Anthropic API Archives - LLM Fly Blog

Claude Fable 5.1 Thinking Block Error: Fix the 400 “Different Conversation” Error

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Fix the Claude Fable 5.1 thinking block error: append-only history, prefix mismatch, drop_block, beta headers, fallbacks, and logging.

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Migrate to Claude Fable 5.1 safely: model ID, breaking changes, thinking blocks, refusals, fallbacks, caching, cost, and rollout.

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Compare Claude Fable 5.1 vs Fable 5 and Opus 5 using coding benchmarks, CodeRabbit review data, KOL tests, API changes, cost, and migration advice.

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Access the Claude Fable 5.1 API through LLMFly AI at 50% off. Compare official pricing, cache savings, setup steps, use cases, and production checks.

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Compare OpenAI and Anthropic API formats for messages, tools, streams, reasoning, errors, usage, compatibility layers, and production migration.