Enable Codex Agent in VSCode | Generated by AI

Home 2026.04

Question: How do you trigger the “Codex agent using 5.4 nano” architecture in VSCode? I only see Agent mode and Ask mode.

Answer:

Seeing Agent and Ask mode means you are already in the correct UI. But Codex vs non-Codex is not a separate button — it’s controlled by model selection.

You trigger:

Agent mode
   + model = codex / 5.4 / 5.4 nano

That becomes:

VSCode
 └─ Copilot Chat
     └─ Agent mode
         └─ Model (5.4 nano / codex / etc)

Step-by-step: how to trigger Codex agent

Do this inside VSCode:

1. Open Copilot Chat

Cmd/Ctrl + Shift + I

You should see:

Ask
Agent

Switch to Agent

2. Change the model (THIS is the key step)

Top of chat panel → model dropdown

Example:

GPT-5.4
GPT-5.4 mini
GPT-5.4 nano
Claude
Codex

Pick:

5.4 nano

Now Agent mode will use:

Agent planner + 5.4 nano executor

That is exactly:

Copilot
  → Agent
     → 5.4 nano

If you don’t see model picker

Enterprise org may:

lock model selection
set default model
hide dropdown

Then Agent mode already uses admin configured model.

You can check:

VSCode settings
→ GitHub Copilot Chat
→ Model

Command palette
→ "Copilot: Change Chat Model"

Ask vs Agent difference (important)

Ask mode:

single response
no file edits
no planning

Agent mode:

multi-step plan
edit files
run commands
iterative

Codex only activates in Agent mode

So you’re already in the right place.

How to confirm you’re using agent (Codex-style)

When Agent is active you’ll see:

“Planning…”
“Analyzing repository…”
“Editing 4 files…”
“Running command…”

That is Codex-style behavior.

If you want full Codex behavior

Use prompts like:

upgrade angular 14 to 17 across repo

refactor all services to use fetch instead of axios

Ask mode won’t do this Agent mode will

Most likely your situation

You see:

Ask

Agent

You just need:

switch to Agent
choose model (5.4 nano)
run repo-level task

That’s it.

You’re already using Codex-style agent.

No extension needed.

Back Donate