diff --git a/packages/coding-agent/CHANGELOG.md b/packages/coding-agent/CHANGELOG.md
index dcbd68a54..d85974302 100644
--- a/packages/coding-agent/CHANGELOG.md
+++ b/packages/coding-agent/CHANGELOG.md
@@ -2,6 +2,10 @@
 
 ## [Unreleased]
 
+### Fixed
+
+- Fixed `provider.appendOnlyContext: "auto"` staying inactive for Xiaomi Token Plan/SGLang endpoints, preserving prefix-cache hits without forcing append-only mode globally ([#1851](https://github.com/can1357/oh-my-pi/issues/1851)).
+
 ## [15.9.0] - 2026-06-04
 
 ### Breaking Changes
diff --git a/packages/coding-agent/src/config/append-only-context-mode.ts b/packages/coding-agent/src/config/append-only-context-mode.ts
new file mode 100644
index 000000000..0efb1a8dd
--- /dev/null
+++ b/packages/coding-agent/src/config/append-only-context-mode.ts
@@ -0,0 +1,37 @@
+/** Provider metadata needed to resolve append-only context mode. */
+export interface AppendOnlyContextModel {
+	provider: string;
+	baseUrl: string;
+	compat?: object;
+}
+
+function isXiaomiHost(baseUrl: string): boolean {
+	try {
+		const host = new URL(baseUrl).hostname;
+		return host === "xiaomimimo.com" || host.endsWith(".xiaomimimo.com");
+	} catch {
+		return false;
+	}
+}
+
+function shouldAutoEnableAppendOnlyContext(model: AppendOnlyContextModel | null | undefined): boolean {
+	if (!model) return false;
+	if (model.provider === "deepseek") return true;
+	if (isXiaomiHost(model.baseUrl)) return true;
+	return !!model.compat && "supportsStore" in model.compat && model.compat.supportsStore === true;
+}
+
+/** Resolves whether append-only context should be active for a model and setting. */
+export function shouldEnableAppendOnlyContext(
+	setting: "auto" | "on" | "off" | undefined,
+	model: AppendOnlyContextModel | null | undefined,
+): boolean {
+	switch (setting ?? "auto") {
+		case "on":
+			return true;
+		case "off":
+			return false;
+		default:
+			return shouldAutoEnableAppendOnlyContext(model);
+	}
+}
diff --git a/packages/coding-agent/src/config/settings-schema.ts b/packages/coding-agent/src/config/settings-schema.ts
index d6661967e..277d70eba 100644
--- a/packages/coding-agent/src/config/settings-schema.ts
+++ b/packages/coding-agent/src/config/settings-schema.ts
@@ -3057,9 +3057,9 @@ export const SETTINGS_SCHEMA = {
 			tab: "providers",
 			label: "Append-Only Context",
 			description:
-				"Cache system prompt + tool specs and keep an append-only message log so provider prefix caches (DeepSeek, Anthropic) hit at maximum rate. Auto enables for DeepSeek.",
+				"Cache system prompt + tool specs and keep an append-only message log so provider prefix caches (DeepSeek, Xiaomi/SGLang, Anthropic) hit at maximum rate. Auto enables for known prefix-cache providers.",
 			options: [
-				{ value: "auto", label: "Auto", description: "Enable for DeepSeek (recommended)" },
+				{ value: "auto", label: "Auto", description: "Enable for known prefix-cache providers (recommended)" },
 				{ value: "on", label: "On", description: "Always enable append-only context" },
 				{ value: "off", label: "Off", description: "Disable append-only context" },
 			],
diff --git a/packages/coding-agent/src/modes/controllers/command-controller.ts b/packages/coding-agent/src/modes/controllers/command-controller.ts
index 60552ecb5..6cfce5c9e 100644
--- a/packages/coding-agent/src/modes/controllers/command-controller.ts
+++ b/packages/coding-agent/src/modes/controllers/command-controller.ts
@@ -13,6 +13,7 @@ import {
 import { Loader, Markdown, padding, Spacer, Text, visibleWidth } from "@oh-my-pi/pi-tui";
 import { formatDuration, Snowflake } from "@oh-my-pi/pi-utils";
 import { $ } from "bun";
+import { shouldEnableAppendOnlyContext } from "../../config/append-only-context-mode";
 import { loadCustomShare } from "../../export/custom-share";
 import type { CompactOptions } from "../../extensibility/extensions/types";
 import {
@@ -397,10 +398,10 @@ export class CommandController {
 		// Append-only context
 		{
 			const setting = this.ctx.settings.get("provider.appendOnlyContext") ?? "auto";
-			const provider = this.ctx.session.model?.provider;
-			const mode = setting === "on" ? true : setting === "off" ? false : provider === "deepseek";
+			const model = this.ctx.session.model;
+			const mode = shouldEnableAppendOnlyContext(setting, model);
 			const activeLabel = mode ? theme.fg("success", "active") : theme.fg("dim", "inactive");
-			const settingLabel = setting === "auto" ? `${setting} (${provider ?? "?"})` : setting;
+			const settingLabel = setting === "auto" ? `${setting} (${model?.provider ?? "?"})` : setting;
 			info += `${theme.fg("dim", "Append-Only:")} ${activeLabel} (setting: ${settingLabel})\n`;
 		}
 		info += `${theme.bold("Tokens")}\n`;
diff --git a/packages/coding-agent/src/sdk.ts b/packages/coding-agent/src/sdk.ts
index 53473ab9f..dbcbf078d 100644
--- a/packages/coding-agent/src/sdk.ts
+++ b/packages/coding-agent/src/sdk.ts
@@ -39,6 +39,7 @@ import { createAutoresearchExtension } from "./autoresearch";
 import { loadCapability } from "./capability";
 import { type Rule, ruleCapability, setActiveRules } from "./capability/rule";
 import { bucketRules } from "./capability/rule-buckets";
+import { shouldEnableAppendOnlyContext } from "./config/append-only-context-mode";
 import { ModelRegistry } from "./config/model-registry";
 import {
 	formatModelString,
@@ -646,24 +647,6 @@ function registerPythonCleanup(): void {
 	postmortem.register("python-cleanup", disposeAllKernelSessions);
 }
 
-/**
- * Resolve whether to enable append-only context mode based on the setting and provider.
- *
- * - `"on"` → always enable
- * - `"off"` → never enable
- * - `"auto"` → enable for DeepSeek (prefix-caching provider)
- */
-function resolveAppendOnlyMode(setting: "auto" | "on" | "off" | undefined, provider: string): boolean {
-	switch (setting ?? "auto") {
-		case "on":
-			return true;
-		case "off":
-			return false;
-		default:
-			return provider === "deepseek";
-	}
-}
-
 function customToolToDefinition(tool: CustomTool): ToolDefinition {
 	const definition: ToolDefinition & { [TOOL_DEFINITION_MARKER]: true } = {
 		name: tool.name,
@@ -2028,7 +2011,7 @@ export async function createAgentSession(options: CreateAgentSessionOptions = {}
 			getToolChoice: () => session?.nextToolChoice(),
 			telemetry: options.telemetry,
 			appendOnlyContext: model
-				? resolveAppendOnlyMode(settings.get("provider.appendOnlyContext"), model.provider)
+				? shouldEnableAppendOnlyContext(settings.get("provider.appendOnlyContext"), model)
 					? new AppendOnlyContextManager()
 					: undefined
 				: undefined,
diff --git a/packages/coding-agent/src/session/agent-session.ts b/packages/coding-agent/src/session/agent-session.ts
index 2691b2167..c1891819d 100644
--- a/packages/coding-agent/src/session/agent-session.ts
+++ b/packages/coding-agent/src/session/agent-session.ts
@@ -100,6 +100,7 @@ import { type AsyncJob, type AsyncJobDeliveryState, AsyncJobManager } from "../a
 import { classifyDifficulty } from "../auto-thinking/classifier";
 import { reset as resetCapabilities } from "../capability";
 import type { Rule } from "../capability/rule";
+import { shouldEnableAppendOnlyContext } from "../config/append-only-context-mode";
 import { MODEL_ROLE_IDS, type ModelRegistry } from "../config/model-registry";
 import {
 	extractExplicitThinkingSelector,
@@ -6735,8 +6736,8 @@ export class AgentSession {
 	 */
 	#syncAppendOnlyContext(model: Model | null | undefined): void {
 		const setting = this.settings.get("provider.appendOnlyContext") ?? "auto";
+		const enable = shouldEnableAppendOnlyContext(setting, model);
 		const providerId = model?.provider;
-		const enable = setting === "on" || (setting === "auto" && providerId === "deepseek");
 		const prev = this.#lastAppendOnlyResolution;
 		if (prev && prev.enable === enable && prev.providerId === providerId) return;
 		this.#lastAppendOnlyResolution = { enable, providerId };
diff --git a/packages/coding-agent/test/append-only-context-mode.test.ts b/packages/coding-agent/test/append-only-context-mode.test.ts
new file mode 100644
index 000000000..381c3215c
--- /dev/null
+++ b/packages/coding-agent/test/append-only-context-mode.test.ts
@@ -0,0 +1,44 @@
+import { describe, expect, test } from "bun:test";
+import { shouldEnableAppendOnlyContext } from "@oh-my-pi/pi-coding-agent/config/append-only-context-mode";
+
+const XIAOMI_TOKEN_PLAN_ANTHROPIC = {
+	provider: "xiaomi-token-plan-sgp",
+	baseUrl: "https://token-plan-sgp.xiaomimimo.com/anthropic",
+};
+
+const GENERIC_PROXY = {
+	provider: "generic-proxy",
+	baseUrl: "https://llm.example.com/v1",
+};
+
+describe("shouldEnableAppendOnlyContext", () => {
+	test("honors explicit on and off settings", () => {
+		expect(shouldEnableAppendOnlyContext("on", GENERIC_PROXY)).toBe(true);
+		expect(shouldEnableAppendOnlyContext("off", { provider: "deepseek", baseUrl: "https://api.deepseek.com" })).toBe(
+			false,
+		);
+	});
+
+	test("auto enables for DeepSeek", () => {
+		expect(shouldEnableAppendOnlyContext("auto", { provider: "deepseek", baseUrl: "https://api.deepseek.com" })).toBe(
+			true,
+		);
+	});
+
+	test("auto enables for Xiaomi Token Plan SGLang HiCache endpoints", () => {
+		expect(shouldEnableAppendOnlyContext("auto", XIAOMI_TOKEN_PLAN_ANTHROPIC)).toBe(true);
+	});
+
+	test("auto enables when model compat explicitly supports stored requests", () => {
+		expect(
+			shouldEnableAppendOnlyContext("auto", {
+				...GENERIC_PROXY,
+				compat: { supportsStore: true },
+			}),
+		).toBe(true);
+	});
+
+	test("auto remains off for unknown providers without prefix-cache signals", () => {
+		expect(shouldEnableAppendOnlyContext("auto", GENERIC_PROXY)).toBe(false);
+	});
+});