Quick reference vs the official Anthropic Messages API.

Generally compatible

AreaNotes
POST /v1/messagesmodel, messages, max_tokens, system
StreamingAnthropic SSE event semantics
Toolstools, tool_use, tool_result
GET /v1/modelsAnthropic-shaped data[]
Authx-api-key + anthropic-version

Base URL

ItemRouterBrain
HostYour https://51kik.com
Prefix/anthropic/v1

Do not point at api.anthropic.com.

Model ids

Shared catalog id with the OpenAI surface (custom_models.code). Use the catalog id, not assumed Anthropic version strings.

Gateway extensions

FieldDescription
pdf_preprocessSame as OpenAI chat
extra_bodyMerged upstream

Errors

Failures include request_id:

{ "type": "error", "error": { "type": "...", "message": "..." }, "request_id": "req_..." }

Streaming

Events aim to match Anthropic; validate with your SDK version before production rollout.

Related

From Anthropic · Create message