feat: Support 1M context window and model-aware effort options (#1245)

1. Add 1M context window support for Opus 4.6 and Sonnet 4.6 models
  2. Use model-aware default context window instead of hardcoded 200k fallback
  3. Increase JSONL hydration token budget to 800k for 1M-context models
  4. Show effort dropdown only for models that support it (Opus 4.5+, Sonnet 4.6)
  5. Restrict "Max" effort option to Opus 4.6 only
  6. Rebuild effort config options dynamically when switching models

Author: charlesvien

packages/agent/src/adapters/claude/claude-agent.ts

@@ -59,7 +59,12 @@ import { fetchMcpToolMetadata } from "./mcp/tool-metadata";
 import { canUseTool } from "./permissions/permission-handlers";
 import { getAvailableSlashCommands } from "./session/commands";
 import { parseMcpServers } from "./session/mcp-config";
-import { DEFAULT_MODEL, toSdkModelId } from "./session/models";
+import {
+  DEFAULT_MODEL,
+  getDefaultContextWindow,
+  getEffortOptions,
+  toSdkModelId,
+} from "./session/models";
 import {
   buildSessionOptions,
   buildSystemPrompt,
@@ -337,7 +342,9 @@ export class ClaudeAcpAgent extends BaseAcpAgent {
               (m) => m.contextWindow,
             );
             const contextWindowSize =
-              contextWindows.length > 0 ? Math.min(...contextWindows) : 200000;
+              contextWindows.length > 0
+                ? Math.min(...contextWindows)
+                : getDefaultContextWindow(this.session.modelId ?? "");
 
             // Send usage_update notification
             if (lastAssistantTotalUsage !== null) {
@@ -509,6 +516,7 @@ export class ClaudeAcpAgent extends BaseAcpAgent {
     const sdkModelId = toSdkModelId(params.modelId);
     await this.session.query.setModel(sdkModelId);
     this.session.modelId = params.modelId;
+    this.rebuildEffortConfigOption(params.modelId);
     await this.updateConfigOption("model", params.modelId);
     return {};
   }
@@ -559,6 +567,7 @@ export class ClaudeAcpAgent extends BaseAcpAgent {
       const sdkModelId = toSdkModelId(params.value);
       await this.session.query.setModel(sdkModelId);
       this.session.modelId = params.value;
+      this.rebuildEffortConfigOption(params.value);
     } else if (params.configId === "effort") {
       const newEffort = params.value as EffortLevel;
       this.session.effort = newEffort;
@@ -865,7 +874,7 @@ export class ClaudeAcpAgent extends BaseAcpAgent {
       description: mode.description ?? undefined,
     }));
 
-    return [
+    const configOptions: SessionConfigOption[] = [
       {
         id: "mode",
         name: "Approval Preset",
@@ -885,21 +894,67 @@ export class ClaudeAcpAgent extends BaseAcpAgent {
         category: "model" as SessionConfigOptionCategory,
         description: "Choose which model Claude should use",
       },
-      {
+    ];
+
+    const effortOptions = getEffortOptions(modelOptions.currentModelId);
+    if (effortOptions) {
+      configOptions.push({
         id: "effort",
         name: "Effort",
         type: "select",
         currentValue: currentEffort,
-        options: [
-          { value: "low", name: "Low" },
-          { value: "medium", name: "Medium" },
-          { value: "high", name: "High" },
-          { value: "max", name: "Max" },
-        ],
+        options: effortOptions,
         category: "thought_level" as SessionConfigOptionCategory,
         description: "Controls how much effort Claude puts into its response",
-      },
-    ];
+      });
+    }
+
+    return configOptions;
+  }
+
+  private rebuildEffortConfigOption(modelId: string): void {
+    const effortOptions = getEffortOptions(modelId);
+    const existingEffort = this.session.configOptions.find(
+      (o) => o.id === "effort",
+    );
+
+    if (!effortOptions) {
+      this.session.configOptions = this.session.configOptions.filter(
+        (o) => o.id !== "effort",
+      );
+      if (this.session.effort) {
+        this.session.effort = undefined;
+        this.session.queryOptions.effort = undefined;
+      }
+      return;
+    }
+
+    const currentValue = existingEffort?.currentValue ?? "high";
+    const isValidValue = effortOptions.some((o) => o.value === currentValue);
+    const resolvedValue = isValidValue ? currentValue : "high";
+
+    if (resolvedValue !== currentValue && this.session.effort) {
+      this.session.effort = resolvedValue as EffortLevel;
+      this.session.queryOptions.effort = resolvedValue as EffortLevel;
+    }
+
+    const effortConfig: SessionConfigOption = {
+      id: "effort",
+      name: "Effort",
+      type: "select",
+      currentValue: resolvedValue,
+      options: effortOptions,
+      category: "thought_level" as SessionConfigOptionCategory,
+      description: "Controls how much effort Claude puts into its response",
+    };
+
+    if (existingEffort) {
+      this.session.configOptions = this.session.configOptions.map((o) =>
+        o.id === "effort" ? effortConfig : o,
+      );
+    } else {
+      this.session.configOptions.push(effortConfig);
+    }
   }
 
   private async sendAvailableCommandsUpdate(): Promise<void> {

packages/agent/src/adapters/claude/session/jsonl-hydration.ts

@@ -5,6 +5,7 @@ import * as path from "node:path";
 import type { ContentBlock } from "@agentclientprotocol/sdk";
 import type { PostHogAPIClient } from "../../../posthog-api";
 import type { StoredEntry } from "../../../types";
+import { supports1MContext } from "./models";
 
 interface ConversationTurn {
   role: "user" | "assistant";
@@ -188,6 +189,7 @@ export function rebuildConversation(
 
 const CHARS_PER_TOKEN = 4;
 const DEFAULT_MAX_TOKENS = 150_000;
+const LARGE_CONTEXT_MAX_TOKENS = 800_000;
 
 function estimateTurnTokens(turn: ConversationTurn): number {
   let chars = 0;
@@ -546,7 +548,10 @@ export async function hydrateSessionJsonl(params: {
       return;
     }
 
-    const conversation = selectRecentTurns(allTurns);
+    const maxTokens = supports1MContext(params.model ?? "")
+      ? LARGE_CONTEXT_MAX_TOKENS
+      : DEFAULT_MAX_TOKENS;
+    const conversation = selectRecentTurns(allTurns, maxTokens);
     log.info("Selected recent turns for hydration", {
       totalTurns: allTurns.length,
       selectedTurns: conversation.length,

packages/agent/src/adapters/claude/session/models.ts

@@ -11,3 +11,53 @@ const GATEWAY_TO_SDK_MODEL: Record<string, string> = {
 export function toSdkModelId(modelId: string): string {
   return GATEWAY_TO_SDK_MODEL[modelId] ?? modelId;
 }
+
+const MODELS_WITH_1M_CONTEXT = new Set([
+  "claude-opus-4-6",
+  "claude-sonnet-4-6",
+]);
+
+export function supports1MContext(modelId: string): boolean {
+  return MODELS_WITH_1M_CONTEXT.has(modelId);
+}
+
+export function getDefaultContextWindow(modelId: string): number {
+  return supports1MContext(modelId) ? 1_000_000 : 200_000;
+}
+
+const MODELS_WITH_EFFORT = new Set([
+  "claude-opus-4-5",
+  "claude-opus-4-6",
+  "claude-sonnet-4-6",
+]);
+
+const MODELS_WITH_MAX_EFFORT = new Set(["claude-opus-4-6"]);
+
+export function supportsEffort(modelId: string): boolean {
+  return MODELS_WITH_EFFORT.has(modelId);
+}
+
+export function supportsMaxEffort(modelId: string): boolean {
+  return MODELS_WITH_MAX_EFFORT.has(modelId);
+}
+
+interface EffortOption {
+  value: string;
+  name: string;
+}
+
+export function getEffortOptions(modelId: string): EffortOption[] | null {
+  if (!supportsEffort(modelId)) return null;
+
+  const options: EffortOption[] = [
+    { value: "low", name: "Low" },
+    { value: "medium", name: "Medium" },
+    { value: "high", name: "High" },
+  ];
+
+  if (supportsMaxEffort(modelId)) {
+    options.push({ value: "max", name: "Max" });
+  }
+
+  return options;
+}