Responses API · Sylphx Models docs

EndpointsLink to this section

All paths are relative to the base URL and require your Bearer key.

Method	Path	Purpose
POST	`/responses`	Create a response. Add stream: true for SSE.
POST	`/responses/compact`	Compact a stored response into an official compaction object.
GET	`/responses/{response_id}`	Retrieve a stored response while it is retained.
GET	`/responses/{response_id}/input_items`	List the input items stored for one response.
DELETE	`/responses/{response_id}`	Forget a stored response.
POST	`/responses/{response_id}/cancel`	Official cancel route. Responses are not background jobs.
POST	`/files`	Multipart upload. Mints a file-* id for input_file and input_image.
GET	`/files`	List the files owned by your key.
GET	`/files/{file_id}`	File metadata, no bytes.
GET	`/files/{file_id}/content`	Raw file bytes.
DELETE	`/files/{file_id}`	Delete a file you own.

Create a responseLink to this section

POST /responses takes a strict JSON document. The only required field is model; input carries what you want the model to answer.

POST https://api.models.sylphx.ai/v1/responses

curl https://api.models.sylphx.ai/v1/responses \
  -H "Authorization: Bearer $SYLPHX_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "openai/gpt-5.5",
    "instructions": "Answer as a concise technical writer.",
    "input": "Summarise this incident report in three bullets.",
    "max_output_tokens": 400,
    "store": true
  }'

Field	Type	What it does
`model`required	string	A model id from the catalog — for example `openai/gpt-5.5`. There is no router alias: an id we do not sell is a typed `404`, never a silent substitution.
`input`	string \| array	The user turn, or a full item list. Replayed function calls pair with their outputs by `call_id`, so a retried transcript keeps its causality.
`instructions`	string	System-level guidance for this turn. Only text you write is sent — the platform never appends its own.
`stream`	boolean	`false` (default) returns one JSON response. `true` returns `text/event-stream`. See streaming.
`store`	boolean	Defaults to `true`: the response is retained and can be retrieved or used as `previous_response_id`. `false` skips persistence.
`previous_response_id`	string	Continue a stored conversation from an earlier response id.
`max_output_tokens`	integer	Upper bound on the tokens this turn may generate.
`tools`	array	Function tools your code executes, plus hosted tools the platform executes. See hosted tools.
`tool_choice`	string \| object	`auto` (default) lets the model decide, `required` forces a tool, or name one tool. The model authors the arguments in every case.
`max_tool_calls`	integer	Caps tool calls for the whole request. An explicit cap is never dropped: a route that cannot honor it fails before any tool runs.
`parallel_tool_calls`	boolean	Allow several independent tool calls in one model round.
`include`	array	Extra response fields you want returned, such as the sources a hosted web search used.
`context_management`	array	Official compaction configuration, for example `[{"type":"compaction","compact_threshold":100000}]`. See compaction.
`metadata`	object	Your own key-value labels, carried on the response for bookkeeping.

CautionStrict by design

Requests are strict JSON: duplicate keys, malformed tool definitions, non-finite numbers, and unknown fields fail before any model runs. The contract lists the complete accepted key set.

The response objectLink to this section

A non-streaming call returns one application/json Responses object. Visible text, refusals, function calls, and hosted tool items keep their identity and order.

200 OK · application/json

{
  "id": "resp_9f2c41d0a8",
  "object": "response",
  "created_at": 1789123456,
  "status": "completed",
  "model": "openai/gpt-5.5",
  "output": [
    {
      "type": "message",
      "role": "assistant",
      "content": [
        { "type": "output_text", "text": "…", "annotations": [] }
      ]
    }
  ],
  "usage": {
    "input_tokens": 128,
    "output_tokens": 96,
    "total_tokens": 224,
    "cached_tokens": 0
  }
}

model is the model id you sent — the price you are charged and the transcript you keep are both traceable to it.
usage counts tokens as the serving model counted them; cached_tokens reports the part served from the provider’s prompt cache, when the model reports it.
output can contain messages, refusals, function calls, and hosted tool items — each with its own identity and status.
The official SDKs expose the assistant text as output_text; on the raw wire, read the text parts inside output.

StreamingLink to this section

stream: true returns server-sent events. Events are complete JSON values with the official OpenAI Responses event names, and the stream commits when client-visible output is produced.

The rules that matter

The stream ends exactly once, with response.completed, response.incomplete, response.failed, or response.cancelled. EOF, [DONE], or HTTP 200 alone is not a successful terminal.
Hosted tool activity is an item on the way to that terminal — a search never ends the stream and never replaces the assistant answer.
If you sent stream: false, you always get one JSON object — the response content type never flips under you.

Events you will see

Event	Carries
`response.created / response.in_progress`	The response shell, before output.
`response.output_item.added / .done`	Each output item as it opens and closes.
`response.content_part.added / .done`	Text, refusal, or reasoning parts.
`response.output_text.delta / .done`	Assistant text as it is produced.
`response.function_call_arguments.delta / .done`	Arguments for a function call you will execute.
`response.web_search_call.in_progress / .searching / .completed`	Hosted web search trajectory with real outcomes.
`response.tool_search_call.in_progress / .completed`	Hosted tool discovery over the tools you declared.
`response.completed / .incomplete / .failed / .cancelled`	The single terminal, with reason.

The stream follows the official OpenAI Responses event vocabulary; other official events (reasoning summaries, refusals handles) pass through with their own names.

curl -N https://api.models.sylphx.ai/v1/responsestext/event-stream

curl -N https://api.models.sylphx.ai/v1/responses \
  -H "Authorization: Bearer $SYLPHX_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "openai/gpt-5.5",
    "input": "Count to five.",
    "stream": true
  }'

Stored responsesLink to this section

With the default store: true, a completed response stays retrievable. This is what makes conversation continuation and safe retries possible.

Method	Path	Purpose
GET	`/responses/{response_id}`	Retrieve a stored response while it is retained.
GET	`/responses/{response_id}/input_items`	List the input items stored for one response.
DELETE	`/responses/{response_id}`	Forget a stored response.
POST	`/responses/{response_id}/cancel`	Official cancel route. Responses are not background jobs.

A completed response is retained for a seven-day window from completion. Retries of the completion acknowledgement do not extend it.
GET /responses/{id} returns the stored response; GET /responses/{id}/input_items returns its input items. Both are tenant-isolated: another organization’s key sees 404, not someone else’s data.
DELETE /responses/{id} returns the official {"id": …, "object": "response", "deleted": true} object. Deleting is how you forget a stored turn before its window ends.
POST /responses/{id}/cancel exists as the official route, but this product does not admit background: true. A stored hit returns 400 response_not_cancellable; an unknown id returns 404.
store: false skips persistence. A later previous_response_id that points at an unpersisted response is a 400, so choose one shape per conversation.

CompactionLink to this section

POST /responses/compact compacts a stored conversation into an official response.compaction object you can continue from — useful when a transcript approaches the context window.

POST https://api.models.sylphx.ai/v1/responses/compactUnary — stream is rejected

curl https://api.models.sylphx.ai/v1/responses/compact \
  -H "Authorization: Bearer $SYLPHX_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "openai/gpt-5.5",
    "previous_response_id": "resp_9f2c41d0a8"
  }'

Compact is unary: stream: true is rejected on this route.
The result is the model family’s official compaction object. Sealed encrypted_content inside it belongs to that model family and is not portable to a different one — continue the conversation on the same family.
You can also let the API compact during a create by sending context_management. Where a model cannot compact, the request fails with a typed error instead of substituting a local summary; there is no fabricated digest.

FilesLink to this section

Upload once, then reference the file id from a Responses input item. File ids are tenant-isolated and expire with the same seven-day retention window.

POST https://api.models.sylphx.ai/v1/filesmultipart/form-data

curl https://api.models.sylphx.ai/v1/files \
  -H "Authorization: Bearer $SYLPHX_API_KEY" \
  -F "[email protected]" \
  -F "purpose=user_data"

# → { "id": "file-3c9…", "object": "file", "status": "processed", … }

Reference the uploadinput_file or input_image

{
  "model": "openai/gpt-5.5",
  "input": [
    {
      "role": "user",
      "content": [
        { "type": "input_text", "text": "Summarise the attached report." },
        { "type": "input_file", "file_id": "file-3c9…" }
      ]
    }
  ]
}

purpose is one of user_data (default), vision, assistants, fine-tune, or evals.
GET /files lists your key’s files with first_id, last_id, and has_more; GET /files/{id}/content returns the raw bytes.
A request that names a missing file id fails with 400 file_not_found — the API does not guess which file you meant.

Messages: a second encodingLink to this section

POST /messages accepts the Anthropic Messages format. It decodes under Anthropic rules, normalizes once into the same Responses document, and can call any model in the catalog.

Hosted tools follow the same ownership on Messages: the model initiates, the platform executes, and you observe server-tool blocks. No instruction coaching is added to your system prompt.
Streaming follows Anthropic stream semantics with one typed terminal.
POST /chat/completions is retired: it returns 404 chat_completions_retired with the replacement path in the message. Use Responses for new code.

Switching models safelyLink to this section

Because model is a field, you can move a conversation to another model without changing facades. Keep the transcript, drop the model-specific state.

Keep the visible transcript and your function or tool results.
Remove execution observations and provider-sealed content (for example encrypted_content from a compaction) before sending the transcript to a different model family.
Send the remaining items as a new request with the new model id on the same endpoint. If the new model cannot honor the transcript, you get a typed error — never a silently rewritten request.

TipPrices travel with the model

Every id in the catalog has its own published input, output, and cached-input rate. See models and pricing before you switch in production.