# Mid-conversation system messages are available on Claude Fable 5, Claude Mythos 5, and Claude Opus 4.8

By Steven Van · 2026-07-15

Mid-conversation system messages are available on Claude Fable 5, Claude Mythos 5, and Claude Opus 4.8, on the Claude API, Claude in Amazon Bedrock…

[Anthropic](<https://creatorstoolbox.com/tools/anthropic>)'s mid-conversation system messages are now available on Claude Fable 5, Claude Mythos 5, and Claude Opus 4.8, on the Claude API, Claude in Amazon Bedrock, and Google Cloud. No beta header is required to use them. The [release note](<https://platform.claude.com/docs/en/release-notes/overview#july-15-2026>) corrects earlier information about which models and platforms supported the feature.

[![](<https://platform.claude.com/web-api/og/docs/en/release-notes/overview?design-rev=2>)](<https://platform.claude.com/docs/en/release-notes/overview#july-15-2026>)

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Anthropic

Anthropic is an AI safety and research company that's working to build reliable, interpretable, and steerable AI systems.

[View Anthropic →](<https://creatorstoolbox.com/tools/anthropic>)

Sources

[Original source](<https://platform.claude.com/docs/en/release-notes/overview#july-15-2026>)

[Read Mid-conversation system messages are available on Claude Fable 5, Claude Mythos 5, and Claude Opus 4.8 on Creators Toolbox](<https://creatorstoolbox.com/blog/anthropic-mid-conversation-system-messages-are-available-on-claude-fable-5-claud>)

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Canonical source: https://creatorstoolbox.com/blog/anthropic-mid-conversation-system-messages-are-available-on-claude-fable-5-claud