feat: add selectable context window (200K/1M) in model picker

Adds a "Context Window" dropdown in the Copilot Chat model
configuration panel, letting users switch between 200K and
1M token context windows per model.

- Combine reasoningEffort and contextSize into a single
  configurationSchema so both controls appear in the
  model picker dropdown (non-public VS Code API, same
  mechanism used by Copilot for thinking effort).
- maxInputTokens raised from 656K to 1,000,000 to support
  1M mode.
- maxOutputTokens set to 128,000 — a conservative middle
  ground that keeps the displayed context window reasonable
  (200K input + 128K output = 328K, 1M input + 128K output
  = ~1.1M) without sacrificing DeepSeek's actual generation
  headroom. This does NOT affect API-level max_tokens, which
  is controlled by a separate VS Code setting.
- Sync dropdown choice back to workspace setting
  (deepseek-copilot.contextSize) after each request so
  the value persists across sessions.
- Both DeepSeek V4 Flash and Pro supported.
- English and Chinese i18n for dropdown labels and descriptions.

Why: the default 656K input window was too small for long
sessions, while always reserving 1M adds latency and cost.
Giving users control lets them pick the right trade-off between
speed/cost (200K) and capacity (1M).

Author: rbinar

package-lock.json

@@ -127,6 +127,20 @@
           "minimum": 0,
           "description": "%deepseek-copilot.config.maxTokens.description%"
         },
+        "deepseek-copilot.contextSize": {
+          "type": "number",
+          "default": 1000000,
+          "enum": [200000, 1000000],
+          "enumItemLabels": [
+            "%deepseek-copilot.config.contextSize.200k.label%",
+            "%deepseek-copilot.config.contextSize.1m.label%"
+          ],
+          "markdownEnumDescriptions": [
+            "%deepseek-copilot.config.contextSize.200k.description%",
+            "%deepseek-copilot.config.contextSize.1m.description%"
+          ],
+          "markdownDescription": "%deepseek-copilot.config.contextSize.description%"
+        },
         "deepseek-copilot.experimental.stabilizeToolList": {
           "type": "boolean",
           "default": false,

package.json

@@ -17,6 +17,11 @@
   "deepseek-copilot.config.title": "DeepSeek Copilot",
   "deepseek-copilot.config.baseUrl.description": "DeepSeek API base URL. Defaults to official DeepSeek API endpoint.",
   "deepseek-copilot.config.maxTokens.description": "Maximum number of output tokens per request. Set to 0 to use the API default (no limit). Useful for controlling costs.",
+  "deepseek-copilot.config.contextSize.description": "Input context window size reported to VS Code. Larger context allows longer conversations without compaction but may increase cost.",
+  "deepseek-copilot.config.contextSize.200k.label": "200K",
+  "deepseek-copilot.config.contextSize.200k.description": "200K tokens — safe default for most sessions.",
+  "deepseek-copilot.config.contextSize.1m.label": "1M",
+  "deepseek-copilot.config.contextSize.1m.description": "1M tokens — longer sessions without compaction.",
   "deepseek-copilot.config.experimental.stabilizeToolList.description": "**Experimental**: improve DeepSeek context-cache hit rate by pre-activating available tools.\n- When the enabled tools list changes across turns, this may improve DeepSeek context-cache hit rate.\n- Requests will include more function definitions, so input tokens may increase. Cache-hit input tokens are billed at a lower price, but still count toward usage.\n- This may add internal preflight tool calls to the current Copilot chat history. If you switch to another model in the same conversation, that model provider may reject or mishandle the replayed history. Start a new chat if model switching behaves unexpectedly.\n\nUse [Configure Tools](command:workbench.action.chat.configureTools) to **view and manage** your tool list:\n\n- 64 or fewer enabled tools: usually no need to enable this unless the tool list still changes across turns.\n- More than 128 enabled tools: not recommended. DeepSeek supports at most 128 functions in one `tools` request. Consider disabling tools you rarely use.",
   "deepseek-copilot.config.debugMode.description": "Controls what diagnostic information DeepSeek Copilot writes. Token usage is always reported to Copilot regardless of this setting.\n\n- **Minimal** — Token usage only. No diagnostic logs or request dumps.\n- **Metadata** — Privacy-safe diagnostic metadata (request hashes, prefix overlap, tool schema changes). Does not contain prompt text — safe to share in public issue reports. View with [`DeepSeek: Show Logs`](command:deepseek-copilot.showLogs).\n- **Verbose** — Complete request payloads written to disk for local debugging. **Warning: contains sensitive prompt content.** View with [`DeepSeek: Open Request Dumps Folder`](command:deepseek-copilot.openRequestDumpsFolder).",
   "deepseek-copilot.config.debugMode.minimal.label": "Minimal",

package.nls.json

@@ -36,6 +36,15 @@ export function getMaxTokens(): number | undefined {
 	return value > 0 ? value : undefined;
 }
 
+/**
+ * Get the configured context window size in tokens.
+ * Returns the value set by the user (200K or 1M), defaulting to 1M.
+ */
+export function getContextSize(): number {
+	const config = vscode.workspace.getConfiguration(CONFIG_SECTION);
+	return config.get<number>('contextSize', 1000000);
+}
+
 /**
  * Diagnostic mode. `verbose` also enables metadata logs.
  *

src/config.ts

@@ -54,8 +54,8 @@ export const MODELS: ModelDefinition[] = [
 		family: 'deepseek',
 		version: 'v4',
 		detail: 'Fast, general-purpose model',
-		maxInputTokens: 655360,
-		maxOutputTokens: 393216,
+		maxInputTokens: 1000000,
+		maxOutputTokens: 128000,
 		capabilities: {
 			toolCalling: DEEPSEEK_TOOLS_LIMIT,
 			imageInput: true,
@@ -74,8 +74,8 @@ export const MODELS: ModelDefinition[] = [
 		family: 'deepseek',
 		version: 'v4',
 		detail: 'Most capable reasoning model',
-		maxInputTokens: 655360,
-		maxOutputTokens: 393216,
+		maxInputTokens: 1000000,
+		maxOutputTokens: 128000,
 		capabilities: {
 			toolCalling: DEEPSEEK_TOOLS_LIMIT,
 			imageInput: true,

src/consts.ts

@@ -42,6 +42,13 @@ const zh: Translations = {
 	'thinking.max': '深度',
 	'thinking.max.desc': '深度推理，适合复杂任务',
 
+	// Context Size — model picker dropdown
+	'contextSize.title': '上下文窗口',
+	'contextSize.200k': '200K',
+	'contextSize.200k.desc': '200K token 上下文（更快）',
+	'contextSize.1m': '1M',
+	'contextSize.1m.desc': '1M token 上下文（更大容量）',
+
 	// Vision
 	'vision.proxyUsing': '视觉代理：{0}',
 	'vision.notFound': '未找到视觉模型 "{0}"',
@@ -232,6 +239,13 @@ const en: Translations = {
 	'thinking.max': 'Max',
 	'thinking.max.desc': 'Maximum reasoning depth for complex agent tasks',
 
+	// Context Size — model picker dropdown
+	'contextSize.title': 'Context Window',
+	'contextSize.200k': '200K',
+	'contextSize.200k.desc': '200K token context (faster)',
+	'contextSize.1m': '1M',
+	'contextSize.1m.desc': '1M token context (larger capacity)',
+
 	// Vision
 	// NOTE: vision.unableToDescribe has been moved to consts.ts as
 	// IMAGE_DESCRIPTION_UNAVAILABLE — it is prompt content, not UI text.

src/i18n.ts

@@ -1,7 +1,7 @@
 import vscode from 'vscode';
 import { AuthManager } from '../auth';
-import { getStabilizeToolListEnabled } from '../config';
-import { MODELS } from '../consts';
+import { getContextSize, getStabilizeToolListEnabled } from '../config';
+import { CONFIG_SECTION, MODELS } from '../consts';
 import { t } from '../i18n';
 import { logger } from '../logger';
 import { createCacheDiagnosticsRecorder, dumpProviderInput } from './debug';
@@ -133,10 +133,11 @@ export class DeepSeekChatProvider implements vscode.LanguageModelChatProvider {
 
 		const hasKey = await this.authManager.hasApiKey();
 		const pricingCurrency = this.balanceCurrencyResolver.getDisplayCurrency();
+		const contextSize = getContextSize();
 		if (hasKey) {
 			this.balanceCurrencyResolver.refreshInBackground();
 		}
-		return MODELS.map((model) => toChatInfo(model, hasKey, pricingCurrency));
+		return MODELS.map((model) => toChatInfo(model, hasKey, pricingCurrency, contextSize));
 	}
 
 	async provideLanguageModelChatResponse(
@@ -184,6 +185,17 @@ export class DeepSeekChatProvider implements vscode.LanguageModelChatProvider {
 			getVisionDescriber: () => this.vision.get(),
 		});
 
+		// Sync context size back to VS Code setting when user changes it via the
+		// model-picker dropdown. The updated maxInputTokens takes effect on the
+		// next request after Copilot Chat re-queries model information.
+		const currentContextSize = getContextSize();
+		if (prepared.configuredContextSize !== currentContextSize) {
+			await vscode.workspace
+				.getConfiguration(CONFIG_SECTION)
+				.update('contextSize', prepared.configuredContextSize, vscode.ConfigurationTarget.Global);
+			this.onDidChangeLanguageModelChatInformationEmitter.fire();
+		}
+
 		return streamChatCompletion({
 			prepared,
 			progress,

src/provider/index.ts

@@ -15,24 +15,27 @@ import { toModelCostInfo, type ModelCostInformation } from './pricing/costs';
 
 export type ThinkingEffort = 'none' | 'high' | 'max';
 
+export type ContextSize = 200000 | 1000000;
+
 export type ModelConfigurationOptions = vscode.ProvideLanguageModelChatResponseOptions & {
 	readonly modelConfiguration?: Record<string, unknown>;
 	readonly configuration?: Record<string, unknown>;
 };
 
-type ThinkingEffortConfigurationSchema = ReturnType<typeof buildThinkingEffortSchema>;
+type ModelConfigurationSchema = ReturnType<typeof buildModelConfigurationSchema>;
 
 export type ModelPickerChatInformation = vscode.LanguageModelChatInformation &
 	ModelCostInformation & {
 		readonly isUserSelectable: boolean;
 		readonly statusIcon?: vscode.ThemeIcon;
-		readonly configurationSchema?: ThinkingEffortConfigurationSchema;
+		readonly configurationSchema?: ModelConfigurationSchema;
 	};
 
 export function toChatInfo(
 	m: ModelDefinition,
 	hasApiKey: boolean,
 	pricingCurrency?: PricingCurrency,
+	contextSize?: number,
 ): ModelPickerChatInformation {
 	const modelDetail = resolveModelText(m, 'detail') ?? m.detail;
 	const modelTooltip = resolveModelText(m, 'tooltip');
@@ -44,15 +47,15 @@ export function toChatInfo(
 		detail: hasApiKey ? modelDetail : t('auth.apiKeyRequiredDetail'),
 		tooltip: hasApiKey ? modelTooltip : t('auth.apiKeyRequiredDetail'),
 		statusIcon: hasApiKey ? undefined : new vscode.ThemeIcon('warning'),
-		maxInputTokens: m.maxInputTokens,
+		maxInputTokens: contextSize ?? m.maxInputTokens,
 		maxOutputTokens: m.maxOutputTokens,
 		isUserSelectable: true,
 		capabilities: {
 			toolCalling: m.capabilities.toolCalling,
 			imageInput: m.capabilities.imageInput,
 		},
 		...toModelCostInfo(m, pricingCurrency),
-		...(m.capabilities.thinking ? { configurationSchema: buildThinkingEffortSchema() } : {}),
+		...(hasApiKey ? { configurationSchema: buildModelConfigurationSchema(m) } : {}),
 	};
 }
 
@@ -71,24 +74,49 @@ export function getConfiguredThinkingEffort(options: ModelConfigurationOptions):
 	return configuredEffort === 'max' ? 'max' : 'high';
 }
 
-function buildThinkingEffortSchema() {
-	return {
-		properties: {
-			reasoningEffort: {
-				type: 'string',
-				title: t('status.thinking'),
-				enum: ['none', 'high', 'max'],
-				enumItemLabels: [t('thinking.none'), t('thinking.high'), t('thinking.max')],
-				enumDescriptions: [
-					t('thinking.none.desc'),
-					t('thinking.high.desc'),
-					t('thinking.max.desc'),
-				],
-				default: 'high',
-				group: 'navigation',
-			},
-		},
-	} as const;
+/**
+ * Read the context size selected by the user via the model-picker dropdown.
+ * Falls back to the VS Code setting when the dropdown hasn't been used yet.
+ */
+export function getConfiguredContextSize(options: ModelConfigurationOptions): ContextSize {
+	const configured =
+		options.modelConfiguration?.contextSize ?? options.configuration?.contextSize;
+	if (configured === 200000) {
+		return 200000;
+	}
+	return 1000000;
+}
+
+function buildModelConfigurationSchema(m: ModelDefinition) {
+	const properties: Record<string, unknown> = {};
+
+	if (m.capabilities.thinking) {
+		properties.reasoningEffort = {
+			type: 'string',
+			title: t('status.thinking'),
+			enum: ['none', 'high', 'max'],
+			enumItemLabels: [t('thinking.none'), t('thinking.high'), t('thinking.max')],
+			enumDescriptions: [
+				t('thinking.none.desc'),
+				t('thinking.high.desc'),
+				t('thinking.max.desc'),
+			],
+			default: 'high',
+			group: 'navigation',
+		};
+	}
+
+	properties.contextSize = {
+		type: 'number',
+		title: t('contextSize.title'),
+		enum: [200000, 1000000],
+		enumItemLabels: [t('contextSize.200k'), t('contextSize.1m')],
+		enumDescriptions: [t('contextSize.200k.desc'), t('contextSize.1m.desc')],
+		default: 1000000,
+		group: 'tokens',
+	};
+
+	return { properties } as const;
 }
 
 function resolveModelText(m: ModelDefinition, field: 'detail' | 'tooltip'): string | undefined {

src/provider/models.ts

@@ -8,13 +8,13 @@ import { t } from '../i18n';
 import type { DeepSeekRequest } from '../types';
 import { convertMessages, countMessageChars } from './convert';
 import {
-	dumpDeepSeekRequest,
-	type CacheDiagnosticsRecorder,
-	type CacheDiagnosticsRun,
+    dumpDeepSeekRequest,
+    type CacheDiagnosticsRecorder,
+    type CacheDiagnosticsRun,
 } from './debug';
-import { getConfiguredThinkingEffort, type ModelConfigurationOptions } from './models';
-import { classifyDeepSeekRequest, shouldForceThinkingNone, type RequestKind } from './routing';
+import { getConfiguredContextSize, getConfiguredThinkingEffort, type ContextSize, type ModelConfigurationOptions } from './models';
 import type { ReplayMarkerMetadata } from './replay';
+import { classifyDeepSeekRequest, shouldForceThinkingNone, type RequestKind } from './routing';
 import type { ConversationSegment } from './segment';
 import { collectTrailingToolResultIds, prepareRequestTools } from './tools/request';
 import { resolveImageMessages, type VisionDescriber } from './vision';
@@ -31,6 +31,8 @@ export interface PreparedChatRequest {
 	replayMarkerMetadata: ReplayMarkerMetadata;
 	visionMarkerTextChars?: number;
 	initialResponseNotice?: string;
+	/** The context size selected via the model-picker dropdown (if any). */
+	configuredContextSize: ContextSize;
 }
 
 export interface PrepareChatRequestOptions {
@@ -88,6 +90,7 @@ export async function prepareChatRequest({
 	const configuredThinkingEffort = getConfiguredThinkingEffort(
 		options as ModelConfigurationOptions,
 	);
+	const configuredContextSize = getConfiguredContextSize(options as ModelConfigurationOptions);
 	// Only force helper requests into disabled thinking on the official API.
 	// Custom endpoints keep their configured effort to preserve pre-#137 request shape.
 	const forceNoneThinking =
@@ -147,5 +150,6 @@ export async function prepareChatRequest({
 		replayMarkerMetadata: visionResolution.replayMarkerMetadata,
 		visionMarkerTextChars: visionResolution.stats.markerVisionTextChars || undefined,
 		initialResponseNotice: visionResolution.initialResponseNotice,
+		configuredContextSize,
 	};
 }