> ## Documentation Index > Fetch the complete documentation index at: https://docs.flex.ai/llms.txt > Use this file to discover all available pages before exploring further. # OpenAI Compatibility > What is and isn't supported at launch when you point an OpenAI SDK at tokens.flex.ai. The Inference API implements a subset of OpenAI's v1 surface. For everything below marked Supported, code written against `api.openai.com` works by changing only `base_url` and `model`. ## Spec version we track The chat-completions request validator at our gateway is authored against **`openai-python` 1.109.1** — specifically the request shape `openai.types.chat.completion_create_params.CompletionCreateParamsBase`. That same version is pinned in our gateway image, so the SDK you call against and the shape we validate can't drift apart silently. We validate a focused subset of the SDK's surface — the fields where validation gaps were causing real problems (off-spec inputs returning `200` with garbage, or `500` with a stack trace). Unknown or unsupported fields are forwarded to the engine and accepted or rejected there. The matrix below is the exact subset. Bumps are deliberate: when we upgrade the pin, a snapshot test fails until we audit the SDK diff, and we update this page in the same PR. ## Endpoints | Endpoint | Supported | Notes | | ------------------------------------------------ | --------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | `POST /v1/chat/completions` | Yes | Streaming, tools, vision (on multimodal models), seed, response\_format. | | `POST /v1/completions` | Yes | Legacy; prefer chat completions for new integrations. | | `GET /v1/models` | Yes | Lists every **live** model across all modalities — text, code, reasoning, multimodal, embeddings, image, audio, video — in OpenAI's `Model` shape, each annotated with a `category` field so you can pick the matching endpoint. Only models currently serving appear. See [model discovery](/inference-api/guides/model-discovery) for the category→endpoint mapping, or the [catalog](https://flex.ai/models) for the full roster with pricing. | | `POST /v1/embeddings` | Yes | `bge-m3` (multilingual, 1024-dim, 8K context). `encoding_format` is optional and defaults to `"float"`; `"base64"` is also accepted. (Pass `"float"` or omit the field — don't send an explicit `null`.) See the [model catalog](https://flex.ai/models). | | `POST /v1/fine-tuning` | No | Use [FlexAI Fine-Tuning](/core-services/fine-tuning) instead. | | `POST /v1/assistants`, `/v1/threads`, `/v1/runs` | No | Not planned. | | `POST /v1/batches` | No | Not supported — use client-side fan-out instead. See [Batching](/inference-api/guides/batch). | | `GET /v1/files`, `/v1/files/*` | No | Use inline request payloads. | ## Request fields | Field on `POST /v1/chat/completions` | Supported | Notes | | --------------------------------------------------------------------------------- | --------- | ---------------------------------------------------------------------------------------- | | `model`, `messages`, `temperature`, `top_p`, `max_tokens`, `stop`, `seed`, `user` | Yes | — | | `stream`, `stream_options.include_usage` | Yes | Set `include_usage: true` when streaming for correct billing. | | `tools`, `tool_choice` | Yes | On models labeled `tool_use` in the catalog. | | `response_format: { type: "json_object" }` | Yes | On most text models. | | `response_format: { type: "json_schema", ... }` | Partial | Supported where the underlying model supports it; falls back to `json_object` otherwise. | | `logprobs`, `top_logprobs` | No | Not at launch. | | `n` (multiple completions per request) | No | Gateway returns a single choice; sending `n > 1` returns a `400` with `param: "n"`. | | `presence_penalty`, `frequency_penalty` | Yes | — | ## Response fields | Field | Supported | Notes | | -------------------------------------------------------------------- | --------- | -------------------------------------------------------------------------- | | `id`, `created`, `model`, `choices`, `usage` | Yes | — | | `usage.cache_read_input_tokens`, `usage.cache_creation_input_tokens` | Yes | Zero on models without prompt caching; populated for cache-capable models. | | `system_fingerprint` | No | Not exposed. | ## Authentication & headers * Bearer tokens only (`Authorization: Bearer sk-…`). No OAuth, no organization header. * Our rate limit response includes `Retry-After` and `x-ratelimit-*` headers — see [errors](/inference-api/reference/errors). * CORS is restricted; the API is intended for server-to-server calls, not browsers. ## Error shape Errors use OpenAI's envelope — `{ "error": { "message", "type", … } }` — in two flavors. **Request-validation failures** (`400`) come back verbatim in OpenAI's shape, with `param` set to the offending field path (or `null` when it isn't field-specific) and `code` set to `null` — we reserve non-null `code` strings the way OpenAI does, for a narrow documented set like `context_length_exceeded`: ```json theme={null} { "error": { "message": "…", "type": "invalid_request_error", "param": "messages[0].role", "code": null } } ``` **Auth and quota failures** add a FlexAI-only `doc_url` extension so your first failure points you at the dashboard: ```json theme={null} { "error": { "message": "Invalid API key. Create one from the dashboard.", "type": "authentication_error", "code": "invalid_api_key", "doc_url": "https://tokens.flex.ai/dashboard/keys" } } ``` See [the error reference](/inference-api/reference/errors) for the full list of codes.