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Synth 2.5 Pro Preview

Added Sep 5, 2026

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Use in the app

Synth 2.5 Pro Preview is a low-cost text model designed for role-play, character dialogue, and collaborative storytelling.

Input
Text
Output
Text
Discovery tier
Efficient

Pricing

USD per 1M tokens
Input
$0.10
Output
$0.20

Reference prices as published by the model provider. API example

Specifications

Context window
30K
Max output
—

Side by side

Synth 2.5 Pro Preview compared

Specifications, prices, speed and benchmark scores next to each other. Benchmarks below show every compared model too.

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Synth 2.5 Pro PreviewlucidityThis modelClaude Haiku 5.5AnthropicRemove
ProviderlucidityAnthropic
Discovery tierEfficientEfficient
AddedSep 5, 2026Oct 7, 2026
Limits
Context window30K1MBest
Max output—128K
Average output—1.5K tokens
Pricing, USD per 1M tokens
Input$0.10$0.10
Output$0.20Best$0.50
Cache read—$0.01
Cache write—$0.13
Performance
Throughput—308.9 tok/s
Time to first token—3.1 s
Request success (24h)0.0%99.9%Best
Benchmark indexes
Intelligence Index—43.4
Capabilities
ReasoningNoYes
ToolsNoYes
VisionNoYes
Structured outputNoYes
PDF inputNoYes
Reasoning effort—low, medium, high, xhigh, max

Public evaluations

Benchmarks

Independent evaluation results, with how each score ranks among the models in the Noumen catalog.

  • Synth 2.5 Pro Preview
  • Claude Haiku 5.5

Intelligence Index

  • Synth 2.5 Pro Preview—
  • Claude Haiku 5.543.4
3.8Catalog models by score55.1

Agentic work

  • AutomationBench-AA

    Workflow automation, penalized for guardrail violations

    • Synth 2.5 Pro Preview: —
    • Claude Haiku 5.5: 35.4%

  • AutomationBench-AA tasks completed

    Workflows finished end to end without a guardrail violation

    • Synth 2.5 Pro Preview: —
    • Claude Haiku 5.5: 13.9%

  • Harvey LAB-AAv1.1

    Legal tasks passed in full, with no material hallucination

    • Synth 2.5 Pro Preview: —
    • Claude Haiku 5.5: 0.6%

  • AA-Briefcasev1.1

    Agentic knowledge work, rated head to head

    • Synth 2.5 Pro Preview: —
    • Claude Haiku 5.5: 1,575 Elo

  • GDPval-AAv2.1

    Economically valuable occupational tasks, rated head to head

    • Synth 2.5 Pro Preview: —
    • Claude Haiku 5.5: 1,619 Elo

Document reasoning

  • GDP.pdf

    Professional reasoning over PDF documents, all-pass rate

    • Synth 2.5 Pro Preview: —
    • Claude Haiku 5.5: 20.8%

  • AA-LCRv1.1

    Reasoning across long documents

    • Synth 2.5 Pro Preview: —
    • Claude Haiku 5.5: 82.7%

  • MLCR-AA

    Long-context reasoning over medical records

    • Synth 2.5 Pro Preview: —
    • Claude Haiku 5.5: 35.0%

Reasoning and knowledge

  • Humanity’s Last Exam

    Expert-level questions across academic fields

    • Synth 2.5 Pro Preview: —
    • Claude Haiku 5.5: 44.4%

Coding

  • Terminal-Benchv4.0

    Practical software engineering in a terminal

    • Synth 2.5 Pro Preview: —
    • Claude Haiku 5.5: 32.8%

  • SciCode

    Scientific computing in Python

    • Synth 2.5 Pro Preview: —
    • Claude Haiku 5.5: 55.0%

Legacy evaluations

  • AA-LCR (unversioned)

    Long-context reasoning, earlier grading

    • Synth 2.5 Pro Preview: —
    • Claude Haiku 5.5: 82.7%

Scores from Artificial Analysis, updated Oct 26, 2026. Artificial Analysis

Live routing data

Performance and reliability

Recent averages across requests routed for this model. Your own speed depends on prompt length, reasoning effort and load.

Request success (24h)
0.0%
Failing
Hourly request success · last 72 hoursLowest hour 0.0%
  • Healthy (98% or more)
  • Degraded (90–98%)
  • Down (under 90%)
  • No requests

Developers

Use it through the API

Noumen’s API is OpenAI-compatible: any Chat Completions client works with a base URL and a key.

Read the quickstart
curl https://www.noumen.xyz/api/v1/chat/completions \
  -H "Authorization: Bearer $NOUMEN_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "synth-2.5-pro",
    "messages": [{ "role": "user", "content": "Explain this stack trace." }]
  }'
import os
from openai import OpenAI

client = OpenAI(base_url="https://www.noumen.xyz/api/v1", api_key=os.environ["NOUMEN_API_KEY"])
reply = client.chat.completions.create(
    model="synth-2.5-pro",
    messages=[{"role": "user", "content": "Explain this stack trace."}],
)
print(reply.choices[0].message.content)

lucidity

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