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
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. |
| 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 and web_search_preview tools are accepted for OpenAI-client compatibility and removed from the request; the model has no web-search tool to call. file_search, code_interpreter, computer_use, mcp, image_generation, shell, and apply_patch are not supported. |
| Multimodal input | Audio and file input blocks are not supported. Image input is supported on multimodal models (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
Supported features
| Feature | Details |
|---|
| Core parameters | model, messages, max_completion_tokens, temperature, top_p, user |
| 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 |
| 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. |
Not yet supported
| Feature | Notes |
|---|
| Multiple choices | n must be 1. |
| Multimodal content | Audio (input_audio) content parts are not supported. Image (image_url) input is supported on multimodal models (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 is either "stop" or "tool_calls". Other values like "length" and "content_filter" are not returned.system_fingerprint and service_tier are not included in responses.logprobs is always null.
Messages API
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 tool_use/tool_result content blocks round-trip. |
| 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, …) |
| 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. |
| 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). |
| 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 — "end_turn" normally, "tool_use" when the model calls a tool.- 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).
Compatibility notes
- Sail uses
Authorization: Bearer <key> for authentication. The Anthropic x-api-key header is not supported. When using the Anthropic SDK, pass your key via auth_token instead of api_key:
from anthropic import Anthropic
client = Anthropic(
auth_token="YOUR_SAIL_API_KEY",
base_url="https://api.sailresearch.com",
)
- The
anthropic-version header is not required or checked.
- Error responses use the OpenAI-style error envelope format.
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.
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. 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.
