apicheats.dev anthropic/llms.txt Raw .md
POST

POST /v1/sessions?beta=true — Claude API

Beta

Anthropic API key (required); https://api.anthropic.com

Claude API

Create Session

Base URL
https://api.anthropic.com
Auth
x-api-key: <ANTHROPIC_API_KEY>
Last verified
2026-10-20 · upstream hash matched
Actions Try in browser→
Agents: curl -H "Accept: text/markdown" this URL
→ 377 tokens · Vary: Accept

Critical gotchas

Authentication uses the x-api-key header and requests also require an anthropic-version header.

The official OpenAPI URL is discovered from the SDK repository manifest and must remain under Anthropic's trusted Stainless storage prefix.

cURL

curl -X POST 'https://api.anthropic.com/v1/sessions?beta=true' \  -H "x-api-key: $ANTHROPIC_API_KEY" \  -H 'anthropic-version: 2023-06-01' \  -H 'Content-Type: application/json' \  -d '{  "agent": "example-agent",  "environment_id": "environment-id"}'

Parameters

Name In Type Required Description
agent body string Yes Agent identifier. Accepts the `agent` ID string, which pins the latest version for the session, or an `agent` object with both id and version specified.
environment_id body string Yes ID of the `environment` defining the container configuration for this session.
title body string No Human-readable session title.
metadata body object No Arbitrary key-value metadata attached to the session. Maximum 16 pairs, keys up to 64 chars, values up to 512 chars.
resources body object[] No Resources (e.g. repositories, files) to mount into the session's container.
vault_ids body string[] No Vault IDs for stored credentials the agent can use during the session.
initial_events body object[] No Initial events to send to the `session` at creation, processed in order. Supports `user.message` and `user.define_outcome` events. Maximum 50 events.
budget body object No Enforced spend ceiling for the session. Omit to create an uncapped session. Every model the session can run — the agent's model and each callable agent's model — must have a public list price, or the request is rejected with reason `model_not_budgetable`.

Response 200 OK

{
  "type": "session",
  "id": "sesn_011CZkZAtmR3yMPDzynEDxu7",
  "status": "idle",
  "created_at": "2026-03-15T10:00:00Z",
  "updated_at": "2026-03-15T10:00:00Z",
  "archived_at": null,
  "budget": null,
  "environment_id": "env_011CZkZ9X2dpNyB7HsEFoRfW",
  "title": "Order #1234 inquiry",
  "metadata": {},
  "agent": {
    "type": "agent",
    "id": "agent_011CZkYpogX7uDKUyvBTophP",
    "version": 1,
    "name": "My First Agent",
    "description": "A general-purpose starter agent.",
    "model": {
      "id": "claude-opus-5",
      "speed": "standard"
    },
    "system": "You are a general-purpose agent that can research, write code, run commands, and use connected tools to complete the user's task end to end.",
    "tools": [
      {
        "type": "agent_toolset_20260401",
        "default_config": {
          "enabled": true,
          "permission_policy": {
            "type": "always_ask"
          }
        },
        "configs": []
      }
    ],
    "mcp_servers": [
      {
        "type": "url",
        "name": "example-mcp",
        "url": "https://example-server.modelcontextprotocol.io/sse"
      }
    ],
    "skills": [
      {
        "type": "anthropic",
        "skill_id": "xlsx",
        "version": "1"
      },
      {
        "type": "custom",
        "skill_id": "skill_011CZkZFNu9hAbo3jZPRgTlx",
        "version": "2"
      }
    ],
    "multiagent": null
  },
  "resources": [
    {
      "type": "file",
      "id": "sesrsc_011CZkZBJq5dWxk9fVLNcPht",
      "file_id": "file_011CNha8iCJcU1wXNR6q4V8w",
      "mount_path": "/uploads/receipt.pdf",
      "created_at": "2026-03-15T10:00:00Z",
      "updated_at": "2026-03-15T10:00:00Z"
    },
    {
      "type": "github_repository",
      "id": "sesrsc_011CZkZCKr6eXyl0gWMOdQiu",
      "url": "https://github.com/example-org/example-repo",
      "mount_path": "/workspace/example-repo",
      "checkout": {
        "type": "branch",
        "name": "main"
      },
      "created_at": "2026-03-15T10:00:00Z",
      "updated_at": "2026-03-15T10:00:00Z"
    }
  ],
  "vault_ids": [
    "vlt_011CZkZDLs7fYzm1hXNPeRjv"
  ],
  "usage": {
    "input_tokens": 0,
    "output_tokens": 0,
    "cache_read_input_tokens": 0
  },
  "stats": {
    "duration_seconds": 0,
    "active_seconds": 0
  },
  "outcome_evaluations": [
    {
      "type": "outcome_evaluation",
      "outcome_id": "outc_011CZkZRSw2kEfs6ncTVljxP",
      "description": "Produce a 2-page summary as summary.md",
      "result": "satisfied",
      "iteration": 0,
      "completed_at": "2026-03-15T10:02:31Z",
      "explanation": "All five sections present with inline citations."
    }
  ]
}
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