claude-opus-4-6 — pricing, context window and limits

The last of the old request shape

Opus 4.6 is the final Opus that still accepts the older sampling controls (temperature, top_p, top_k) and the deprecated thinking-budget mechanism, and the last without the effort tier every later generation offers. Every Opus released after it rejects all four of those fields outright, which makes this model the boundary line for a whole category of migration work rather than one incremental step along it.

The highest cache minimum among active models

This model's minimum cacheable prefix sits at the top of the range across the active lineup. A prompt engineered to cache here will cache almost everywhere else too, but the reverse isn't guaranteed — and moving away from this model often means prompts that never cached here start caching on the destination with no code change.

What breaks first on a migration away

The older sampling fields usually surface first in testing, because removing them produces an immediate, hard error rather than a subtle behaviour change. See temperature, top_p and top_k are not supported on this model and budget_tokens is not supported on Opus 4.7 and later for both fields this model is the last to accept. The current migration target is Opus 5.5, reached through the Opus 4.7, 4.8 and 5 changes in order.

Related

See migrating: Opus 4.6 to Opus 5 for the largest single diff, and what actually changed from Opus 5 to Opus 5.5 for the last step on the way to the current Opus.