accepted but not yet applied.

Supported features

Feature	Details
Core parameters	model, max_tokens, messages
System prompt	The top-level system parameter (string or array of text blocks)
Sampling	temperature (0–1), top_p (0–1)
Tools	tools and tool_choice ("auto", "any", "tool", "none"). The model calls tools; responses include tool_use blocks, and text tool_result blocks round-trip. Tool results with is_error: true retain an error signal for the model.
Extended thinking	thinking is translated to the model’s reasoning
Streaming	stream: true returns Anthropic Server-Sent Events (message_start, content_block_delta, message_stop, …) after generation completes. It is not incremental token delivery.
Structured outputs	output_config.format with type: "json_schema"
Metadata	metadata with string key-value pairs, including completion_window and completion_webhook
Image input	image content blocks on multimodal models. Non-multimodal models accept text only.
Request routing	routing.allowed_countries: ["US"] restricts that request to United States capacity
Voyage attribution	X-Sail-Voyage-Id, with optional span and agent headers, associates the model call with a Voyage
Token counting	POST /v1/messages/count_tokens returns the request’s input token count without running the model

Not yet supported

Feature	Notes
Prompt caching	cache_control on content blocks is accepted but ignored (no cache read/write).
Stop sequences	stop_sequences is not supported.
Top-K sampling	top_k is not supported.
Multimodal content	Document content blocks are not supported. Image input is supported on multimodal models (see above).
Tool result images	Images inside tool_result are replaced with [Image omitted: Sail does not yet support images inside tool results.]. The request still succeeds.
Redacted thinking	Replayed redacted_thinking blocks are accepted so conversations can continue, but the opaque reasoning is not forwarded to the model.
Service tier	service_tier is not supported.
Inference geo	inference_geo is not supported.
Batches	POST /v1/messages/batches and related endpoints are not implemented.

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}.

Compatibility notes

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

Python

from anthropic import Anthropic

client = Anthropic(
    api_key="YOUR_SAIL_API_KEY",
    base_url="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": "standard"})

metadata: {
  completion_window: "standard",
} 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

The Batch API runs large numbers of Responses API requests asynchronously. Every item targets /v1/responses — batching /v1/chat/completions or /v1/messages is not currently supported. You can submit up to 100,000 requests in a single POST /v1/batches call, then poll GET /v1/batches/{id} for status and fetch each result by custom_id.

See Sending Requests at Scale for the end-to-end workflow and the Batch API reference for the request and response schemas.

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Cross-API behavior

These behaviors apply across the inference API surfaces:

• 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 — set metadata.completion_window to "asap", "priority", "standard", or "flex" to control scheduling and pricing. See Completion Windows and Pricing.
• 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.