diff --git a/package.json b/package.json
index 2931f4b..32d30ae 100644
--- a/package.json
+++ b/package.json
@@ -11,7 +11,7 @@
     "test": "bun test",
     "test:unit": "bun test tests/unit",
     "test:integration": "bun test tests/integration",
-    "test:ci:unit": "bun test tests/tools/defaults.test.ts tests/tools/executor-chain.test.ts tests/tools/sdk-executor.test.ts tests/tools/mcp-executor.test.ts tests/tools/skills.test.ts tests/tools/registry.test.ts tests/unit/cli/model-discovery.test.ts tests/unit/proxy/prompt-builder.test.ts tests/unit/proxy/tool-loop.test.ts tests/unit/provider-boundary.test.ts tests/unit/provider-runtime-interception.test.ts tests/unit/provider-tool-schema-compat.test.ts tests/unit/provider-tool-loop-guard.test.ts tests/unit/plugin.test.ts tests/unit/plugin-tools-hook.test.ts tests/unit/plugin-tool-resolution.test.ts tests/unit/plugin-config.test.ts tests/unit/auth.test.ts tests/unit/streaming/line-buffer.test.ts tests/unit/streaming/parser.test.ts tests/unit/streaming/types.test.ts tests/unit/streaming/delta-tracker.test.ts tests/competitive/edge.test.ts",
+    "test:ci:unit": "bun test tests/tools/defaults.test.ts tests/tools/executor-chain.test.ts tests/tools/sdk-executor.test.ts tests/tools/mcp-executor.test.ts tests/tools/skills.test.ts tests/tools/registry.test.ts tests/unit/cli/model-discovery.test.ts tests/unit/proxy/prompt-builder.test.ts tests/unit/proxy/tool-loop.test.ts tests/unit/provider-boundary.test.ts tests/unit/provider-runtime-interception.test.ts tests/unit/provider-tool-schema-compat.test.ts tests/unit/provider-tool-loop-guard.test.ts tests/unit/plugin.test.ts tests/unit/plugin-tools-hook.test.ts tests/unit/plugin-tool-resolution.test.ts tests/unit/plugin-config.test.ts tests/unit/plugin-stream-extraction.test.ts tests/unit/auth.test.ts tests/unit/streaming/line-buffer.test.ts tests/unit/streaming/parser.test.ts tests/unit/streaming/types.test.ts tests/unit/streaming/delta-tracker.test.ts tests/unit/streaming/openai-sse.test.ts tests/unit/streaming/ai-sdk-parts.test.ts tests/competitive/edge.test.ts",
     "test:ci:integration": "bun test tests/integration/comprehensive.test.ts tests/integration/tools-router.integration.test.ts tests/integration/stream-router.integration.test.ts tests/integration/opencode-loop.integration.test.ts",
     "discover": "bun run src/cli/discover.ts",
     "prepublishOnly": "bun run build"
diff --git a/src/plugin.ts b/src/plugin.ts
index ad3b2b2..2b5d5e3 100644
--- a/src/plugin.ts
+++ b/src/plugin.ts
@@ -362,11 +362,12 @@ function createChatCompletionChunk(id: string, created: number, model: string, d
   };
 }
 
-function extractCompletionFromStream(output: string): { assistantText: string; reasoningText: string } {
+export function extractCompletionFromStream(output: string): { assistantText: string; reasoningText: string } {
   const lines = output.split("\n");
   let assistantText = "";
   let reasoningText = "";
   let sawAssistantPartials = false;
+  let sawThinkingPartials = false;
 
   for (const line of lines) {
     const event = parseStreamJsonLine(line);
@@ -390,7 +391,13 @@ function extractCompletionFromStream(output: string): { assistantText: string; r
     if (isThinking(event)) {
       const thinking = extractThinking(event);
       if (thinking) {
-        reasoningText += thinking;
+        const isPartial = typeof (event as any).timestamp_ms === "number";
+        if (isPartial) {
+          reasoningText += thinking;
+          sawThinkingPartials = true;
+        } else if (!sawThinkingPartials) {
+          reasoningText += thinking;
+        }
       }
     }
   }
diff --git a/tests/unit/plugin-stream-extraction.test.ts b/tests/unit/plugin-stream-extraction.test.ts
new file mode 100644
index 0000000..3b80c89
--- /dev/null
+++ b/tests/unit/plugin-stream-extraction.test.ts
@@ -0,0 +1,71 @@
+import { describe, expect, it } from "bun:test";
+
+import { extractCompletionFromStream } from "../../src/plugin";
+
+describe("extractCompletionFromStream", () => {
+  it("does not duplicate assistant text when partial events are followed by final accumulated event", () => {
+    const output = [
+      JSON.stringify({
+        type: "assistant",
+        timestamp_ms: 1,
+        message: {
+          role: "assistant",
+          content: [{ type: "text", text: "Hello" }],
+        },
+      }),
+      JSON.stringify({
+        type: "assistant",
+        timestamp_ms: 2,
+        message: {
+          role: "assistant",
+          content: [{ type: "text", text: " world" }],
+        },
+      }),
+      JSON.stringify({
+        type: "assistant",
+        message: {
+          role: "assistant",
+          content: [{ type: "text", text: "Hello world" }],
+        },
+      }),
+      JSON.stringify({
+        type: "assistant",
+        message: {
+          role: "assistant",
+          content: [{ type: "text", text: "Hello world" }],
+        },
+      }),
+    ].join("\n");
+
+    expect(extractCompletionFromStream(output)).toEqual({
+      assistantText: "Hello world",
+      reasoningText: "",
+    });
+  });
+
+  it("does not duplicate thinking text when partial events are followed by final accumulated event", () => {
+    const output = [
+      JSON.stringify({
+        type: "thinking",
+        subtype: "delta",
+        timestamp_ms: 1,
+        text: "Plan",
+      }),
+      JSON.stringify({
+        type: "thinking",
+        subtype: "delta",
+        timestamp_ms: 2,
+        text: " more",
+      }),
+      JSON.stringify({
+        type: "thinking",
+        text: "Plan more",
+      }),
+    ].join("\n");
+
+    expect(extractCompletionFromStream(output)).toEqual({
+      assistantText: "",
+      reasoningText: "Plan more",
+    });
+  });
+});