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Anthropic promotes Claude Opus 4.5 snapshot 20260805 to API default
Draft — pending editorial review
Anthropic promoted snapshot claude-opus-4-5-20260805 to the API default for Claude Opus 4.5 on August 8, 2026. The update tightens tool-call formatting compliance and fixes a long-context truncation edge case. Anthropic reports unchanged benchmark scores. Requests pinned to the prior snapshot continue to resolve until deprecation notice.
Anthropic switched the default resolution of claude-opus-4-5 to snapshot claude-opus-4-5-20260805 on August 8, 2026, per the model documentation. Requests that pin the previous snapshot explicitly continue to resolve; Anthropic’s deprecation policy provides notice before any snapshot retirement.
What changed
The 20260805 snapshot addresses two production behaviors:
- Tool-call formatting compliance. The update reduces malformed JSON in parallel tool-call blocks under long system prompts — a failure mode agent framework maintainers have tracked since June.
- Long-context truncation. A fix for an edge case where responses near the 64K output ceiling could terminate mid-token sequence when streaming with stop sequences configured.
Anthropic states benchmark scores are unchanged from the launch measurement (80.9% SWE-bench Verified, November 24, 2025). We will re-measure in the September leaderboard refresh and note any drift on the Claude Opus 4.5 model page.
Practitioner notes
Teams pinning snapshots for reproducibility should schedule validation against 20260805 before the prior default enters deprecation. Teams resolving the bare claude-opus-4-5 alias received the new snapshot automatically on August 8. No pricing or rate-limit changes accompany this promotion; current pricing remains $5 input / $25 output per million tokens (verified August 8, 2026).
The full version history for this model is on its changelog section.