diff --git a/packages/ai/CHANGELOG.md b/packages/ai/CHANGELOG.md
index 1330e4e2..64bace68 100644
--- a/packages/ai/CHANGELOG.md
+++ b/packages/ai/CHANGELOG.md
@@ -4,6 +4,7 @@
 
 ### Fixed
 
+- Fixed DeepSeek V4 Flash `xhigh` thinking support so requests preserve `xhigh` and map it to DeepSeek's `max` reasoning effort ([#3944](https://github.com/badlogic/pi-mono/issues/3944)).
 - Fixed Anthropic streams that end before `message_stop` to be treated as errors instead of successful partial responses ([#3936](https://github.com/badlogic/pi-mono/issues/3936)).
 - Fixed generated OpenAI-compatible DeepSeek V4 models to carry the provider-specific reasoning effort mapping outside the direct DeepSeek provider ([#3940](https://github.com/badlogic/pi-mono/issues/3940)).
 - Fixed DeepSeek V4 Flash and V4 Pro pricing metadata to match current official rates ([#3910](https://github.com/badlogic/pi-mono/issues/3910)).
diff --git a/packages/ai/src/models.ts b/packages/ai/src/models.ts
index ee095205..47fdc3c5 100644
--- a/packages/ai/src/models.ts
+++ b/packages/ai/src/models.ts
@@ -50,7 +50,7 @@ export function calculateCost<TApi extends Api>(model: Model<TApi>, usage: Usage
  *
  * Supported today:
  * - GPT-5.2 / GPT-5.3 / GPT-5.4 / GPT-5.5 model families
- * - DeepSeek V4 Pro
+ * - DeepSeek V4 Pro and Flash
  * - Opus 4.6+ models (xhigh maps to adaptive effort "max" on Anthropic-compatible providers)
  */
 export function supportsXhigh<TApi extends Api>(model: Model<TApi>): boolean {
@@ -59,7 +59,8 @@ export function supportsXhigh<TApi extends Api>(model: Model<TApi>): boolean {
 		model.id.includes("gpt-5.3") ||
 		model.id.includes("gpt-5.4") ||
 		model.id.includes("gpt-5.5") ||
-		model.id.includes("deepseek-v4-pro")
+		model.id.includes("deepseek-v4-pro") ||
+		model.id.includes("deepseek-v4-flash")
 	) {
 		return true;
 	}
diff --git a/packages/ai/test/supports-xhigh.test.ts b/packages/ai/test/supports-xhigh.test.ts
index eb5eeba8..8474d7ef 100644
--- a/packages/ai/test/supports-xhigh.test.ts
+++ b/packages/ai/test/supports-xhigh.test.ts
@@ -26,6 +26,24 @@ describe("supportsXhigh", () => {
 		expect(supportsXhigh(model!)).toBe(true);
 	});
 
+	it("returns true for DeepSeek V4 Flash on the DeepSeek provider", () => {
+		const model = getModel("deepseek", "deepseek-v4-flash");
+		expect(model).toBeDefined();
+		expect(supportsXhigh(model!)).toBe(true);
+	});
+
+	it("returns true for DeepSeek V4 Flash on opencode-go", () => {
+		const model = getModel("opencode-go", "deepseek-v4-flash");
+		expect(model).toBeDefined();
+		expect(supportsXhigh(model!)).toBe(true);
+	});
+
+	it("returns true for DeepSeek V4 Flash on OpenRouter", () => {
+		const model = getModel("openrouter", "deepseek/deepseek-v4-flash");
+		expect(model).toBeDefined();
+		expect(supportsXhigh(model!)).toBe(true);
+	});
+
 	it("returns true for OpenRouter Opus 4.6 (openai-completions API)", () => {
 		const model = getModel("openrouter", "anthropic/claude-opus-4.6");
 		expect(model).toBeDefined();