diff --git a/packages/opencode/src/plugin/github-copilot/copilot.ts b/packages/opencode/src/plugin/github-copilot/copilot.ts
index c018f72bd5..9b6f54459d 100644
--- a/packages/opencode/src/plugin/github-copilot/copilot.ts
+++ b/packages/opencode/src/plugin/github-copilot/copilot.ts
@@ -334,6 +334,13 @@ export async function CopilotAuthPlugin(input: PluginInput): Promise<Hooks> {
       if (incoming.model.api.id.includes("gpt")) {
         output.maxOutputTokens = undefined
       }
+
+      // GitHub Copilot's /v1/messages shim rejects the GA `eager_input_streaming`
+      // field on tool definitions ("Extra inputs are not permitted"). Opt out of
+      // the @ai-sdk/anthropic default so it stops injecting the field.
+      if (incoming.model.api.npm === "@ai-sdk/anthropic") {
+        output.options.toolStreaming = false
+      }
     },
     "chat.headers": async (incoming, output) => {
       if (!incoming.model.providerID.includes("github-copilot")) return