diff --git a/packages/opencode/src/provider/provider.ts b/packages/opencode/src/provider/provider.ts
index c6784f450244..5842eccee8ea 100644
--- a/packages/opencode/src/provider/provider.ts
+++ b/packages/opencode/src/provider/provider.ts
@@ -916,7 +916,27 @@ export namespace Provider {
           : undefined,
       },
       limit: {
-        context: model.limit.context,
+        context: iife(() => {
+          // Override stale context window data from models.dev for GitHub Copilot Claude models.
+          // Anthropic official context windows: https://docs.anthropic.com/en/docs/about-claude/models
+          if (m.api.npm === "@ai-sdk/github-copilot") {
+            const contextOverrides: Record<string, number> = {
+              "claude-opus-4.6": 1_000_000,
+              "claude-opus-4-6": 1_000_000,
+              "claude-sonnet-4.6": 1_000_000,
+              "claude-sonnet-4-6": 1_000_000,
+              "claude-opus-4.5": 200_000,
+              "claude-opus-4-5": 200_000,
+              "claude-sonnet-4.5": 200_000,
+              "claude-sonnet-4-5": 200_000,
+              "claude-haiku-4.5": 200_000,
+              "claude-haiku-4-5": 200_000,
+            }
+            const override = Object.entries(contextOverrides).find(([k]) => model.id.includes(k))
+            if (override) return override[1]
+          }
+          return model.limit.context
+        }),
         input: model.limit.input,
         output: model.limit.output,
       },
diff --git a/packages/opencode/src/provider/transform.ts b/packages/opencode/src/provider/transform.ts
index f651a5b91aaf..8bcfcd404368 100644
--- a/packages/opencode/src/provider/transform.ts
+++ b/packages/opencode/src/provider/transform.ts
@@ -465,7 +465,10 @@ export namespace ProviderTransform {
         }
         if (model.id.includes("claude")) {
           return {
-            thinking: { thinking_budget: 4000 },
+            low: { thinking_budget: 1_000 },
+            medium: { thinking_budget: 4_000 },
+            high: { thinking_budget: 10_000 },
+            max: { thinking_budget: 16_000 },
           }
         }
         const copilotEfforts = iife(() => {