POST /v1/messages

Anthropic-compatible drop-in endpoint. Change one line in your existing @anthropic-ai/sdk code and everything works. Requires the ai:chat scope.

Migrating from Anthropic

import Anthropic from '@anthropic-ai/sdk';

const client = new Anthropic({
  baseURL: 'https://api.usehasp.com',  // ← only this line changes
  apiKey: 'hasp_key_live_...',
});

Request shape, response shape, streaming events, and tool use are Anthropic’s exact wire format. Your existing code, types, and tooling continue to work.

Request

POST https://api.usehasp.com/v1/messages
Authorization: Bearer hasp_key_live_...
Content-Type: application/json

The request body is identical to Anthropic’s Messages API. Key fields:

Parameter	Type	Description
`model`	string	Model ID — same identifiers as Anthropic (`claude-sonnet-4-6`, etc.)
`messages`	array	Conversation turns: `[{"role": "user", "content": "..."}]`
`max_tokens`	integer	Required by Anthropic’s spec.
`stream`	boolean	`true` for SSE, `false` for a single JSON response.
`system`	string	System prompt.
`tools`	array	Tool definitions (same format as Anthropic).

Streaming events

When stream: true, the event stream uses Anthropic’s exact wire format:

event: message_start
event: content_block_start
event: content_block_delta   (repeated)
event: content_block_stop
event: message_delta
event: message_stop
event: ping                  (keep-alive)
event: error                 (on failure)

This means libraries and utilities that parse Anthropic SSE streams work without modification.

Compliance behavior

All HASP compliance checks apply — PHI Guard, BAA enforcement, credit metering — regardless of which endpoint you use. Compliance is a property of your organization, not the endpoint shape.

PHI Guard runs on all messages. If phi_mode=redact (default), PHI is replaced with placeholders before the upstream call. If phi_mode=block, the request returns 403 PHI_BLOCKED using the HASP error envelope.
BAA required. No active BAA → 402 BAA_REQUIRED on every request.
Credit metering. Credits are deducted after each successful response. Exhausted credits → 402 AI_CREDITS_EXHAUSTED.

Native-only flags are rejected

Parameters that exist in the native /v1/ai/chat endpoint but not in Anthropic’s wire format are rejected with 400 UNSUPPORTED_PARAMETER rather than silently accepted:

store — use POST /v1/ai/chat if you need stateless (no-content-storage) requests.
Any other non-Anthropic field.

This keeps the contract honest — if you send store: false and get a 200 back, you might wrongly assume the content wasn’t stored.

Graduating to native features

Customers using /v1/messages can migrate endpoint-by-endpoint to /v1/ai/chat to gain:

store: false for stateless requests
PHI entity metadata in responses
Run and conversation management
Tool use (future phase)

No breaking changes are required for the migration — the two endpoints are independent.

Error codes

Code	HTTP	Description
`INVALID_API_KEY`	401	Missing or revoked token
`BAA_REQUIRED`	402	No active BAA
`AI_CREDITS_EXHAUSTED`	402	Credit allotment exhausted
`MISSING_SCOPE`	403	Key lacks `ai:chat` scope
`PHI_BLOCKED`	403	PHI detected and `phi_mode=block` is configured
`OPUS_NOT_ENABLED`	403	Opus model not enabled for this org
`UNSUPPORTED_PARAMETER`	400	Non-Anthropic parameter sent (e.g. `store`)
`RATE_LIMITED`	429	RPM or daily limit exceeded
`INFERENCE_UPSTREAM_FAILURE`	502	Upstream model provider error — retryable

​Migrating from Anthropic

​Request

​Streaming events

​Compliance behavior

​Native-only flags are rejected

​Graduating to native features

​Error codes