add sim auto model to custom provider json

Author: Sg312

apps/sim/blocks/blocks/agent.test.ts

@@ -53,6 +53,7 @@ describe('AgentBlock', () => {
       })
     )
     expect(AgentBlock.inputs.customModelConfig?.schema).toBeDefined()
+    expect(AgentBlock.inputs.customModelConfig?.schema?.properties.provider.enum).toContain('sim')
 
     const tools = AgentBlock.subBlocks.find((subBlock) => subBlock.id === 'tools')
     const responseFormat = AgentBlock.subBlocks.find((subBlock) => subBlock.id === 'responseFormat')
@@ -79,6 +80,20 @@ describe('AgentBlock', () => {
     ).toBe('fireworks')
   })
 
+  it('serializes custom Sim Auto with the same fallback provider shape as first-class Auto', () => {
+    const toolFunction = AgentBlock.tools.config?.tool
+
+    expect(
+      toolFunction?.({
+        model: CUSTOM_MODEL_ID,
+        customModelConfig: {
+          provider: 'sim',
+          model: 'sim-auto',
+        },
+      } as never)
+    ).toBe('anthropic')
+  })
+
   describe('tools.config.params function', () => {
     it('should pass through params when no tools array is provided', () => {
       const params = {

apps/sim/blocks/blocks/agent.ts

@@ -151,7 +151,7 @@ Return ONLY the JSON array.`,
       language: 'json',
       placeholder: 'Enter custom provider and model configuration...',
       description:
-        'Provider, model, credentials, and provider-specific generation settings. Tools, response format, skills, files, prompts, and memory remain configured separately.',
+        'Provider, model, credentials, and provider-specific generation settings. Use provider "sim" with model "sim-auto" for automatic routing. Tools, response format, skills, files, prompts, and memory remain configured separately.',
       defaultValue: CUSTOM_MODEL_CONFIG_DEFAULT,
       superUserOnly: true,
       required: {
@@ -550,7 +550,13 @@ Return ONLY the JSON array.`,
           throw new Error('No model selected')
         }
         if (isCustomModel(model)) {
-          return parseCustomModelConfig(params.customModelConfig).provider
+          const customConfig = parseCustomModelConfig(params.customModelConfig)
+          if (customConfig.provider !== 'sim') return customConfig.provider
+
+          // Like the first-class Auto option below, custom Sim Auto resolves to
+          // a concrete provider only at execution time. Serialization stores a
+          // valid fallback provider shape that the Agent handler never uses.
+          return getBaseModelProviders()['claude-sonnet-5']
         }
         // sim-auto resolves to a concrete pool model at execution time, where
         // the agent handler derives the provider from the resolved model and
@@ -639,7 +645,7 @@ Return ONLY the JSON array.`,
     customModelConfig: {
       type: 'json',
       description:
-        'Custom provider/model execution configuration. Tools, response format, skills, files, prompts, and memory are separate Agent inputs.',
+        'Custom provider/model execution configuration. Use provider "sim" with model "sim-auto" for automatic routing. Tools, response format, skills, files, prompts, and memory are separate Agent inputs.',
       schema: CUSTOM_MODEL_CONFIG_JSON_SCHEMA,
     },
     apiKey: { type: 'string', description: 'Provider API key' },

apps/sim/executor/handlers/agent/agent-handler.test.ts

@@ -386,6 +386,35 @@ describe('AgentBlockHandler', () => {
       expect(result.cost).toEqual({ input: 0.001, output: 0.002, total: 0.003 })
     })
 
+    it('runs Sim Auto from the custom contract through catalog capability handling', async () => {
+      mockContext.userId = 'super-user'
+
+      const result = (await handler.execute(mockContext, mockBlock, {
+        model: CUSTOM_MODEL_ID,
+        customModelConfig: {
+          provider: 'sim',
+          model: SIM_AUTO_MODEL_ID,
+          parameters: { reasoningEffort: 'high', temperature: 0.2 },
+          credentials: { mode: 'auto' },
+        },
+        userPrompt: 'Route this automatically',
+      })) as { model: string }
+
+      expect(mockVerifyEffectiveSuperUser).toHaveBeenCalledWith('super-user')
+      expect(mockExecuteProviderRequest).toHaveBeenCalledWith(
+        'mock-provider',
+        expect.objectContaining({
+          model: AGENT.DEFAULT_MODEL,
+          capabilityPolicy: 'catalog',
+          credentialMode: 'auto',
+          reasoningEffort: 'high',
+          temperature: 0.2,
+        }),
+        expect.anything()
+      )
+      expect(result.model).toBe(SIM_AUTO_MODEL_ID)
+    })
+
     /** Reaches the private signal builder; routing depends on nothing else. */
     const buildAutoRoutingSignalsFor = (inputs: Record<string, unknown>) =>
       (

apps/sim/executor/handlers/agent/agent-handler.ts

@@ -125,7 +125,12 @@ export class AgentBlockHandler implements BlockHandler {
         customModelConfig.credentials.mode === 'explicit'
           ? customModelConfig.credentials.apiKey
           : undefined
-    } else if (isAutoModel(configuredModel)) {
+    }
+
+    if (
+      isAutoModel(configuredModel) ||
+      (customModelConfig !== undefined && customModelConfig.provider === 'sim')
+    ) {
       autoRouting = await resolveAutoModel({
         ctx,
         blockId: block.id,
@@ -148,7 +153,10 @@ export class AgentBlockHandler implements BlockHandler {
         .join('\n\n')
     }
 
-    const providerId = customModelConfig?.provider ?? getProviderFromModel(model)
+    const providerId =
+      customModelConfig && customModelConfig.provider !== 'sim'
+        ? customModelConfig.provider
+        : getProviderFromModel(model)
     await validateModelProvider(ctx.userId, ctx.workspaceId, model, ctx, providerId)
     const formattedTools = await this.formatTools(
       ctx,
@@ -1179,7 +1187,10 @@ export class AgentBlockHandler implements BlockHandler {
       verbosity: inputs.verbosity,
       thinkingLevel: inputs.thinkingLevel,
       promptCaching: inputs.promptCaching === true,
-      capabilityPolicy: customModelConfig ? ('passthrough' as const) : ('catalog' as const),
+      capabilityPolicy:
+        customModelConfig && customModelConfig.provider !== 'sim'
+          ? ('passthrough' as const)
+          : ('catalog' as const),
       credentialMode: customModelConfig?.credentials.mode,
       providerOptions: customModelConfig?.providerOptions,
       previousInteractionId: inputs.previousInteractionId,

apps/sim/providers/custom-model.test.ts

@@ -49,6 +49,47 @@ describe('custom model config', () => {
     }
   })
 
+  it('supports Sim Auto through the custom contract', () => {
+    expect(
+      parseCustomModelConfig({
+        provider: 'auto',
+        model: 'sim-auto',
+        parameters: { reasoningEffort: 'high', temperature: 0.2 },
+        credentials: { mode: 'auto' },
+      })
+    ).toMatchObject({
+      provider: 'sim',
+      model: 'sim-auto',
+      parameters: { reasoningEffort: 'high', temperature: 0.2 },
+      credentials: { mode: 'auto' },
+    })
+  })
+
+  it('keeps Sim Auto provider-independent', () => {
+    expect(() =>
+      parseCustomModelConfig({
+        provider: 'sim',
+        model: 'gpt-5.6-terra',
+      })
+    ).toThrow('model must be "sim-auto"')
+
+    expect(() =>
+      parseCustomModelConfig({
+        provider: 'sim',
+        model: 'sim-auto',
+        credentials: { mode: 'explicit', apiKey: 'sk-secret' },
+      })
+    ).toThrow('credentials.mode must be "auto"')
+
+    expect(() =>
+      parseCustomModelConfig({
+        provider: 'sim',
+        model: 'sim-auto',
+        providerOptions: { service_tier: 'priority' },
+      })
+    ).toThrow('providerOptions must be empty for Sim Auto')
+  })
+
   it('rejects reserved provider option overrides', () => {
     expect(() =>
       parseCustomModelConfig({

apps/sim/providers/custom-model.ts

@@ -1,16 +1,19 @@
+import { isAutoModel, SIM_AUTO_MODEL_ID } from '@/providers/models'
 import type { ProviderId } from '@/providers/types'
 
 /** Stored in the Agent block's `model` field when Super User custom routing is active. */
 export const CUSTOM_MODEL_ID = 'sim-custom'
 
-export const CUSTOM_MODEL_PROVIDERS = [
+export const CUSTOM_DIRECT_MODEL_PROVIDERS = [
   'openai',
   'anthropic',
   'google',
   'fireworks',
   'xai',
 ] as const satisfies readonly ProviderId[]
 
+export const CUSTOM_MODEL_PROVIDERS = [...CUSTOM_DIRECT_MODEL_PROVIDERS, 'sim'] as const
+
 export type CustomModelProvider = (typeof CUSTOM_MODEL_PROVIDERS)[number]
 export type CustomCredentialMode = 'auto' | 'explicit'
 
@@ -45,6 +48,9 @@ const PROVIDER_ALIASES: Record<string, CustomModelProvider> = {
   fireworks: 'fireworks',
   xai: 'xai',
   grok: 'xai',
+  sim: 'sim',
+  auto: 'sim',
+  'sim-auto': 'sim',
 }
 
 const TOP_LEVEL_KEYS = new Set([
@@ -247,6 +253,23 @@ export function parseCustomModelConfig(value: unknown): CustomModelConfig {
     providerOptions: parseProviderOptions(parsed.providerOptions),
   }
 
+  if (config.provider === 'sim') {
+    if (!isAutoModel(config.model)) {
+      throw new Error(
+        `customModelConfig.model must be "${SIM_AUTO_MODEL_ID}" when provider is "sim"`
+      )
+    }
+    config.model = SIM_AUTO_MODEL_ID
+    if (config.credentials.mode !== 'auto') {
+      throw new Error('customModelConfig.credentials.mode must be "auto" for Sim Auto')
+    }
+    if (Object.keys(config.providerOptions).length > 0) {
+      throw new Error(
+        'customModelConfig.providerOptions must be empty for Sim Auto because the routed provider is dynamic'
+      )
+    }
+  }
+
   validateCustomModelParameterSupport(config)
   return config
 }
@@ -256,6 +279,10 @@ export function validateCustomModelParameterSupport(config: CustomModelConfig):
   const { provider, parameters } = config
   const hasValue = (value: unknown) => value !== undefined && value !== null && value !== 'auto'
 
+  // Sim Auto validates parameters against the concrete routed model through
+  // the ordinary catalog capability policy after routing.
+  if (provider === 'sim') return
+
   if (hasValue(parameters.verbosity) && provider !== 'openai') {
     throw new Error(`customModelConfig.parameters.verbosity is not supported for ${provider}`)
   }
@@ -324,7 +351,7 @@ export const CUSTOM_MODEL_CONFIG_JSON_SCHEMA: Record<string, any> = {
       type: 'string',
       enum: [...CUSTOM_MODEL_PROVIDERS],
       description:
-        'Provider adapter. Aliases gemini, claude, and grok are normalized on execution.',
+        'Provider adapter. Use sim with model sim-auto for dynamic routing. Aliases gemini, claude, grok, and auto are normalized on execution.',
     },
     model: {
       type: 'string',