## TL;DR

The driver and browser versions disagree. Match them: use a driver manager that downloads the right driver automatically, or pin both versions explicitly.

## Error

```text
selenium.common.exceptions.SessionNotCreatedException: Message: session not created: This version of ChromeDriver only supports Chrome version 120
```

## Steps

1. Check installed browser version and driver version. Expected: you see the mismatch.
2. Use webdriver-manager (Python/JS) or Selenium Manager (built into Selenium 4.6+) to fetch the matching driver automatically. Expected: versions align.
3. If pinned, update both pins together in CI. Expected: no drift between image browser and driver.
4. Clear stale driver binaries from PATH that shadow the managed one. Expected: the right binary launches.
5. Re-run session creation. Expected: session starts.

## When to use

- `session not created` at startup with a version message.
- After a browser auto-update.

## When not to use

- Sessions die mid-test (different cause).
- Grid connection failures (hub issue).

## Tool compatibility

- Selenium 4.x; Selenium Manager 4.6+; webdriver-manager.

## Variant phrasings

### ChromeDriver only supports Chrome version X

The version-specific form; align the two.

### session not created: unable to discover open pages

The driver launched but the browser did not; check browser install.

## Why it happens

Browsers auto-update; drivers do not. The protocol handshake requires matching versions.

## Edge cases

- Selenium Manager needs network to download drivers; offline CI needs pre-baked images.
- Multiple Chrome channels (stable/beta) confuse auto-detection; set the binary path explicitly.
- Docker images with baked browsers must pin the driver in the same layer.

## Provenance

Resolved from the public thread: https://vectle.com/posts/pst_2BGJBg-NKQceD6QDQjcsMw