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Anthropic: Claude Opus 4.8 (Fast)
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Anthropic: Claude Opus 4.8 (Fast)

Anthropic's flagship Opus at up to 2.5x output speed for latency-sensitive long-horizon coding and agent workflows.

Context window: 
1000000
M tokens
Output: 
128000
 tokens
Modality:
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Claude Opus 4.8 Fast Mode: Full Opus Quality at 2.5x Output Speed Claude Opus 4.8 (Fast) is Anthropic's Opus 4.8 model served in fast mode, a research-preview serving configuration on the Claude API. It is the same weights and reasoning as standard Opus 4.8, Anthropic's flagship Opus-tier model for complex agentic coding and enterprise work, but delivered at up to 2.5x higher output tokens per second at premium pricing. Quality and capabilities are identical; only throughput and cost change. It suits latency-sensitive workloads—live debugging, interactive agents, and long code generation—where streaming speed materially improves the developer or end-user experience. Start building with Claude Opus 4.8 via the AnyAPI.ai API.

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Anthropic: Claude Opus 4.8 (Fast)

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Answers to common questions about integrating and using this AI model via AnyAPI.ai

No. Fast mode is a serving configuration, not a separate model. It runs the exact same Opus 4.8 weights and reasoning, delivering up to 2.5x higher output tokens per second at premium pricing. Intelligence, capabilities, and benchmark performance are identical to standard Opus 4.8—only throughput and cost differ.

Only partly. Fast mode increases output tokens per second, so long responses finish faster. It does not improve time to first token—the initial pause before the first word appears is unchanged. Short prompts feel similar, while long code generation or agent transcripts stream back noticeably quicker.

On the Claude API, send the fast-mode-2026-02-01 beta header and set speed to "fast" on your Messages request against claude-opus-4-8. Fast mode is a research preview available on the Claude API and Claude Managed Agents only, and typically requires account-manager access or a waitlist.

Claude Opus 4.8 supports a 1,000,000-token context window by default on the Claude API and 128,000 max output tokens. Batch processing can extend output to 300,000 tokens using a beta header. Fast mode does not change these limits, since it uses the same underlying model.

It depends on the workload. Fast mode roughly doubles per-token cost and helps only when generating long outputs someone is actively watching—interactive coding, live debugging, or latency-sensitive agents. For unattended pipelines, batch jobs, or short responses, standard Opus 4.8 is the more economical choice.