Feature Request: Support proxying Anthropic Managed Agents API endpoints (/v1/agents, /v1/sessions)

[saixso]

Summary

Anthropic recently launched Claude Managed Agents (public beta), which introduces a new set of stateful API endpoints beyond /v1/messages. Currently, Envoy AI Gateway only proxies model inference endpoints — enterprises deploying the gateway as a centralized AI access layer have no way to route, authenticate, or audit Managed Agents traffic through it.

Background

Managed Agents introduces a new API surface for long-running, stateful agent sessions:

Endpoint	Purpose
POST /v1/agents	Create a persisted, versioned agent config
POST /v1/sessions	Start a session against an agent
GET /v1/sessions/{id}/events/stream	SSE stream of agent events
POST /v1/sessions/{id}/events	Send user messages / tool results
GET /v1/sessions/{id}/events	Poll events (paginated)
POST /v1/environments	Provision sandbox environments
POST /v1/vaults	Manage MCP credentials

Key characteristics that make gateway support non-trivial:

• SSE streaming on /events/stream — long-lived connections, not request/response
• Stateful sessions — clients reconnect to existing sessions; the gateway must not break session affinity
• Beta headers — requires anthropic-beta: managed-agents-2026-04-01
• First-party Anthropic only — cannot route through AWS Bedrock; requires a direct api.anthropic.com backend

Problem

Enterprises using Envoy AI Gateway as a centralized proxy gain:

• Unified auth (API key / JWT)
• Token cost tracking
• Audit logging
• Rate limiting
• Policy enforcement

Today, any team wanting to use Managed Agents must bypass the gateway entirely and call api.anthropic.com directly with a raw Anthropic API key — losing all of the above.

Desired Behavior

1. New Backend type (or config option) pointing to api.anthropic.com for first-party Anthropic endpoints
2. HTTPRoute support for /v1/agents*, /v1/sessions*, /v1/environments*, /v1/vaults*
3. SSE-aware proxying for /v1/sessions/{id}/events/stream (no buffering, proper text/event-stream passthrough)
4. Beta header passthrough (anthropic-beta)
5. Cost metadata extraction from SSE events (token usage is in span.model_request_end events)

Related Issues

• Feature Request: Enable Proxy Support for AI Agents #1759 — Agent proxy support (network-level)
• Support Open Responses specification #1830 — Open Responses / stateful agentic workflows

References

• Claude Managed Agents announcement
• Anthropic Managed Agents API docs
• SSE event reference