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Chat model · Anthropic

Claude Sonnet 4.5

Included in Pro · came out September 2025

Thoughtful help with letters, stories and everyday writing

Claude Sonnet 4.5 is an earlier version of Anthropic's everyday Claude model. It suits writing jobs and questions you want thought through, when you don't need anything from the web.

Chat with Claude Sonnet 4.5

Claude Sonnet 4.5 in numbers

What it knows about

Up to July 2025

It learned from information up to July 2025. It can't search the web, so for recent news or prices pick a model that can.

What you can give it

  • Your wordsYes
  • PhotosYes
  • PDFs and filesYes
  • The webNot this one

Real answers

See how Claude Sonnet 4.5 answers

We asked it the same everyday questions as every other model in chatmodel, one try each. This is exactly what came back.

My neighbour watered my plants for two weeks while I was away. Write a short, warm thank-you note I can leave with a small gift. Keep it under 80 words.

Dear [Neighbor's Name],

Thank you so much for taking care of my plants while I was away! It's such a relief to come home to happy, thriving greenery. Your kindness means more than you know, and I'm grateful to have such a thoughtful neighbor.

Please accept this small token of my appreciation. I owe you one!

With thanks, [Your name]

Answered in about 3 seconds · 60 words

Ask it yourself

The Claude family in chatmodel

The newest is Claude Fable 5.1. Ordered by release date.

  1. September 2025Claude Sonnet 4.5You're here
  2. October 2025Claude Haiku 4.5
  3. November 2025Claude Opus 4.5
  4. February 2026Claude Opus 4.6
  5. February 2026Claude Sonnet 4.6
  6. April 2026Claude Opus 4.7
  7. May 2026Claude Opus 4.8

What it's good for

Try it with one of these

Press “Try this” and chatmodel opens with Claude Sonnet 4.5 selected and the message already written. Change any word you like.

Write down a family story

“Help me write down a story my father used to tell about working on a farm as a boy. I'll give you the rough details. Keep it in simple, warm language, about 300 words, as if he were telling it.”

Try this

Polite complaint letter

“Help me write a polite complaint to a restaurant. We booked for a birthday, waited 50 minutes for our food and one dish was cold. I'd like an apology, not a fight. Under 150 words.”

Try this

Say sorry to a friend

“I forgot my best friend's birthday and she's hurt. Help me write a short, honest message to say sorry, without making excuses.”

Try this

Weigh up a choice

“I've been offered early retirement with a smaller pension, or I can work three more years. Help me list the questions I should ask myself before deciding.”

Try this

In plain words

Claude Sonnet 4.5 is a chat assistant from Anthropic. Sonnet is the middle size of Claude, between the quick Haiku and the careful Opus, and 4.5 is one of its earlier versions in chatmodel.

It thinks before it answers, reads photos and documents, and writes in the natural style Claude is known for. It doesn’t search the web.

How to get the most out of it

  1. Give it the raw material. Names, places, what happened. It turns notes into flowing text.
  2. Say who will read it. A grandchild, a manager, a local newspaper.
  3. Ask for a first draft, then adjust. “Warmer”, “shorter”, “less formal”.
  4. Use another model for recent facts, since this one doesn’t search the web.

How it compares with its siblings

Claude Sonnet 4.6 is the next version, and Claude Sonnet 5 is newer still and can also search the web. Claude Haiku 4.5 is quicker but doesn’t think it through. For more care, see Claude Opus 4.5 or Claude Opus 5.

When to pick another model

For writing in general, see best AI for writing. If you want web answers too, GPT 5.5 is an all-rounder.

Other models worth a look

Claude Sonnet 4.6

Anthropic

Read the guide

Claude Sonnet 5

Anthropic

Read the guide

Claude Haiku 4.5

Anthropic

Read the guide

Frequently asked questions

Should I use Sonnet 4.5 or Sonnet 5?

Claude Sonnet 5 is the newer version and can search the web. Sonnet 4.5 is still a good writer, so try the same message on both if you're curious.

Does it think before it answers?

Yes. On harder questions it takes a moment to think, which makes it more careful.

Can it search the web?

No. In chatmodel it doesn't search the web.

Can it read my PDFs?

Yes. It reads documents and understands photos.

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