GuidesClaude

What changed in Claude (and what to do)

By Stephen Thorn · 3 minute read ·

What changed in Claude: which model to use when, and how to check a file Claude made

Two recent changes, and what to do about each:

  1. Claude Code now starts on Opus. It's the most capable model, and it's also the one that uses up your limit fastest.

  2. Claude now signs the images, video and audio it makes. Anyone can check a file in their browser.

This page gets a new section whenever something changes that's worth acting on. Last updated 15 Oct 2026.

What you need

  • For the models: Claude Code. Check your version with claude --version, and run claude update if you're behind.

    • The Opus default came in 2.1.280 (22 Sep).

    • Sonnet 5.5 needs 2.1.284.

    • Haiku 5.5 needs 2.1.293.

  • For checking a file: a browser and the file. Nothing to install.

1. Which model to use when

What changed

Claude Code changelog 2.1.280: "Changed the default model on Pro and Team Standard plans from Sonnet to Opus, matching Max, Team Premium, and Enterprise". The model docs now say: "Pro, Max, Team, Enterprise, and Anthropic API: defaults to Opus 5.5".

So unless you've picked a model yourself, every job runs on Opus, including the small ones.

Pick the model by the job

Anthropic's own help page gives the split:

  • Opus 5.5: When you're stuck, or the change is big. Example jobs: Hard debugging, changes across many files, architecture calls

  • Sonnet 5.5: Everyday work. Example jobs: A new feature, tests, known bugs, refactors

  • Haiku 5.5: Quick, mechanical jobs. Example jobs: Renames, log lines, explaining a regex, boilerplate

On Opus, the same page says: "It uses meaningfully more of your quota, so consider switching to Sonnet for routine work."

Haiku 5.5 arrived on 7 Oct. Anthropic's release notes call it "the cheapest, fastest, and most capable small model we've released, designed for high-volume, cost-sensitive tasks". That makes it a good fit for bulk jobs, like sorting a long list.

Switch models

  1. Type /model. It shows which model you're on.

  2. Arrow down to Sonnet 5.5 or Haiku 5.5 and press Enter.

  3. Switch back to Opus when you hit something hard.

Check your effort level

The docs: "Opus 5.5, Sonnet 5.5, and Haiku 5.5 default to medium".

If you'd set effort to high before, that setting doesn't carry over to these models. Changelog 2.1.280: an effort level saved before /effort became per-model will "no longer apply to newly released models such as Opus 5.5; they start at their default until you pick a level".

Type /effort to see where you are and set the level you want.

2. How to check whether Claude made a file

What changed

From Anthropic's checker page: "When Claude produces a supported file type (such as a .png, .jpg, or .svg), it attaches a Content Credential in the form of a small, cryptographically signed note in the file's metadata, saying that the file may have been made or processed with Claude."

Check a file

  1. Go to claude.com/check-files.

  2. Drop the file in. "This tool runs in your browser. Your file never leaves your device."

  3. Read the result.

I tested it on 12 Oct.

  • A PNG chart Claude made: "This file shows signs it was processed by Claude."

  • A screenshot of that same chart: "We didn't find any signs this file was processed by Claude."

What it can check

  • Supported files: JPG, PNG, GIF, WEBP, TIFF, HEIC, AVIF, SVG, DNG, JXL, MP4, MOV, AVI, WAV, MP3, M4A and FLAC, up to 100 MB.

  • Never signed: "Text files, PDFs, and office documents are not signed because they are not supported formats for signing." So a Word file or a PDF from Claude won't show anything.

  • Text: "The tool does not check text." Text gets a different mark. "When a supported Claude model generates text, it weaves an imperceptible watermark directly into the text itself."

    • Checking for it isn't open to everyone yet. "Watermark detection is currently in private preview, available to eligible organizations as required under EU law (such as regulators, law enforcement, media, fact-checkers, independent researchers, educational organizations, and EU civil society groups)."

The mistake to avoid

  • Leaving Opus on for everything. It's the right call when you're stuck, but routine work on Opus uses your limit faster for no better result. Check /model and /effort at the start of a session.

  • Reading "nothing found" as proof a person made the file. My screenshot test shows how easily the signature disappears. A found credential also only says the file "may have been made or processed with Claude". It doesn't say who wrote what's in it.