From aa2484f83c422565307c44de48203deb09f29b84 Mon Sep 17 00:00:00 2001
From: Felix-Hz <feluhv@outlook.es>
Date: Mon, 27 Apr 2026 16:23:56 +1200
Subject: [PATCH] fix(opencode): prevent negative cost when cache tokens exceed
 input

---
 packages/opencode/src/session/session.ts      |  2 +-
 .../opencode/test/session/compaction.test.ts  | 28 +++++++++++++++++++
 2 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/packages/opencode/src/session/session.ts b/packages/opencode/src/session/session.ts
index 6c67b8517e9f..444ba07d4736 100644
--- a/packages/opencode/src/session/session.ts
+++ b/packages/opencode/src/session/session.ts
@@ -298,7 +298,7 @@ export function plan(input: { slug: string; time: { created: number } }) {
 
 export const getUsage = (input: { model: Provider.Model; usage: LanguageModelUsage; metadata?: ProviderMetadata }) => {
   const safe = (value: number) => {
-    if (!Number.isFinite(value)) return 0
+    if (!Number.isFinite(value) || value < 0) return 0
     return value
   }
   const inputTokens = safe(input.usage.inputTokens ?? 0)
diff --git a/packages/opencode/test/session/compaction.test.ts b/packages/opencode/test/session/compaction.test.ts
index 1b2b120b6164..51574c785a77 100644
--- a/packages/opencode/test/session/compaction.test.ts
+++ b/packages/opencode/test/session/compaction.test.ts
@@ -2089,6 +2089,34 @@ describe("SessionNs.getUsage", () => {
     expect(result.cost).toBe(3 + 1.5)
   })
 
+  test("does not return negative cost when cache tokens exceed input tokens", () => {
+    const model = createModel({
+      context: 100_000,
+      output: 32_000,
+      cost: { input: 10, output: 0, cache: { read: 0, write: 0 } },
+    })
+    const result = SessionNs.getUsage({
+      model,
+      usage: {
+        inputTokens: 100,
+        outputTokens: 50,
+        totalTokens: 150,
+        inputTokenDetails: {
+          noCacheTokens: undefined,
+          cacheReadTokens: 200,
+          cacheWriteTokens: undefined,
+        },
+        outputTokenDetails: {
+          textTokens: undefined,
+          reasoningTokens: undefined,
+        },
+      },
+    })
+
+    expect(result.tokens.input).toBe(0)
+    expect(result.cost).toBe(0)
+  })
+
   test.each(["@ai-sdk/anthropic", "@ai-sdk/amazon-bedrock", "@ai-sdk/google-vertex/anthropic"])(
     "computes total from components for %s models",
     (npm) => {