diff --git a/apps/sim/executor/execution/executor.ts b/apps/sim/executor/execution/executor.ts
index 44697eb429..14ed7aa9a4 100644
--- a/apps/sim/executor/execution/executor.ts
+++ b/apps/sim/executor/execution/executor.ts
@@ -250,7 +250,6 @@ export class DAGExecutor {
     const blockOutput = buildStartBlockOutput({
       resolution: startResolution,
       workflowInput: this.workflowInput,
-      isDeployedExecution: this.contextExtensions?.isDeployedContext === true,
     })
 
     state.setBlockState(startResolution.block.id, {
diff --git a/apps/sim/executor/utils/start-block.test.ts b/apps/sim/executor/utils/start-block.test.ts
index aee3f798f6..4c6fd708e0 100644
--- a/apps/sim/executor/utils/start-block.test.ts
+++ b/apps/sim/executor/utils/start-block.test.ts
@@ -33,14 +33,14 @@ function createBlock(
 }
 
 describe('start-block utilities', () => {
-  it('buildResolutionFromBlock returns null when metadata id missing', () => {
+  it.concurrent('buildResolutionFromBlock returns null when metadata id missing', () => {
     const block = createBlock('api_trigger')
     ;(block.metadata as Record<string, unknown>).id = undefined
 
     expect(buildResolutionFromBlock(block)).toBeNull()
   })
 
-  it('resolveExecutorStartBlock prefers unified start block', () => {
+  it.concurrent('resolveExecutorStartBlock prefers unified start block', () => {
     const blocks = [
       createBlock('api_trigger', 'api'),
       createBlock('starter', 'starter'),
@@ -56,7 +56,7 @@ describe('start-block utilities', () => {
     expect(resolution?.path).toBe(StartBlockPath.UNIFIED)
   })
 
-  it('buildStartBlockOutput normalizes unified start payload', () => {
+  it.concurrent('buildStartBlockOutput normalizes unified start payload', () => {
     const block = createBlock('start_trigger', 'start')
     const resolution = {
       blockId: 'start',
@@ -67,7 +67,6 @@ describe('start-block utilities', () => {
     const output = buildStartBlockOutput({
       resolution,
       workflowInput: { payload: 'value' },
-      isDeployedExecution: true,
     })
 
     expect(output.payload).toBe('value')
@@ -75,7 +74,7 @@ describe('start-block utilities', () => {
     expect(output.conversationId).toBeUndefined()
   })
 
-  it('buildStartBlockOutput uses trigger schema for API triggers', () => {
+  it.concurrent('buildStartBlockOutput uses trigger schema for API triggers', () => {
     const apiBlock = createBlock('api_trigger', 'api', {
       subBlocks: {
         inputFormat: {
@@ -113,11 +112,108 @@ describe('start-block utilities', () => {
         },
         files,
       },
-      isDeployedExecution: false,
     })
 
     expect(output.name).toBe('Ada')
     expect(output.input).toEqual({ name: 'Ada', count: 5 })
     expect(output.files).toEqual(files)
   })
+
+  describe('inputFormat default values', () => {
+    it.concurrent('uses default value when runtime does not provide the field', () => {
+      const block = createBlock('start_trigger', 'start', {
+        subBlocks: {
+          inputFormat: {
+            value: [
+              { name: 'input', type: 'string' },
+              { name: 'customField', type: 'string', value: 'defaultValue' },
+            ],
+          },
+        },
+      })
+
+      const resolution = {
+        blockId: 'start',
+        block,
+        path: StartBlockPath.UNIFIED,
+      } as const
+
+      const output = buildStartBlockOutput({
+        resolution,
+        workflowInput: { input: 'hello' },
+      })
+
+      expect(output.input).toBe('hello')
+      expect(output.customField).toBe('defaultValue')
+    })
+
+    it.concurrent('runtime value overrides default value', () => {
+      const block = createBlock('start_trigger', 'start', {
+        subBlocks: {
+          inputFormat: {
+            value: [{ name: 'customField', type: 'string', value: 'defaultValue' }],
+          },
+        },
+      })
+
+      const resolution = {
+        blockId: 'start',
+        block,
+        path: StartBlockPath.UNIFIED,
+      } as const
+
+      const output = buildStartBlockOutput({
+        resolution,
+        workflowInput: { customField: 'runtimeValue' },
+      })
+
+      expect(output.customField).toBe('runtimeValue')
+    })
+
+    it.concurrent('empty string from runtime overrides default value', () => {
+      const block = createBlock('start_trigger', 'start', {
+        subBlocks: {
+          inputFormat: {
+            value: [{ name: 'customField', type: 'string', value: 'defaultValue' }],
+          },
+        },
+      })
+
+      const resolution = {
+        blockId: 'start',
+        block,
+        path: StartBlockPath.UNIFIED,
+      } as const
+
+      const output = buildStartBlockOutput({
+        resolution,
+        workflowInput: { customField: '' },
+      })
+
+      expect(output.customField).toBe('')
+    })
+
+    it.concurrent('null from runtime does not override default value', () => {
+      const block = createBlock('start_trigger', 'start', {
+        subBlocks: {
+          inputFormat: {
+            value: [{ name: 'customField', type: 'string', value: 'defaultValue' }],
+          },
+        },
+      })
+
+      const resolution = {
+        blockId: 'start',
+        block,
+        path: StartBlockPath.UNIFIED,
+      } as const
+
+      const output = buildStartBlockOutput({
+        resolution,
+        workflowInput: { customField: null },
+      })
+
+      expect(output.customField).toBe('defaultValue')
+    })
+  })
 })
diff --git a/apps/sim/executor/utils/start-block.ts b/apps/sim/executor/utils/start-block.ts
index 17192906b8..279d390047 100644
--- a/apps/sim/executor/utils/start-block.ts
+++ b/apps/sim/executor/utils/start-block.ts
@@ -176,8 +176,7 @@ interface DerivedInputResult {
 
 function deriveInputFromFormat(
   inputFormat: InputFormatField[],
-  workflowInput: unknown,
-  isDeployedExecution: boolean
+  workflowInput: unknown
 ): DerivedInputResult {
   const structuredInput: Record<string, unknown> = {}
 
@@ -205,7 +204,8 @@ function deriveInputFromFormat(
       }
     }
 
-    if ((fieldValue === undefined || fieldValue === null) && !isDeployedExecution) {
+    // Use the default value from inputFormat if the field value wasn't provided at runtime
+    if (fieldValue === undefined || fieldValue === null) {
       fieldValue = field.value
     }
 
@@ -255,13 +255,28 @@ function ensureString(value: unknown): string {
   return typeof value === 'string' ? value : ''
 }
 
-function buildUnifiedStartOutput(workflowInput: unknown): NormalizedBlockOutput {
+function buildUnifiedStartOutput(
+  workflowInput: unknown,
+  structuredInput: Record<string, unknown>,
+  hasStructured: boolean
+): NormalizedBlockOutput {
   const output: NormalizedBlockOutput = {}
 
+  if (hasStructured) {
+    for (const [key, value] of Object.entries(structuredInput)) {
+      output[key] = value
+    }
+  }
+
   if (isPlainObject(workflowInput)) {
     for (const [key, value] of Object.entries(workflowInput)) {
       if (key === 'onUploadError') continue
-      output[key] = value
+      // Runtime values override defaults (except undefined/null which mean "not provided")
+      if (value !== undefined && value !== null) {
+        output[key] = value
+      } else if (!Object.hasOwn(output, key)) {
+        output[key] = value
+      }
     }
   }
 
@@ -401,17 +416,19 @@ function extractSubBlocks(block: SerializedBlock): Record<string, unknown> | und
 export interface StartBlockOutputOptions {
   resolution: ExecutorStartResolution
   workflowInput: unknown
-  isDeployedExecution: boolean
 }
 
 export function buildStartBlockOutput(options: StartBlockOutputOptions): NormalizedBlockOutput {
-  const { resolution, workflowInput, isDeployedExecution } = options
+  const { resolution, workflowInput } = options
   const inputFormat = extractInputFormat(resolution.block)
-  const { finalInput } = deriveInputFromFormat(inputFormat, workflowInput, isDeployedExecution)
+  const { finalInput, structuredInput, hasStructured } = deriveInputFromFormat(
+    inputFormat,
+    workflowInput
+  )
 
   switch (resolution.path) {
     case StartBlockPath.UNIFIED:
-      return buildUnifiedStartOutput(workflowInput)
+      return buildUnifiedStartOutput(workflowInput, structuredInput, hasStructured)
 
     case StartBlockPath.SPLIT_API:
     case StartBlockPath.SPLIT_INPUT: