Capabilities are local gating data on model.Model; they are not sent to a provider. The request gate reports unsupported features before encoding. Dialect-specific rejections stay in the codec: the Anthropic encoder returns UndeclaredThinkingDialectError when a thinking-capable model declares no Caps.ThinkingDialect.

Model

type Capabilities struct {
	AcceptsImages             bool
	Tools                     bool
	Thinking                  bool
	ThinkingDialect           ThinkingDialect
	StructuredOutput          bool
	StructuredOutputWithTools bool
	PromptCaching             bool
}

StructuredOutputWithTools requires both StructuredOutput and Tools in Model.Validate, which also rejects an unknown ThinkingDialect and a declared dialect on a model that is not Thinking-capable, both as a ValidationError on field Caps.ThinkingDialect. ThinkingDialect is "" when undeclared, or "adaptive" or "budget". PromptCaching is an opt-in hint used by the Anthropic encoder only; other bundled encoders ignore it for request construction.

Behavior

An unsupported capability is a typed client error, not an HTTP or retryable provider error. The gateway classifies these feature errors as 400 when it receives them from request validation. Choose another model or remove the feature instead of retrying the same request.

Source and proof

Run go test ./model ./gateway.