Tag Routing

Guarantee the capabilities your request needs Not every backend supports every feature for a given model. Tag routing lets you declare exactly which capabilities your request requires — and AnyAPI guarantees it lands on a backend that supports them all. No more random failures because a backend can’t handle your PDFs, audio, or tool calls.

{
  "model": "anthropic/claude-sonnet-4",
  "messages": [{"role": "user", "content": "Summarize this document"}],
  "tags": ["messages:pdf_input"]
}

How It Works

Add the tags parameter to your request with the capabilities you need. AnyAPI filters available backends to only those that match all your requested tags, then routes to the best one.

All tags must match — if you send ["vision", "streaming"], the backend must support both
No match = 503 — if no backend supports all your tags, you’ll get a clear error instead of a cryptic failure
Fully optional — skip tags entirely and AnyAPI routes as usual

🏷️ Tag Format

Tags use a simple two-level naming scheme:

endpoint:capability    → scoped to a specific API endpoint
capability             → matches any endpoint

Use endpoint-scoped tags when possible. A capability might be available on one endpoint but not another — scoped tags give you precision.

Endpoint Prefixes

Prefix	API Endpoint
`chat_completions`	`/v1/chat/completions`
`messages`	`/v1/messages`
`responses`	`/v1/responses`

Available Capabilities

Tag	What it guarantees
`vision`	Image input support
`pdf_input`	PDF file input support
`audio_input`	Audio file input support
`reasoning`	Extended thinking / chain-of-thought
`streaming`	Streaming response support
`function_calling`	Function / tool calling
`parallel_function_calling`	Multiple tool calls in one turn
`tool_choice`	Explicit tool selection (`auto`, `required`, `none`, named)
`computer_use`	Computer use tool support
`assistant_prefill`	Pre-fill assistant response
`prompt_caching`	Prompt caching support
`web_search`	Built-in web search
`url_context`	URL context fetching

Every capability works as a generic tag (vision) and as an endpoint-scoped tag (chat_completions:vision, messages:vision, responses:vision).

📨 Sending Tags

Request Body (recommended)

Pass a tags array alongside your usual parameters:

{
  "model": "anthropic/claude-sonnet-4",
  "messages": [{"role": "user", "content": "Describe this image"}],
  "tags": ["chat_completions:vision"]
}

HTTP Header

Use the x-router-tags header with comma-separated values:

curl https://api.anyapi.ai/v1/chat/completions \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "x-router-tags: chat_completions:vision,streaming" \
  -H "Content-Type: application/json" \
  -d '{"model": "anthropic/claude-sonnet-4", "messages": [...]}'

If both tags in the body and x-router-tags header are present, the body takes precedence.

🧪 Examples

Vision — analyze an image

curl https://api.anyapi.ai/v1/chat/completions \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "anthropic/claude-sonnet-4",
    "messages": [
      {"role": "user", "content": [
        {"type": "text", "text": "What is in this image?"},
        {"type": "image_url", "image_url": {"url": "https://example.com/photo.jpg"}}
      ]}
    ],
    "tags": ["chat_completions:vision"]
  }'

PDF — summarize a document

curl https://api.anyapi.ai/v1/messages \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "anthropic/claude-sonnet-4",
    "max_tokens": 1024,
    "messages": [
      {"role": "user", "content": [
        {"type": "document", "source": {"type": "base64", "media_type": "application/pdf", "data": "..."}},
        {"type": "text", "text": "Summarize this document"}
      ]}
    ],
    "tags": ["messages:pdf_input"]
  }'

Streaming + Tool Calling

curl https://api.anyapi.ai/v1/chat/completions \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "openai/gpt-4.1",
    "messages": [{"role": "user", "content": "What is the weather in Berlin?"}],
    "tools": [{"type": "function", "function": {"name": "get_weather", "parameters": {"type": "object", "properties": {"city": {"type": "string"}}}}}],
    "stream": true,
    "tags": ["chat_completions:function_calling", "chat_completions:streaming"]
  }'

Reasoning via header

curl https://api.anyapi.ai/v1/chat/completions \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "x-router-tags: chat_completions:reasoning" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "anthropic/claude-sonnet-4",
    "messages": [{"role": "user", "content": "Solve step by step: what is 7! + 3!?"}]
  }'

⚠️ Error Handling

When no backend matches your tags, AnyAPI returns a 503 with a clear message:

{
  "error": {
    "message": "There is no available model deployment that meets your routing requirements",
    "type": "None",
    "code": "503"
  }
}

Common causes:

The model doesn’t support this capability on any backend
Typo in a tag name — check the tag list above
You’re using a generic tag but the capability is only available on specific endpoints

🔍 Discovering Tags for a Model

Query which tags any model supports:

curl https://api.anyapi.ai/v1/models \
  -H "Authorization: Bearer YOUR_API_KEY" | \
  jq '.data[] | select(.id == "anthropic/claude-sonnet-4") | .tags'

This returns every tag available across all backends for the model. If a tag appears in the list, at least one backend supports it. Models with no capability tags omit the tags field.

Tips

Start without tags — only add them when you need a specific capability that isn’t available everywhere
Use endpoint-scoped tags — chat_completions:vision is safer than just vision because it guarantees the capability on the exact endpoint you’re calling
Combine with fallback chains — use the models parameter alongside tags for maximum reliability
Check before you build — query /v1/models to see which tags your target model supports before hardcoding them

Get started

Features

Use Cases

Developer guides

Integrations

API Reference

Tag Routing

Tag Routing

How It Works

🏷️ Tag Format

Endpoint Prefixes

Available Capabilities

📨 Sending Tags

Request Body (recommended)

HTTP Header

🧪 Examples

Vision — analyze an image

PDF — summarize a document

Streaming + Tool Calling

Reasoning via header

⚠️ Error Handling

🔍 Discovering Tags for a Model

Tips

​Tag Routing

​How It Works

​🏷️ Tag Format

​Endpoint Prefixes

​Available Capabilities

​📨 Sending Tags

​Request Body (recommended)

​HTTP Header

​🧪 Examples

​Vision — analyze an image

​PDF — summarize a document

​Streaming + Tool Calling

​Reasoning via header

​⚠️ Error Handling

​🔍 Discovering Tags for a Model

​Tips

Tag Routing

How It Works

🏷️ Tag Format

Endpoint Prefixes

Available Capabilities

📨 Sending Tags

Request Body (recommended)

HTTP Header

🧪 Examples

Vision — analyze an image

PDF — summarize a document

Streaming + Tool Calling

Reasoning via header

⚠️ Error Handling

🔍 Discovering Tags for a Model

Tips