Response Headers

Overview

Every response from /v1/responses, /v1/chat/completions, and /v1/messages carries a request id, a trace id, and (where it’s known) the request’s cost. Clients migrating from another gateway can also ask for that gateway’s own response headers, so existing logging and spend tracking keep working unchanged.

Default Headers

Header	Value	Streaming
`x-request-id`	Unique id for the request (UUID). Shown in your dashboard logs; include it when contacting support	Yes
`x-trace-id`	Trace id for the request (UUID)	Yes
`x-concentrate-cost`	Total cost of the request in USD, e.g. `0.000123`. Same value as `cost.total` in the response body	No
`request-id`	`/v1/messages` only. Same value as `x-request-id`, under Anthropic’s header name	Yes

x-request-id and x-trace-id are also returned on error responses.

Why cost isn’t on streams: headers are sent before the first streamed event, when the cost isn’t known yet. For streamed requests, read cost from the final event instead (on Chat Completions, set stream_options.include_usage to get it). The same applies to long-running non-streaming requests, where Concentrate sends keep-alive whitespace and so commits the headers early: read cost.total from the response body.

Compatibility Headers

To get another gateway’s response headers, send x-concentrate-compat-headers with a comma-separated list of gateway names:

curl https://api.concentrate.ai/v1/chat/completions \
  -H "Authorization: Bearer $CONCENTRATE_API_KEY" \
  -H "Content-Type: application/json" \
  -H "x-concentrate-compat-headers: litellm,openrouter" \
  -d '{
    "model": "anthropic/claude-opus-4-6",
    "messages": [{"role": "user", "content": "Say hello in one word"}]
  }'

Names are case-insensitive, spaces around them are ignored, and unknown names are skipped. Without the header, none of these are sent.

Name	Headers returned
`litellm`	`x-litellm-call-id`, `x-litellm-model-name`, `x-litellm-model-group`, `x-litellm-response-duration-ms`, `x-litellm-response-cost`
`openrouter`	`x-generation-id`, `x-provider-name`
`portkey`	`x-portkey-trace-id`
`helicone`	`helicone-id`
`bifrost`	`x-bifrost-trace-id`, `x-bifrost-original-model`, `x-bifrost-routing-info-provider`, `x-bifrost-routing-info-model`
`merge`	`x-merge-vendor`, `x-merge-model`

Header values

Values are Concentrate’s, in each gateway’s header name. Ids are Concentrate UUIDs, and providers and models are Concentrate slugs. For example, x-generation-id is a UUID rather than OpenRouter’s gen-... id.

Header	Value
`x-litellm-call-id`, `x-generation-id`, `helicone-id`	Same as `x-request-id`
`x-portkey-trace-id`, `x-bifrost-trace-id`	Same as `x-trace-id`
`x-litellm-model-name`	The `provider/model` that served the request, e.g. `anthropic/claude-opus-4-6`
`x-litellm-model-group`, `x-bifrost-original-model`	The `model` you sent, e.g. `auto`
`x-provider-name`, `x-bifrost-routing-info-provider`, `x-merge-vendor`	The provider that served the request, e.g. `anthropic`
`x-bifrost-routing-info-model`, `x-merge-model`	The model that served the request, without the provider, e.g. `claude-opus-4-6`
`x-litellm-response-duration-ms`	Milliseconds from receiving the request until the provider responded
`x-litellm-response-cost`	Same as `x-concentrate-cost`. Non-streaming only, like LiteLLM

When compatibility headers are sent

They are only added once a provider serves the request, so they aren’t sent on error responses. They are also missing on responses whose headers were sent while Concentrate was still waiting on the provider: long-running non-streaming requests (see the note above) and flex streams that queue before connecting.

Responses

Chat Completions (Beta)

Messages (Beta)

Decisions (Beta)

Models API

Features

Utilities

Reference

Catalog

Overview

Default Headers

Compatibility Headers

Header values

When compatibility headers are sent

​Overview

​Default Headers

​Compatibility Headers

​Header values

​When compatibility headers are sent

Overview

Default Headers

Compatibility Headers

Header values

When compatibility headers are sent