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Anthropic: Claude Opus 4.1 to 4.8

Use this guide when you are moving from anthropic/claude-opus-4.1 to anthropic/claude-opus-4.8. Anthropic deprecated Claude Opus 4.1 on June 5, 2026 and scheduled retirement for August 5, 2026. Their migration guidance for Opus 4.1 is cumulative: first apply the Claude Opus 4.7 request-shape changes, then review the Claude Opus 4.8 behavior changes.

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What changed

• the target model becomes claude-opus-4-8
• Opus 4.7 and later reject non-default sampling params like temperature, top_p, and top_k
• Opus 4.7 and later reject manual extended-thinking budgets; use adaptive thinking instead
• Opus 4.8 defaults output_config.effort to high
• Opus 4.8 adds mid-conversation system messages
• Opus 4.8 raises the baseline context/output ceilings to 1M context and 128K max output on the Claude API, Claude Platform on AWS, Amazon Bedrock, and Vertex AI

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What to change in your integration

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1. Update the model ID

Move from:

• anthropic/claude-opus-4.1

to:

• anthropic/claude-opus-4.8

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2. Remove non-default sampling parameters

If your Opus 4.1 requests still set any of these, remove them before rollout:

• temperature
• top_p
• top_k

On Opus 4.7 and later, non-default values for those fields return 400.

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3. Replace manual thinking budgets with adaptive thinking

If you send legacy thinking payloads such as:

• thinking: { "type": "enabled", "budget_tokens": 32000 }

move to:

• thinking: { "type": "adaptive" }
• output_config.effort = "high" as the baseline

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4. Rebaseline effort and long-context expectations

Opus 4.8 defaults effort to high, and it supports a much larger context window than Opus 4.1 on Anthropic-operated API surfaces. Re-test:

• latency budgets
• token usage
• prompt caching behavior
• long-document and long-agent traces

If you run on Microsoft Foundry, do not assume the 1M context window there at launch; Anthropic documents a 200K context window for Foundry on Opus 4.8.

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5. Re-check instruction updates in long conversations

Opus 4.8 supports mid-conversation system messages. If your agent loop currently rewrites the full system prompt every turn, you may be able to simplify that flow and preserve more cache hits.

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What to test

• requests that still send temperature, top_p, or top_k
• thinking-enabled routes that previously relied on budget_tokens
• long-horizon agent and tool workflows
• schema-sensitive outputs at explicit effort levels
• token-cost and latency deltas on your highest-volume Opus 4.1 prompt classes

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Safe rollout

1. Remove sampling params and legacy thinking budgets before switching traffic.
2. Shadow Opus 4.8 on production-like prompts and tool flows.
3. Canary with a fallback path still available during the overlap window before August 5, 2026.
4. Promote only after latency, cost, and task-completion deltas are within target.

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Sources

• Anthropic model deprecations
• Anthropic migration guide
• What’s new in Claude Opus 4.8