diff --git a/packages/agent-core-v2/src/agent/fullCompaction/fullCompactionService.ts b/packages/agent-core-v2/src/agent/fullCompaction/fullCompactionService.ts
index e89c49a6ab..4fd66d470d 100644
--- a/packages/agent-core-v2/src/agent/fullCompaction/fullCompactionService.ts
+++ b/packages/agent-core-v2/src/agent/fullCompaction/fullCompactionService.ts
@@ -33,6 +33,7 @@ import {
   isRetryableGenerateError,
 } from '#/kosong/contract/errors';
 import { createUserMessage, type Message } from '#/kosong/contract/message';
+import { getModelInputTokenLimit } from '#/kosong/contract/capability';
 import type { Tool } from '#/kosong/contract/tool';
 import { inputTotal, type TokenUsage } from '#/kosong/contract/usage';
 import { IEventBus } from '#/app/event/eventBus';
@@ -173,7 +174,7 @@ export class AgentFullCompactionService extends Disposable implements IAgentFull
 
   private getEffectiveMaxContextTokens(): number {
     const capability = this.profile.data().modelCapabilities;
-    const configured = capability.max_input_tokens ?? capability.max_context_tokens;
+    const configured = getModelInputTokenLimit(capability);
     const modelAlias = this.profile.data().modelAlias;
     const observed =
       modelAlias === undefined ? undefined : this.observedMaxContextTokensByModel.get(modelAlias);
diff --git a/packages/agent-core-v2/src/agent/fullCompaction/strategy.ts b/packages/agent-core-v2/src/agent/fullCompaction/strategy.ts
index c8ebb8e579..31b5d88235 100644
--- a/packages/agent-core-v2/src/agent/fullCompaction/strategy.ts
+++ b/packages/agent-core-v2/src/agent/fullCompaction/strategy.ts
@@ -1,4 +1,5 @@
 import type { Message } from '#/kosong/contract/message';
+import { getModelInputTokenLimit } from '#/kosong/contract/capability';
 import type { ProfileModelContext } from '#/agent/profile/profile';
 import type { CompactionSource } from './types';
 import { estimateTokensForMessage } from '#/kosong/contract/tokens';
@@ -71,14 +72,14 @@ export class RuntimeCompactionStrategy implements CompactionStrategy {
   private delegate(): DefaultCompactionStrategy {
     const model = this.context();
     return new DefaultCompactionStrategy(
-      () => model.modelCapabilities.max_input_tokens ?? model.modelCapabilities.max_context_tokens,
+      () => getModelInputTokenLimit(model.modelCapabilities),
       this.config(model),
     );
   }
 
   private windowDelegate(): DefaultCompactionStrategy {
     return new DefaultCompactionStrategy(
-      () => this.context().modelCapabilities.max_input_tokens ?? this.context().modelCapabilities.max_context_tokens,
+      () => getModelInputTokenLimit(this.context().modelCapabilities),
       DEFAULT_COMPACTION_CONFIG,
     );
   }
diff --git a/packages/agent-core-v2/src/agent/profile/profileService.ts b/packages/agent-core-v2/src/agent/profile/profileService.ts
index 2dcd419555..f518982833 100644
--- a/packages/agent-core-v2/src/agent/profile/profileService.ts
+++ b/packages/agent-core-v2/src/agent/profile/profileService.ts
@@ -49,7 +49,11 @@
 import { InstantiationType } from '#/_base/di/extensions';
 import { Disposable } from '#/_base/di/lifecycle';
 import { LifecycleScope, registerScopedService } from '#/_base/di/scope';
-import { UNKNOWN_CAPABILITY, type ModelCapability } from '#/kosong/contract/capability';
+import {
+  UNKNOWN_CAPABILITY,
+  getModelInputTokenLimit,
+  type ModelCapability,
+} from '#/kosong/contract/capability';
 import { type SamplingOptions, type ThinkingEffort } from '#/kosong/contract/provider';
 import { IModelCatalog, type Model } from '#/kosong/model/catalog';
 import { type ModelOverrides } from '#/kosong/model/model.types';
@@ -587,9 +591,7 @@ export class AgentProfileService extends Disposable implements IAgentProfileServ
       thinkingEffort: includeThinkingEffort
         ? this.getEffectiveThinkingLevel()
         : undefined,
-      maxContextTokens:
-        this.getModelCapabilities().max_input_tokens ??
-        this.getModelCapabilities().max_context_tokens,
+      maxContextTokens: getModelInputTokenLimit(this.getModelCapabilities()),
     });
   }
 
diff --git a/packages/agent-core-v2/src/app/sessionLegacy/sessionLegacyService.ts b/packages/agent-core-v2/src/app/sessionLegacy/sessionLegacyService.ts
index bf03d35159..69a7afa56d 100644
--- a/packages/agent-core-v2/src/app/sessionLegacy/sessionLegacyService.ts
+++ b/packages/agent-core-v2/src/app/sessionLegacy/sessionLegacyService.ts
@@ -28,6 +28,7 @@ import { IAgentProfileService } from '#/agent/profile/profile';
 import { IAgentSwarmService } from '#/agent/swarm/swarm';
 import { IConfigService } from '#/app/config/config';
 import { IModelCatalog } from '#/kosong/model/catalog';
+import { getModelInputTokenLimit } from '#/kosong/contract/capability';
 import { ISessionLifecycleService } from '#/app/sessionLifecycle/sessionLifecycle';
 import { ErrorCodes, Error2 } from '#/errors';
 import { ensureMainAgent } from '#/session/agentLifecycle/mainAgent';
@@ -160,14 +161,11 @@ export class SessionLegacyService implements ISessionLegacyService {
     const swarm = agent.accessor.get(IAgentSwarmService);
 
     const model = profile.getModel();
-    const caps = profile.getModelCapabilities() as {
-      max_context_tokens?: number;
-      max_input_tokens?: number;
-    };
+    const caps = profile.getModelCapabilities();
     const maxTokens =
       model === ''
         ? resolveDefaultModelContextTokens(agent)
-        : (caps.max_input_tokens ?? caps.max_context_tokens ?? 0);
+        : getModelInputTokenLimit(caps);
     const tokens = contextSize.get().size;
     const planData = await plan.status();
 
@@ -210,7 +208,7 @@ function resolveDefaultModelContextTokens(agent: IAgentScopeHandle): number {
   if (typeof defaultModel !== 'string' || defaultModel.length === 0) return 0;
   try {
     const capabilities = agent.accessor.get(IModelCatalog).get(defaultModel).capabilities;
-    return capabilities.max_input_tokens ?? capabilities.max_context_tokens;
+    return getModelInputTokenLimit(capabilities);
   } catch {
     return 0;
   }
diff --git a/packages/agent-core-v2/src/kosong/contract/capability.ts b/packages/agent-core-v2/src/kosong/contract/capability.ts
index fa75b8187e..273a02f06a 100644
--- a/packages/agent-core-v2/src/kosong/contract/capability.ts
+++ b/packages/agent-core-v2/src/kosong/contract/capability.ts
@@ -5,9 +5,10 @@
  * so callers can gate requests against what the model accepts without
  * dispatching the request and watching it fail upstream.
  *
- * `UNKNOWN_CAPABILITY` is the marker value returned when nothing is known
- * about a model: `max_context_tokens: 0` means "unknown"; callers that do
- * not gate on context length can ignore the field.
+ * `getModelInputTokenLimit` resolves the prompt/input ceiling before callers
+ * make compaction or status decisions. `UNKNOWN_CAPABILITY` is the marker
+ * value returned when nothing is known about a model:
+ * `max_context_tokens: 0` means "unknown".
  */
 
 export interface ModelCapability {
@@ -21,6 +22,10 @@ export interface ModelCapability {
   readonly dynamically_loaded_tools?: boolean;
 }
 
+export function getModelInputTokenLimit(capability: ModelCapability | undefined): number {
+  return capability?.max_input_tokens ?? capability?.max_context_tokens ?? 0;
+}
+
 const UNKNOWN_CAPABILITY_MARKER = Symbol.for('moonshot-ai.kosong.UNKNOWN_CAPABILITY');
 
 export const UNKNOWN_CAPABILITY: ModelCapability = Object.freeze(
diff --git a/packages/agent-core-v2/test/kosong/provider/composition.test.ts b/packages/agent-core-v2/test/kosong/provider/composition.test.ts
index e51b436967..0a0fd5c374 100644
--- a/packages/agent-core-v2/test/kosong/provider/composition.test.ts
+++ b/packages/agent-core-v2/test/kosong/provider/composition.test.ts
@@ -40,7 +40,12 @@
 
 import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
 
-import { isUnknownCapability, UNKNOWN_CAPABILITY } from '#/kosong/contract/capability';
+import {
+  getModelInputTokenLimit,
+  isUnknownCapability,
+  UNKNOWN_CAPABILITY,
+  type ModelCapability,
+} from '#/kosong/contract/capability';
 import { APIConnectionError } from '#/kosong/contract/errors';
 import type { Message } from '#/kosong/contract/message';
 import type {
@@ -300,6 +305,25 @@ describe('resolveCapability', () => {
   });
 });
 
+describe('getModelInputTokenLimit', () => {
+  const capability: ModelCapability = {
+    image_in: false,
+    video_in: false,
+    audio_in: false,
+    thinking: false,
+    tool_use: true,
+    max_context_tokens: 128_000,
+  };
+
+  it.each([
+    ['the declared input cap', { ...capability, max_input_tokens: 64_000 }, 64_000],
+    ['the total context window when no input cap is declared', capability, 128_000],
+    ['zero when the capability is unavailable', undefined, 0],
+  ])('resolves %s', (_label, value, expected) => {
+    expect(getModelInputTokenLimit(value)).toBe(expected);
+  });
+});
+
 describe('explainCapability', () => {
   it('reports the definition level when the pair declares a capability', () => {
     const { capability, source } = registry.explainCapability('openai', 'gpt-4o', 'kimi');
diff --git a/packages/agent-core/src/agent/compaction/full.ts b/packages/agent-core/src/agent/compaction/full.ts
index f56c7bc919..efeccdf00f 100644
--- a/packages/agent-core/src/agent/compaction/full.ts
+++ b/packages/agent-core/src/agent/compaction/full.ts
@@ -16,6 +16,7 @@ import {
   APIRequestTooLargeError,
   APIStatusError,
   createUserMessage,
+  getModelInputTokenLimit,
   isImageFormatError,
 } from '@moonshot-ai/kosong';
 
@@ -125,7 +126,7 @@ export class FullCompaction {
 
   getEffectiveMaxContextTokens(): number {
     const capability = this.agent.config.modelCapabilities;
-    const configured = capability.max_input_tokens ?? capability.max_context_tokens;
+    const configured = getModelInputTokenLimit(capability);
     const modelAlias = this.agent.config.modelAlias;
     const observed =
       modelAlias === undefined ? undefined : this.observedMaxContextTokensByModel.get(modelAlias);
diff --git a/packages/agent-core/src/agent/context/index.ts b/packages/agent-core/src/agent/context/index.ts
index 2ac5096e76..e2f2716375 100644
--- a/packages/agent-core/src/agent/context/index.ts
+++ b/packages/agent-core/src/agent/context/index.ts
@@ -1,4 +1,9 @@
-import { createToolMessage, type ContentPart, type Message } from '@moonshot-ai/kosong';
+import {
+  createToolMessage,
+  getModelInputTokenLimit,
+  type ContentPart,
+  type Message,
+} from '@moonshot-ai/kosong';
 
 import type { Agent } from '..';
 import { ErrorCodes, KimiError } from '../../errors';
@@ -220,7 +225,7 @@ export class ContextMemory {
     const importTokenCount = estimateTokensForMessages([message]);
     const totalTokenCount = currentTokenCount + importTokenCount;
     const capability = this.agent.config.modelCapabilities;
-    const maxContextTokens = capability.max_input_tokens ?? capability.max_context_tokens;
+    const maxContextTokens = getModelInputTokenLimit(capability);
     if (maxContextTokens > 0 && totalTokenCount > maxContextTokens) {
       throw new KimiError(
         ErrorCodes.CONTEXT_OVERFLOW,
diff --git a/packages/agent-core/src/agent/index.ts b/packages/agent-core/src/agent/index.ts
index 26a2efe99c..09b7eba284 100644
--- a/packages/agent-core/src/agent/index.ts
+++ b/packages/agent-core/src/agent/index.ts
@@ -6,7 +6,7 @@ import { ErrorCodes, KimiError, makeErrorPayload } from '#/errors';
 import { log } from '#/logging/logger';
 import type { Logger } from '#/logging/types';
 import type { AgentAPI, AgentEvent, KimiConfig, SDKAgentRPC, UsageStatus } from '#/rpc';
-import { generate, type ChatProvider } from '@moonshot-ai/kosong';
+import { generate, getModelInputTokenLimit, type ChatProvider } from '@moonshot-ai/kosong';
 
 import type { EnabledPluginSessionStart, PluginCommandDef } from '#/plugin';
 import { expandCommandArguments } from '../plugin/commands';
@@ -674,7 +674,7 @@ export class Agent {
 
     const contextTokens = this.context.tokenCount;
     const capability = this.config.modelCapabilities;
-    const maxContextTokens = capability.max_input_tokens ?? capability.max_context_tokens;
+    const maxContextTokens = getModelInputTokenLimit(capability);
     const contextUsage =
       maxContextTokens !== undefined && maxContextTokens > 0
         ? contextTokens / maxContextTokens
diff --git a/packages/agent-core/src/index.ts b/packages/agent-core/src/index.ts
index 46b97172a5..2efff073f0 100644
--- a/packages/agent-core/src/index.ts
+++ b/packages/agent-core/src/index.ts
@@ -20,6 +20,7 @@ export {
 export { resolveLoggingConfig } from './logging/resolve-config';
 export type { ResolveLoggingInput } from './logging/resolve-config';
 export { installGlobalProxyDispatcher } from './utils/proxy';
+export { getModelInputTokenLimit } from '@moonshot-ai/kosong';
 export type {
   LogContext,
   LogEntry,
diff --git a/packages/agent-core/src/services/session/sessionService.ts b/packages/agent-core/src/services/session/sessionService.ts
index 8424f30457..7902267356 100644
--- a/packages/agent-core/src/services/session/sessionService.ts
+++ b/packages/agent-core/src/services/session/sessionService.ts
@@ -23,6 +23,7 @@ import {
   type UndoSessionRequest,
   type UndoSessionResponse,
 } from '@moonshot-ai/protocol';
+import { getModelInputTokenLimit } from '@moonshot-ai/kosong';
 
 import { IApprovalService } from '../approval/approval';
 import { ICoreProcessService } from '../coreProcess/coreProcess';
@@ -473,7 +474,7 @@ export class SessionService extends Disposable implements ISessionService {
     ]);
 
     const capability = config.modelCapabilities;
-    const maxContextTokens = capability?.max_input_tokens ?? capability?.max_context_tokens ?? 0;
+    const maxContextTokens = getModelInputTokenLimit(capability);
     const contextTokens = context.tokenCount;
     const contextUsage = maxContextTokens > 0 ? Math.min(1, contextTokens / maxContextTokens) : 0;
 
diff --git a/packages/kap-server/src/services/legacyStatus/legacyStatus.ts b/packages/kap-server/src/services/legacyStatus/legacyStatus.ts
index c70057c034..1c8819fe8a 100644
--- a/packages/kap-server/src/services/legacyStatus/legacyStatus.ts
+++ b/packages/kap-server/src/services/legacyStatus/legacyStatus.ts
@@ -20,6 +20,7 @@ import {
   IAgentProfileService,
   IAgentUsageService,
   IWireService,
+  getModelInputTokenLimit,
   type IAgentScopeHandle,
   type UsageStatus,
 } from '@moonshot-ai/agent-core-v2';
@@ -134,7 +135,7 @@ export function readLegacyStatus(agent: IAgentScopeHandle): LegacyStatusSnapshot
   const measured = wire.getModel(ContextSizeModel);
   const contextTokens = Math.max(contextSize.get().size, measured.tokens);
   const capabilities = profile.getModelCapabilities();
-  const maxContextTokens = capabilities.max_input_tokens ?? capabilities.max_context_tokens;
+  const maxContextTokens = getModelInputTokenLimit(capabilities);
   const model = profile.getModel();
   return { usage, contextTokens, maxContextTokens, model };
 }
diff --git a/packages/kosong/src/capability.ts b/packages/kosong/src/capability.ts
index f2d8249908..99c44c7d31 100644
--- a/packages/kosong/src/capability.ts
+++ b/packages/kosong/src/capability.ts
@@ -33,6 +33,11 @@ export interface ModelCapability {
   readonly dynamically_loaded_tools?: boolean;
 }
 
+/** Return the model's prompt/input limit, or 0 when the limit is unknown. */
+export function getModelInputTokenLimit(capability: ModelCapability | undefined): number {
+  return capability?.max_input_tokens ?? capability?.max_context_tokens ?? 0;
+}
+
 const UNKNOWN_CAPABILITY_MARKER = Symbol.for('moonshot-ai.kosong.UNKNOWN_CAPABILITY');
 
 /**
diff --git a/packages/kosong/src/index.ts b/packages/kosong/src/index.ts
index d999a02bc6..f68c078cec 100644
--- a/packages/kosong/src/index.ts
+++ b/packages/kosong/src/index.ts
@@ -34,7 +34,7 @@ export { KimiChatProvider } from './providers/kimi';
 export type { ExtraBody, GenerationKwargs, KimiOptions, ThinkingConfig } from './providers/kimi';
 
 // Model capability matrix
-export { isUnknownCapability, UNKNOWN_CAPABILITY } from './capability';
+export { getModelInputTokenLimit, isUnknownCapability, UNKNOWN_CAPABILITY } from './capability';
 export type { ModelCapability } from './capability';
 
 // Model catalog (models.dev-style) metadata
diff --git a/packages/kosong/test/capability.test.ts b/packages/kosong/test/capability.test.ts
index 93846103b0..e7df01ea64 100644
--- a/packages/kosong/test/capability.test.ts
+++ b/packages/kosong/test/capability.test.ts
@@ -1,13 +1,35 @@
 /**
- * `ModelCapability` type and `UNKNOWN_CAPABILITY` default — pure
+ * `ModelCapability` type, input-limit resolution, and `UNKNOWN_CAPABILITY` default — pure
  * type/helper layer. Per-wire `getModelCapability` tables live in
  * `capability-providers.test.ts`.
  */
 
-import { UNKNOWN_CAPABILITY, isUnknownCapability, type ModelCapability } from '#/capability';
+import {
+  UNKNOWN_CAPABILITY,
+  getModelInputTokenLimit,
+  isUnknownCapability,
+  type ModelCapability,
+} from '#/capability';
 import { describe, expect, it } from 'vitest';
 
 describe('ModelCapability / UNKNOWN_CAPABILITY', () => {
+  const capability: ModelCapability = {
+    image_in: false,
+    video_in: false,
+    audio_in: false,
+    thinking: false,
+    tool_use: true,
+    max_context_tokens: 128_000,
+  };
+
+  it.each([
+    ['the declared input cap', { ...capability, max_input_tokens: 64_000 }, 64_000],
+    ['the total context window when no input cap is declared', capability, 128_000],
+    ['zero when the capability is unavailable', undefined, 0],
+  ])('resolves %s', (_label, value, expected) => {
+    expect(getModelInputTokenLimit(value)).toBe(expected);
+  });
+
   it('UNKNOWN_CAPABILITY has all boolean fields false', () => {
     expect(UNKNOWN_CAPABILITY.image_in).toBe(false);
     expect(UNKNOWN_CAPABILITY.video_in).toBe(false);
diff --git a/packages/node-sdk/src/rpc.ts b/packages/node-sdk/src/rpc.ts
index 1315812c0b..4d80915f45 100644
--- a/packages/node-sdk/src/rpc.ts
+++ b/packages/node-sdk/src/rpc.ts
@@ -2,6 +2,7 @@ import { AsyncLocalStorage } from 'node:async_hooks';
 
 import {
   ErrorCodes,
+  getModelInputTokenLimit,
   makeErrorPayload,
   type AgentContextData,
   type ApprovalRequest,
@@ -579,7 +580,7 @@ export abstract class SDKRpcClientBase {
       agentId,
     });
     const capability = config.modelCapabilities;
-    const maxContextTokens = capability?.max_input_tokens ?? capability?.max_context_tokens ?? 0;
+    const maxContextTokens = getModelInputTokenLimit(capability);
     const contextTokens = context.tokenCount;
     // Deliberately unclamped: >100% is the documented overflow signal on this
     // path (see acp-adapter's formatContextUsage), unlike the schema-bounded