Virtual Models

GoModel dashboard models page with the New virtual model button and an active redirect row

What virtual models do

A virtual model is a model you define, instead of one a provider advertises. GoModel picks the kind from whether you give it a target:

A redirect (an alias) is a stable name that points to a concrete provider model. Your app sends the name in the model field, and GoModel resolves it before sending the request upstream.
An access policy has no target. It gates an existing model selector by user_path — or disables it entirely — without adding a new name. See User Path for access control.

Create and manage both in the admin dashboard at Models -> New virtual model. Fill Target model to make a redirect; leave it empty to make an access policy on the Source selector. GoModel does not persist empty, ineffective access policies, whether saved from the dashboard or through the admin API. If a saved policy has no target, user paths, description, or slowdown and its enabled state matches the inherited/default access state, GoModel removes the stored row. It retains an otherwise empty policy when that row still overrides a disabled default or an inherited user-path restriction.

Add artificial model latency

Set Slowdown on a concrete model or redirect to add a fraction of measured inference time. Active values range from 0.1 to 10; for example, 0.5 adds 50%, so a response that takes 2 seconds upstream is returned after about 3 seconds. Set 0 to explicitly disable slowdown, including slowdown inherited from a concrete model. Leaving the field empty leaves the setting unspecified. Delays honor request cancellation. For Chat Completions and Responses API SSE streams, GoModel drains the upstream in the background and releases each read chunk on the scaled timeline. This preserves the provider’s relative chunk timing while delayed chunks accumulate in memory. A large factor on a long or high-volume stream can therefore use substantial memory. Realtime WebSocket sessions are not slowed. When an alias and its concrete target both have a slowdown, the alias value wins. An alias without its own value inherits the selected target model’s slowdown; set the alias to 0 to override that inheritance. This also applies to load-balanced virtual models after a target is selected. The rest of this page covers redirects.

Use stable names

You can expose names like regular and smarter instead of provider-specific model IDs.

regular -> anthropic/claude-sonnet-4-6
smarter -> anthropic/claude-opus-4-6

Your app can then send:

{
  "model": "regular",
  "messages": []
}

Load balance across models

A redirect can point at several target models and spread requests across them. Add more than one target in the editor (Add target) and pick a strategy:

Round-robin (default) rotates requests evenly across the targets. Set a per-target weight to bias the share — a target with weight 2 receives twice the traffic of a target with weight 1.
Lowest cost routes every request to the cheapest currently-available target, ranked by the model registry’s input + output per-token price. When a target has no registry pricing it is skipped while a priced target exists; if none are priced, the first listed target is used.

Targets that the gateway cannot currently serve (unknown model, provider down) are skipped automatically, so a redirect keeps working as long as one target is available. A redirect with a single target behaves exactly like a plain alias. Requests belonging to one detected client session stick to the target that served the session first (Session keeping, on by default), so conversations keep their provider prompt cache warm across turns. Untick the editor’s Session keeping checkbox (or set session_affinity: false) to restore stateless balancing — see Session Keeping.

{
  "model": "smart",
  "messages": []
}

For example, point smart at both openai/gpt-4o and anthropic/claude-sonnet-4-6 with the round-robin strategy to split load, or at a premium and a budget model with the cost strategy to always take the cheaper one.

Rename or repoint a redirect

Open a redirect in the dashboard and edit its Source to rename it. GoModel moves the definition to the new name in one step — the old name stops resolving, so update any app still sending it. Renaming onto a name that already belongs to another virtual model is rejected; renaming onto a concrete model name shadows that model (see Shadow a model). Redirects that shadow a model can be edited the same way — use the model row’s Edit redirect action. Virtual models declared as code keep their source fixed in configuration; rename them by editing the declaration.

Define virtual models as code

Operators who manage configuration as infrastructure-as-code can declare virtual models in config.yaml or the VIRTUAL_MODELS environment variable instead of the dashboard. Declarative entries are applied at startup, override any admin-store row with the same source, and are shown read-only in the dashboard (a Config badge). Edit the configuration to change them. In config.yaml:

virtual_models:
  # A plain alias.
  - source: regular
    target: anthropic/claude-sonnet-4-6
    slowdown: 0.5

  # A weighted round-robin load balancer.
  - source: smart
    strategy: round_robin
    targets:
      - model: openai/gpt-4o
        weight: 2
      - model: anthropic/claude-sonnet-4-6

  # A cost-based load balancer.
  - source: cheap
    strategy: cost
    targets:
      - { model: openai/gpt-4o }
      - { model: groq/llama-3.3-70b }

The same list as a single environment variable (JSON), which overrides config.yaml entries with a matching source:

VIRTUAL_MODELS=[{"source":"smart","strategy":"cost","targets":[{"model":"openai/gpt-4o"},{"model":"groq/llama-3.3-70b"}]}]

Each entry accepts source, a single target (shorthand) or a targets list, strategy (round_robin or cost), session_affinity (default true; see Session Keeping), user_paths, description, slowdown (0 disables inherited slowdown; active factors range from 0.1 to 10), and enabled. Leave the targets empty to declare an access policy on the source selector. An invalid declaration (unknown strategy, missing or self-referential target, or a target provider that matches no configured provider — a typo) fails startup with a clear error listing the registered provider names. Two lenient exceptions keep valid setups booting:

A target provider that is declared under providers: but did not register — typically because its credentials are unset in this environment — only logs a warning; the target stays unavailable until the credentials resolve. A config.yaml shared across environments still boots everywhere.
Whether a target model exists is never checked at startup: the model catalog loads asynchronously, so availability is a runtime concern and an unavailable target is simply skipped at resolve time.

Expose only redirects

To hide provider models from GET /v1/models, set:

KEEP_ONLY_ALIASES_AT_MODELS_ENDPOINT=true

When this is enabled, GoModel returns enabled redirects from /v1/models instead of the full provider model list. The setting is also listed in .env.template.

Shadow a model

A redirect can “shadow” a model by using the same name as an existing model and pointing it somewhere else. This lets you override a requested model without changing application code. For example:

source: anthropic/claude-opus-4-6
target model: anthropic/claude-sonnet-4-6

Your app can keep sending anthropic/claude-opus-4-6, while GoModel routes the request to anthropic/claude-sonnet-4-6.

A/B testing

Redirects are useful for short model experiments. Move a redirect from one target to another, then compare app behavior, latency, and usage. For example, point smarter at Opus for one test and Sonnet for another. You can also shadow opus-4-6 with sonnet-4-6 to check whether the same app flow still works.

Getting Started

Features

MCP Proxy

Advanced

About

What virtual models do

Add artificial model latency

Use stable names

Load balance across models

Rename or repoint a redirect

Define virtual models as code

Expose only redirects

Shadow a model

A/B testing

​What virtual models do

​Add artificial model latency

​Use stable names

​Load balance across models

​Rename or repoint a redirect

​Define virtual models as code

​Expose only redirects

​Shadow a model

​A/B testing

What virtual models do

Add artificial model latency

Use stable names

Load balance across models

Rename or repoint a redirect

Define virtual models as code

Expose only redirects

Shadow a model

A/B testing