---
title: "Confirm numbers in Instruments"
lesson_id: "05"
---

# Confirm numbers in Instruments

- **Lesson ID:** 05
- **Goal:** Confirm TTFT and token rate in the Xcode 27 Foundation Models instrument. Write a four-line speed budget.
- **Human lesson:** [05-instruments-and-budget.html](05-instruments-and-budget.html)

## Prerequisites

- Lesson 04, or logs from both models.

## Inputs, outputs, and artifacts

- **Inputs:** A recorded Instruments trace and your in-app metrics.
- **Outputs:** A weekly speed budget.
- **Artifacts:** Progressive `.flow` diagrams and a four-item list.

## Agent build steps

1. Name Product → Profile and the Foundation Models template.
2. Name TTFT, tokens per second, and total latency from [session 243](https://developer.apple.com/videos/play/wwdc2026/243/).
3. Warn that traces can contain prompts.
4. Write the four-line budget.
5. Link the tracer and eval courses.

## Constraints

Keep the language simple, friendly, and literal. iOS 27 and macOS 27 only. No quizzes, Mermaid, or em dashes. Do not invent API names. Mark sketches as sketches and tell the reader to confirm them in the Xcode 27 SDK.

## Key concepts

- Use Product, Profile, Foundation Models template in Xcode 27.
- Trace files hold prompts and replies. Treat them as sensitive.
- Hold a four-line speed budget: on-device TTFT, PCC TTFT, mean gap, and what to cut first.
- A TTFT jump after a Dynamic Profile change often means longer instructions or more tools.

## Takeaways

- Stream in the UI, log TTFT and gaps, confirm in Instruments, hold a four-line budget.
- Use the tracer course for hops around the model.
- In-app logs can drift. Instruments is the check.

## Acceptance checks

- Instruments template is named.
- Trace files are marked sensitive.
- The budget has four concrete lines.
- Sibling links, progressive `.flow` diagrams, and an Agent brief link are present.