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Since June 2026: what Claude Fable 5.1 cannot know

Claude Fable 5.1 was trained on data up to June 2026. Since then, 239 models, APIs and runtimes have reached their end date and packages have shipped 146,109 breaking changes. Code it writes from memory can still use any of them.

Knowledge cutoff June 2026

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The model ID is claude-fable-5-1, from Anthropic, released September 1, 2026. The endings and the package changes below came after its training data ends, so they are not in what the model learned.

Ended since June 2026

239 models, APIs and runtimes have reached their end date since the cutoff. The newest of each:

AI models

And 209 more on the calendar.

Still ahead

450 end dates are still ahead. Some were announced after the cutoff, so the model may write what they end. The soonest of each:

AI models

APIs

And 420 more on the calendar.

Packages that changed most

Since the cutoff, package versions shipped 146,109 breaking changes, and 25,157 security advisories were published. The packages with the most breaking changes in versions released since:

Check before it writes

Run npx since-dev init in a repository and your coding agent checks a version or a model ID before it writes one, whatever model it runs on. To see what a repository already uses that has ended, scan it, or run npx since-dev inside it.

Knowledge cutoffs are from models.dev (MIT License). A cutoff given as a month is read as that month’s last day.

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Put your code on continuous maintenance.

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See how out of date your code is.

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Tell your agent what changed since it was trained.

claude mcp add --transport http since https://api.since.dev/mcp
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Codex, Cursor and any MCP client use https://api.since.dev/mcp.