docs(rfd): Сustom LLM endpoints

[xtmq]

---

title: "Configurable LLM Providers"

• Author(s): @anna239, @xtmq

Elevator pitch

What are you proposing to change?

Add the ability for clients to discover and configure agent LLM providers (identified by id) via dedicated provider methods:

• providers/list
• providers/set
• providers/disable

This allows clients to route LLM requests through their own infrastructure (proxies, gateways, or self-hosted models) without agents needing to know about this configuration in advance.

Status quo

How do things work today and what problems does this cause? Why would we change things?

ACP does not currently define a standard method for configuring LLM providers.

In practice, provider configuration is usually done via environment variables or agent-specific config files. That creates several problems:

• No standard way for clients to discover what providers an agent exposes
• No standard way to update one specific provider by id
• No standard way to disable a specific provider at runtime while preserving provider discoverability
• Secret-bearing values in headers are difficult to handle safely when configuration must be round-tripped

This particularly affects:

• Client proxies: clients want to route agent traffic through their own proxies, for example to add headers or logging
• Enterprise deployments: organizations want to route LLM traffic through internal gateways for compliance, logging, and cost controls
• Self-hosted models: users running local servers (vLLM, Ollama, etc.) need to redirect agent traffic to local infrastructure
• API gateways: organizations using multi-provider routing, rate limiting, and caching need standardized endpoint configuration

Shiny future

How will things play out once this feature exists?

Clients will be able to:

1. Understand whether an agent supports client-managed LLM routing
2. See where the agent is currently sending LLM requests (for example in settings UI)
3. Route agent LLM traffic through their own infrastructure (enterprise proxy, gateway, self-hosted stack)
4. Update routing settings from the client instead of relying on agent-specific env vars
5. Disable a provider when needed and later re-enable it explicitly
6. Apply these settings before starting new work in sessions

Implementation details and plan

Tell me more about your implementation. What is your detailed implementation plan?

Intended flow

sequenceDiagram
    participant Client
    participant Agent

    Client->>Agent: initialize
    Agent-->>Client: initialize response (agentCapabilities.providers = true)

    Client->>Agent: providers/list
    Agent-->>Client: providers/list response

    Client->>Agent: providers/set (id = "main")
    Agent-->>Client: providers/set response

    Client->>Agent: providers/disable (optional)
    Agent-->>Client: providers/disable response

    Client->>Agent: session/new

Loading

1. Client initializes and checks agentCapabilities.providers.
2. Client calls providers/list to discover available providers, their current routing targets (or disabled state), supported protocol types, and whether they are required.
3. Client calls providers/set to apply new (required) configuration for a specific provider id.
4. Client may call providers/disable when a non-required provider should be disabled.
5. Client creates or loads sessions.

Capability advertisement

The agent advertises support with a single boolean capability:

interface AgentCapabilities {
  // ... existing fields ...

  /**
   * Provider configuration support.
   * If true, the agent supports providers/list, providers/set, and providers/disable.
   */
  providers?: boolean;
}

If providers is absent or false, clients must treat provider methods as unsupported.

Types

/** Well-known API protocol identifiers. */
type LlmProtocol = "anthropic" | "openai" | "azure" | "vertex" | "bedrock";

interface ProviderCurrentConfig {
  /** Protocol currently used by this provider. */
  apiType: LlmProtocol;

  /** Base URL currently used by this provider. */
  baseUrl: string;
}

interface ProviderInfo {
  /** Provider identifier, for example "main" or "openai". */
  id: string;

  /** Supported protocol types for this provider. */
  supported: LlmProtocol[];

  /**
   * Whether this provider is mandatory and cannot be disabled via providers/disable.
   * If true, clients must not call providers/disable for this id.
   */
  required: boolean;

  /**
   * Current effective non-secret routing config.
   * Null means provider is disabled.
   */
  current: ProviderCurrentConfig | null;

  /** Extension metadata */
  _meta?: Record<string, unknown>;
}

providers/list

interface ProvidersListRequest {
  /** Extension metadata */
  _meta?: Record<string, unknown>;
}

interface ProvidersListResponse {
  /** Configurable providers with current routing info suitable for UI display. */
  providers: ProviderInfo[];

  /** Extension metadata */
  _meta?: Record<string, unknown>;
}

providers/set

providers/set updates the full configuration for one provider id.

interface ProvidersSetRequest {
  /** Provider id to configure. */
  id: string;

  /** Protocol type for this provider. */
  apiType: LlmProtocol;

  /** Base URL for requests sent through this provider. */
  baseUrl: string;

  /**
   * Full headers map for this provider.
   * May include authorization, routing, or other integration-specific headers.
   */
  headers: Record<string, string>;

  /** Extension metadata */
  _meta?: Record<string, unknown>;
}

interface ProvidersSetResponse {
  /** Extension metadata */
  _meta?: Record<string, unknown>;
}

providers/disable

interface ProvidersDisableRequest {
  /** Provider id to disable. */
  id: string;

  /** Extension metadata */
  _meta?: Record<string, unknown>;
}

interface ProvidersDisableResponse {
  /** Extension metadata */
  _meta?: Record<string, unknown>;
}

Example exchange

initialize Response:

{
  "jsonrpc": "2.0",
  "id": 0,
  "result": {
    "protocolVersion": 1,
    "agentInfo": {
      "name": "MyAgent",
      "version": "2.0.0"
    },
    "agentCapabilities": {
      "providers": true,
      "sessionCapabilities": {}
    }
  }
}

providers/list Request:

{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "providers/list",
  "params": {}
}

providers/list Response:

{
  "jsonrpc": "2.0",
  "id": 1,
  "result": {
    "providers": [
      {
        "id": "main",
        "supported": ["bedrock", "vertex", "azure", "anthropic"],
        "required": true,
        "current": {
          "apiType": "anthropic",
          "baseUrl": "http://localhost/anthropic"
        }
      },
      {
        "id": "openai",
        "supported": ["openai"],
        "required": false,
        "current": null
      }
    ]
  }
}

providers/set Request:

{
  "jsonrpc": "2.0",
  "id": 2,
  "method": "providers/set",
  "params": {
    "id": "main",
    "apiType": "anthropic",
    "baseUrl": "https://llm-gateway.corp.example.com/anthropic/v1",
    "headers": {
      "X-Request-Source": "my-ide"
    }
  }
}

providers/set Response:

{
  "jsonrpc": "2.0",
  "id": 2,
  "result": {}
}

providers/disable Request:

{
  "jsonrpc": "2.0",
  "id": 3,
  "method": "providers/disable",
  "params": {
    "id": "openai"
  }
}

providers/disable Response:

{
  "jsonrpc": "2.0",
  "id": 3,
  "result": {}
}

Behavior

1. Capability discovery: agents that support provider methods MUST advertise agentCapabilities.providers: true in initialize. Clients SHOULD only call providers/* when this capability is present and true.
2. Timing and session impact: provider methods MUST be called after initialize. Clients SHOULD configure providers before creating or loading sessions. Agents MAY choose not to apply changes to already running sessions, but SHOULD apply them to sessions created or loaded after the change.
3. List semantics: providers/list returns configurable providers, their supported protocol types, current effective routing, and required flag. Providers SHOULD remain discoverable in list after providers/disable.
4. Client behavior for required providers: clients SHOULD NOT call providers/disable for providers where required: true.
5. Disabled state encoding: in providers/list, current: null means the provider is disabled and MUST NOT be used by the agent for LLM calls.
6. Set semantics and validation: providers/set replaces the full configuration for the target id (apiType, baseUrl, full headers). If id is unknown, apiType is unsupported for that provider, or params are malformed, agents SHOULD return invalid_params.
7. Disable semantics: providers/disable disables the target provider at runtime. A disabled provider MUST appear in providers/list with current: null. If target provider has required: true, agents MUST return invalid_params. Disabling an unknown id SHOULD be treated as success (idempotent behavior).
8. Scope and persistence: provider configuration is process-scoped and SHOULD NOT be persisted to disk.

Frequently asked questions

What questions have arisen over the course of authoring this document?

What does null mean in providers/list?

current: null means the provider is disabled.

When disabled, the agent MUST NOT route LLM calls through that provider until the client enables it again with providers/set.

Why is there a required flag?

Some providers are mandatory for agent operation and must not be disabled.

required lets clients hide or disable the provider-disable action in UI and avoid calling providers/disable for those ids.

Why not a single providers/update method for full list replacement?

A full-list update means the client must send complete configuration (including headers) for all providers every time.

If the client wants to change only one provider, it may not know headers for the others. In that case it cannot safely build a correct full-list payload.

Also, providers/list does not return headers, so the client cannot simply "take what the agent returned" and send it back with one edit.

Per-provider methods (set and disable) avoid this problem and keep updates explicit.

Why doesn't providers/list return headers?

Header values may contain secrets and should not be echoed by the agent. providers/list is intentionally limited to non-secret routing information (current.apiType, current.baseUrl).

Why are providers/list and providers/set payloads different?

providers/set accepts headers, including secrets, and is write-oriented.

providers/list is read-oriented and returns only non-secret routing summary (current) for UI and capability discovery.

Why is this separate from initialize params?

Clients need capability discovery first, then provider discovery, then configuration. A dedicated method family keeps initialization focused on negotiation and leaves provider mutation to explicit steps.

Why not use session-config with a provider category instead?

session-config is a possible alternative, and we may revisit it as the spec evolves.

We did not choose it as the primary approach in this proposal because provider routing here needs dedicated semantics that are difficult to express with today's session config model:

• Multiple providers identified by id, each with its own lifecycle
• Structured payloads (apiType, baseUrl, full headers map) rather than simple scalar values
• Explicit discoverable (providers/list) and disable (providers/disable) semantics

Today, session-config values are effectively string-oriented and do not define a standard multi-value/structured model for this use case.

Revision history

• 2026-03-22: Finalized provider disable semantics - providers/remove renamed to providers/disable, required providers are non-disableable, and disabled state is represented as current: null
• 2026-03-21: Initial draft of provider configuration API (providers/list, providers/set, providers/remove)
• 2026-03-07: Rename "provider" to "protocol" to reflect API compatibility level; make LlmProtocol an open string type with well-known values; resolve open questions on identifier standardization and model availability
• 2026-03-04: Revised to use dedicated setLlmEndpoints method with capability advertisement
• 2026-02-02: Initial draft - preliminary proposal to start discussion

[benbrandt]

Overall I really like this! Some questions but no major objections

[cdxiaodong]

nice sir！！！

[IceyLiu]

good PR, we do need it

[leovigna]

I like the concept of client-side LLM providers.
Regarding config isn't session-config with a "provider" category sufficient for this though? https://agentclientprotocol.com/protocol/session-config-options#session-config-options
I suppose the main limitation is that the spec for config only defines string values at the moment and doesn't have the option to add multiple values

[xtmq]

I like the concept of client-side LLM providers. Regarding config isn't session-config with a "provider" category sufficient for this though? https://agentclientprotocol.com/protocol/session-config-options#session-config-options I suppose the main limitation is that the spec for config only defines string values at the moment and doesn't have the option to add multiple values

I replied in the FAQ section

[anna239]

I think having it like this

"params": {
    "id": "main",
   "current": {
 "apiType": "anthropic",
    "baseUrl": "https://llm-gateway.corp.example.com/anthropic/v1",
    "headers": {
      "X-Request-Source": "my-ide"
    }
}
  }

would be better because we'll be able to use the same objects for parsing providers/list and setting a new value. In this case we can also get rid of disable method, as you can just invoke

"params": {
    "id": "main",
   "current": null
  }

[xtmq]

Yes, you are right! But this API urges agents to expose their headers (with possible tokens) to a client.

[anna239]

Why is that? I mean you can still skip headers when you return list of the providers