diff --git a/src/features/background-agent/session-validator.ts b/src/features/background-agent/session-validator.ts
index 6181dec9be..639e9316bb 100644
--- a/src/features/background-agent/session-validator.ts
+++ b/src/features/background-agent/session-validator.ts
@@ -70,6 +70,7 @@ export async function validateSessionHasOutput(
         if (type === "tool") return true
         if (type === "text" && hasNonEmptyText(part.text)) return true
         if (type === "reasoning" && hasNonEmptyText(part.text)) return true
+        if (type === "reasoning.encrypted" && hasNonEmptyText(part.text)) return true
         if (type === "tool_result" && isToolResultContentNonEmpty(part.content)) return true
         return false
       })
diff --git a/src/hooks/session-recovery/constants.ts b/src/hooks/session-recovery/constants.ts
index a45b8026fa..b2230580d9 100644
--- a/src/hooks/session-recovery/constants.ts
+++ b/src/hooks/session-recovery/constants.ts
@@ -5,6 +5,6 @@ export const OPENCODE_STORAGE = getOpenCodeStorageDir()
 export const MESSAGE_STORAGE = join(OPENCODE_STORAGE, "message")
 export const PART_STORAGE = join(OPENCODE_STORAGE, "part")
 
-export const THINKING_TYPES = new Set(["thinking", "redacted_thinking", "reasoning"])
+export const THINKING_TYPES = new Set(["thinking", "redacted_thinking", "reasoning", "reasoning.encrypted"])
 export const META_TYPES = new Set(["step-start", "step-finish"])
 export const CONTENT_TYPES = new Set(["text", "tool", "tool_use", "tool_result"])
diff --git a/src/hooks/session-recovery/reasoning-encrypted.test.ts b/src/hooks/session-recovery/reasoning-encrypted.test.ts
new file mode 100644
index 0000000000..837b2cc684
--- /dev/null
+++ b/src/hooks/session-recovery/reasoning-encrypted.test.ts
@@ -0,0 +1,23 @@
+import { describe, expect, it } from "bun:test"
+import { THINKING_TYPES } from "./constants"
+
+describe("reasoning.encrypted support", () => {
+  //#given reasoning.encrypted is a valid thinking-family type from Grok models
+  
+  it("should include reasoning.encrypted in THINKING_TYPES Set", () => {
+    //#when checking if reasoning.encrypted is in THINKING_TYPES
+    const result = THINKING_TYPES.has("reasoning.encrypted")
+    
+    //#then it should return true
+    expect(result).toBe(true)
+  })
+  
+  it("should recognize reasoning.encrypted as a ThinkingPartType", () => {
+    //#given a type assertion for reasoning.encrypted
+    //#when assigning to ThinkingPartType
+    const thinkingType: import("./types").ThinkingPartType = "reasoning.encrypted"
+    
+    //#then it should compile without error
+    expect(thinkingType).toBe("reasoning.encrypted")
+  })
+})
diff --git a/src/hooks/session-recovery/types.ts b/src/hooks/session-recovery/types.ts
index 23d19fd935..b38a4d8164 100644
--- a/src/hooks/session-recovery/types.ts
+++ b/src/hooks/session-recovery/types.ts
@@ -1,4 +1,4 @@
-export type ThinkingPartType = "thinking" | "redacted_thinking" | "reasoning"
+export type ThinkingPartType = "thinking" | "redacted_thinking" | "reasoning" | "reasoning.encrypted"
 export type MetaPartType = "step-start" | "step-finish"
 export type ContentPartType = "text" | "tool" | "tool_use" | "tool_result"
 
diff --git a/src/hooks/thinking-block-validator/hook.ts b/src/hooks/thinking-block-validator/hook.ts
index a4217b3e8d..99748f313f 100644
--- a/src/hooks/thinking-block-validator/hook.ts
+++ b/src/hooks/thinking-block-validator/hook.ts
@@ -71,7 +71,7 @@ function startsWithThinkingBlock(parts: Part[]): boolean {
 
   const firstPart = parts[0]
   const type = firstPart.type as string
-  return type === "thinking" || type === "reasoning"
+  return type === "thinking" || type === "reasoning" || type === "reasoning.encrypted"
 }
 
 /**
@@ -90,7 +90,7 @@ function findPreviousThinkingContent(
     if (!msg.parts) continue
     for (const part of msg.parts) {
       const type = part.type as string
-      if (type === "thinking" || type === "reasoning") {
+      if (type === "thinking" || type === "reasoning" || type === "reasoning.encrypted") {
         const thinking = (part as any).thinking || (part as any).text
         if (thinking && typeof thinking === "string" && thinking.trim().length > 0) {
           return thinking
diff --git a/src/hooks/thinking-block-validator/reasoning-encrypted.test.ts b/src/hooks/thinking-block-validator/reasoning-encrypted.test.ts
new file mode 100644
index 0000000000..9c950c08f5
--- /dev/null
+++ b/src/hooks/thinking-block-validator/reasoning-encrypted.test.ts
@@ -0,0 +1,58 @@
+import { describe, expect, it } from "bun:test"
+import { createThinkingBlockValidatorHook } from "./hook"
+
+describe("reasoning.encrypted in thinking-block-validator", () => {
+  const hook = createThinkingBlockValidatorHook()
+  const transform = hook["experimental.chat.messages.transform"]!
+
+  function makeMessages(msgs: Array<{ role: string; parts: Array<Record<string, unknown>>; modelID?: string }>) {
+    return msgs.map((m, i) => ({
+      info: { id: `msg_${i}`, role: m.role, modelID: m.modelID } as Record<string, unknown>,
+      parts: m.parts.map((p, j) => ({ id: `prt_${i}_${j}`, sessionID: "ses_test", messageID: `msg_${i}`, ...p })),
+    }))
+  }
+
+  it("should not prepend thinking when message starts with reasoning.encrypted", async () => {
+    //#given an assistant message that starts with a reasoning.encrypted block
+    const messages = makeMessages([
+      { role: "user", parts: [{ type: "text", text: "test" }], modelID: "claude-opus-4" },
+      { role: "assistant", parts: [
+        { type: "reasoning.encrypted", text: "encrypted reasoning" },
+        { type: "text", text: "response" },
+      ]},
+    ])
+
+    //#when the hook processes the messages
+    const output = { messages }
+    await transform({} as Record<string, never>, output)
+
+    //#then no synthetic thinking block should be prepended
+    const assistantParts = output.messages[1].parts
+    expect(assistantParts[0].type).toBe("reasoning.encrypted")
+    expect(assistantParts).toHaveLength(2)
+  })
+
+  it("should find previous reasoning.encrypted content for messages missing thinking", async () => {
+    //#given a previous message with reasoning.encrypted and a current message without thinking
+    const messages = makeMessages([
+      { role: "user", parts: [{ type: "text", text: "test" }], modelID: "claude-opus-4" },
+      { role: "assistant", parts: [
+        { type: "reasoning.encrypted", text: "previous encrypted reasoning" },
+        { type: "text", text: "first response" },
+      ]},
+      { role: "user", parts: [{ type: "text", text: "follow up" }], modelID: "claude-opus-4" },
+      { role: "assistant", parts: [
+        { type: "tool_use", name: "bash" },
+      ]},
+    ])
+
+    //#when the hook processes the messages
+    const output = { messages }
+    await transform({} as Record<string, never>, output)
+
+    //#then the second assistant message should have a prepended thinking block with previous reasoning content
+    const secondAssistantParts = output.messages[3].parts
+    expect(secondAssistantParts[0].type).toBe("thinking")
+    expect((secondAssistantParts[0] as Record<string, unknown>).thinking).toBe("previous encrypted reasoning")
+  })
+})
diff --git a/src/hooks/unstable-agent-babysitter/unstable-agent-babysitter-hook.ts b/src/hooks/unstable-agent-babysitter/unstable-agent-babysitter-hook.ts
index 52a6ac86d8..72cfe05ea1 100644
--- a/src/hooks/unstable-agent-babysitter/unstable-agent-babysitter-hook.ts
+++ b/src/hooks/unstable-agent-babysitter/unstable-agent-babysitter-hook.ts
@@ -97,6 +97,9 @@ async function getThinkingSummary(ctx: BabysitterContext, sessionID: string): Pr
         if (part.type === "reasoning" && part.text) {
           chunks.push(part.text)
         }
+        if (part.type === "reasoning.encrypted" && part.text) {
+          chunks.push(part.text)
+        }
       }
     }
 
diff --git a/src/tools/background-task/full-session-format.ts b/src/tools/background-task/full-session-format.ts
index 9b50a09fb6..707bbd8ec4 100644
--- a/src/tools/background-task/full-session-format.ts
+++ b/src/tools/background-task/full-session-format.ts
@@ -81,7 +81,7 @@ export async function formatFullSession(
   const normalizedMessages: BackgroundOutputMessage[] = []
   for (const message of filteredMessages) {
     const parts = (message.parts ?? []).filter((part) => {
-      if (part.type === "thinking" || part.type === "reasoning") {
+      if (part.type === "thinking" || part.type === "reasoning" || part.type === "reasoning.encrypted") {
         return includeThinking
       }
       if (part.type === "tool_result") {
@@ -135,6 +135,8 @@ export async function formatFullSession(
         lines.push(`[thinking] ${truncateText(part.thinking, thinkingMaxChars)}`)
       } else if (part.type === "reasoning" && part.text) {
         lines.push(`[thinking] ${truncateText(part.text, thinkingMaxChars)}`)
+      } else if (part.type === "reasoning.encrypted" && part.text) {
+        lines.push(`[thinking] ${truncateText(part.text, thinkingMaxChars)}`)
       } else if (part.type === "tool_result") {
         const toolTexts = extractToolResultText(part)
         for (const toolText of toolTexts) {
diff --git a/src/tools/background-task/modules/formatters.ts b/src/tools/background-task/modules/formatters.ts
index aa17e7d9e6..1645bf35dc 100644
--- a/src/tools/background-task/modules/formatters.ts
+++ b/src/tools/background-task/modules/formatters.ts
@@ -244,7 +244,7 @@ export async function formatFullSession(
   const normalizedMessages: FullSessionMessage[] = []
   for (const message of filteredMessages) {
     const parts = (message.parts ?? []).filter((part) => {
-      if (part.type === "thinking" || part.type === "reasoning") {
+      if (part.type === "thinking" || part.type === "reasoning" || part.type === "reasoning.encrypted") {
         return includeThinking
       }
       if (part.type === "tool_result") {
@@ -302,6 +302,8 @@ export async function formatFullSession(
         lines.push(`[thinking] ${truncateText(part.thinking, thinkingMaxChars)}`)
       } else if (part.type === "reasoning" && part.text) {
         lines.push(`[thinking] ${truncateText(part.text, thinkingMaxChars)}`)
+      } else if (part.type === "reasoning.encrypted" && part.text) {
+        lines.push(`[thinking] ${truncateText(part.text, thinkingMaxChars)}`)
       } else if (part.type === "tool_result") {
         const toolTexts = extractToolResultText(part)
         for (const toolText of toolTexts) {
diff --git a/src/tools/background-task/modules/message-processing.ts b/src/tools/background-task/modules/message-processing.ts
index 18ac17316f..73d56d2f47 100644
--- a/src/tools/background-task/modules/message-processing.ts
+++ b/src/tools/background-task/modules/message-processing.ts
@@ -62,7 +62,7 @@ export function extractToolResultText(part: FullSessionMessagePart): string[] {
 
   if (Array.isArray(part.content)) {
     const blocks = part.content
-      .filter((block) => (block.type === "text" || block.type === "reasoning") && block.text)
+      .filter((block) => (block.type === "text" || block.type === "reasoning" || block.type === "reasoning.encrypted") && block.text)
       .map((block) => block.text as string)
     if (blocks.length > 0) return blocks
   }
diff --git a/src/tools/background-task/reasoning-encrypted-extraction.test.ts b/src/tools/background-task/reasoning-encrypted-extraction.test.ts
new file mode 100644
index 0000000000..009219a6cf
--- /dev/null
+++ b/src/tools/background-task/reasoning-encrypted-extraction.test.ts
@@ -0,0 +1,49 @@
+import { describe, expect, it } from "bun:test"
+
+describe("reasoning.encrypted content extraction", () => {
+  //#given content parts with reasoning.encrypted type
+  
+  it("should extract text from reasoning.encrypted part when text is present", () => {
+    //#given a part with reasoning.encrypted type and text
+    const part = { type: "reasoning.encrypted" as const, text: "decrypted reasoning content" }
+    
+    //#when filtering for text or reasoning.encrypted with text guard
+    const shouldInclude = !!((part.type === "text" || part.type === "reasoning" || part.type === "reasoning.encrypted") && part.text)
+    
+    //#then it should be included
+    expect(shouldInclude).toBe(true)
+  })
+  
+  it("should skip reasoning.encrypted part when text is missing", () => {
+    //#given a part with reasoning.encrypted type but no text
+    const part = { type: "reasoning.encrypted" as const }
+    
+    //#when filtering for text or reasoning.encrypted with text guard
+    const shouldInclude = !!((part.type === "text" || part.type === "reasoning" || part.type === "reasoning.encrypted") && (part as any).text)
+    
+    //#then it should be excluded
+    expect(shouldInclude).toBe(false)
+  })
+  
+  it("should extract text from reasoning part when text is present", () => {
+    //#given a part with reasoning type and text
+    const part = { type: "reasoning" as const, text: "reasoning content" }
+    
+    //#when filtering for text or reasoning with text guard
+    const shouldInclude = !!((part.type === "text" || part.type === "reasoning" || part.type === "reasoning.encrypted") && part.text)
+    
+    //#then it should be included
+    expect(shouldInclude).toBe(true)
+  })
+  
+  it("should extract text from text part", () => {
+    //#given a part with text type
+    const part = { type: "text" as const, text: "text content" }
+    
+    //#when filtering for text or reasoning with text guard
+    const shouldInclude = !!((part.type === "text" || part.type === "reasoning" || part.type === "reasoning.encrypted") && part.text)
+    
+    //#then it should be included
+    expect(shouldInclude).toBe(true)
+  })
+})
diff --git a/src/tools/delegate-task/sync-result-fetcher.ts b/src/tools/delegate-task/sync-result-fetcher.ts
index 64d1a27876..67c5c5a6b5 100644
--- a/src/tools/delegate-task/sync-result-fetcher.ts
+++ b/src/tools/delegate-task/sync-result-fetcher.ts
@@ -41,7 +41,7 @@ export async function fetchSyncResult(
     return { ok: false, error: `No assistant response found.\n\nSession ID: ${sessionID}` }
   }
 
-  const textParts = lastMessage?.parts?.filter((p) => p.type === "text" || p.type === "reasoning") ?? []
+  const textParts = lastMessage?.parts?.filter((p) => p.type === "text" || p.type === "reasoning" || p.type === "reasoning.encrypted") ?? []
   const textContent = textParts.map((p) => p.text ?? "").filter(Boolean).join("\n")
 
   return { ok: true, textContent }
diff --git a/src/tools/delegate-task/sync-session-poller.ts b/src/tools/delegate-task/sync-session-poller.ts
index 3f7b2fd991..01827a14fe 100644
--- a/src/tools/delegate-task/sync-session-poller.ts
+++ b/src/tools/delegate-task/sync-session-poller.ts
@@ -98,7 +98,7 @@ export async function pollSyncSession(
       if (m.info?.role !== "assistant") return false
       const parts = m.parts ?? []
       return parts.some((p) => {
-        if (p.type !== "text" && p.type !== "reasoning") return false
+        if (p.type !== "text" && p.type !== "reasoning" && p.type !== "reasoning.encrypted") return false
         const text = (p.text ?? "").trim()
         return text.length > 0
       })
diff --git a/src/tools/delegate-task/unstable-agent-task.ts b/src/tools/delegate-task/unstable-agent-task.ts
index ae97153bd2..caa84d463d 100644
--- a/src/tools/delegate-task/unstable-agent-task.ts
+++ b/src/tools/delegate-task/unstable-agent-task.ts
@@ -120,7 +120,7 @@ export async function executeUnstableAgentTask(
       return `No assistant response found (task ran in background mode).\n\nSession ID: ${sessionID}`
     }
 
-    const textParts = lastMessage?.parts?.filter((p) => p.type === "text" || p.type === "reasoning") ?? []
+    const textParts = lastMessage?.parts?.filter((p) => p.type === "text" || p.type === "reasoning" || p.type === "reasoning.encrypted") ?? []
     const textContent = textParts.map((p) => p.text ?? "").filter(Boolean).join("\n")
     const duration = formatDuration(startTime)