Overview

Mistral is an OpenAI-compatible provider with custom compatibility handling for specific features. Bifrost converts requests to Mistral’s expected format while supporting their unique API endpoints. Key characteristics:

OpenAI-compatible format - Chat and streaming endpoints
Transcription API - Native audio transcription support
OCR API - Native document and image OCR support
Tool calling support - Function definitions with string-based tool choice
Streaming support - Server-Sent Events for chat and transcription
Parameter compatibility - max_completion_tokens → max_tokens conversion

Supported Operations

Operation	Non-Streaming	Streaming	Endpoint
Chat Completions	✅	✅	`/v1/chat/completions`
Responses API	✅	✅	`/v1/chat/completions`
Transcriptions (STT)	✅	✅	`/v1/audio/transcriptions`
OCR	✅	-	`/v1/ocr`
Embeddings	✅	-	`/v1/embeddings`
List Models	✅	-	`/v1/models`
Image Generation	❌	❌	-
Text Completions	❌	❌	-
Speech (TTS)	❌	❌	-
Files	❌	❌	-
Batch	❌	❌	-

Unsupported Operations (❌): Text Completions, Speech (TTS), Files, and Batch are not supported by the upstream Mistral API. Image Generation is not currently supported by Bifrost’s Mistral integration (Mistral API supports image generation, but Bifrost has not yet implemented this feature). These return UnsupportedOperationError.

1. Chat Completions

Request Parameters

Mistral supports most OpenAI chat completion parameters with some conversions. For standard OpenAI parameter reference, see OpenAI Chat Completions.

Parameter Mapping & Conversions

Parameter	OpenAI	Mistral	Notes
`max_completion_tokens`	✅	`max_tokens`	Conversion required
`temperature`	✅	✅	Direct pass-through
`top_p`	✅	✅	Direct pass-through
`stop`	✅	✅	Stop sequences
`tools`	✅	✅	Function definitions
`tool_choice`	String only	String only	Limitations apply
`user`	✅	✅	Max 64 characters
`frequency_penalty`, `presence_penalty`	✅	✅	Direct pass-through

Critical Conversions

max_completion_tokens → max_tokens:

// Bifrost request
{"max_completion_tokens": 4096}

// Mistral API
{"max_tokens": 4096}

Tool Choice Simplification: Mistral only supports simple string tool choice, not structured constraints:

// OpenAI supports specific tool forcing
{"tool_choice": {"type": "function", "function": {"name": "specific_tool"}}}

// Mistral only supports
{"tool_choice": "any"}  // or "none", "auto"

Filtered Parameters

Removed for Mistral compatibility:

prompt_cache_key - Not supported
cache_control - Stripped from content blocks
verbosity - Anthropic-specific
store - Not supported
service_tier - Not supported

Message Conversion

Full OpenAI message support:

All roles: user, assistant, system, tool, developer
Content types: text, images, audio, files

Tool Conversion

Tool definitions supported with constraints:

Aspect	Support	Notes
Function definitions	✅	Full parameter schema support
Tool choice “auto”	✅	Default mode
Tool choice “any”	✅	Requires any tool
Tool choice “none”	✅	No tools
Specific tool forcing	❌	Not supported - simplified to “any”
Parallel tools	✅	Multiple tools in one turn

Limitation Caveat:

// Bifrost allows specifying a specific tool
{
  "tool_choice": {
    "type": "function",
    "function": {"name": "get_weather"}  // ❌ Not supported
  }
}

// Mistral compatibility - converted to generic "any"
{
  "tool_choice": "any"
}

Response Conversion

Standard OpenAI-compatible response:

choices[].message.content - Response text
choices[].message.tool_calls - Function calls
usage - Token counts (prompt_tokens, completion_tokens)
finish_reason - stop, tool_calls, length

2. Responses API

Converted internally to Chat Completions with format transformation:

ResponsesRequest → ChatRequest → ChatCompletion → ResponsesResponse

Same parameter support and tool handling as Chat Completions.

3. Transcription

Mistral provides native audio transcription with streaming support.

Request Parameters

Parameter Mapping

Parameter	Bifrost	Mistral	Notes
`file`	Binary audio	Multipart form	Converted to multipart
`model`	Model name	model
`language`	ISO-639-1	language	Optional language hint
`prompt`	Optional	prompt	Context for recognition
`response_format`	Format type	response_format	json, text, etc.
`temperature`	float	temperature	Sampling temperature
`timestamp_granularities`	Array	Array field	Segment/word timestamps

Multipart Form Structure

Transcription requests are sent as multipart/form-data:

--boundary
Content-Disposition: form-data; name="file"; filename="audio.mp3"
[binary audio data]
--boundary
Content-Disposition: form-data; name="model"
voxtral-mini-latest
--boundary
Content-Disposition: form-data; name="language"
en
--boundary--

Transcription Response

{
  "text": "transcribed text",
  "language": "en",
  "duration": 3.5,
  "segments": [
    {
      "id": 0,
      "start": 0.0,
      "end": 1.5,
      "text": "transcribed segment",
      "temperature": 0.0,
      "avg_logprob": -0.45,
      "compression_ratio": 1.2,
      "no_speech_prob": 0.001
    }
  ],
  "words": [
    {
      "word": "transcribed",
      "start": 0.0,
      "end": 0.8
    }
  ]
}

Transcription Streaming

Mistral supports SSE streaming for transcription with custom event types:

Event Type	Content	Notes
`transcription.language`	Language code	Language detected
`transcription.text.delta`	Text delta	Incremental text
`transcription.segment`	Full segment	Complete segment data
`transcription.done`	Final usage	Completion with tokens

4. Embeddings

Mistral supports text embeddings:

Parameter	Notes
`input`	Text or array of texts
`model`	Embedding model name
`dimensions`	Custom output dimensions (optional)
`encoding_format`	”float” or “base64”

Response returns embedding vectors with token usage.

5. OCR

Mistral provides native OCR support for extracting text and content from documents and images via the mistral-ocr-latest model.

Request Parameters

Parameter	Notes
`model`	OCR model name (e.g., `mistral/mistral-ocr-latest`)
`document`	Document input - see document types below
`include_image_base64`	Return extracted images as base64
`pages`	Specific page indices to process (0-based)
`image_limit`	Max images to extract per page
`image_min_size`	Minimum image size in pixels to extract
`table_format`	Format for extracted tables (e.g., `"markdown"`, `"html"`)
`extract_header`	Extract page headers
`extract_footer`	Extract page footers
`confidence_scores_granularity`	Confidence detail level: `page`, `block`, `word`, or `document`
`bbox_annotation_format`	Format for bounding box annotations
`document_annotation_format`	Format for document-level annotations
`document_annotation_prompt`	Custom prompt for document annotation

Document Types

`type`	Required field	Use case
`document_url`	`document_url`	PDF URL or base64 data URL
`image_url`	`image_url`	Image URL

6. List Models

Lists available Mistral models with context length and capabilities.

Unsupported Features

Feature	Reason
Text Completions	Not offered by Mistral API
Image Generation	Not yet implemented in Bifrost integration (Mistral API supports this)
Speech/TTS	Not offered by Mistral API
File Management	Not offered by Mistral API
Batch Operations	Not offered by Mistral API

Caveats

Cache Control Stripped

Severity: Medium Behavior: Cache control directives removed from messages Impact: Prompt caching features unavailable Code: Stripped during JSON marshaling

Parameter Filtering

Severity: Low Behavior: OpenAI-specific parameters filtered Impact: prompt_cache_key, verbosity, store removed Code: filterOpenAISpecificParameters

User Field Size Limit

Severity: Low Behavior: User field > 64 characters silently dropped Impact: Longer user identifiers are lost Code: SanitizeUserField enforces 64-char max

Overview

Quick Start

Release Cadence

Migration Guides

SDK Integrations

Providers & Guides

MCP Gateway

Custom plugins

Open Source Features

Mistral

Overview

Supported Operations

1. Chat Completions

Request Parameters

Parameter Mapping & Conversions

Critical Conversions

Filtered Parameters

Message Conversion

Tool Conversion

Response Conversion

2. Responses API

3. Transcription

Request Parameters

Parameter Mapping

Multipart Form Structure

Transcription Response

Transcription Streaming

4. Embeddings

5. OCR

Request Parameters

Document Types

6. List Models

Unsupported Features

Caveats

Overview

Quick Start

Release Cadence

Migration Guides

SDK Integrations

Providers & Guides

MCP Gateway

Custom plugins

Open Source Features

Documentation Index

​Overview

​Supported Operations

​1. Chat Completions

​Request Parameters

​Parameter Mapping & Conversions

​Critical Conversions

​Filtered Parameters

​Message Conversion

​Tool Conversion

​Response Conversion

​2. Responses API

​3. Transcription

​Request Parameters

​Parameter Mapping

​Multipart Form Structure

​Transcription Response

​Transcription Streaming

​4. Embeddings

​5. OCR

​Request Parameters

​Document Types

​6. List Models

​Unsupported Features

​Caveats

Overview

Supported Operations

1. Chat Completions

Request Parameters

Parameter Mapping & Conversions

Critical Conversions

Filtered Parameters

Message Conversion

Tool Conversion

Response Conversion

2. Responses API

3. Transcription

Request Parameters

Parameter Mapping

Multipart Form Structure

Transcription Response

Transcription Streaming

4. Embeddings

5. OCR

Request Parameters

Document Types

6. List Models

Unsupported Features

Caveats