feat(router): support custom model overrides

Author: TheodoreSpeaks

apps/sim/blocks/blocks/router.test.ts

@@ -0,0 +1,54 @@
+import { describe, expect, it } from 'vitest'
+import { RouterBlock, RouterV2Block } from '@/blocks/blocks/router'
+import type { BlockConfig } from '@/blocks/types'
+import { CUSTOM_MODEL_ID } from '@/providers/custom-model'
+
+describe.each([
+  ['legacy Router', RouterBlock],
+  ['Router V2', RouterV2Block],
+] as const)('%s custom model configuration', (_label, block: BlockConfig) => {
+  it('exposes the Super User custom option and JSON configuration', () => {
+    const modelIndex = block.subBlocks.findIndex((subBlock) => subBlock.id === 'model')
+    const modelOptions = block.subBlocks[modelIndex].options
+    const evaluatedModelOptions = typeof modelOptions === 'function' ? modelOptions() : modelOptions
+
+    expect(evaluatedModelOptions).toContainEqual(
+      expect.objectContaining({ id: CUSTOM_MODEL_ID, requiresSuperUser: true })
+    )
+    expect(block.subBlocks[modelIndex + 1]).toEqual(
+      expect.objectContaining({
+        id: 'customModelConfig',
+        type: 'code',
+        language: 'json',
+        superUserOnly: true,
+        condition: { field: 'model', value: CUSTOM_MODEL_ID },
+        required: { field: 'model', value: CUSTOM_MODEL_ID },
+      })
+    )
+    expect(block.inputs.customModelConfig?.schema?.properties.provider.enum).toContain('sim')
+  })
+
+  it('serializes the provider selected by the custom configuration', () => {
+    expect(
+      block.tools.config?.tool?.({
+        model: CUSTOM_MODEL_ID,
+        customModelConfig: {
+          provider: 'fireworks',
+          model: 'accounts/fireworks/models/kimi-k3',
+        },
+      } as never)
+    ).toBe('fireworks')
+  })
+
+  it('serializes custom Sim Auto with the fallback provider shape', () => {
+    expect(
+      block.tools.config?.tool?.({
+        model: CUSTOM_MODEL_ID,
+        customModelConfig: {
+          provider: 'sim',
+          model: 'sim-auto',
+        },
+      } as never)
+    ).toBe('anthropic')
+  })
+})

apps/sim/blocks/blocks/router.ts

@@ -1,11 +1,18 @@
 import { ConnectIcon } from '@/components/icons'
-import { AuthMode, type BlockConfig } from '@/blocks/types'
+import { AuthMode, type BlockConfig, type SubBlockConfig } from '@/blocks/types'
 import {
-  getModelOptions,
+  getCustomModelOptions,
   getProviderCredentialSubBlocks,
   PROVIDER_CREDENTIAL_INPUTS,
 } from '@/blocks/utils'
-import { getBaseModelProviders } from '@/providers/models'
+import {
+  CUSTOM_MODEL_CONFIG_DEFAULT,
+  CUSTOM_MODEL_CONFIG_JSON_SCHEMA,
+  CUSTOM_MODEL_ID,
+  isCustomModel,
+  parseCustomModelConfig,
+} from '@/providers/custom-model'
+import { getBaseModelProviders, isAutoModel } from '@/providers/models'
 import type { ProviderId } from '@/providers/types'
 import type { ToolResponse } from '@/tools/types'
 
@@ -41,6 +48,47 @@ interface TargetBlock {
   currentState?: any
 }
 
+function getCustomModelSubBlock(): SubBlockConfig {
+  return {
+    id: 'customModelConfig',
+    title: 'Custom Model Configuration',
+    type: 'code',
+    language: 'json',
+    placeholder: 'Enter custom provider and model configuration...',
+    description:
+      'Provider, model, credentials, and provider-specific generation settings for routing inference. Use provider "sim" with model "sim-auto" for automatic routing.',
+    defaultValue: CUSTOM_MODEL_CONFIG_DEFAULT,
+    superUserOnly: true,
+    required: {
+      field: 'model',
+      value: CUSTOM_MODEL_ID,
+    },
+    condition: {
+      field: 'model',
+      value: CUSTOM_MODEL_ID,
+    },
+  }
+}
+
+function resolveRouterTool(params: Record<string, any>): string {
+  const model = params.model || 'claude-sonnet-5'
+  if (!model) {
+    throw new Error('No model selected')
+  }
+  if (isCustomModel(model)) {
+    const customConfig = parseCustomModelConfig(params.customModelConfig)
+    if (customConfig.provider !== 'sim') return customConfig.provider
+
+    return getBaseModelProviders()['claude-sonnet-5']
+  }
+  const lookupModel = isAutoModel(model) ? 'claude-sonnet-5' : model
+  const tool = getBaseModelProviders()[lookupModel as ProviderId]
+  if (!tool) {
+    throw new Error(`Invalid model selected: ${model}`)
+  }
+  return tool
+}
+
 /**
  * Generates the system prompt for the legacy router (block-based).
  */
@@ -173,8 +221,9 @@ export const RouterBlock: BlockConfig<RouterResponse> = {
       placeholder: 'Type or select a model...',
       required: true,
       defaultValue: 'claude-sonnet-5',
-      options: getModelOptions,
+      options: getCustomModelOptions,
     },
+    getCustomModelSubBlock(),
     ...getProviderCredentialSubBlocks(),
     {
       id: 'temperature',
@@ -204,22 +253,17 @@ export const RouterBlock: BlockConfig<RouterResponse> = {
       'deepseek_reasoner',
     ],
     config: {
-      tool: (params: Record<string, any>) => {
-        const model = params.model || 'gpt-4o'
-        if (!model) {
-          throw new Error('No model selected')
-        }
-        const tool = getBaseModelProviders()[model as ProviderId]
-        if (!tool) {
-          throw new Error(`Invalid model selected: ${model}`)
-        }
-        return tool
-      },
+      tool: resolveRouterTool,
     },
   },
   inputs: {
     prompt: { type: 'string', description: 'Routing prompt content' },
     model: { type: 'string', description: 'AI model to use' },
+    customModelConfig: {
+      type: 'json',
+      description: 'Custom provider/model execution configuration for routing inference.',
+      schema: CUSTOM_MODEL_CONFIG_JSON_SCHEMA,
+    },
     ...PROVIDER_CREDENTIAL_INPUTS,
     temperature: {
       type: 'number',
@@ -300,8 +344,9 @@ export const RouterV2Block: BlockConfig<RouterV2Response> = {
       placeholder: 'Type or select a model...',
       required: true,
       defaultValue: 'claude-sonnet-5',
-      options: getModelOptions,
+      options: getCustomModelOptions,
     },
+    getCustomModelSubBlock(),
     ...getProviderCredentialSubBlocks(),
   ],
   tools: {
@@ -314,23 +359,18 @@ export const RouterV2Block: BlockConfig<RouterV2Response> = {
       'deepseek_reasoner',
     ],
     config: {
-      tool: (params: Record<string, any>) => {
-        const model = params.model || 'gpt-4o'
-        if (!model) {
-          throw new Error('No model selected')
-        }
-        const tool = getBaseModelProviders()[model as ProviderId]
-        if (!tool) {
-          throw new Error(`Invalid model selected: ${model}`)
-        }
-        return tool
-      },
+      tool: resolveRouterTool,
     },
   },
   inputs: {
     context: { type: 'string', description: 'Context for routing decision' },
     routes: { type: 'json', description: 'Route definitions with descriptions' },
     model: { type: 'string', description: 'AI model to use' },
+    customModelConfig: {
+      type: 'json',
+      description: 'Custom provider/model execution configuration for routing inference.',
+      schema: CUSTOM_MODEL_CONFIG_JSON_SCHEMA,
+    },
     ...PROVIDER_CREDENTIAL_INPUTS,
   },
   outputs: {

apps/sim/blocks/utils.test.ts

@@ -336,7 +336,7 @@ describe('getModelOptions', () => {
     expect(ids).not.toContain('fireworks/accounts/fireworks/models/minimax-m2p7')
   })
 
-  it('adds the super-user custom option only to the Agent model options', () => {
+  it('adds the super-user custom option only to custom-capable model options', () => {
     expect(getModelOptions().some((option) => option.id === 'sim-custom')).toBe(false)
     expect(getAgentModelOptions()).toContainEqual({
       label: 'Custom',

apps/sim/blocks/utils.ts

@@ -103,10 +103,10 @@ export function getModelOptions() {
 }
 
 /**
- * Agent-only model options. The custom passthrough entry is filtered by the
- * editor unless the user has effective super-user mode enabled.
+ * Model options for blocks that support the custom passthrough contract. The
+ * editor filters the custom entry unless effective Super User mode is enabled.
  */
-export function getAgentModelOptions() {
+export function getCustomModelOptions() {
   return [
     ...getModelOptions(),
     {
@@ -118,6 +118,8 @@ export function getAgentModelOptions() {
   ]
 }
 
+export const getAgentModelOptions = getCustomModelOptions
+
 /**
  * Model options filtered to exact provider/model pairs in Pi's pinned catalog.
  * Unresolved or blacklisted models (which `getProviderFromModel` can throw on)