diff --git a/src/agents/pi-embedded-runner.sanitize-session-history.test.ts b/src/agents/pi-embedded-runner.sanitize-session-history.test.ts
index dbdf38989b2..c0b6361e1d7 100644
--- a/src/agents/pi-embedded-runner.sanitize-session-history.test.ts
+++ b/src/agents/pi-embedded-runner.sanitize-session-history.test.ts
@@ -816,7 +816,7 @@ describe("sanitizeSessionHistory", () => {
       messages,
       modelApi: "anthropic-messages",
       provider: "anthropic",
-      modelId: "claude-opus-4-6",
+      modelId: "claude-sonnet-4-6",
       sessionManager,
       sessionId: TEST_SESSION_ID,
     });
@@ -856,7 +856,7 @@ describe("sanitizeSessionHistory", () => {
       messages,
       modelApi: "anthropic-messages",
       provider: "anthropic",
-      modelId: "claude-opus-4-6",
+      modelId: "claude-sonnet-4-6",
       sessionManager,
       sessionId: TEST_SESSION_ID,
     });
diff --git a/src/agents/pi-embedded-runner/run/attempt.test.ts b/src/agents/pi-embedded-runner/run/attempt.test.ts
index 175744b226c..9f985879716 100644
--- a/src/agents/pi-embedded-runner/run/attempt.test.ts
+++ b/src/agents/pi-embedded-runner/run/attempt.test.ts
@@ -907,7 +907,11 @@ describe("wrapStreamFnSanitizeMalformedToolCalls", () => {
       createFakeStream({ events: [], resultMessage: { role: "assistant", content: [] } }),
     );
 
-    const wrapped = wrapStreamFnSanitizeMalformedToolCalls(baseFn as never, new Set(["read"]));
+    const wrapped = wrapStreamFnSanitizeMalformedToolCalls(
+      baseFn as never,
+      new Set(["read"]),
+      { validateAnthropicTurns: true } as never,
+    );
     const stream = wrapped({} as never, { messages } as never, {} as never) as
       | FakeWrappedStream
       | Promise<FakeWrappedStream>;
@@ -935,7 +939,11 @@ describe("wrapStreamFnSanitizeMalformedToolCalls", () => {
       createFakeStream({ events: [], resultMessage: { role: "assistant", content: [] } }),
     );
 
-    const wrapped = wrapStreamFnSanitizeMalformedToolCalls(baseFn as never, new Set(["read"]));
+    const wrapped = wrapStreamFnSanitizeMalformedToolCalls(
+      baseFn as never,
+      new Set(["read"]),
+      { validateAnthropicTurns: true } as never,
+    );
     const stream = wrapped({} as never, { messages } as never, {} as never) as
       | FakeWrappedStream
       | Promise<FakeWrappedStream>;
@@ -964,7 +972,11 @@ describe("wrapStreamFnSanitizeMalformedToolCalls", () => {
       createFakeStream({ events: [], resultMessage: { role: "assistant", content: [] } }),
     );
 
-    const wrapped = wrapStreamFnSanitizeMalformedToolCalls(baseFn as never, new Set(["read"]));
+    const wrapped = wrapStreamFnSanitizeMalformedToolCalls(
+      baseFn as never,
+      new Set(["read"]),
+      { validateAnthropicTurns: true } as never,
+    );
     const stream = wrapped(
       { api: "anthropic-messages" } as never,
       { messages } as never,
@@ -1012,6 +1024,7 @@ describe("wrapStreamFnSanitizeMalformedToolCalls", () => {
     const wrapped = wrapStreamFnSanitizeMalformedToolCalls(
       baseFn as never,
       new Set(["sessions_spawn"]),
+      { validateAnthropicTurns: true } as never,
     );
     const stream = wrapped(
       { api: "anthropic-messages" } as never,
@@ -1055,6 +1068,7 @@ describe("wrapStreamFnSanitizeMalformedToolCalls", () => {
     const wrapped = wrapStreamFnSanitizeMalformedToolCalls(
       baseFn as never,
       new Set(["sessions_spawn"]),
+      { validateAnthropicTurns: true } as never,
     );
     const stream = wrapped({} as never, { messages } as never, {} as never) as
       | FakeWrappedStream
@@ -1073,6 +1087,40 @@ describe("wrapStreamFnSanitizeMalformedToolCalls", () => {
     expect(toolCall.input?.attachments?.[0]?.content).toBe(attachmentContent);
   });
 
+  it("keeps non-Anthropic thinking turns mutable when Anthropic replay validation is off", async () => {
+    const messages = [
+      {
+        role: "assistant",
+        content: [
+          { type: "thinking", thinking: "internal", thinkingSignature: "sig_1" },
+          { type: "toolCall", id: "call_read", name: " read ", arguments: { path: "README.md" } },
+        ],
+      },
+      {
+        role: "user",
+        content: [{ type: "text", text: "retry" }],
+      },
+    ];
+    const baseFn = vi.fn((_model, _context) =>
+      createFakeStream({ events: [], resultMessage: { role: "assistant", content: [] } }),
+    );
+
+    const wrapped = wrapStreamFnSanitizeMalformedToolCalls(baseFn as never, new Set(["read"]));
+    const stream = wrapped({ api: "google-gemini" } as never, { messages } as never, {} as never) as
+      | FakeWrappedStream
+      | Promise<FakeWrappedStream>;
+    await Promise.resolve(stream);
+
+    expect(baseFn).toHaveBeenCalledTimes(1);
+    const seenContext = baseFn.mock.calls[0]?.[1] as {
+      messages: Array<{ content?: unknown[] }>;
+    };
+    expect(seenContext.messages[0]?.content).toEqual([
+      { type: "thinking", thinking: "internal", thinkingSignature: "sig_1" },
+      { type: "toolCall", id: "call_read", name: "read", arguments: { path: "README.md" } },
+    ]);
+  });
+
   it("preserves allowlisted tool names that contain punctuation", async () => {
     const messages = [
       {
diff --git a/src/agents/pi-embedded-runner/run/attempt.tool-call-normalization.ts b/src/agents/pi-embedded-runner/run/attempt.tool-call-normalization.ts
index 27d8f7c2649..e7b5fad16a8 100644
--- a/src/agents/pi-embedded-runner/run/attempt.tool-call-normalization.ts
+++ b/src/agents/pi-embedded-runner/run/attempt.tool-call-normalization.ts
@@ -331,6 +331,7 @@ function resolveReplayToolCallName(
 function sanitizeReplayToolCallInputs(
   messages: AgentMessage[],
   allowedToolNames?: Set<string>,
+  preserveImmutableThinkingTurns?: boolean,
 ): ReplayToolCallSanitizeReport {
   let changed = false;
   let droppedAssistantMessages = 0;
@@ -345,7 +346,11 @@ function sanitizeReplayToolCallInputs(
       out.push(message);
       continue;
     }
-    if (message.content.some((block) => isThinkingLikeReplayBlock(block))) {
+    if (
+      preserveImmutableThinkingTurns &&
+      message.content.some((block) => isThinkingLikeReplayBlock(block)) &&
+      message.content.some((block) => isReplayToolCallBlock(block))
+    ) {
       if (isReplaySafeThinkingTurn(message.content, allowedToolNames)) {
         out.push(message);
       } else {
@@ -633,7 +638,11 @@ export function wrapStreamFnSanitizeMalformedToolCalls(
     if (!Array.isArray(messages)) {
       return baseFn(model, context, options);
     }
-    const sanitized = sanitizeReplayToolCallInputs(messages as AgentMessage[], allowedToolNames);
+    const sanitized = sanitizeReplayToolCallInputs(
+      messages as AgentMessage[],
+      allowedToolNames,
+      transcriptPolicy?.validateAnthropicTurns === true,
+    );
     if (sanitized.messages === messages) {
       return baseFn(model, context, options);
     }