[bot] Anthropic Message Batches API not instrumented

[braintrust-bot]

What instrumentation is missing

The Anthropic SDK (anthropic-sdk-go v1.23.0) exposes a Message Batches API for submitting multiple message requests for asynchronous batch processing. The anthropicRouter in trace/contrib/anthropic/traceanthropic.go only matches the exact path /v1/messages:

func anthropicRouter(cfg *middlewareConfig, path string) internal.MiddlewareTracer {
    if path == "/v1/messages" {
        return newMessagesTracer(cfg)
    }
    return nil
}

The Message Batches API paths are:

Method	Path	Purpose
POST	/v1/messages/batches	Submit a batch of message requests
GET	/v1/messages/batches/{id}	Poll batch status
GET	/v1/messages/batches/{id}/results	Stream back per-request results

None of these match, so all batch LLM calls are silently untraced.

What could be traced

Batch creation (POST /v1/messages/batches): The request body is an array of requests[], each containing a custom_id and a full params object (model, messages, max_tokens, tools, etc.) — identical to the fields already captured by messagesTracer. A dedicated tracer could record:

• braintrust.input_json: the array of message requests
• braintrust.metadata: model, params from the first request (or per-request summary)

Batch results (GET /v1/messages/batches/{id}/results): The response body is an NDJSON stream where each line contains a custom_id and a full message result (including usage). This maps directly to the fields already parsed by parseUsageTokens().

Each entry in the results stream is structurally a complete Messages API response — the same token fields (input_tokens, output_tokens, cache_creation_input_tokens, cache_read_input_tokens) that parseUsageTokens() already handles.

SDK access point

// Create a batch
batch, err := client.Beta.Messages.Batches.New(ctx, anthropic.BetaMessageBatchNewParams{
    Requests: []anthropic.BetaMessageBatchNewParamsRequests{...},
})

// Stream results
stream := client.Beta.Messages.Batches.ResultsStreaming(ctx, batch.ID)
for stream.Next() {
    result := stream.Current()  // BetaMessageBatchIndividualResponse
}

Braintrust docs status

unclear — The Braintrust Anthropic integration guide covers messages.create (including streaming, tool use, and prompt caching) but does not mention Message Batches. No evidence this surface is excluded by design.

Source: https://www.braintrust.dev/docs/integrations/ai-providers/anthropic

Upstream sources

• Anthropic Message Batches API reference: https://docs.anthropic.com/en/api/creating-message-batches
• Anthropic Message Batches overview: https://docs.anthropic.com/en/docs/build-with-claude/message-batches
• anthropic-sdk-go v1.23.0: client.Beta.Messages.Batches

Local repo files inspected

• trace/contrib/anthropic/traceanthropic.go — anthropicRouter (line 105): exact-match on /v1/messages, no coverage for /v1/messages/batches or /v1/messages/batches/{id}/results
• trace/contrib/anthropic/messages.go — messagesTracer and parseUsageTokens: reference pattern reusable for batch results
• trace/contrib/anthropic/go.mod — anthropic-sdk-go v1.23.0 (Message Batches is available in this version)
• trace/contrib/anthropic/traceanthropic_test.go — no batch-related tests