fix(models): advertise the context window Kiro actually serves

src/__tests__/context-windows.test.ts

@@ -0,0 +1,48 @@
+import { describe, expect, test } from 'bun:test'
+import { getModelContextWindow } from '../plugin/context-windows.js'
+import { getContextWindowSize } from '../plugin/models.js'
+
+describe('getModelContextWindow', () => {
+  test('returns the measured 600K family regardless of the -thinking suffix', () => {
+    for (const id of [
+      'auto',
+      'claude-opus-4-7',
+      'claude-opus-4-8',
+      'claude-opus-5',
+      'claude-opus-5-5',
+      'claude-sonnet-5',
+      'claude-sonnet-5-5',
+      'claude-fable-5-1'
+    ]) {
+      expect(getModelContextWindow(id)).toBe(600_000)
+      expect(getModelContextWindow(`${id}-thinking`)).toBe(600_000)
+    }
+  })
+
+  test('returns 1M only for the models the service really serves at 1M', () => {
+    expect(getModelContextWindow('claude-opus-4-6')).toBe(1_000_000)
+    expect(getModelContextWindow('claude-sonnet-4-6')).toBe(1_000_000)
+    expect(getModelContextWindow('claude-opus-4-6-1m')).toBe(1_000_000)
+    expect(getModelContextWindow('claude-sonnet-4-6-1m-thinking')).toBe(1_000_000)
+  })
+
+  test('returns 200K for the older Claude models and unknown ids', () => {
+    expect(getModelContextWindow('claude-sonnet-4-5')).toBe(200_000)
+    expect(getModelContextWindow('claude-haiku-4-5')).toBe(200_000)
+    expect(getModelContextWindow('claude-opus-4-5')).toBe(200_000)
+    expect(getModelContextWindow('brand-new-model')).toBe(200_000)
+  })
+
+  test('keeps the open-weight windows', () => {
+    expect(getModelContextWindow('deepseek-3.2')).toBe(128_000)
+    expect(getModelContextWindow('minimax-m2.5')).toBe(196_000)
+    expect(getModelContextWindow('qwen3-coder-next')).toBe(256_000)
+  })
+
+  test('getContextWindowSize delegates to the measured table', () => {
+    expect(getContextWindowSize('claude-opus-5-5')).toBe(600_000)
+    expect(getContextWindowSize('claude-opus-5')).toBe(600_000)
+    expect(getContextWindowSize('claude-opus-4-6')).toBe(1_000_000)
+    expect(getContextWindowSize('claude-sonnet-4-5')).toBe(200_000)
+  })
+})

src/__tests__/model-registry.test.ts

@@ -27,11 +27,13 @@ describe('model registry', () => {
       [
         'claude-opus-4-5-thinking',
         'claude-opus-4-6-thinking',
+        'claude-opus-4-6-1m-thinking',
         'claude-opus-4-7-thinking',
         'claude-opus-4-8-thinking',
         'claude-opus-5-thinking',
         'claude-sonnet-4-5-thinking',
         'claude-sonnet-4-6-thinking',
+        'claude-sonnet-4-6-1m-thinking',
         'claude-sonnet-5-thinking'
       ].sort()
     )
@@ -94,10 +96,20 @@ describe('model registry', () => {
   })
 
   test('carries limit and modalities through to both entries', () => {
-    expect(registry['claude-opus-5'].limit).toEqual({ context: 1000000, output: 64000 })
+    // 5.x is advertised as 1M but the service caps it at 600K (measured 2026-11-03).
+    expect(registry['claude-opus-5'].limit).toEqual({ context: 600000, output: 64000 })
     expect(registry['claude-opus-5-thinking'].limit).toEqual(registry['claude-opus-5'].limit)
     expect(registry['claude-opus-5-thinking'].modalities).toEqual(
       registry['claude-opus-5'].modalities
     )
   })
+
+  test('advertises the measured served window per model family', () => {
+    expect(registry['claude-sonnet-4-5'].limit.context).toBe(200000)
+    expect(registry['claude-opus-4-6'].limit.context).toBe(1000000)
+    expect(registry['claude-opus-4-6-1m'].limit.context).toBe(1000000)
+    expect(registry['claude-opus-4-7'].limit.context).toBe(600000)
+    expect(registry['claude-opus-4-8'].limit.context).toBe(600000)
+    expect(registry['auto'].limit.context).toBe(600000)
+  })
 })

src/plugin/context-windows.ts

@@ -0,0 +1,83 @@
+/**
+ * Context windows the Kiro backend actually serves.
+ *
+ * The numbers in Kiro's marketing material are not what the Q layer enforces.
+ * The only reliable way to find the real ceiling is to send an oversized
+ * `generateAssistantResponse` payload and watch `contextUsagePercentage` climb
+ * to ~100% before the service answers
+ * `{"message":"Input is too long.","reason":"CONTENT_LENGTH_EXCEEDS_THRESHOLD"}`.
+ *
+ * Measured 2026-11-03 against a Kiro Pro Max (Q_DEVELOPER_STANDALONE_PRO_MAX)
+ * account, growing a single prompt through 1.8M / 2.1M / 2.4M / 2.7M chars:
+ *
+ * - claude-sonnet-4-5, claude-haiku-4-5, claude-opus-4-5 : 200K
+ * - claude-opus-4-6, claude-sonnet-4-6 (and -1m)        : 1M
+ * - claude-opus-4-7, claude-opus-4-8, claude-opus-5,
+ *   claude-opus-5-5, claude-sonnet-5, claude-sonnet-5-5,
+ *   claude-fable-5-1, auto                             : 600K
+ *
+ * (claude-sonnet-5-1m and claude-opus-4-7-1m are rejected by the service with
+ * INVALID_MODEL_ID today, so they are not advertised in the registry.)
+ *
+ * This table is the single source of truth for BOTH:
+ *  - the `limit.context` advertised to OpenCode, and
+ *  - the denominator used to turn `contextUsagePercentage` into real tokens.
+ *
+ * Splitting the two was the original bug: the registry advertised 1M while
+ * `getContextWindowSize()` fell back to 200K for any id without a `-1m`
+ * suffix, so reported input tokens were ~2.75x too low on 5.x models and
+ * auto-compaction never fired.
+ *
+ * Keyed by the OpenCode-facing model id.
+ */
+export const DEFAULT_CONTEXT_WINDOW = 200_000
+
+/** Output cap shared by every model the plugin advertises (Kiro's P_T max). */
+export const OUTPUT_TOKEN_LIMIT = 64_000
+
+/** Served at the full 1M. */
+const LONG_CONTEXT_MODELS = new Set(['claude-opus-4-6', 'claude-sonnet-4-6'])
+
+/** Advertised as 1M, actually capped at 600K by the service. */
+const SIX_HUNDRED_K_MODELS = new Set([
+  'auto',
+  'claude-opus-4-7',
+  'claude-opus-4-8',
+  'claude-opus-5',
+  'claude-opus-5-5',
+  'claude-sonnet-5',
+  'claude-sonnet-5-5',
+  'claude-fable-5-1'
+])
+
+/** Open-weight and legacy models with per-model windows instead of the Claude defaults. */
+const EXPLICIT_WINDOWS: Readonly<Record<string, number>> = {
+  'deepseek-3.2': 128_000,
+  'minimax-m2.1': 196_000,
+  'minimax-m2.5': 196_000,
+  'qwen3-coder-next': 256_000,
+  'glm-5': 200_000
+}
+
+function stripThinkingSuffix(model: string): string {
+  return model.endsWith('-thinking') ? model.slice(0, -'-thinking'.length) : model
+}
+
+/**
+ * Resolve the input-token window Kiro serves for an OpenCode-facing model id.
+ *
+ * Accepts both the base id (`claude-opus-5-5`) and its `-thinking` companion.
+ * Unknown ids fall back to the conservative 200K so a newly added model never
+ * overflows before we have measured it.
+ */
+export function getModelContextWindow(model: string): number {
+  const base = stripThinkingSuffix(model)
+
+  const explicit = EXPLICIT_WINDOWS[base]
+  if (explicit !== undefined) return explicit
+
+  if (LONG_CONTEXT_MODELS.has(base) || base.includes('-1m')) return 1_000_000
+  if (SIX_HUNDRED_K_MODELS.has(base)) return 600_000
+
+  return DEFAULT_CONTEXT_WINDOW
+}

src/plugin/model-registry.ts

@@ -1,3 +1,4 @@
+import { OUTPUT_TOKEN_LIMIT, getModelContextWindow } from './context-windows.js'
 import { EFFORT_LEVELS, supportsEffort, supportsXHighEffort, THINKING_BUDGETS } from './effort.js'
 import { resolveKiroModel } from './models.js'
 
@@ -10,15 +11,11 @@ const TEXT_ONLY: Modalities = { input: ['text'], output: ['text'] }
 const TEXT_IMAGE: Modalities = { input: ['text', 'image'], output: ['text'] }
 const MULTIMODAL: Modalities = { input: ['text', 'image', 'pdf'], output: ['text'] }
 
-const CONTEXT_200K = { context: 200000, output: 64000 }
-const CONTEXT_1M = { context: 1000000, output: 64000 }
-
 interface ModelSpec {
   /** Display name, without the credit multiplier suffix. */
   name: string
   /** Kiro credit multiplier, rendered into the display name. */
   rate: string
-  limit: { context: number; output: number }
   modalities: Modalities
   /**
    * Emit a companion `-thinking` entry. Only set for Claude models that accept
@@ -34,35 +31,41 @@ interface ModelSpec {
  * Anthropic and open-weight models only. Kiro's GPT-5.6 tiers are deliberately
  * absent: they configure reasoning through `reasoning.effort` / `reasoning.mode`
  * rather than `output_config.effort`, so they need their own request path.
+ *
+ * The context window is NOT declared here — `getModelContextWindow()` owns it,
+ * because the advertised limit and the denominator for `contextUsagePercentage`
+ * must always agree (see context-windows.ts).
  */
 const MODEL_SPECS: Record<string, ModelSpec> = {
-  auto: { name: 'Auto', rate: '1.0x', limit: CONTEXT_200K, modalities: MULTIMODAL },
+  auto: { name: 'Auto', rate: '1.0x', modalities: MULTIMODAL },
 
   // Claude Sonnet
   'claude-sonnet-4': {
     name: 'Claude Sonnet 4.0',
     rate: '1.3x',
-    limit: CONTEXT_200K,
     modalities: MULTIMODAL
   },
   'claude-sonnet-4-5': {
     name: 'Claude Sonnet 4.5',
     rate: '1.3x',
-    limit: CONTEXT_200K,
     modalities: MULTIMODAL,
     thinking: true
   },
   'claude-sonnet-4-6': {
     name: 'Claude Sonnet 4.6',
     rate: '1.3x',
-    limit: CONTEXT_1M,
+    modalities: MULTIMODAL,
+    thinking: true
+  },
+  'claude-sonnet-4-6-1m': {
+    name: 'Claude Sonnet 4.6 1M',
+    rate: '1.3x',
     modalities: MULTIMODAL,
     thinking: true
   },
   'claude-sonnet-5': {
     name: 'Claude Sonnet 5',
     rate: '1.3x',
-    limit: CONTEXT_1M,
     modalities: MULTIMODAL,
     thinking: true
   },
@@ -71,43 +74,43 @@ const MODEL_SPECS: Record<string, ModelSpec> = {
   'claude-haiku-4-5': {
     name: 'Claude Haiku 4.5',
     rate: '0.4x',
-    limit: CONTEXT_200K,
     modalities: TEXT_IMAGE
   },
 
   // Claude Opus
   'claude-opus-4-5': {
     name: 'Claude Opus 4.5',
     rate: '2.2x',
-    limit: CONTEXT_200K,
     modalities: MULTIMODAL,
     thinking: true
   },
   'claude-opus-4-6': {
     name: 'Claude Opus 4.6',
     rate: '2.2x',
-    limit: CONTEXT_1M,
+    modalities: MULTIMODAL,
+    thinking: true
+  },
+  'claude-opus-4-6-1m': {
+    name: 'Claude Opus 4.6 1M',
+    rate: '2.2x',
     modalities: MULTIMODAL,
     thinking: true
   },
   'claude-opus-4-7': {
     name: 'Claude Opus 4.7',
     rate: '2.2x',
-    limit: CONTEXT_1M,
     modalities: MULTIMODAL,
     thinking: true
   },
   'claude-opus-4-8': {
     name: 'Claude Opus 4.8',
     rate: '2.2x',
-    limit: CONTEXT_1M,
     modalities: MULTIMODAL,
     thinking: true
   },
   'claude-opus-5': {
     name: 'Claude Opus 5',
     rate: '2.2x',
-    limit: CONTEXT_1M,
     modalities: MULTIMODAL,
     thinking: true
   },
@@ -116,26 +119,22 @@ const MODEL_SPECS: Record<string, ModelSpec> = {
   'deepseek-3.2': {
     name: 'DeepSeek 3.2',
     rate: '0.25x',
-    limit: { context: 128000, output: 64000 },
     modalities: TEXT_ONLY
   },
-  'glm-5': { name: 'GLM-5', rate: '0.5x', limit: CONTEXT_200K, modalities: TEXT_ONLY },
+  'glm-5': { name: 'GLM-5', rate: '0.5x', modalities: TEXT_ONLY },
   'minimax-m2.5': {
     name: 'MiniMax M2.5',
     rate: '0.25x',
-    limit: { context: 196000, output: 64000 },
     modalities: TEXT_ONLY
   },
   'minimax-m2.1': {
     name: 'MiniMax M2.1',
     rate: '0.15x',
-    limit: { context: 196000, output: 64000 },
     modalities: TEXT_ONLY
   },
   'qwen3-coder-next': {
     name: 'Qwen3 Coder Next',
     rate: '0.05x',
-    limit: { context: 256000, output: 64000 },
     modalities: TEXT_ONLY
   }
 }
@@ -170,9 +169,14 @@ export function buildModelRegistry(): Record<string, unknown> {
   const models: Record<string, unknown> = {}
 
   for (const [modelID, spec] of Object.entries(MODEL_SPECS)) {
+    const limit = {
+      context: getModelContextWindow(modelID),
+      output: OUTPUT_TOKEN_LIMIT
+    }
+
     models[modelID] = {
       name: `${spec.name} (${spec.rate})`,
-      limit: spec.limit,
+      limit,
       modalities: spec.modalities
     }
 
@@ -185,7 +189,7 @@ export function buildModelRegistry(): Record<string, unknown> {
 
     models[`${modelID}-thinking`] = {
       name: `${spec.name} Thinking (${spec.rate})`,
-      limit: spec.limit,
+      limit,
       modalities: spec.modalities,
       reasoning: true,
       interleaved: { field: 'reasoning_content' },

src/plugin/models.ts

@@ -1,4 +1,5 @@
-import { MODEL_MAPPING, SUPPORTED_MODELS, isLongContextModel } from '../constants'
+import { MODEL_MAPPING, SUPPORTED_MODELS } from '../constants'
+import { getModelContextWindow } from './context-windows.js'
 
 export function resolveKiroModel(model: string): string {
   const resolved = MODEL_MAPPING[model]
@@ -8,6 +9,13 @@ export function resolveKiroModel(model: string): string {
   return resolved
 }
 
+/**
+ * Input-token window Kiro serves for this model.
+ *
+ * Delegates to the measured table in `context-windows.ts`; the old
+ * `-1m`-suffix heuristic returned 200K for the 5.x models, which are actually
+ * served at 600K, so every reported token count was ~2.75x too low.
+ */
 export function getContextWindowSize(model: string): number {
-  return isLongContextModel(model) ? 1000000 : 200000
-}
+  return getModelContextWindow(model)
+}