diff --git a/src/api/providers/__tests__/openai.spec.ts b/src/api/providers/__tests__/openai.spec.ts
index f45b311f6..ebe86fdb5 100644
--- a/src/api/providers/__tests__/openai.spec.ts
+++ b/src/api/providers/__tests__/openai.spec.ts
@@ -219,6 +219,45 @@ describe("OpenAiHandler", () => {
 			expect(textChunks[0].text).toBe("Test response")
 		})
 
+		it("streams reasoning chunks from delta.reasoning_content", async () => {
+			mockCreate.mockImplementationOnce(async () => ({
+				[Symbol.asyncIterator]: async function* () {
+					yield { choices: [{ delta: { reasoning_content: "thinking..." }, index: 0 }] }
+					yield { choices: [{ delta: { content: "answer" }, index: 0 }] }
+					yield {
+						choices: [{ delta: {}, index: 0 }],
+						usage: { prompt_tokens: 1, completion_tokens: 1, total_tokens: 2 },
+					}
+				},
+			}))
+
+			const chunks: any[] = []
+			for await (const chunk of handler.createMessage(systemPrompt, messages)) {
+				chunks.push(chunk)
+			}
+
+			expect(chunks).toContainEqual({ type: "reasoning", text: "thinking..." })
+		})
+
+		it("falls back to delta.reasoning when reasoning_content is absent", async () => {
+			mockCreate.mockImplementationOnce(async () => ({
+				[Symbol.asyncIterator]: async function* () {
+					yield { choices: [{ delta: { reasoning: "router-style thought" }, index: 0 }] }
+					yield {
+						choices: [{ delta: {}, index: 0 }],
+						usage: { prompt_tokens: 1, completion_tokens: 1, total_tokens: 2 },
+					}
+				},
+			}))
+
+			const chunks: any[] = []
+			for await (const chunk of handler.createMessage(systemPrompt, messages)) {
+				chunks.push(chunk)
+			}
+
+			expect(chunks).toContainEqual({ type: "reasoning", text: "router-style thought" })
+		})
+
 		it("should handle tool calls in streaming responses", async () => {
 			mockCreate.mockImplementation(async (options) => {
 				return {
diff --git a/src/api/providers/__tests__/requesty.spec.ts b/src/api/providers/__tests__/requesty.spec.ts
index feacf3f87..1e272d1b6 100644
--- a/src/api/providers/__tests__/requesty.spec.ts
+++ b/src/api/providers/__tests__/requesty.spec.ts
@@ -249,6 +249,49 @@ describe("RequestyHandler", () => {
 			await expect(generator.next()).rejects.toThrow("API Error")
 		})
 
+		it("streams reasoning chunks from delta.reasoning_content", async () => {
+			const handler = new RequestyHandler(mockOptions)
+			mockCreate.mockResolvedValue({
+				async *[Symbol.asyncIterator]() {
+					yield { id: "1", choices: [{ delta: { reasoning_content: "thinking..." } }] }
+					yield { id: "1", choices: [{ delta: { content: "answer" } }] }
+					yield {
+						id: "1",
+						choices: [{ delta: {} }],
+						usage: { prompt_tokens: 1, completion_tokens: 1 },
+					}
+				},
+			})
+
+			const chunks: any[] = []
+			for await (const chunk of handler.createMessage("sys", [{ role: "user", content: "hi" }])) {
+				chunks.push(chunk)
+			}
+
+			expect(chunks).toContainEqual({ type: "reasoning", text: "thinking..." })
+		})
+
+		it("falls back to delta.reasoning when reasoning_content is absent", async () => {
+			const handler = new RequestyHandler(mockOptions)
+			mockCreate.mockResolvedValue({
+				async *[Symbol.asyncIterator]() {
+					yield { id: "1", choices: [{ delta: { reasoning: "router-style thought" } }] }
+					yield {
+						id: "1",
+						choices: [{ delta: {} }],
+						usage: { prompt_tokens: 1, completion_tokens: 1 },
+					}
+				},
+			})
+
+			const chunks: any[] = []
+			for await (const chunk of handler.createMessage("sys", [{ role: "user", content: "hi" }])) {
+				chunks.push(chunk)
+			}
+
+			expect(chunks).toContainEqual({ type: "reasoning", text: "router-style thought" })
+		})
+
 		describe("native tool support", () => {
 			const systemPrompt = "test system prompt"
 			const messages: Anthropic.Messages.MessageParam[] = [
diff --git a/src/api/providers/__tests__/unbound.spec.ts b/src/api/providers/__tests__/unbound.spec.ts
index 261968190..8771e636e 100644
--- a/src/api/providers/__tests__/unbound.spec.ts
+++ b/src/api/providers/__tests__/unbound.spec.ts
@@ -50,6 +50,57 @@ describe("UnboundHandler", () => {
 		)
 	})
 
+	it("streams reasoning chunks from delta.reasoning_content", async () => {
+		const mockCreate = (OpenAI as unknown as any)().chat.completions.create
+		mockCreate.mockResolvedValue({
+			async *[Symbol.asyncIterator]() {
+				yield { choices: [{ delta: { reasoning_content: "thinking..." } }] }
+				yield { choices: [{ delta: { content: "answer" } }] }
+				yield { choices: [{ delta: {} }], usage: { prompt_tokens: 1, completion_tokens: 1 } }
+			},
+		})
+
+		const handler = new UnboundHandler({
+			unboundApiKey: "test-key",
+			unboundModelId: "openai/gpt-4o",
+		})
+
+		const chunks: any[] = []
+		for await (const chunk of handler.createMessage("system", [{ role: "user", content: "hi" }], {
+			taskId: "t",
+			tools: [],
+		})) {
+			chunks.push(chunk)
+		}
+
+		expect(chunks).toContainEqual({ type: "reasoning", text: "thinking..." })
+	})
+
+	it("falls back to delta.reasoning when reasoning_content is absent", async () => {
+		const mockCreate = (OpenAI as unknown as any)().chat.completions.create
+		mockCreate.mockResolvedValue({
+			async *[Symbol.asyncIterator]() {
+				yield { choices: [{ delta: { reasoning: "router-style thought" } }] }
+				yield { choices: [{ delta: {} }], usage: { prompt_tokens: 1, completion_tokens: 1 } }
+			},
+		})
+
+		const handler = new UnboundHandler({
+			unboundApiKey: "test-key",
+			unboundModelId: "openai/gpt-4o",
+		})
+
+		const chunks: any[] = []
+		for await (const chunk of handler.createMessage("system", [{ role: "user", content: "hi" }], {
+			taskId: "t",
+			tools: [],
+		})) {
+			chunks.push(chunk)
+		}
+
+		expect(chunks).toContainEqual({ type: "reasoning", text: "router-style thought" })
+	})
+
 	it("identifies itself as Zoo Code in per-request Unbound metadata", async () => {
 		const mockCreate = (OpenAI as unknown as any)().chat.completions.create
 		mockCreate.mockResolvedValue({
diff --git a/src/api/providers/deepseek.ts b/src/api/providers/deepseek.ts
index e2ffd2916..819fe6c7b 100644
--- a/src/api/providers/deepseek.ts
+++ b/src/api/providers/deepseek.ts
@@ -16,6 +16,7 @@ import { getModelParams } from "../transform/model-params"
 import { convertToR1Format } from "../transform/r1-format"
 
 import { OpenAiHandler } from "./openai"
+import { extractReasoningFromDelta } from "./utils/extract-reasoning"
 import type { ApiHandlerCreateMessageMetadata } from "../index"
 
 // Custom interface for DeepSeek params to support thinking mode
@@ -155,11 +156,9 @@ export class DeepSeekHandler extends OpenAiHandler {
 
 			// Handle reasoning_content from DeepSeek's interleaved thinking
 			// This is the proper way DeepSeek sends thinking content in streaming
-			if ("reasoning_content" in delta && delta.reasoning_content) {
-				yield {
-					type: "reasoning",
-					text: (delta.reasoning_content as string) || "",
-				}
+			const reasoningText = extractReasoningFromDelta(delta)
+			if (reasoningText) {
+				yield { type: "reasoning", text: reasoningText }
 			}
 
 			// Handle tool calls
diff --git a/src/api/providers/mimo.ts b/src/api/providers/mimo.ts
index f842926b6..2901c2e92 100644
--- a/src/api/providers/mimo.ts
+++ b/src/api/providers/mimo.ts
@@ -9,6 +9,7 @@ import { convertToR1Format } from "../transform/r1-format"
 import { getModelParams } from "../transform/model-params"
 import { calculateApiCostOpenAI } from "../../shared/cost"
 import { handleProviderError } from "./utils/error-handler"
+import { extractReasoningFromDelta } from "./utils/extract-reasoning"
 
 import { OpenAiHandler } from "./openai"
 import type { ApiHandlerCreateMessageMetadata } from "../index"
@@ -127,11 +128,9 @@ export class MimoHandler extends OpenAiHandler {
 				}
 			}
 
-			if ("reasoning_content" in delta && delta.reasoning_content) {
-				yield {
-					type: "reasoning",
-					text: (delta.reasoning_content as string) || "",
-				}
+			const reasoningText = extractReasoningFromDelta(delta)
+			if (reasoningText) {
+				yield { type: "reasoning", text: reasoningText }
 			}
 
 			yield* this.processToolCalls(sanitizedDelta, finishReason, activeToolCallIds)
diff --git a/src/api/providers/openai.ts b/src/api/providers/openai.ts
index 532ed38ba..f80544b40 100644
--- a/src/api/providers/openai.ts
+++ b/src/api/providers/openai.ts
@@ -24,6 +24,7 @@ import { BaseProvider } from "./base-provider"
 import type { SingleCompletionHandler, ApiHandlerCreateMessageMetadata } from "../index"
 import { getApiRequestTimeout } from "./utils/timeout-config"
 import { handleOpenAIError } from "./utils/openai-error-handler"
+import { extractReasoningFromDelta } from "./utils/extract-reasoning"
 
 // TODO: Rename this to OpenAICompatibleHandler. Also, I think the
 // `OpenAINativeHandler` can subclass from this, since it's obviously
@@ -207,11 +208,9 @@ export class OpenAiHandler extends BaseProvider implements SingleCompletionHandl
 					}
 				}
 
-				if ("reasoning_content" in delta && delta.reasoning_content) {
-					yield {
-						type: "reasoning",
-						text: (delta.reasoning_content as string | undefined) || "",
-					}
+				const reasoningText = extractReasoningFromDelta(delta)
+				if (reasoningText) {
+					yield { type: "reasoning", text: reasoningText }
 				}
 
 				yield* this.processToolCalls(delta, finishReason, activeToolCallIds)
diff --git a/src/api/providers/opencode-go.ts b/src/api/providers/opencode-go.ts
index 6b66aa684..43d32e619 100644
--- a/src/api/providers/opencode-go.ts
+++ b/src/api/providers/opencode-go.ts
@@ -10,6 +10,7 @@ import { convertToOpenAiMessages } from "../transform/openai-format"
 
 import type { SingleCompletionHandler, ApiHandlerCreateMessageMetadata } from "../index"
 import { RouterProvider } from "./router-provider"
+import { extractReasoningFromDelta } from "./utils/extract-reasoning"
 
 /**
  * API handler for the Opencode "Go" subscription plan.
@@ -80,8 +81,9 @@ export class OpencodeGoHandler extends RouterProvider implements SingleCompletio
 			}
 
 			// Several Go-plan models (GLM, DeepSeek) stream reasoning via this field.
-			if (delta && "reasoning_content" in delta && delta.reasoning_content) {
-				yield { type: "reasoning", text: (delta.reasoning_content as string | undefined) || "" }
+			const reasoningText = extractReasoningFromDelta(delta)
+			if (reasoningText) {
+				yield { type: "reasoning", text: reasoningText }
 			}
 
 			// Emit raw tool call chunks - NativeToolCallParser handles state management.
diff --git a/src/api/providers/qwen-code.ts b/src/api/providers/qwen-code.ts
index f2a207051..0b7d7598a 100644
--- a/src/api/providers/qwen-code.ts
+++ b/src/api/providers/qwen-code.ts
@@ -14,6 +14,7 @@ import { convertToOpenAiMessages } from "../transform/openai-format"
 import { ApiStream } from "../transform/stream"
 
 import { BaseProvider } from "./base-provider"
+import { extractReasoningFromDelta } from "./utils/extract-reasoning"
 import type { SingleCompletionHandler, ApiHandlerCreateMessageMetadata } from "../index"
 
 const QWEN_OAUTH_BASE_URL = "https://chat.qwen.ai"
@@ -283,11 +284,9 @@ export class QwenCodeHandler extends BaseProvider implements SingleCompletionHan
 				}
 			}
 
-			if ("reasoning_content" in delta && delta.reasoning_content) {
-				yield {
-					type: "reasoning",
-					text: (delta.reasoning_content as string | undefined) || "",
-				}
+			const reasoningText = extractReasoningFromDelta(delta)
+			if (reasoningText) {
+				yield { type: "reasoning", text: reasoningText }
 			}
 
 			// Handle tool calls in stream - emit partial chunks for NativeToolCallParser
diff --git a/src/api/providers/requesty.ts b/src/api/providers/requesty.ts
index 3e50adf9c..df3dc35af 100644
--- a/src/api/providers/requesty.ts
+++ b/src/api/providers/requesty.ts
@@ -18,6 +18,7 @@ import type { SingleCompletionHandler, ApiHandlerCreateMessageMetadata } from ".
 import { toRequestyServiceUrl } from "../../shared/utils/requesty"
 import { handleOpenAIError } from "./utils/openai-error-handler"
 import { applyRouterToolPreferences } from "./utils/router-tool-preferences"
+import { extractReasoningFromDelta } from "./utils/extract-reasoning"
 
 // Requesty usage includes an extra field for Anthropic use cases.
 // Safely cast the prompt token details section to the appropriate structure.
@@ -174,8 +175,9 @@ export class RequestyHandler extends BaseProvider implements SingleCompletionHan
 				yield { type: "text", text: delta.content }
 			}
 
-			if (delta && "reasoning_content" in delta && delta.reasoning_content) {
-				yield { type: "reasoning", text: (delta.reasoning_content as string | undefined) || "" }
+			const reasoningText = extractReasoningFromDelta(delta)
+			if (reasoningText) {
+				yield { type: "reasoning", text: reasoningText }
 			}
 
 			// Handle native tool calls
diff --git a/src/api/providers/unbound.ts b/src/api/providers/unbound.ts
index a1de7dfa1..f0c6fe758 100644
--- a/src/api/providers/unbound.ts
+++ b/src/api/providers/unbound.ts
@@ -17,6 +17,7 @@ import { BaseProvider } from "./base-provider"
 import type { SingleCompletionHandler, ApiHandlerCreateMessageMetadata } from "../index"
 import { handleOpenAIError } from "./utils/openai-error-handler"
 import { applyRouterToolPreferences } from "./utils/router-tool-preferences"
+import { extractReasoningFromDelta } from "./utils/extract-reasoning"
 
 // Unbound usage includes extra fields for Anthropic cache tokens.
 interface UnboundUsage extends OpenAI.CompletionUsage {
@@ -162,8 +163,9 @@ export class UnboundHandler extends BaseProvider implements SingleCompletionHand
 				yield { type: "text", text: delta.content }
 			}
 
-			if (delta && "reasoning_content" in delta && delta.reasoning_content) {
-				yield { type: "reasoning", text: (delta.reasoning_content as string | undefined) || "" }
+			const reasoningText = extractReasoningFromDelta(delta)
+			if (reasoningText) {
+				yield { type: "reasoning", text: reasoningText }
 			}
 
 			// Handle native tool calls