chore: update OpenAPI spec from monorepo (#455)

## OpenAPI Spec Update

Automated update of the OpenAPI specification from the monorepo release.

This PR was created by the SDK release workflow and will be merged
automatically.

[Workflow
run](https://github.com/OpenRouterTeam/openrouter-web/actions/runs/27370451817)

Co-authored-by: OpenRouter SDK Bot <sdk-bot@openrouter.ai>

Author: robert-j-y

.speakeasy/in.openapi.yaml

@@ -1202,6 +1202,8 @@ components:
       allOf:
         - $ref: '#/components/schemas/AnthropicBaseUsageIteration'
         - properties:
+            model:
+              type: string
             type:
               enum:
                 - message
@@ -10760,6 +10762,20 @@ components:
         - type
         - error
       type: object
+    MessagesFallbackParam:
+      additionalProperties:
+        nullable: true
+      description: >-
+        Fallback model to try when the primary model fails or refuses. Only the `model` field is supported; per-attempt
+        overrides are rejected.
+      example:
+        model: claude-opus-4-8
+      properties:
+        model:
+          type: string
+      required:
+        - model
+      type: object
     MessagesMessageParam:
       description: Anthropic message with OpenRouter extensions
       example:
@@ -11105,6 +11121,17 @@ components:
                     type: object
               type: array
           type: object
+        fallbacks:
+          description: >-
+            Fallback models to try if the primary model fails or refuses, in order. Handled by OpenRouter multi-model
+            routing rather than Anthropic server-side fallbacks; cannot be combined with `models`. Each entry accepts
+            only `model`. Maximum of 3 entries.
+          example:
+            - model: claude-opus-4-8
+          items:
+            $ref: '#/components/schemas/MessagesFallbackParam'
+          nullable: true
+          type: array
         max_tokens:
           type: integer
         messages: