diff --git a/src/agents/embedded-agent-runner.sanitize-session-history.test.ts b/src/agents/embedded-agent-runner.sanitize-session-history.test.ts
index 43504487c97f..e53c1515fa54 100644
--- a/src/agents/embedded-agent-runner.sanitize-session-history.test.ts
+++ b/src/agents/embedded-agent-runner.sanitize-session-history.test.ts
@@ -1013,7 +1013,6 @@ describe("sanitizeSessionHistory", () => {
           preserveNativeAnthropicToolUseIds: false,
           repairToolUseResultPairing: false,
           preserveSignatures: false,
-          sanitizeThinkingSignatures: false,
           dropThinkingBlocks: false,
           dropReasoningFromHistory: false,
           applyGoogleTurnOrdering: false,
@@ -1472,7 +1471,6 @@ describe("sanitizeSessionHistory", () => {
       preserveNativeAnthropicToolUseIds: true,
       repairToolUseResultPairing: true,
       preserveSignatures: true,
-      sanitizeThinkingSignatures: false,
       dropThinkingBlocks: false,
       dropReasoningFromHistory: false,
       applyGoogleTurnOrdering: false,
@@ -2137,7 +2135,6 @@ describe("sanitizeSessionHistory", () => {
         repairToolUseResultPairing: true,
         preserveSignatures: true,
         sanitizeThoughtSignatures: undefined,
-        sanitizeThinkingSignatures: false,
         dropThinkingBlocks: false,
         applyGoogleTurnOrdering: false,
         validateGeminiTurns: false,
@@ -2273,7 +2270,6 @@ describe("sanitizeSessionHistory", () => {
           preserveNativeAnthropicToolUseIds: false,
           repairToolUseResultPairing: true,
           preserveSignatures: false,
-          sanitizeThinkingSignatures: false,
           dropThinkingBlocks: false,
           applyGoogleTurnOrdering: false,
           validateGeminiTurns: false,
@@ -2488,7 +2484,6 @@ describe("sanitizeSessionHistory", () => {
       repairToolUseResultPairing: true,
       preserveSignatures: true,
       sanitizeThoughtSignatures: undefined,
-      sanitizeThinkingSignatures: false,
       dropThinkingBlocks: true,
       applyGoogleTurnOrdering: false,
       validateGeminiTurns: false,
@@ -2609,7 +2604,6 @@ describe("sanitizeSessionHistory", () => {
         preserveNativeAnthropicToolUseIds: false,
         repairToolUseResultPairing: true,
         preserveSignatures: false,
-        sanitizeThinkingSignatures: false,
         dropThinkingBlocks: false,
         applyGoogleTurnOrdering: false,
         validateGeminiTurns: false,
@@ -2659,7 +2653,6 @@ describe("sanitizeSessionHistory", () => {
         preserveNativeAnthropicToolUseIds: false,
         repairToolUseResultPairing: true,
         preserveSignatures: false,
-        sanitizeThinkingSignatures: false,
         dropThinkingBlocks: false,
         dropReasoningFromHistory: false,
         applyGoogleTurnOrdering: false,
@@ -2702,7 +2695,6 @@ describe("sanitizeSessionHistory", () => {
         preserveNativeAnthropicToolUseIds: false,
         repairToolUseResultPairing: true,
         preserveSignatures: false,
-        sanitizeThinkingSignatures: false,
         dropThinkingBlocks: false,
         dropReasoningFromHistory: false,
         applyGoogleTurnOrdering: false,
@@ -2744,7 +2736,6 @@ describe("sanitizeSessionHistory", () => {
         preserveNativeAnthropicToolUseIds: false,
         repairToolUseResultPairing: true,
         preserveSignatures: false,
-        sanitizeThinkingSignatures: false,
         dropThinkingBlocks: false,
         applyGoogleTurnOrdering: false,
         validateGeminiTurns: false,
diff --git a/src/agents/embedded-agent-runner/compact.hooks.harness.ts b/src/agents/embedded-agent-runner/compact.hooks.harness.ts
index 97cc01a48661..512db6fd3704 100644
--- a/src/agents/embedded-agent-runner/compact.hooks.harness.ts
+++ b/src/agents/embedded-agent-runner/compact.hooks.harness.ts
@@ -303,7 +303,6 @@ function createCompactHooksRuntimePlan(params: BuildAgentRuntimePlanParams): Age
     preserveNativeAnthropicToolUseIds: false,
     repairToolUseResultPairing: false,
     preserveSignatures: false,
-    sanitizeThinkingSignatures: false,
     dropThinkingBlocks: false,
     applyGoogleTurnOrdering: false,
     validateGeminiTurns: false,
diff --git a/src/agents/embedded-agent-runner/run.overflow-compaction.test.ts b/src/agents/embedded-agent-runner/run.overflow-compaction.test.ts
index 53fe4bd180f0..30ed78f05717 100644
--- a/src/agents/embedded-agent-runner/run.overflow-compaction.test.ts
+++ b/src/agents/embedded-agent-runner/run.overflow-compaction.test.ts
@@ -141,7 +141,6 @@ function makeForwardedRuntimePlan(overrides: RuntimePlanOverrides = {}): AgentRu
     preserveNativeAnthropicToolUseIds: false,
     repairToolUseResultPairing: true,
     preserveSignatures: false,
-    sanitizeThinkingSignatures: true,
     dropThinkingBlocks: false,
     applyGoogleTurnOrdering: false,
     validateGeminiTurns: false,
diff --git a/src/agents/embedded-agent-runner/run/attempt.spawn-workspace.context-engine.test.ts b/src/agents/embedded-agent-runner/run/attempt.spawn-workspace.context-engine.test.ts
index e36929465c15..a7d78feaa82d 100644
--- a/src/agents/embedded-agent-runner/run/attempt.spawn-workspace.context-engine.test.ts
+++ b/src/agents/embedded-agent-runner/run/attempt.spawn-workspace.context-engine.test.ts
@@ -737,7 +737,6 @@ describe("runEmbeddedAttempt context engine sessionKey forwarding", () => {
               preserveNativeAnthropicToolUseIds: false,
               repairToolUseResultPairing: true,
               preserveSignatures: true,
-              sanitizeThinkingSignatures: false,
               dropThinkingBlocks: false,
               dropReasoningFromHistory: false,
               applyGoogleTurnOrdering: false,
diff --git a/src/agents/embedded-agent-runner/run/attempt.transcript-policy.test.ts b/src/agents/embedded-agent-runner/run/attempt.transcript-policy.test.ts
index 9867d36b8eac..cc90a4ac3f3c 100644
--- a/src/agents/embedded-agent-runner/run/attempt.transcript-policy.test.ts
+++ b/src/agents/embedded-agent-runner/run/attempt.transcript-policy.test.ts
@@ -26,7 +26,6 @@ describe("resolveAttemptTranscriptPolicy", () => {
       preserveNativeAnthropicToolUseIds: false,
       repairToolUseResultPairing: true,
       preserveSignatures: true,
-      sanitizeThinkingSignatures: false,
       dropThinkingBlocks: true,
       applyGoogleTurnOrdering: false,
       validateGeminiTurns: false,
diff --git a/src/agents/runtime-plan/types.ts b/src/agents/runtime-plan/types.ts
index ec8fe7682f83..f3d3d4f12925 100644
--- a/src/agents/runtime-plan/types.ts
+++ b/src/agents/runtime-plan/types.ts
@@ -361,7 +361,6 @@ export type AgentRuntimeTranscriptPolicy = {
     allowBase64Only?: boolean;
     includeCamelCase?: boolean;
   };
-  sanitizeThinkingSignatures: boolean;
   dropThinkingBlocks: boolean;
   dropReasoningFromHistory?: boolean;
   applyGoogleTurnOrdering: boolean;
diff --git a/src/agents/test-helpers/embedded-agent-runner-e2e-mocks.ts b/src/agents/test-helpers/embedded-agent-runner-e2e-mocks.ts
index a7c28f241eca..985e30a21a37 100644
--- a/src/agents/test-helpers/embedded-agent-runner-e2e-mocks.ts
+++ b/src/agents/test-helpers/embedded-agent-runner-e2e-mocks.ts
@@ -116,7 +116,6 @@ export function installEmbeddedRunnerFastRunE2eMocks(
             preserveNativeAnthropicToolUseIds: false,
             repairToolUseResultPairing: true,
             preserveSignatures: false,
-            sanitizeThinkingSignatures: true,
             dropThinkingBlocks: false,
             applyGoogleTurnOrdering: false,
             validateGeminiTurns: false,
diff --git a/src/agents/transcript-policy.ts b/src/agents/transcript-policy.ts
index 5c4b2599d48f..336555c1aa85 100644
--- a/src/agents/transcript-policy.ts
+++ b/src/agents/transcript-policy.ts
@@ -31,7 +31,6 @@ export type TranscriptPolicy = {
     allowBase64Only?: boolean;
     includeCamelCase?: boolean;
   };
-  sanitizeThinkingSignatures: boolean;
   dropThinkingBlocks: boolean;
   dropReasoningFromHistory?: boolean;
   applyGoogleTurnOrdering: boolean;
@@ -75,7 +74,6 @@ const DEFAULT_TRANSCRIPT_POLICY: TranscriptPolicy = {
   repairToolUseResultPairing: true,
   preserveSignatures: false,
   sanitizeThoughtSignatures: undefined,
-  sanitizeThinkingSignatures: false,
   dropThinkingBlocks: false,
   dropReasoningFromHistory: false,
   applyGoogleTurnOrdering: false,