Mistral

Mistral API conversion guide - parameter mapping, message handling, tool support, transcription, OCR, and streaming behavior

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.

Setup & Configuration

Configure Mistral as a provider.

Web UI

1. Navigate to Models > Model Providers. Look for Mistral under Configured Providers. If it is missing, click on Add New Provider and select Mistral.
2. Click Add Key or edit an existing key.
3. Set a name for your key.
4. Paste your API key directly or use an environment variable (for example, env.MISTRAL_API_KEY).
5. Set Allowed Models to All Models (default) or the specific model allowlist you want this key to serve.
6. Save the provider configuration.

config.json

{
  "providers": {
    "mistral": {
      "keys": [
        {
          "name": "mistral-key-1",
          "value": "env.MISTRAL_API_KEY",
          "models": [
            "*"
          ],
          "weight": 1.0
        }
      ]
    }
  }
}

API

Refer to the API documentation for Provider Keys Management.

Go SDK

case schemas.Mistral:
    return []schemas.Key{{
        Name:   "mistral-key-1",
        Value:  *schemas.NewSecretVar("env.MISTRAL_API_KEY"),
        Models: []string{"*"},
        Weight: 1.0,
    }}, nil

---

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