diff --git a/packages/ai/CHANGELOG.md b/packages/ai/CHANGELOG.md
index e269d4cbd..1befacee9 100644
--- a/packages/ai/CHANGELOG.md
+++ b/packages/ai/CHANGELOG.md
@@ -63,6 +63,7 @@
 ### Removed
 
 - Removed legacy local request-cost estimation machinery and database schemas previously used for OpenCode Go estimates.
+- Fixed Anthropic-compatible streams dropping thinking bytes supplied by `content_block_start`, which invalidated signed-thinking replay ([#8319](https://github.com/can1357/oh-my-pi/pull/8319) by [@max12525k](https://github.com/max12525k)).
 
 ## [17.2.15] - 2026-08-12
 
diff --git a/packages/ai/src/providers/anthropic.ts b/packages/ai/src/providers/anthropic.ts
index ef427bc3f..fd9fcac01 100644
--- a/packages/ai/src/providers/anthropic.ts
+++ b/packages/ai/src/providers/anthropic.ts
@@ -2416,6 +2416,14 @@ const streamAnthropicOnce = (
 									contentIndex,
 									partial: output,
 								});
+								if (block.thinking) {
+									stream.push({
+										type: "thinking_delta",
+										contentIndex,
+										delta: block.thinking,
+										partial: output,
+									});
+								}
 							} else if (event.content_block.type === "redacted_thinking") {
 								streamedReplayUnsafeContent = true;
 								const block: Block = {
diff --git a/packages/ai/test/anthropic-stream-envelope.test.ts b/packages/ai/test/anthropic-stream-envelope.test.ts
index 257aa4451..f6c2f9364 100644
--- a/packages/ai/test/anthropic-stream-envelope.test.ts
+++ b/packages/ai/test/anthropic-stream-envelope.test.ts
@@ -902,31 +902,6 @@ describe("anthropic stream envelope handling", () => {
 		]);
 	});
 
-	it("preserves signed thinking content from content_block_start", async () => {
-		const events = createThinkingSuccessEvents(" summary tail");
-		events[1] = {
-			type: "content_block_start",
-			index: 0,
-			content_block: { type: "thinking", thinking: "Summary prefix" },
-		};
-		vi.spyOn(AnthropicMessages.prototype, "create").mockImplementation(() => createMockRequest(events) as never);
-
-		const stream = streamAnthropic(model, context, { apiKey: "sk-ant-test" });
-		for await (const _ of stream) {
-			// drain stream
-		}
-		const result = await stream.result();
-
-		expect(result.content).toHaveLength(1);
-		const block = result.content[0];
-		expect(block?.type).toBe("thinking");
-		if (block?.type !== "thinking") {
-			throw new Error("Expected thinking content from content_block_start");
-		}
-		expect(block.thinking).toBe("Summary prefix summary tail");
-		expect(block.thinkingSignature).toBe("sig_thinking");
-	});
-
 	it("drops replayed closed blocks after a duplicate message_start instead of duplicating content", async () => {
 		const events: MockAnthropicEvent[] = [
 			{
diff --git a/packages/ai/test/leaked-thinking-stream.test.ts b/packages/ai/test/leaked-thinking-stream.test.ts
index bd0564d22..104432e93 100644
--- a/packages/ai/test/leaked-thinking-stream.test.ts
+++ b/packages/ai/test/leaked-thinking-stream.test.ts
@@ -659,6 +659,43 @@ describe("leaked thinking healing through stream()", () => {
 		return Object.assign(fn, { preconnect: fetch.preconnect });
 	}
 
+	function anthropicThinkingFetch(): FetchImpl {
+		const body = [
+			sseFrame("message_start", {
+				type: "message_start",
+				message: { id: "msg_thinking_prefix", usage: { input_tokens: 5, output_tokens: 0 } },
+			}),
+			sseFrame("content_block_start", {
+				type: "content_block_start",
+				index: 0,
+				content_block: { type: "thinking", thinking: "Summary prefix" },
+			}),
+			sseFrame("content_block_delta", {
+				type: "content_block_delta",
+				index: 0,
+				delta: { type: "thinking_delta", thinking: " summary tail" },
+			}),
+			sseFrame("content_block_delta", {
+				type: "content_block_delta",
+				index: 0,
+				delta: { type: "signature_delta", signature: "sig_thinking" },
+			}),
+			sseFrame("content_block_stop", { type: "content_block_stop", index: 0 }),
+			sseFrame("message_delta", {
+				type: "message_delta",
+				delta: { stop_reason: "end_turn" },
+				usage: { input_tokens: 5, output_tokens: 4 },
+			}),
+			sseFrame("message_stop", { type: "message_stop" }),
+		].join("");
+		const fn = async (_input: string | URL | Request, _init?: RequestInit): Promise<Response> =>
+			new Response(body, {
+				status: 200,
+				headers: { "content-type": "text/event-stream", "request-id": "req_thinking_prefix" },
+			});
+		return Object.assign(fn, { preconnect: fetch.preconnect });
+	}
+
 	function anthropicModel(overrides: Partial<Model<"anthropic-messages">> = {}): Model<"anthropic-messages"> {
 		return buildModel({
 			id: "claude-sonnet-4-5",
@@ -711,6 +748,25 @@ describe("leaked thinking healing through stream()", () => {
 		expect(texts(result).join("").trim()).toBe("Final answer.");
 	});
 
+	it("preserves thinking bytes from content_block_start through a non-official endpoint", async () => {
+		const result = await stream(
+			anthropicModel({ provider: "zai", baseUrl: "https://api.z.ai/api/anthropic" }),
+			context,
+			{
+				apiKey: "test",
+				fetch: anthropicThinkingFetch(),
+			},
+		).result();
+
+		expect(thinks(result)).toEqual([
+			{
+				type: "thinking",
+				thinking: "Summary prefix summary tail",
+				thinkingSignature: "sig_thinking",
+			},
+		]);
+	});
+
 	it("replays native web-search history on a custom Anthropic continuation", async () => {
 		const searchResult = {
 			type: "web_search_tool_result",