From 2e5199a40d8791e99dc304ad722bf6baa707f09c Mon Sep 17 00:00:00 2001
From: chrarnoldus <12196001+chrarnoldus@users.noreply.github.com>
Date: Mon, 10 Aug 2026 12:49:48 +0000
Subject: [PATCH] feat(cli): exclude ChatGPT subscriptions from explicit prompt
 cache breakpoints

---
 ...de-chatgpt-from-prompt-cache-breakpoint.md |  5 ++
 packages/opencode/src/provider/transform.ts   | 19 ++++--
 .../opencode/test/provider/transform.test.ts  | 64 +++++++++++++++++++
 3 files changed, 82 insertions(+), 6 deletions(-)
 create mode 100644 .changeset/exclude-chatgpt-from-prompt-cache-breakpoint.md

diff --git a/.changeset/exclude-chatgpt-from-prompt-cache-breakpoint.md b/.changeset/exclude-chatgpt-from-prompt-cache-breakpoint.md
new file mode 100644
index 00000000000..6362bdd7ff1
--- /dev/null
+++ b/.changeset/exclude-chatgpt-from-prompt-cache-breakpoint.md
@@ -0,0 +1,5 @@
+---
+"@kilocode/cli": patch
+---
+
+Exclude ChatGPT subscriptions from explicit prompt cache breakpoints.
diff --git a/packages/opencode/src/provider/transform.ts b/packages/opencode/src/provider/transform.ts
index ff534bf107f..7a9659b25d2 100644
--- a/packages/opencode/src/provider/transform.ts
+++ b/packages/opencode/src/provider/transform.ts
@@ -328,15 +328,22 @@ function normalizeMessages(
   return msgs
 }
 
-// kilocode_change start - explicit prompt cache breakpoints for GPT-5.6+
-function supportsPromptCacheBreakpoint(modelId: string): boolean {
-  const match = modelId.match(/gpt-(\d+)\.(\d+)/)
+// kilocode_change start - explicit prompt cache breakpoints for GPT-5.6+ (excluding ChatGPT subscriptions)
+function isChatGPTSubscription(model: Provider.Model): boolean {
+  if (model.providerID === "openai" && model.cost?.input === 0 && model.cost?.output === 0) return true
+  if (typeof model.api.url === "string" && model.api.url.includes("chatgpt.com")) return true
+  return false
+}
+
+function supportsPromptCacheBreakpoint(model: Provider.Model): boolean {
+  if (isChatGPTSubscription(model)) return false
+  const match = model.api.id.match(/gpt-(\d+)\.(\d+)/)
   if (match) {
     const major = Number(match[1])
     const minor = Number(match[2])
     if (major > 5 || (major === 5 && minor >= 6)) return true
   }
-  const majorMatch = modelId.match(/gpt-(\d+)/)
+  const majorMatch = model.api.id.match(/gpt-(\d+)/)
   if (majorMatch && Number(majorMatch[1]) >= 6) return true
   return false
 }
@@ -366,7 +373,7 @@ function applyCaching(msgs: ModelMessage[], model: Provider.Model): ModelMessage
       cacheControl: { type: "ephemeral" },
     },
     // kilocode_change start
-    ...(supportsPromptCacheBreakpoint(model.api.id)
+    ...(supportsPromptCacheBreakpoint(model)
       ? {
           openai: {
             promptCacheBreakpoint: { mode: "explicit" },
@@ -494,7 +501,7 @@ export function message(msgs: ModelMessage[], model: Provider.Model, options: Re
       ((model.api.npm === "@ai-sdk/openai" ||
         model.api.npm === "@ai-sdk/azure" ||
         model.api.npm === "@kilocode/kilo-gateway") &&
-        supportsPromptCacheBreakpoint(model.api.id))) &&
+        supportsPromptCacheBreakpoint(model))) &&
     model.api.npm !== "@ai-sdk/gateway"
   ) {
     msgs = applyCaching(msgs, model)
diff --git a/packages/opencode/test/provider/transform.test.ts b/packages/opencode/test/provider/transform.test.ts
index 74ef174ade8..508f6a8cd0b 100644
--- a/packages/opencode/test/provider/transform.test.ts
+++ b/packages/opencode/test/provider/transform.test.ts
@@ -3162,6 +3162,70 @@ describe("ProviderTransform.message - cache control on gateway", () => {
       },
     })
   })
+
+  test("openai gpt-5.6 with ChatGPT subscription (zero cost) does not apply promptCacheBreakpoint", () => {
+    const model = createModel({
+      providerID: "openai",
+      api: {
+        id: "gpt-5.6",
+        url: "https://api.openai.com/v1",
+        npm: "@ai-sdk/openai",
+      },
+      id: "gpt-5.6",
+      cost: {
+        input: 0,
+        output: 0,
+        cache: { read: 0, write: 0 },
+      },
+    })
+    const msgs = [
+      {
+        role: "system",
+        content: "You are a helpful assistant",
+      },
+      {
+        role: "user",
+        content: "Hello",
+      },
+    ] as any[]
+
+    const result = ProviderTransform.message(msgs, model, {}) as any[]
+
+    expect(result[0].providerOptions?.openai?.promptCacheBreakpoint).toBeUndefined()
+    expect(result[1].providerOptions?.openai?.promptCacheBreakpoint).toBeUndefined()
+  })
+
+  test("openai gpt-5.6 with ChatGPT backend endpoint does not apply promptCacheBreakpoint", () => {
+    const model = createModel({
+      providerID: "openai",
+      api: {
+        id: "gpt-5.6",
+        url: "https://chatgpt.com/backend-api/codex/responses",
+        npm: "@ai-sdk/openai",
+      },
+      id: "gpt-5.6",
+      cost: {
+        input: 0.002,
+        output: 0.008,
+        cache: { read: 0.0005, write: 0.002 },
+      },
+    })
+    const msgs = [
+      {
+        role: "system",
+        content: "You are a helpful assistant",
+      },
+      {
+        role: "user",
+        content: "Hello",
+      },
+    ] as any[]
+
+    const result = ProviderTransform.message(msgs, model, {}) as any[]
+
+    expect(result[0].providerOptions?.openai?.promptCacheBreakpoint).toBeUndefined()
+    expect(result[1].providerOptions?.openai?.promptCacheBreakpoint).toBeUndefined()
+  })
   // kilocode_change end
 })