fix(openai): scope prompt cache key to official endpoint, unify usage mapping, tier ChatGPT model routing (claude-code-best#1300)

Co-authored-by: DavidShawa <DavidShawa@users.noreply.github.com>

Author: claude-code-best

packages/@ant/model-provider/src/index.ts

@@ -67,3 +67,7 @@ export {
   anthropicToolChoiceToOpenAI,
 } from './shared/openaiConvertTools.js'
 export { adaptOpenAIStreamToAnthropic } from './shared/openaiStreamAdapter.js'
+export {
+  normalizeOpenAIUsage,
+  type AnthropicUsage,
+} from './shared/openaiUsage.js'

packages/@ant/model-provider/src/shared/__tests__/openaiStreamAdapter.test.ts

@@ -34,11 +34,15 @@ function makeChunk(
 }
 
 /** Collect all emitted Anthropic events from the stream adapter for assertion */
-async function collectEvents(chunks: ChatCompletionChunk[]) {
+async function collectEvents(
+  chunks: ChatCompletionChunk[],
+  options?: { includeCacheWriteTokens?: boolean },
+) {
   const events: any[] = []
   for await (const event of adaptOpenAIStreamToAnthropic(
     mockStream(chunks),
     'gpt-4o',
+    options,
   )) {
     events.push(event)
   }
@@ -521,6 +525,60 @@ describe('thinking support (reasoning_content)', () => {
 })
 
 describe('prompt caching support', () => {
+  test('maps official OpenAI cache writes when explicitly enabled', async () => {
+    const events = await collectEvents(
+      [
+        makeChunk({
+          choices: [
+            { index: 0, delta: { content: 'hi' }, finish_reason: null },
+          ],
+        }),
+        makeChunk({
+          choices: [{ index: 0, delta: {}, finish_reason: 'stop' }],
+          usage: {
+            prompt_tokens: 1000,
+            completion_tokens: 50,
+            total_tokens: 1050,
+            prompt_tokens_details: {
+              cached_tokens: 600,
+              cache_write_tokens: 250,
+            },
+          } as any,
+        }),
+      ],
+      { includeCacheWriteTokens: true },
+    )
+
+    const msgDelta = events.find(e => e.type === 'message_delta') as any
+    expect(msgDelta.usage.input_tokens).toBe(150)
+    expect(msgDelta.usage.cache_read_input_tokens).toBe(600)
+    expect(msgDelta.usage.cache_creation_input_tokens).toBe(250)
+  })
+
+  test('ignores cache writes for compatible providers by default', async () => {
+    const events = await collectEvents([
+      makeChunk({
+        choices: [{ index: 0, delta: { content: 'hi' }, finish_reason: null }],
+      }),
+      makeChunk({
+        choices: [{ index: 0, delta: {}, finish_reason: 'stop' }],
+        usage: {
+          prompt_tokens: 1000,
+          completion_tokens: 50,
+          total_tokens: 1050,
+          prompt_tokens_details: {
+            cached_tokens: 600,
+            cache_write_tokens: 250,
+          },
+        } as any,
+      }),
+    ])
+
+    const msgDelta = events.find(e => e.type === 'message_delta') as any
+    expect(msgDelta.usage.input_tokens).toBe(400)
+    expect(msgDelta.usage.cache_creation_input_tokens).toBe(0)
+  })
+
   test('maps cached_tokens to cache_read_input_tokens', async () => {
     const events = await collectEvents([
       makeChunk({

packages/@ant/model-provider/src/shared/__tests__/openaiUsage.test.ts

@@ -0,0 +1,52 @@
+import { describe, expect, test } from 'bun:test'
+import { normalizeOpenAIUsage } from '../openaiUsage.js'
+
+describe('normalizeOpenAIUsage', () => {
+  test('partitions total input into ordinary, cache-read, and cache-write tokens', () => {
+    expect(
+      normalizeOpenAIUsage({
+        totalInputTokens: 1000,
+        outputTokens: 50,
+        cacheReadTokens: 600,
+        cacheWriteTokens: 250,
+      }),
+    ).toEqual({
+      input_tokens: 150,
+      output_tokens: 50,
+      cache_creation_input_tokens: 250,
+      cache_read_input_tokens: 600,
+    })
+  })
+
+  test('clamps overlapping cache segments to the total input', () => {
+    expect(
+      normalizeOpenAIUsage({
+        totalInputTokens: 5000,
+        outputTokens: 10,
+        cacheReadTokens: 4000,
+        cacheWriteTokens: 4000,
+      }),
+    ).toEqual({
+      input_tokens: 0,
+      output_tokens: 10,
+      cache_creation_input_tokens: 1000,
+      cache_read_input_tokens: 4000,
+    })
+  })
+
+  test('clamps negative provider values to zero', () => {
+    expect(
+      normalizeOpenAIUsage({
+        totalInputTokens: -1,
+        outputTokens: -2,
+        cacheReadTokens: -3,
+        cacheWriteTokens: -4,
+      }),
+    ).toEqual({
+      input_tokens: 0,
+      output_tokens: 0,
+      cache_creation_input_tokens: 0,
+      cache_read_input_tokens: 0,
+    })
+  })
+})

packages/@ant/model-provider/src/shared/openaiStreamAdapter.ts

@@ -1,6 +1,7 @@
 import type { BetaRawMessageStreamEvent } from '@anthropic-ai/sdk/resources/beta/messages/messages.mjs'
 import type { ChatCompletionChunk } from 'openai/resources/chat/completions/completions.mjs'
 import { randomUUID } from 'crypto'
+import { normalizeOpenAIUsage } from './openaiUsage.js'
 
 /**
  * Adapt an OpenAI streaming response into Anthropic BetaRawMessageStreamEvent.
@@ -13,10 +14,10 @@ import { randomUUID } from 'crypto'
  *   finish_reason            → message_delta(stop_reason) + message_stop
  *
  * Usage field mapping (OpenAI → Anthropic):
- *   prompt_tokens - cached_tokens             → input_tokens (non-cached input only)
+ *   prompt_tokens - cached_tokens - cache_write_tokens → input_tokens
  *   completion_tokens                         → output_tokens
  *   prompt_tokens_details.cached_tokens       → cache_read_input_tokens
- *   (no OpenAI equivalent)                    → cache_creation_input_tokens (always 0)
+ *   prompt_tokens_details.cache_write_tokens  → cache_creation_input_tokens
  *
  *   All four fields are emitted in the post-loop message_delta (not message_start)
  *   so that trailing usage chunks (sent after finish_reason by some
@@ -35,6 +36,7 @@ import { randomUUID } from 'crypto'
 export async function* adaptOpenAIStreamToAnthropic(
   stream: AsyncIterable<ChatCompletionChunk>,
   model: string,
+  options?: { includeCacheWriteTokens?: boolean },
 ): AsyncGenerator<BetaRawMessageStreamEvent, void> {
   const messageId = `msg_${randomUUID().replace(/-/g, '').slice(0, 24)}`
 
@@ -53,13 +55,13 @@ export async function* adaptOpenAIStreamToAnthropic(
   // Track text block state
   let textBlockOpen = false
 
-  // Track usage — all four Anthropic fields, populated from OpenAI usage fields:
-  // rawInputTokens tracks the raw prompt_tokens (OpenAI total, including cached).
-  // inputTokens is the derived Anthropic value (non-cached only = rawInputTokens - cachedReadTokens).
+  // Track raw OpenAI usage across chunks. The normalized Anthropic fields are
+  // disjoint: ordinary input + cache reads + cache writes = total input.
   let rawInputTokens = 0
-  let inputTokens = 0
   let outputTokens = 0
-  let cachedReadTokens = 0
+  let rawCacheReadTokens = 0
+  let rawCacheWriteTokens = 0
+  let usage = normalizeOpenAIUsage({ totalInputTokens: 0, outputTokens: 0 })
 
   // Track all open content block indices (for cleanup)
   const openBlockIndices = new Set<number>()
@@ -75,16 +77,32 @@ export async function* adaptOpenAIStreamToAnthropic(
     // Extract usage from any chunk that carries it.
     if (chunk.usage) {
       rawInputTokens = chunk.usage.prompt_tokens ?? rawInputTokens
-      const rawCached =
-        ((chunk.usage as any).prompt_tokens_details?.cached_tokens as
-          | number
-          | undefined) ?? cachedReadTokens
-      // Anthropic's input_tokens = non-cached input only. OpenAI's prompt_tokens
-      // includes cached tokens, so subtract. Clamp to 0 in case cached > total
-      // due to a streaming race.
-      inputTokens = Math.max(0, rawInputTokens - rawCached)
       outputTokens = chunk.usage.completion_tokens ?? outputTokens
-      cachedReadTokens = rawCached
+
+      const usageRecord = chunk.usage as unknown as Record<string, unknown>
+      const detailsValue = usageRecord.prompt_tokens_details
+      const details =
+        detailsValue && typeof detailsValue === 'object'
+          ? (detailsValue as Record<string, unknown>)
+          : undefined
+      if (typeof details?.cached_tokens === 'number') {
+        rawCacheReadTokens = details.cached_tokens
+      }
+      if (
+        options?.includeCacheWriteTokens &&
+        typeof details?.cache_write_tokens === 'number'
+      ) {
+        rawCacheWriteTokens = details.cache_write_tokens
+      } else if (!options?.includeCacheWriteTokens) {
+        rawCacheWriteTokens = 0
+      }
+
+      usage = normalizeOpenAIUsage({
+        totalInputTokens: rawInputTokens,
+        outputTokens,
+        cacheReadTokens: rawCacheReadTokens,
+        cacheWriteTokens: rawCacheWriteTokens,
+      })
     }
 
     // Emit message_start on first chunk
@@ -102,10 +120,8 @@ export async function* adaptOpenAIStreamToAnthropic(
           stop_reason: null,
           stop_sequence: null,
           usage: {
-            input_tokens: inputTokens,
+            ...usage,
             output_tokens: 0,
-            cache_creation_input_tokens: 0,
-            cache_read_input_tokens: cachedReadTokens,
           },
         },
       } as unknown as BetaRawMessageStreamEvent
@@ -312,12 +328,7 @@ export async function* adaptOpenAIStreamToAnthropic(
         stop_reason: stopReason,
         stop_sequence: null,
       },
-      usage: {
-        input_tokens: inputTokens,
-        output_tokens: outputTokens,
-        cache_read_input_tokens: cachedReadTokens,
-        cache_creation_input_tokens: 0,
-      },
+      usage,
     } as BetaRawMessageStreamEvent
 
     yield {

packages/@ant/model-provider/src/shared/openaiUsage.ts

@@ -0,0 +1,35 @@
+export type AnthropicUsage = {
+  input_tokens: number
+  output_tokens: number
+  cache_creation_input_tokens: number
+  cache_read_input_tokens: number
+}
+
+/**
+ * Convert OpenAI's total-input usage into Anthropic's disjoint usage fields.
+ * Cache reads take priority when malformed provider data makes segments overlap.
+ */
+export function normalizeOpenAIUsage(params: {
+  totalInputTokens: number
+  outputTokens: number
+  cacheReadTokens?: number
+  cacheWriteTokens?: number
+}): AnthropicUsage {
+  const totalInput = Math.max(0, params.totalInputTokens)
+  const cacheRead = Math.min(
+    Math.max(0, params.cacheReadTokens ?? 0),
+    totalInput,
+  )
+  const remainingAfterRead = Math.max(0, totalInput - cacheRead)
+  const cacheCreation = Math.min(
+    Math.max(0, params.cacheWriteTokens ?? 0),
+    remainingAfterRead,
+  )
+
+  return {
+    input_tokens: Math.max(0, remainingAfterRead - cacheCreation),
+    output_tokens: Math.max(0, params.outputTokens),
+    cache_creation_input_tokens: cacheCreation,
+    cache_read_input_tokens: cacheRead,
+  }
+}

src/services/api/openai/__tests__/openaiShared.test.ts

@@ -0,0 +1,50 @@
+import { describe, expect, test } from 'bun:test'
+import {
+  getOfficialOpenAIPromptCacheKey,
+  isOfficialOpenAIBaseURL,
+} from '../openaiShared.js'
+
+describe('isOfficialOpenAIBaseURL', () => {
+  test('treats the SDK default endpoint as official OpenAI', () => {
+    expect(isOfficialOpenAIBaseURL(undefined)).toBe(true)
+    expect(isOfficialOpenAIBaseURL('')).toBe(true)
+  })
+
+  test('accepts global and regional official OpenAI endpoints', () => {
+    expect(isOfficialOpenAIBaseURL('https://api.openai.com/v1')).toBe(true)
+    expect(isOfficialOpenAIBaseURL('https://eu.api.openai.com/v1')).toBe(true)
+    expect(isOfficialOpenAIBaseURL('https://api.openai.com:443/v1')).toBe(true)
+  })
+
+  test('rejects OpenAI-compatible and spoofed endpoints', () => {
+    expect(isOfficialOpenAIBaseURL('https://api.deepseek.com/v1')).toBe(false)
+    expect(isOfficialOpenAIBaseURL('http://api.openai.com/v1')).toBe(false)
+    expect(isOfficialOpenAIBaseURL('https://api.openai.com.evil.test/v1')).toBe(
+      false,
+    )
+    expect(isOfficialOpenAIBaseURL('https://api.openai.com:8443/v1')).toBe(
+      false,
+    )
+    expect(isOfficialOpenAIBaseURL('not-a-url')).toBe(false)
+  })
+})
+
+describe('getOfficialOpenAIPromptCacheKey', () => {
+  test('returns a session key for the SDK default and official endpoint', () => {
+    expect(getOfficialOpenAIPromptCacheKey(undefined, 'session-1')).toBe(
+      'ccb:session-1',
+    )
+    expect(
+      getOfficialOpenAIPromptCacheKey('https://api.openai.com/v1', 'session-2'),
+    ).toBe('ccb:session-2')
+  })
+
+  test('returns undefined for compatible endpoints', () => {
+    expect(
+      getOfficialOpenAIPromptCacheKey(
+        'https://api.deepseek.com/v1',
+        'session-1',
+      ),
+    ).toBeUndefined()
+  })
+})